WO2020129906A1

WO2020129906A1 - A tread for improved winter performance

Info

Publication number: WO2020129906A1
Application number: PCT/JP2019/049206
Authority: WO
Inventors: Tomotake UCHIDA; Kaori ONOZAKI
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2018-12-17
Filing date: 2019-12-16
Publication date: 2020-06-25

Abstract

Tread (1) for a tire having a contact face (2) intended to come into contact with ground during rolling, the tread being provided with a plurality of groove (3) and/or a plurality of incision (4), the plurality of groove and/or the plurality of incision delimiting a plurality of contact element (5), the contact element having a top face (51) and a frontal face (52), the top face and the frontal face creating an edge (53), at least one of the contact element being provided with at least one projection portion (6) projecting radially outwardly from the top face (51), the projection portion being provided with a chamfered portion (61) on a side facing to the closest edge (53), the contact element comprises at least one pocket portion (7) recessed from the top face (51) toward radially inward of the contact element, and the pocket portion (7) is composed of at least two pocket faces (71), and the at least one pocket portion (7) is provided circumferentially next to the projection portion.

Description

A TREAD FOR IMPROVED WINTER PERFORMANCE

The present invention relates to a tread for a tire, in particular to a tread for a tire for improving snow performance while maintaining wet performance.

In recent years, a tire so-called “all-season” tire which has capability to drive on wintry surface while maintaining high speed driving capability on non-wintry surface is beginning to popularize.

Also to a tire so-called “studless” tire which is suitable for driving on ice covered and/or snow covered wintry surface, there is a desire to increase performance on non-wintry surface that is not covered by ice nor snow while still improving performance on wintry surface.

In order to increase performance on wintry surface especially snow performance, it is known to provide a stud-like projection, made of rubber or a metal or other, projecting from a contact face is effective as such the stud-like projection generates high pressure to scrape snow. It is also known that such the way impacts negatively performance on non-wintry surface especially wet performance. Also, use of metal stud is prohibited in many countries for environmental reason.

JP2017-105411 discloses a pneumatic tire having a tread consists of a projection portion projecting radially for improving tire noise.

JP2011-140254 discloses also a pneumatic tire having a tread consists of a projection portion projecting radially for improving tire noise.

JP2011-031831 discloses a pneumatic tire having a tread with predetermined rotational direction consists of a projection portion projecting radially for irregular wear improvement while maintaining traction performance on wet and wintry surface.

JP2007-022242 discloses a pneumatic tire having a tread with predetermined rotational direction consists of a plurality of fine ribs (projection portion) each having a triangular cross sectional shape being arranged as a saw blade for better traction performance on wintry surface.

JP2017-105411 JP2011-140254 JP2011-031831 JP2007-022242

However with the solutions disclosed in these documents, improvement of performance on wintry surface especially ice performance is not satisfactory, and there is a desire to further improvement of overall performance on wintry surface.

Therefore, there is a need for a tread for a tire which provides higher performance on wintry surface especially ice performance.

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.

An “incision”, also referred to as a “sipe”, is a narrow cutout formed toward radially inwardly from a surface of a tread made by, for example a thin blade having a shape like a knife blade. A width of the incision at the surface of the tread is narrower than a groove, for example less than or equal to 2.0mm. This incision may, different from the groove, be partly or completely closed when such the incision is in a contact patch and under usual rolling condition.

A “contact patch” is a footprint of a tire mounted onto its standard rim as identified in tire standards such as ETRTO, JATMA or TRA, and inflated at its nominal pressure and under its nominal load.

It is thus an object of the invention to provide higher performance on wintry surface especially ice performance.

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 a plurality of groove of a depth D and/or a plurality of incision of a depth d extending generally in axial orientation of the tire and being disposed such that at least two grooves or two incisions or one groove and one incision being always located within a contact patch, the plurality of groove and/or the plurality of incision delimitating a plurality of contact element, the plurality of contact element having a top face constituting a part of the contact face and a frontal face facing to the groove or to the incision, the top face and the frontal face creating an edge at an intersection between the top face and the frontal face, at least one of the plurality of contact element being provided with at least one projection portion projecting radially outwardly from the top face with a radial height h in a region between the closest edge and 40% of a circumferential length of the contact element from the closest edge, the projection portion being provided with a chamfered portion on a side facing to the closest edge, the chamfered portion having an angle A relative to the top face on cross sectional view along with circumferential orientation, the contact element comprises at least one pocket portion recessed from the top face toward radially inward of the contact element, the pocket portion is composed of at least two pocket faces, the at least one pocket portion is provided circumferentially next to the projection portion.

