WO2018199273A1

WO2018199273A1 - A noise reducing tread

Info

Publication number: WO2018199273A1
Application number: PCT/JP2018/017117
Authority: WO
Inventors: Kenji Fukuda
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2017-04-27
Filing date: 2018-04-27
Publication date: 2018-11-01
Anticipated expiration: 2019-10-27

Abstract

A tread for a tire having a contact face intended to come into contact with ground during rolling being provided with at least one groove (3) of a radial depth D and a width W being composed of two opposed groove walls (31, 32) and a groove bottom (33) connecting radially innermost of the two opposed groove walls (31, 32), the groove having at least one protrusion (4) protruding radially from the groove bottom (33) with a radial height h having two opposed protrusion faces (41, 42) distant with a length L, each the two opposed protrusion faces (41, 42) facing to a direction the groove provided with the protrusion extends, and a protrusion top face (43) connecting radially outermost of the two opposed protrusion faces (41, 42), the protrusion (4) having at least two slots (5) of a radial depth d and a width w, each opening to the protrusion top face (43) and the two opposed protrusion faces (41, 42), the radial height h of the protrusion (4) is at least equal to 75% of the radial depth D of the groove (3) provided with the protrusion (4).

Description

A NOISE REDUCING TREAD

The present invention relates to a tread for a tire, in particular to a tread for a tire having a device for attenuating a noise generated by groove resonance in a groove possible to wear out similarly as the tread while ensuring a good productivity.

A groove resonance is generated by occurrence of resonance in an air column defined between a groove in a tread and a road surface in contact with the tire. The frequency of this groove resonance is dependent on a length of the air column formed between groove and the road surface in the contact patch.

This groove resonance has a consequence in an interior noise and an exterior noise on a vehicle equipping such tires, a frequency of which interior and exterior noise is often at around 1 kHz where human ear is sensitive.

In order to reduce such groove resonance, it is known to provide a plurality of closing device in the form of a flexible fence made of rubber-based material and relatively thin in thickness in each groove. It is effective that each flexible fence covers all or at least major part of the sectional area in the groove. Each flexible fence can extend from a groove bottom, or be fixed onto at least one of a groove sidewall delimiting such groove.

Thanks to such flexible fences, the length of the air column is reduced so as to be shorter than the total length of the groove in a contact patch, which leads to change the frequency of the groove resonance. This change of resonance frequency makes the sound generated by the groove resonance less sensitive to human ear.

WO2010/063749 discloses a tire provided with a plurality of flexible fence extending radially from a groove bottom.

JP2004-181980 discloses a tire provided with a plurality of beard-shaped projections extending radially from a groove bottom.

However, with the above arrangements, since a thickness of the flexible fence or the beard-shaped projections measured in a direction the groove extends is thin and thus such the flexible fence or the beard-shaped projections deform easily, the flexible fence or the beard-shaped projections tend to wear less than a tread portion during rolling that would result a difference in an amount of wear. Due to such the difference in wear amount, the flexible fence or the beard-shaped projection protrude from a surface of the tread portion. The flexible fence or the beard-shaped projection protruding from the surface of the tread portion strike road surface to generate an abnormal noise. An occurrence of such the abnormal noise contradicts the original role of the flexible fence or the beard-shaped projection; reduction of the noise by reducing the air column resonance.

Moreover, due to the thin thickness of the flexible fence or the beard-shaped projection, it is difficult to mold such the flexible fence or the beard-shaped projection properly as it is hard for rubber-based material to flow into a molding part for molding the flexible fence or the beard-shaped projection, and also air tends to remain in the molding part.

WO2010/063749 JP2004-181980

Therefore, there is a need for a tread for a tire which improves noise due to air column resonance without generating an abnormal noise during usage while maintaining good productivity of such the tread.

Definitions:

A “radial direction/orientation” is a direction/orientation perpendicular to axis of rotation of the tire. This direction/orientation corresponds to thickness orientation of the tread.