This arrangement provides higher performance on wintry surface especially ice performance.

Since the contact element is provided with at least one projection portion projecting radially outwardly from the top face with a radial height h, such the projection portion is able to generate high pressure to scrape snow, performance on wintry surface especially snow performance can be improved.

Since the projection portion is provided with a chamfered portion on a side facing to the closest edge and the chamfered portion has an angle A relative to the top face on cross sectional view along with circumferential orientation, such the chamfered portion is able to prevent generating too high pressure and avoid curling of the projection portion, performance on non-wintry surface can be improved at the same time.

If the projection portion is provided outside of the region between the closest edge and 40% of a circumferential length of the contact element from the closest edge, there is a risk that performance on wintry surface would be degraded as the projection portion cannot generate high contact pressure efficiently. By placing the projection portion in the region between the closest edge and 40% of a circumferential length of the contact element from the closest edge, the projection portion can generate high contact pressure efficiently.

If the chamfered portion is provided on a side opposite to the closest edge, the chamfered portion would be less effective to prevent generating too high pressure and difficult to prevent curling of the projection portion, performance on non-wintry surface cannot be improved even performance on wintry surface may be improved. By placing the chamfered portion on the side facing to the closest edge, it is possible to improve performance on wintry surface and on non-wintry surface at the same time.

Since the contact element comprises at least one pocket portion recessed from the top face toward radially inward of the contact element, the pocket portion is composed of at least two pocket faces, and the at least one pocket portion is provided circumferentially next to the projection portion, the projection portion deformed by load, acceleration or braking force can be accommodated in the pocket portion, it is possible to increase an area in contact with ground at portions on the top face (the contact face) of the contact element other than the projection portion and the pocket portion, as a result performance on wintry surface especially ice performance can be improved.

In another preferred embodiment, the at least one pocket portion is provided circumferentially inward of the contact element from the projection portion.

According to this arrangement, it is possible to reliably improve performance on wintry surface especially ice performance as the contact element can be provided with the pocket portion even the projection portion is provided closer to the edge.

In another preferred embodiment, the tread has an intended direction of rotation, and the projection portion and the pocket portion are provided on a trailing side of the contact element.

According to this arrangement, it is possible to improve performance on wintry surface in particular braking performance as the trailing side of the contact element plays an important role during braking.

In another preferred embodiment, the pocket portion is provided with at least one recessed portion recessed from the pocket face closer to the projection portion circumferentially toward the closest projection portion.

According to this arrangement, it is possible to improve performance on wintry surface in particular ice performance more reliably as the recessed portion facilitates deformation of the projection portion to be accommodated in the pocket portion.

In another preferred embodiment, the recessed portion is provided at radially innermost of the pocket face.

According to this arrangement, it is possible to improve performance on wintry surface in particular ice performance more reliably as the recessed portion provided at radially innermost of the pocket face further facilitates deformation of the projection portion to be accommodated in the pocket portion.

In another preferred embodiment, the contact element is provided with two projection portions and two pocket portions, and the projection portion and the pocket portion are provided alternately in circumferential orientation.

According to this arrangement, it is possible to improve performance on wintry surface in particular ice performance more reliably as circumferentially positioned two projection portions help to increase an area in contact with ground at portions on the contact face of the contact element other than the projection portion and the pocket portion.

In another preferred embodiment, the pocket face closer to the projection portion is flush with a face of the projection portion facing to the pocket portion.

According to this arrangement, it is possible to increase manufacturing efficiency of the tread having the contact element provided with the projection portion and the pocket portion as a positioning between the projection portion and the pocket portion becomes easier.

In another preferred embodiment, the angle A of the chamfered portion is from 30 to 60 degrees.

If the angle A of the chamfered portion is less than 30 degrees, there is a risk that the chamfered portion would be less effective to prevent generating too high pressure thus performance on non-wintry surface would be degraded. If the angle A of the chamfered portion is more than 60 degrees, there is a risk that the chamfered portion would be less effective to prevent curling of the projection portion, thus performance on non-wintry surface would be degraded also. By setting this angle A of the chamfered portion is from 30 to 60 degrees, it is possible to effectively improve performance on non-wintry surface.