An “axial direction/orientation” is a direction/orientation parallel to axis of rotation of the tire.

A “circumferential direction/orientation” is a direction/orientation which is tangential to any circle centered on axis of rotation. This direction/orientation is perpendicular to both the axial direction/orientation and the radial direction/orientation.

A “tire” means all types of elastic tire whether or not subjected to an internal pressure.

A “tread” of a tire means a quantity of rubber material bounded by lateral surfaces and by two main surfaces one of which is intended to come into contact with ground when the tire is rolling.

A “groove” is a space between two rubber faces/sidewalls which do not contact between themselves under usual rolling condition connected by another rubber face/ bottom. A groove has a width and a depth.

It is thus an object of the invention to provide a tread for a tire provided with a noise reduction device in a groove, such the tread can provide reduction of air column resonance without generating an abnormal noise during usage by wearing the noise reduction device in the groove similarly with the tread while maintaining productivity of such the tread.

The present invention provides a tread for a tire having a contact face intended to come into contact with ground during rolling, the tread being provided with at least one groove of a radial depth D and a width W being composed of two opposed groove walls and a groove bottom connecting radially innermost of the two opposed groove walls, the groove having at least one protrusion protruding radially from the groove bottom with a radial height h, the protrusion having two opposed protrusion faces distant with a length L, each the two opposed protrusion faces facing to a direction the groove provided with the protrusion extends, and a protrusion top face connecting radially outermost of the two opposed protrusion faces, the protrusion having at least two slots of a radial depth d and a width w, each opening to the protrusion top face and the two opposed protrusion faces, the radial height h of the protrusion is at least equal to 75% of the radial depth D of the groove provided with the protrusion.

This arrangement provides improvement of noise due to air column resonance without generating an abnormal noise during usage while maintaining good productivity of such the tread.

According to the above arrangement, the groove is provided with at least one protrusion protruding radially from the groove bottom. Therefore, the length of the air column of the groove formed with the road surface is different from that formed in case there is no protrusion, and the peak of groove resonance is shifted to an outside of the frequency range audible to the human ear. As a result, groove resonance due to air column resonance of the groove can be improved.

Since the protrusion is provided as to have two opposed protrusion faces distant with a length L, the protrusion is constituted by sufficiently large amount of rubber-based material to resist from deformation, the protrusion is able to wear similarly as the tread. As a result, the tread provided with the protrusion would not generate an abnormal noise during usage.

Since the protrusion has at least two slots each opens to the protrusion top face and the two opposed protrusion faces, a sound wave propagating in the groove touches more surfaces as it passes through the slots, and energy of the sound wave is attenuated. As a result, groove resonance due to air column resonance of the groove can further be improved. These at least two slots each opens to the protrusion top face and the two opposed protrusion faces make it possible to secure necessary drainage capability of the groove provided with the protrusion for safety.

Since the protrusion is protruding radially from the groove bottom and the slots opens to the protrusion top face, manufacturing of the tread provided with the protrusion having the slots in the groove doesn’t deteriorate productivity as such the configuration doesn’t hinder an opening of a mold for manufacturing the tread. Sufficiently large amount of rubber-based material for forming the protrusion makes it easier to flow the rubber-based material into a molding part for molding the protrusion and to evacuate air trapped in the molding part during molding of the protrusion.

Since the radial height h of the protrusion is at least equal to 75% of the radial depth D of the groove provided with the protrusion, it is possible to achieve improvement of groove resonance due to air column resonance.

If the radial height h of the protrusion is less than 75% of the radial depth D of the groove provided with the protrusion, there is a risk that coverage of sectional area of the groove provided by the protrusion becomes insufficient which results insufficient groove resonance reduction.

This radial height h of the protrusion is preferably at least equal to 80% of the radial depth D of the groove provided with the protrusion, more preferably at least equal to 90% of the radial depth D of the groove provided with the protrusion.

In another preferred embodiment, the length L of the protrusion is at least equal to 8 mm in the direction the groove provided with the protrusion extends.

If the length L of the protrusion is less than 8 mm, there is a risk that attenuation of sound wave energy due to air column resonance becomes insufficient which results insufficient groove resonance reduction because the sound wave propagating in the groove touches less surface when passes through the slots. By setting this length L of the protrusion more than or equal to 8 mm, it is possible to achieve improvement of groove resonance due to air column resonance.

This length L of the protrusion is preferably at least equal to 10 mm in the direction the groove provided with the protrusion extends.

In another preferred embodiment, the protrusion is attached to at least one of the opposed groove walls.

According to this arrangement, it is possible to wear the protrusion similarly as the tread more reliably as deformation resistance of the protrusion is supported by at least one of the opposed groove walls attached.

In another preferred embodiment, the protrusion is attached to the two opposed groove walls.

According to this arrangement, it is possible to wear the protrusion similarly as the tread even more reliably as deformation resistance of the protrusion is supported by the two opposed groove walls attached.

In another preferred embodiment, the radial depth d of the slots from the protrusion top face is more than or equal to 75% of the radial height h of the protrusion.

If the radial depth d of the slots from the protrusion top face is less than 75% of the radial height h of the protrusion, there is a risk that drainage capability of the groove provided with the protrusion for safety cannot be secured. By setting this radial depth d of the slots from the protrusion top face at least equal to 75% of the radial height h of the protrusion, it is possible to secure necessary drainage capability of the groove provided with the protrusion for safety.

This radial depth d of the slots from the protrusion top face is preferably at least equal to 80% of the radial height h of the protrusion, more preferably at least equal to 90% of the radial height h of the protrusion.

In another preferred embodiment, the protrusion is provided as to at least 3 protrusions exist at least in one groove within a contact patch.

If the protrusion is provided as to less than 3 protrusions exist at least in one groove within the contact patch, there is a risk that attenuation of energy of the sound wave propagating in the groove becomes insufficient resulting insufficient groove resonance reduction. By setting the protrusion being provided as to at least 3 protrusions exist at least in one groove within the contact patch, it is possible to achieve improvement of groove resonance due to air column resonance more reliably.

In another preferred embodiment, the width w of each the slots is at least equal to 1% of the width W of the groove provided with the protrusion.

If the width w of each the slots is less than 1% of the width W of the groove provided with the protrusion, there is a risk that drainage capability of the groove provided with the protrusion for safety cannot be secured. By setting this width w of each the slots at least equal to 1% of the groove provided with the protrusion, it is possible to secure necessary drainage capability of the groove provided with the protrusion for safety.

This width w of each the slots is preferably at least equal to 1.5% of the width W of the groove provided with the protrusion, more preferably at least equal to 2% of the width W of the groove provided with the protrusion.

In another preferred embodiment, the protrusion has at least equal to 10 slots.

If the protrusion has less than 10 slots, there is a risk that drainage capability of the groove provided with the protrusion for safety cannot be secured. By setting the protrusion as to have at least equal to 10 slots, it is possible to secure necessary drainage capability of the groove provided with the protrusion for safety.

The protrusion has preferably at least equal to 12 slots.

According to the arrangements described above, it is possible to provide a tread for a tire provided with a noise reduction device in a groove, such the tread can provide reduction of air column resonance without generating an abnormal noise during usage by wearing the noise reduction device in the groove similarly with the tread while maintaining productivity of such the tread.

Other characteristics and advantages of the invention arise from the description made hereafter in reference to the annexed drawings which show, as nonrestrictive examples, the embodiment of the invention.