In another preferred embodiment, the projection portion is flush with the frontal face of the contact element at least partly.

According to this arrangement, it is possible to place the projection portion where the projection portion generates high contact pressure efficiently, thus performance on wintry surface would further be improved.

In another preferred embodiment, the projection portion is offset from the closest edge.

According to this arrangement, it is possible to increase a degree of freedom for placing the projection portion, thus balance between performance on wintry surface and on non-wintry surface would be improved.

In another preferred embodiment, a rubber composition constituting the projection portion is the same as a rubber composition constituting the contact element.

According to this arrangement, it is possible to manufacture efficiently the tread having the contact element provided with the projection portion comprising the chamfered portion, thus manufacturing efficiency of such the tread would be improved.

According to the arrangements described above, it is possible to provide higher performance on wintry surface especially ice performance.

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 perspective view of a tread according to a first embodiment of the present invention; Fig. 2 is a cross sectional view taken along line II-II in Fig. 1; Fig. 3 is a schematic perspective view of a tread according to a second embodiment of the present invention; Fig. 4 is a cross sectional view taken along line IV-IV in Fig. 3; Fig. 5 is a schematic cross sectional view of a tread according to a third embodiment of the present invention; Fig. 6 is an enlarged schematic view showing a portion indicated as VI in Fig. 5; Fig. 7 is a cross sectional view of a tread according to prior art.

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 and 2.

Fig. 1 is a schematic plan view of a tread according to a first embodiment of the present invention. Fig. 2 is a cross sectional view taken along line II-II in Fig. 1.

The tread 1 is a tread for a tire having a contact face 2 intended to come into contact with ground during rolling, and a plurality of groove 3 of a depth D (shown in Fig. 2) opening to the contact face 2. The plurality of groove 3 includes a lateral groove 3a extending generally in axial orientation and a circumferential groove 3b extending generally in circumferential orientation as indicated by line XX’ (shown in Fig. 2 also). The plurality of groove 3 (the lateral groove 3a and the circumferential groove 3b) is delimiting a plurality of contact element 5, and the circumferential groove 3b is dividing the tread 1 axially into three block rows. Each the plurality of contact element 5 is provided with a plurality of incision 4 of a depth d (shown in Fig. 2) extending generally in the axial orientation. The plurality of incision 4 is opening to the circumferential groove 3b at two axial ends. Each the plurality of contact element 5 having a top face 51 constituting a part of the contact face 2 and a frontal face 52 facing to the groove 3 (the lateral groove 3a). The top face 51 and the frontal face 52 creating an edge 53 at an intersection between the top face 51 and the frontal face 52.

As shown in Fig. 1, each the plurality of contact element 5 being provided with two projection portions 6 projecting radially outwardly from the top face 51 with a radial height h in a region between the closest edge 53 and 40% of a circumferential length of the contact element 5 from the closest edge 53 (shown in Fig. 2). Each the projection portion 6 is provided with a chamfered portion 61 in a whole width of the projection portion 6 on a side facing to the closest edge 53 and having an angle A relative to the top face 51 (shown in Fig. 2), and with a flat portion 62 parallel to the top face 51 (shown in Fig. 2). The projection portion 6 is offset from the closest edge 53.

As shown in Fig. 1, the projection portion 6 has a width narrower than a width of the contact element 5. A rubber composition constituting the projection portion 6 is the same as a rubber composition constituting the contact element 5.

As shown in Fig. 1, the contact element 5 comprises at least one pocket portion 7 recessed from the top face 51 toward radially inward of the contact element 5. The pocket portion 7 is composed of at least two pocket faces 71. The pocket portion 7 is provided circumferentially next to the projection portion 6. The pocket portion 7 is provided circumferentially inward of the contact element 5 from the projection portion 6. The pocket portion 7 is provided circumferentially inward of the contact element 5 from the projection portion 6.

As shown in Fig. 2 the contact element 5 is provided with the projection portion 6 projecting radially outwardly from the top face 51 which is constituting a part of the contact face 2 with a radial height h in the region between the closest edge 53 and 40% of the circumferential length of the contact element 5 from the closest edge 53. A face of the projection portion 6 close to the closest edge 53 is flush with the frontal face 52 of the contact element 5. The radial height h of the projection portion 6 is at most equal to 20% of the depth D of the groove 3 or the depth d of the incision 4 whichever is deeper. In this first embodiment, the height h of the projection portion 6 is 1.0 mm.