In these drawings:
Fig. 1 is a schematic view of a portion of a tread for a tire according to a first embodiment of the present invention; Fig. 2 is a schematic perspective view of a portion of the tread for a tire according to the first embodiment of the present invention; Fig. 3 is a schematic cross sectional view taken along line III-III in Fig. 1; Fig. 4 is a schematic view of a portion of a tread for a tire according to a second embodiment of the present invention; Fig. 5 is a schematic cross sectional view taken along line V-V in Fig. 4; Fig. 6 is a schematic view of a portion of a tread for a tire according to a third embodiment of the present invention; Fig. 7 is a schematic cross sectional view taken along line VII-VII in Fig. 6;

Preferred embodiments of the present invention will be described below referring to the drawings.

A tread 1 for a tire according to a first embodiment of the present invention will be described referring to Figs. 1, 2 and 3.

Fig. 1 is a schematic view of a portion of a tread for a tire according to a first embodiment of the present invention. Fig.2 is a schematic perspective view of a portion of the tread for a tire according to the first embodiment of the present invention. Fig. 3 is a schematic cross sectional view taken along line III-III in Fig. 1.

The tread 1 is a tread for a tire having dimension 225/45R17 and comprises a contact face 2 intended to come into contact with the ground during rolling, and two grooves 3 extending generally in circumferential orientation indicated as XX’. The grooves 3 are delimited by two opposed

groove walls

31, 32 facing each other and being connected by a groove bottom 33 connecting radially innermost of the two

opposed groove walls

31, 32. The groove 3 has a width W at a level of the contact face 2 and a depth D (as shown in Fig. 3). In the present embodiment, the width W of the groove 3 is 20 mm, the depth D of the groove 3 is 8 mm.

As shown in Fig. 1, a contact patch 6 has a contact patch length LCP in a tire circumferential orientation when the tire with the tread 1 is mounted onto its standard rim and inflated at its nominal pressure and its nominal load is applied. According to ‘ETRTO Standard Manual 2017’ the standard rim for this size is 7.5J, the nominal pressure is 250kPa and the nominal load is 615kg.

As shown in Fig. 1, in the groove 3, a plurality of protrusion 4 protruding from the groove bottom 33 with a radial height h (shown in Fig. 3) is provided for dividing an air column created between the ground and the groove 3 in the contact patch 6 during rolling. Each protrusion 4 has two opposed protrusion faces 41, 42 distant with a length L and facing to a direction the groove 3 extends, and a protrusion top face 43 connecting radially outermost of the two opposed protrusion faces 41, 42. The protrusion 4 is attached to the two

opposed groove walls

31, 32, as shown in Fig. 2. Each protrusion 4 is spaced from each other by distance P (distance between one of the two

opposed protrusion face

41, 42 of one protrusion 4 and corresponding one of the two

opposed protrusion face

41, 42 of adjacent protrusion 4) in the direction the groove 3 extends. The distance P is preferably, in relation with the length L, set as to at least 3 protrusions 4 exist at least in one groove 3 within the contact patch 6. In the present embodiment, the length L of the protrusion 4 in the direction the groove 3 provided with the protrusion 4 extends is 10 mm, the distance P is 40 mm, and the radial height h of the protrusion 4 is 6.7 mm.

The protrusion 4 is provided with three slots (or slits) 5 of a radial depth d from the protrusion top face 43 and a width w (shown in Fig. 3), each opens to the protrusion top face 43 and the two opposed protrusion faces 41, 42. In the present embodiment, the radial depth d of the slot (or slit) 5 from the protrusion top face 43 is 6 mm, the width w of the slot (or slit) 5 is 1 mm.

As shown in Fig. 2 and also in Fig. 3, the protrusion top face 43 is offset radially inwardly from the contact face 2. Also, a radially innermost of the slots (or slits) 5 is offset radially outwardly from the groove bottom 33.

Since the groove 3 is provided with at least one protrusion 4 protruding radially from the groove bottom 33, the length of the air column of the groove 3 formed with the road surface is different from that formed in case there is no protrusion 4, and the peak of groove resonance is shifted to an outside of the frequency range audible to the human ear, thus groove resonance due to air column resonance of the groove 3 is improved.