As shown in Fig. 2, the projection portion 6 is provided with the chamfered portion 61 on the side facing to the closest edge 53. The projection portion 6 has the angle A relative to the top face 51 and this angle A is from 30 to 60 degrees. A radially innermost of the chamfered portion 61 is distant from the top face 51 when the tread 1 being bland new. The projection portion 6 further comprises the flat portion 62 parallel to the top face 51. In this first embodiment, the angle A of the chamfered portion 61 relative to the top face 51 is 35 degrees.

As shown in Fig. 2, the contact element 5 delimited by the groove 3 (the lateral groove 3a) of the depth D is provided with one incision 4 of the depth d at around circumferentially a center of the contact element 5, and the depth d of the incision 4 is shallower than the depth D of the groove 3 (the lateral groove 3a). In this first embodiment, the depth D of the groove 3 (the lateral groove 3a) is 9.2 mm, and the depth d of the incision 4 is 8.5 mm.

As shown in Fig. 2, the pocket portion 7 is composed of at least two pocket faces 71, one of the pocket face 71 positioned circumferentially inward of the contact element 5 extends radially downwardly from the top face 51 in straight manner, and another pocket face 71 positioned circumferentially outward of the contact element 5 extends radially downwardly from the top face 51 in curved manner. The pocket face 71 closer to the projection portion 6 is flush with a face of the projection portion 6 facing to the pocket portion 7.

As shown in Fig. 2, the projection portion 6 is provided with the chamfered portion 61 on the side facing to the closest edge 53. The projection portion 6 has the angle A relative to the top face 51 and this angle A is from 30 to 60 degrees. The projection portion 6 further comprises the flat portion 62 parallel to the top face 51. In this first embodiment, the angle A of the chamfered portion 61 relative to the top face 51 is 40 degrees.

Since the contact element 5 is provided with at least one projection portion 6 projecting radially outwardly from the top face 51 with a radial height h, such the projection portion 6 is able to generate high pressure to scrape snow, performance on wintry surface especially snow performance can be improved.

Since the projection portion 6 is provided with a chamfered portion 61 on a side facing to the closest edge 53 and the chamfered portion 61 has an angle A relative to the top face 51 on cross sectional view along with circumferential orientation, such the chamfered portion 61 is able to prevent generating too high pressure and avoid curling of the projection portion 6, performance on non-wintry surface can be improved at the same time.

If the projection portion 6 is provided outside of the region between the closest edge 53 and 40% of a circumferential length of the contact element 5 from the closest edge 53, there is a risk that performance on wintry surface would be degraded as the projection portion 6 cannot generate high contact pressure efficiently. By placing the projection portion 6 in the region between the closest edge 53 and 40% of a circumferential length of the contact element 5 from the closest edge 53, the projection portion 6 can generate high contact pressure efficiently.

If the chamfered portion 61 is provided on a side opposite to the closest edge 53, the chamfered portion 61 would be less effective to prevent generating too high pressure and difficult to prevent curling of the projection portion 6, performance on non-wintry surface cannot be improved even performance on wintry surface may be improved. By placing the chamfered portion 61 on the side facing to the closest edge 53, it is possible to improve performance on wintry surface and on non-wintry surface at the same time.

Since the contact element 5 comprises at least one pocket portion 7 recessed from the top face 51 toward radially inward of the contact element 5, the pocket portion 7 is composed of at least two pocket faces 71, and the at least one pocket portion 7 is provided circumferentially next to the projection portion 6, the projection portion 6 deformed by load, acceleration or braking force can be accommodated in the pocket portion 7, it is possible to increase an area in contact with ground at portions on the top face 51 (the contact face 2) of the contact element 5 other than the projection portion 6 and the pocket portion 7, as a result performance on wintry surface especially ice performance can be improved.

Since the at least one pocket portion 7 is provided circumferentially inward of the contact element 5 from the projection portion 6, it is possible to reliably improve performance on wintry surface especially ice performance as the contact element 5 can be provided with the pocket portion 7 even the projection portion 6 is provided closer to the edge 53.

Since the pocket face 71 closer to the projection portion 6 is flush with a face of the projection portion 6 facing to the pocket portion 7, it is possible to increase manufacturing efficiency of the tread 1 having the contact element 5 provided with the projection portion 6 and the pocket portion 7 as a positioning between the projection portion 6 and the pocket portion 7 becomes easier.