Since the protrusion 4 is provided as to have two opposed protrusion faces 41, 42 distant with a length L, the protrusion 4 is constituted by sufficiently large amount of rubber-based material to resist from deformation, the protrusion 4 is able to wear similarly as the tread 1, thus the tread 1 provided with the protrusion 4 would not generate an abnormal noise during usage.

Since the protrusion 4 has at least two slots (or slits) 5 each opens to the protrusion top face 43 and the two opposed protrusion faces 41, 42, a sound wave propagating in the groove 3 touches more surfaces as it passes through the slots (or slits) 5, and energy of the sound wave is attenuated, thus groove resonance due to air column resonance of the groove 3 can further be improved. These at least two slots (or slits) 5 each opens to the protrusion top face 43 and the two opposed protrusion faces 41, 42 make it possible to secure necessary drainage capability of the groove 3 provided with the protrusion 4 for safety.

Since the protrusion 4 is protruding radially from the groove bottom 33 and the slots (or slits) 5 opens to the protrusion top face 43, manufacturing of the tread 1 provided with the protrusion 4 having the slots (or slits) 5 in the groove 3 doesn’t deteriorate productivity as such the configuration doesn’t hinder an opening of a mold for manufacturing the tread 1. Sufficiently large amount of rubber-based material for forming the protrusion 4 makes it easier to flow the rubber-based material into a molding part for molding the protrusion 4 and to evacuate air trapped in the molding part during molding of the protrusion 4.

Since the length L of the protrusion 4 is at least equal to 8 mm in the direction the groove 3 provided with the protrusion 4 extends, it is possible to achieve improvement of groove resonance due to air column resonance. If the length L of the protrusion 4 is less than 8 mm, there is a risk that attenuation of sound wave energy due to air column resonance becomes insufficient which results insufficient groove resonance reduction because the sound wave propagating in the groove 3 touches less surface when passes through the slots (or slits) 5 on the protrusion 4. This length L of the protrusion 4 is preferably at least equal to 10 mm in the direction the groove 3 provided with the protrusion 4 extends.

Since the radial height h of the protrusion 4 is at least equal to 75% of the radial depth D of the groove 3 provided with the protrusion 4, it is possible to achieve improvement of groove resonance due to air column resonance. If the radial height h of the protrusion 4 is less than 75% of the radial depth D of the groove 3 provided with the protrusion 4, there is a risk that coverage of sectional area of the groove 3 provided by the protrusion 4 becomes insufficient which results insufficient groove resonance reduction. This radial height h of the protrusion 4 is preferably at least equal to 80% of the radial depth D of the groove 3 provided with the protrusion 4, more preferably at least equal to 90% of the radial depth D of the groove 3 provided with the protrusion 4.

Since the protrusion 4 is attached to the two

opposed groove walls

31, 32, it is possible to wear the protrusion 4 similarly as the tread 1 reliably as deformation resistance of the protrusion 4 is supported by the two

opposed groove walls

31, 32 attached.

Since the radial depth d of the slots (or slits) 5 from the protrusion top face 43 is more than or equal to 75% of the radial height h of the protrusion 4, it is possible to secure necessary drainage capability of the groove 3 provided with the protrusion 4 for safety. If the radial depth d of the slots (or slits) 5 from the protrusion top face 43 is less than 75% of the radial height h of the protrusion 4, there is a risk that drainage capability of the groove 3 provided with the protrusion 4 for safety cannot be secured. This radial depth d of the slots (or slits) 5 from the protrusion top face 43 is preferably at least equal to 80% of the radial height h of the protrusion 4, more preferably at least equal to 90% of the radial height h of the protrusion 4.