Since the angle A of the chamfered portion 61 is from 30 to 60 degrees, it is possible to effectively improve performance on non-wintry surface.

If the angle A of the chamfered portion 61 is less than 30 degrees, there is a risk that the chamfered portion 61 would be less effective to prevent generating too high pressure thus performance on non-wintry surface would be degraded. If the angle A of the chamfered portion 61 is more than 60 degrees, there is a risk that the chamfered portion 61 would be less effective to prevent curling of the projection portion 6, thus performance on non-wintry surface would be degraded also.

Since the projection portion 6 is offset from the closest edge 53, balance between performance on wintry surface and on non-wintry surface would be improved as it is possible to increase a degree of freedom for placing the projection portion 6.

Since a rubber composition constituting the projection portion 6 is the same as a rubber composition constituting the contact element 5, manufacturing efficiency of such the tread 1 would be improved as it is possible to manufacture efficiently the tread 1 having the contact element 5 provided with the projection portion 6 comprising the chamfered portion 61.

The projection portion 6 may be made of a material different than the rubber composition constituting the contact element 5, even partly. Such the material may still be a rubber composition.

The pocket portion 7 may be provided in a various kind of form by combining at least two pocket faces 71, for example triangular, rectangular or polygonal shape. The pocket face 71 may also be provided in a various kind of form, for example straight, curved, waved or combination of these forms with or without straight form.

The projection portion 6 may be provided in a various kind of form, for example curved, waved or combination of these forms with straight form. Multiple projection portions 6 may be provided in pair with the pocket portion 7 and relative to the one edge 53. In such the case, each the projection portion 6 and the pocket portion 7 in pair may have the same form, or may have different form one another including its position relative to the edge 53, the height h of the projection portion 6 and/or the angle A of the chamfered portion 61 relative to the top face 51.

The projection portion 6 in pair with the pocket portion 7 may be provided at a region closer to the edge 53 created at the intersection between the top face 51 and a frontal face made via the incision 4.

The chamfered portion 61 may extend to below the edge 53 as to include partly the contact element 5. Or the edge 53 of the contact element 5 may be chamfered also.

A tread 21 for a tire according to a second embodiment of the present invention will be described referring to Figs. 3 and 4. Fig. 3 is a schematic perspective view of a tread according to a second embodiment of the present invention. Fig. 4 is a cross sectional view taken along line IV-IV in Fig. 3. The construction of this second embodiment is similar to that of the first embodiment other than the arrangement shown in Figs. 3 and 4, thus description will be made referring to Figs. 3 and 4.

As shown in Fig. 3, a tread 21 having a contact face 22 intended to come into contact with ground during rolling and being provided with a plurality of groove 23 (a lateral groove 23a and a circumferential groove 23b). The tread 21 having an intended direction of rotation which is a direction from X toward X’ in this Fig. 3. The plurality of groove 23 delimitating a plurality of contact element 25 having a top face 251 constituting a part of the contact face 22. A frontal face 252 is facing to the lateral groove 23a. Each the plurality of contact element 25 is provided with a plurality of incision 24 extending generally in the axial orientation. The plurality of incision 24 is opening to the circumferential groove 23b at two axial ends.

As shown in Fig. 3, each the plurality of contact element 25 being provided with one projection portions 26 in a region between the closest edge 253 and 40% of a circumferential length of the contact element 25 from the closest edge 253 on a trailing side of the contact element 25. In one block row the projection portion 26 has no offset from the edge 253, and has some offset from the edge 253 in other block rows. Each the projection portion 26 is provided with a chamfered portion 261 in a whole width of the projection portion 26 on a side facing to the closest edge 253. On a side opposite to the closest edge 253 of the projection portion 26, a pocket portion 27 recessed from the top face 251 toward radially inward of the contact element 25 is provided circumferentially next to the projection portion 26.

As shown in Fig. 4, the projection portion 26 is provided at an extremity of the top face 251 of the contact element 25. The chamfered portion 261 of the projection portion 26 extends obliquely from the edge 253, and other face of the projection portion 26 extends radially in straight manner.

As shown in Fig. 4, the pocket portion 27 is composed of three pocket faces 271, two pocket faces 271 extending downwardly from the top face 251 are connected by other pocket face 271 at radially innermost of the pocket faces 271. The pocket portion 27 is provided with a recessed portion 72 recessed from the pocket face 271 closer to the projection portion 26 circumferentially toward the closest projection portion 26, making the pocket portion 27 a trapezoid shape.