Since the protrusion 4 is provided as to at least 3 protrusions 4 exist at least in one groove 3 within a contact patch 6, it is possible to achieve improvement of groove resonance due to air column resonance more reliably. If the protrusion 4 is provided as to less than 3 protrusions 4 exist at least in one groove 3 within the contact patch 6, there is a risk that attenuation of energy of the sound wave propagating in the groove 3 becomes insufficient resulting insufficient groove resonance reduction.

Since the width w of each the slots (or slits) 5 is at least equal to 1% of the width W of the groove 3 provided with the protrusion 4, it is possible to secure necessary drainage capability of the groove 3 provided with the protrusion 4 for safety. If the width w of each the slots (or slits) 5 is less than 1% of the width W of the groove 3 provided with the protrusion 4, there is a risk that drainage capability of the groove 3 provided with the protrusion 4 for safety cannot be secured. This width w of each the slots (or slits) 5 is preferably at least equal to 1.5% of the width W of the groove 3 provided with the protrusion 4, more preferably at least equal to 2% of the width W of the groove 3 provided with the protrusion 4.

A sum of the width w of the slots (or slits) 5 in one protrusion 4 may be between 10% and 50% of the width W of the groove 3 for achieving improvement of groove resonance due to air column resonance and for securing necessary drainage capability of the groove 3 provided with the protrusion 4 for safety simultaneously.

The opposed protrusion faces 41, 42 may be provided in curved, waved, zigzagged or any other form. The protrusion top face 43 may be provided in curved, waved, zigzagged, concave, convex or any other form.

The slots (or slits) 5 may be provided in curved, waved or zigzagged form in the direction the groove 3 provided with the protrusion 4 extends, in radial direction or in both the groove 3 provided with the protrusion 4 extends and radial directions.

The protrusion 4 may be provided with a combination of various form, various width w, various depth d and/or various angle relative to circumferential orientation of the slots (or slits) 5 in one protrusion 4.

A tread 21 for a tire according to a second embodiment of the present invention will be described referring to Fig. 4 and Fig. 5. Fig. 4 is a schematic view of a portion of a tread for a tire according to a second embodiment of the present invention. Fig. 5 is a schematic cross sectional view taken along line V-V in Fig. 4.

In the second embodiment, the tread 21 is provided with an obliquely extending curved groove 23 delimited by two opposed

groove walls

231, 232 facing each other and being connected by a groove bottom 233 connecting radially innermost of the two

opposed groove walls

231, 232. In the groove 23, a protrusion 24 protruding from the groove bottom 233 with a radial height h (shown in Fig. 5) is provided for dividing an air column created between ground and the groove 23 during rolling.

The protrusion 24 has two opposed protrusion faces 241, 242 distant with a length L and facing to a direction the groove 23 extends, and a protrusion top face 243 connecting radially outermost of the two opposed protrusion faces 241, 242. The protrusion 24 is attached to one of the two opposed groove walls 232 but not to another one of the two opposed groove walls 231. The length L of the protrusion 24 is measured as a minimum distance between the protrusion faces 241, 242 along the groove 23.

The protrusion 24 is provided with five slots (or slits) 25 of a radial depth d from the protrusion top face 243 and a width w (shown in Fig. 5) extending similarly as the groove 23 extends, each opens to the protrusion top face 243 and the two opposed protrusion faces 241, 242.

As shown in Fig. 5, a radial height h of the protrusion 24 is equal to a depth D of the groove 23, that is to say that the protrusion top face 243 is radially at the same level as a contact face 22 of the tread 21. The radial depth d of the slots (or slits) 25 from the protrusion top face 243 is different with the radial height h of the protrusion 24 but is more than or equal to 75% of the radial height h of the protrusion 24. One slot (or slit) 25 closest to one of the opposed groove wall 232 in which the protrusion 24 being attached is partly cut by one of the opposed groove wall 232.

Since the protrusion 24 is attached to at least one of the opposed

groove walls

231, 232, it is possible to wear the protrusion 24 similarly as the tread 21 more reliably as deformation resistance of the protrusion 24 is supported by at least one of the opposed

groove walls

231, 232 attached.