Since the tread 21 has an intended direction of rotation, and the projection portion 26 and the pocket portion 27 are provided on a trailing side of the contact element 25, it is possible to improve performance on wintry surface in particular braking performance as the trailing side of the contact element 25 plays an important role during braking.

Since the pocket portion 27 is provided with at least one recessed portion 72 recessed from the pocket face 271 closer to the projection portion 26 circumferentially toward the closest projection portion 26, it is possible to improve performance on wintry surface in particular ice performance more reliably as the recessed portion 72 facilitates deformation of the projection portion 26 to be accommodated in the pocket portion 27.

A tread 31 for a tire according to a third embodiment of the present invention will be described referring to Figs. 5 and 6. Fig. 5 is a schematic cross sectional view of a tread according to a third embodiment of the present invention. Fig. 6 is an enlarged schematic view showing a portion indicated as VI in Fig. 5. The construction of this third embodiment is similar to that of the first and the second embodiment other than the arrangement shown in Figs. 5 and 6, thus description will be made referring to Figs. 5 and 6.

As shown in Fig. 5, a tread 31 having a contact face 32 intended to come into contact with ground during rolling and being provided with a plurality of groove 33 (a lateral groove 33a and a circumferential groove 33b (not shown)). The tread 31 having an intended direction of rotation which is a direction from X toward X’ in this Fig. 5. The plurality of groove 33 delimitating a plurality of contact element 35 having a top face 351 constituting a part of the contact face 32. A frontal face 352 is facing to the lateral groove 33a. Each the plurality of contact element 35 is provided with a plurality of incision 34 extending generally in the axial orientation.

As shown in Fig. 5, the contact element 35 is provided with two projection portions 36 and two pocket portions 37, and the projection portion 36 and the pocket portion 37 are provided alternately in circumferential orientation at a trailing side of the contact element 35. Each the pocket portion 37 is composed of 5 pocket faces 371, as shown in Fig. 6.

As shown in Fig. 6, the recessed portion 372 is provided at radially innermost of the pocket face 371. The projection portion 36 is flush with the frontal face 351 of the contact element 35 at least partly.

Since the recessed portion 372 is provided at radially innermost of the pocket face 371, it is possible to improve performance on wintry surface in particular ice performance more reliably as the recessed portion 372 provided at radially innermost of the pocket face 371 further facilitates deformation of the projection portion 36 to be accommodated in the pocket portion 37.

Since the contact element 35 is provided with two projection portions 36 and two pocket portions 37, and the projection portion 36 and the pocket portion 37 are provided alternately in circumferential orientation, it is possible to improve performance on wintry surface in particular ice performance more reliably as circumferentially positioned two projection portions 36 help to increase an area in contact with ground at portions on the top face 351 (the contact face 32) of the contact element 35 other than the projection portion 36 and the pocket portion 37.

Since the projection portion 36 is flush with the frontal face 352 of the contact element 35 at least partly, it is possible to place the projection portion 36 where the projection portion 36 generates high contact pressure efficiently, thus performance on wintry surface would further be improved.

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

Fig. 7 is a cross sectional view of a tread according to prior art. In this Fig. 7, a tread 101 being provided with a plurality of groove 103 of a depth D delimitating a plurality of contact element 105 having a top face 1051 constituting partly a contact face 102 of the tread 101. The contact element 105 is provided with on incision 104 of a depth d at around a center of the contact element 105. The top face 1051 and a frontal face 1052 creating an edge 1053, a projection portion 106 of a height h being provided as to be flush with the frontal face 1052 of the contact element 105. The projection portion 106 is provided with both a chamfered portion 1061 and a flat portion 1062.

In order to confirm the effect of the present invention, one type of block sample of Example to which the present invention is applied and other type of block sample of Reference were prepared.

The Example was a block sample as described in the above the second embodiment having the height h of the projection portion equals to 1.0 mm, the angle A equals to 45 degrees, the depth D equals to 6.1 mm, a distance between two frontal faces in circumferential orientation equals to 20 mm and with one incision provided. The Reference was also a block sample as described in the above prior art. Both the Example and Reference were made of the same rubber material.

Ice performance tests:

The friction coefficient measurement on ice were carried out with the above Example and Reference sliding at a given condition (a displacement: 0 to 0.03 m, a speed: 0 to 0.5 m/s, and an acceleration: 5 m/s²) over an ice track, set at about -2°C, with an imposed normal stress (about 300 kPa). The forces generated in a direction of travel (Fx) of each of the Example and Reference and in another direction perpendicular to the travel (Fz) were measured. The Fx/Fz ratio determines the friction coefficient of each of the Example and Reference on the ice. This test, the principle of which is well known to a person skilled in the art (see, for example, an article entitled “Investigation of rubber friction on snow for tires” written by Sam Ella, Pierre-Yves Formagne, Vasileios Koutsos and Jane R. Blackford (38th LEEDS-Lyons Symposium on tribology, Lyons, 6-9 Sep. 2011)) makes it possible to evaluate, under representative conditions, the grip on ice which would be obtained after a running test on a vehicle fitted with tires whose tread is composed of the same contact elements.

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 performance.

As seen from table 1, the Example shows improvement on ice surface.

1, 21, 31 tread
2, 22, 32 contact face
3(3a, 3b), 23(23a, 23b), 33 groove
4, 24, 34 incision
5, 25, 35 contact element
51, 251, 351 top face
52, 252, 352 frontal face
53, 253, 353 edge
6, 26, 36 projection portion
61, 261, 361 chamfered portion
62, 362 flat portion
7, 27, 37 pocket portion
71, 271, 371 pocket face
72, 372 recessed portion

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 a plurality of groove (3) of a depth D and/or a plurality of incision (4) of a depth d extending generally in axial orientation of the tire and being disposed such that at least two grooves or two incisions or one groove and one incision being always located within a contact patch, the plurality of groove (3) and/or the plurality of incision (4) delimitating a plurality of contact element (5), the plurality of contact element (5) having a top face (51) constituting a part of the contact face (2) and a frontal face (52) facing to the groove (3) or to the incision (4), the top face (51) and the frontal face (52) creating an edge (53) at an intersection between the top face (51) and the frontal face (52), at least one of the plurality of contact element (5) being provided with at least one projection portion (6) projecting radially outwardly from the top face (51) with a radial height h in a region between the closest edge (53) and 40% of a circumferential length of the contact element (5) from the closest edge (53), the projection portion (6) being provided with a chamfered portion (61) on a side facing to the closest edge (53), the chamfered portion (61) having an angle A relative to the top face (51) on cross sectional view along with circumferential orientation,
the tread being characterized in that the contact element (5) comprises at least one pocket portion (7) recessed from the top face (51) toward radially inward of the contact element (5), and in that the pocket portion (7) is composed of at least two pocket faces (71), and in that the at least one pocket portion (7) is provided circumferentially next to the projection portion (6).
The tread (1) according to Claim 1, wherein the at least one pocket portion (7) is provided circumferentially inward of the contact element (5) from the projection portion (6).
The tread (1) according to Claim 1 or Claim 2, wherein the tread (1) has an intended direction of rotation, and wherein the projection portion (6) and the pocket portion (7) are provided on a trailing side of the contact element (5).
The tread (1) according to any one of the Claims 1 to 3, wherein the pocket portion (7) is provided with at least one recessed portion (72) recessed from the pocket face (71) closer to the projection portion (6) circumferentially toward the closest projection portion (6).
The tread (1) according to Claim 4, wherein the recessed portion (72) is provided at radially innermost of the pocket face (71).
The tread (1) according to any one of the Claims 1 to 5, wherein the contact element (5) is provided with two projection portions (6) and two pocket portions (7), and wherein the projection portion (6) and the pocket portion (7) are provided alternately in circumferential orientation.
The tread (1) according to any one of the Claims 1 to 6, wherein the pocket face (71) closer to the projection portion (6) is flush with a face of the projection portion (6) facing to the pocket portion (7).
The tread (1) according to any one of the Claims 1 to 7, wherein the angle A of the chamfered portion (61) is from 30 to 60 degrees.
The tread (1) according to any one of the Claims 1 to 8, wherein the projection portion (6) is flush with the frontal face (52) of the contact element (5) at least partly.
The tread (1) according to any one of the Claims 1 to 8, wherein the projection portion (6) is offset from the closest edge (53).
The tread (1) according to any one of the Claims 1 to 10, wherein a rubber composition constituting the projection portion (6) is the same as a rubber composition constituting the contact element (5).
A tire having a tread according to any one of the claims 1 to 11.