Also with this configuration, a space delimited with the protrusion 24 and one of the opposed groove wall 231 which the protrusion 24 is not attached makes it possible to secure necessary drainage capability of the groove 23 provided with the protrusion 24 for safety.

The protrusion 24 may be provided as to attach alternately to one of the opposed

groove walls

231, 232.

A tread 51 for a tire according to a second embodiment of the present invention will be described referring to Fig. 6 and Fig. 7. Fig. 6 is a schematic view of a portion of a tread for a tire according to a third embodiment of the present invention. Fig. 7 is a schematic cross sectional view taken along line VII-VII in Fig. 6.

In the third embodiment, the tread 51 is provided with a main groove 53(a) extending in circumferential orientation which is top-bottom orientation in Fig. 6 and a groove 53 opening to the main groove 53(a) and extending to transverse orientation which is left-right orientation in Fig. 6. The groove 53 is delimited by two opposed

groove walls

531, 532 facing each other and being connected by a groove bottom 533 connecting radially innermost of the two

opposed groove walls

531, 532. In the groove 53, a protrusion 54 protruding from the groove bottom 533 with a radial height h (shown in Fig. 7) is provided for dividing an air column created between ground and the groove 53 during rolling.

The protrusion 54 has two opposed protrusion faces 541, 542 distant with a length L and facing to a direction the groove 53 extends, and a protrusion top face 543 connecting radially outermost of the two opposed protrusion faces 541, 542. Both the two opposed protrusion faces 541, 542 slants toward the groove bottom 533 as to extend a distance between two opposed protrusion faces 541, 542 for supporting a rigidity of the protrusion 54.

The protrusion 54 is provided with thirteen slots (or slits) 55 of a radial depth d from the protrusion top face 543 and a width w (shown in Fig. 7) extending as to share an opening to the two opposed protrusion faces 541, 542 with adjacent slot (or slit) 55 except those closest to the opposed

groove walls

531, 532.

As shown in Fig. 7, a radial height h of the protrusion 54 is equal to a depth D of the groove 53, that is to say that the protrusion top face 543 is radially at the same level as a contact face 52 of the tread 51. The radial depth d of the slots (or slits) 55 from the protrusion top face 543 is also equal to the depth D of the groove 53 thus equal to the radial height h of the protrusion 54. The width w of the slot (or slit) 55 is decreasing toward the groove bottom 533.

Since the protrusion 54 has at least equal to 10 slots (or slits) 55, it is possible to secure necessary drainage capability of the groove 53 provided with the protrusion 54 for safety. If the protrusion 54 has less than 10 slots 55, there is a risk that drainage capability of the groove 53 provided with the protrusion 54 for safety cannot be secured. The protrusion 54 has preferably at least equal to 12 slots (or slits) 55.

Also with this configuration, a space delimited with the protrusion 54 and the

opposed groove wall

531, 532 makes it possible to secure further necessary drainage capability of the groove 53 provided with the protrusion 54 for safety.

In order to confirm the effect of the present invention, two types of pneumatic tires of Example to which the present invention is applied and other types of pneumatic tires of Reference and Comparative Example were prepared.

The Example 1 was a pneumatic tire as described in the above first embodiment but provided with the protrusion having the height h equals to the depth D of the groove (that is to say 8 mm) and 10 (ten) slots (or slits) of the width w equals to 0.4 mm and the depth d equals to the height h of the protrusion (that is to say 8 mm also), the Example 2 was also a pneumatic tire as described in the above first embodiment but provided with the protrusion having the height h equals to the depth D of the groove (that is to say 8 mm) and 20 (twenty) slots (or slits) of the width w equals to 0.2 mm and the depth d equals to the height h of the protrusion (that is to say 8 mm also). The Reference 1 was a pneumatic tire without the protrusion. The Comparative Example was a pneumatic tire provided with a closing device of prior art as described in WO2010/063749. All the Examples, Reference and Comparative Example were made of the same rubber-based material, using the same typical radial tire construction for passenger car tire.

The tire dimension of the Examples, Comparative Example and Reference were all 225/45R17, mounted onto a rim of 7.5Jx17, and inflated to 180 kPa.

Noise performance tests:

A sound pressure level of the unused test tires mounted onto abovementioned rim, inflated to abovementioned internal pressure were measured while applying a load of 452daN, running 90kph on a drum of 2.7m in diameter having ISO surface in a semi-anechoic chamber, via a microphone installed axially 1 m outward from a center of tire contact, radially 0.2m backward from a tire rolling axis and 0.32m in height. The data acquired through the measurements were processed to calculate an absorption level of a sound between 600 and 1,300 Hz at which groove resonance frequency been contained. The results are shown in table 1. In this table 1, results are represented by an index of 100 for Reference, higher the number indicates better the noise performance.

Appearance tests:

A skilled inspector inspected visually each the pneumatic tires of the Examples, Comparative Example and Reference; evaluate as ○ if no molding defect had been observed, △ if a few molding defect had been observed. The results are also shown in table 1.

As seen from table 1, the Examples show improvement on noise performance while maintaining good productivity represented by appearance.

The invention is not limited to the examples described and represented and various modifications can be made there without leaving its framework.

1, 21, 51 tread
2, 22, 52 contact face
3, 23, 53 groove
31, 32, 231, 232, 531, 532 opposed groove wall(s)
33, 233, 533 groove bottom
4, 24, 54 protrusion
41, 42, 241, 242, 541, 542 opposed protrusion face(s)
43, 243, 543 protrusion top face
5, 25, 55 slot(s) (or slit(s))
6 contact patch

Claims

A tread (1) for a tire having a contact face (2) intended to come into contact with ground during rolling, the tread (1) being provided with at least one groove (3) of a radial depth D and a width W being composed of two opposed groove walls (31, 32) and a groove bottom (33) connecting radially innermost of the two opposed groove walls (31, 32), the groove (3) having at least one protrusion (4) protruding radially from the groove bottom (33) with a radial height h, the protrusion (4) having two opposed protrusion faces (41, 42) distant with a length L, each the two opposed protrusion faces (41, 42) facing to a direction the groove (3) provided with the protrusion (4) extends, and a protrusion top face (43) connecting radially outermost of the two opposed protrusion faces (41, 42), the protrusion (4) having at least two slots (5) of a radial depth d and a width w, each opening to the protrusion top face (43) and the two opposed protrusion faces (41, 42), the tread being characterized in that the radial height h of the protrusion (4) is at least equal to 75% of the radial depth D of the groove (3) provided with the protrusion (4).
The tread (1) according to claim 1, wherein the length L of the protrusion (4) is at least equal to 8 mm in the direction the groove (3) provided with the protrusion (4) extends.
The tread (1) according to claim 1 or claim 2, wherein the protrusion (4) is attached to at least one of the opposed groove walls (31, 32).
The tread (1) according to claim 3, wherein the protrusion (4) is attached to the two opposed groove walls (31, 32).
The tread (1) according to any one of the claims 1 to 4, wherein the radial depth d of the slots (5) from the protrusion top face (43) is more than or equal to 75% of the radial height h of the protrusion (4).
The tread (1) according to any one of the claims 1 to 5, wherein the protrusion (4) is provided as to at least 3 protrusions (4) exist at least in one groove (3) within a contact patch (6).
The tread (1) according to any one of the claims 1 to 6, wherein the width w of each the slots (5) is at least equal to 1% of the width W of the groove (3) provided with the protrusion (4).
The tread (1) according to any one of the claims 1 to 7, wherein the protrusion (4) has at least equal to 10 slots (5).
A tire having a tread according to any one of the claims 1 to 8.