Heavy goods vehicle driven axle tire tread

Abstract

Tread having a maximum thickness PMU of material to be worn away during running, having: at least two grooves of circumferential overall orientation delimiting at least one intermediate row and two edge rows, a plurality of cuts of transverse overall orientation on each intermediate and edge row, representing, in the new state, a void of total volume Vco open onto the tread surface, at most equal to 13% of the total volume of the tread, channels or cavities extending under the tread surface in the new state, adapted to form new grooves after the tread has partially worn away, and having, in the initial state, a total volume Vcc at least equal to 30% of the total void volume Vco in the new state, intermediate rows of suffix (i) and edge rows of suffix (e) each provided with a plurality of cuts of transverse or oblique orientation distributed over each row evenly or near-evenly with a mean pitch of Pi and Pe respectively, having mean depths, Di and De respectively, which are at least equal to 20% of the thickness PMU and at most equal to thickness PMU, wherein: on the edge rows, Pe is such that 1.30<Pe/De<3.00, and on the intermediate rows, Pi satisfies 1.00<Pi/Di<1.70, and Pe is greater than Pi.

Claims

1. A tread for a tire, having a tread surface adapted to come into contact with a roadway, the tread having a width W and a total thickness E, the total thickness E corresponding to the total thickness of material measured on the equatorial plane between the tread surface when the tire is in the initial or new state and the radially outermost part of a crown reinforcement, the tread having a maximum thickness PMU of material to be worn away during running, the maximum thickness PMU being less than the total thickness E, comprising: at least two grooves of circumferential overall orientation delimiting at least one intermediate row of suffix (i) and two edge rows of suffix (e), these edge rows axially delimiting the tread in the width W thereof, a plurality of cuts of transverse overall orientation which are formed on each of the intermediate and edge rows, all of the grooves of circumferential overall orientation and cuts of transverse overall orientation representing, in the new state, a void of total volume Vco open onto the tread surface (open-voids volume), the volume Vco being at most equal to 16% of the total volume Vt of the tread, the total volume Vt being equal to the sum of the volumes of material to be worn away and of all the voids, channels or cavities under the tread surface when the tread is in the new state, these channels forming a hidden void of total volume Vcc and being adapted to form new grooves after the tread has partially worn away, this hidden void having, in the initial state, a total volume Vcc at least equal to 30% of the total void volume Vco opening onto the tread surface in the new state, wherein the at least one intermediate row of suffix (i) and the at least one edge row of suffix (e) are each provided with a plurality of cuts of transverse or oblique orientation distributed over each row evenly or near-evenly with a mean pitch of respectively Pi in the case of the intermediate rows and Pe in the case of the edge rows, these cuts having mean depths, Di and De respectively, which are at least equal to 20% of the thickness PMU and at most equal to this same thickness PMU, wherein: on the edge rows, the mean pitch Pe of the cuts is determined so that the relationship 1.30<Pe/De<3.00 is satisfied, and on the intermediate rows, the mean pitch Pi of the cuts satisfies the relationship 1.00<Pi/Di<1.70, and the mean pitch Pe of the cuts on the edge rows is greater than the pitch Pi on the intermediate rows.

2. The tread according to claim 1, wherein the pitch Pe of the cuts on the edge rows and the pitch Pi on the intermediate rows satisfy the relationship: 1.25<Pe/Pi<1.80.

3. The tread according to claim 1, wherein the open-voids volume Vco in the new state is at most equal to 13% of the total volume Vt of the tread.

4. The tread according to claim 1, wherein the open-voids volume Vco in the new state is at most equal to 10% of the total volume Vt of the tread.

5. The tread according to claim 1, wherein first hidden voids open onto the tread surface following partial wear representing at least 20% of the thickness PMU and at most 70% of that same thickness.

6. The tread according to claim 1, wherein the total thickness to be worn away PMU, which thickness includes any part associated with potential regrooving, is at most equal to 23 mm.

7. The tread according to claim 1, wherein a plurality of channels extend into the thickness of the tread down to a depth greater than the maximum thickness of material to be worn away PMU and at most down to the total thickness E.

8. A heavy goods vehicle tire, this tire comprising a carcass reinforcement surmounted by a crown reinforcement, this crown reinforcement extending on either side of an equatorial plane that divides the tire into two equal or substantially equal parts, this tire comprising, radially on the outside of the crown reinforcement, a tread according to claim 1, this tire being mountable on a driven axle of a heavy goods vehicle.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a plan view of part of a tread of a tire according to an embodiment of the invention;

(2) FIG. 2 shows a view in section on a plane that is oblique with respect to the axis of rotation of the tire, this plane being identified by its line II-II in FIG. 1;

(3) FIG. 3 shows a view in section on a plane sectioning an edge rib and perpendicular to the axis of rotation; this plane is identified on the tread shown in FIG. 1 by its line III-III;

(4) FIG. 4 shows a view in section on a plane perpendicular to the axis of rotation and sectioning an intermediate row and identified on the tread shown in FIG. 1 by its line IV-IV.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(5) In the figures that accompany this description, identical reference symbols may be used to describe alternative forms of the invention if these reference symbols refer to elements of the same nature, whether this is a structural or alternatively a functional nature.

(6) FIG. 1 is a plan view of part of a tread 10 of a tire according to an embodiment of the invention. This tire, of size 315/70 R 22.5, is intended to be fitted to a driven axle of a heavy goods vehicle. This tire comprises a crown reinforcement, not depicted in this figure, and, surmounting this crown reinforcement, a tread 10 of which the tread surface 100 in the new state (namely prior to any running) may be seen; the tread surface corresponds to the radially outermost surface intended to come into contact with a roadway when the tire is being driven on.

(7) This tread of width W equal to 280 mm is provided with four main grooves 1, 2, 3, 4 of circumferential overall orientation which divides the tread into five circumferential rows 11, 12, 13, 14, 15. These five rows comprise two edge rows 14, 15 axially delimiting the width of the tread and three intermediate rows 11, 12, 13.

(8) The main circumferential grooves 1, 2, 3, 4 have the same depth, here equal to 17 mm. The two circumferential grooves 1, 2 flanking the central row 11 formed on the equatorial plane XX′ (the plane that divides the tread into two parts of equal width) have a mean width on the tread surface equal to 10.5 mm. The other two circumferential grooves 3, 4 have a width equal to 3.5 mm on the same tread surface. The latter grooves 3, 4 widen from a depth equal to 11 mm so as to be able to form grooves of width equal to 6 mm as can be seen in FIG. 2 which is a section on a plane sectioning the tread surface along the oblique line II-II.

(9) Furthermore, this tread is designed to allow an operation referred to as “regrooving”, namely that each main groove 1, 2, 3, 4 can, before the tread wear limit is reached, undergo a mechanical regrooving operation to recreate a groove having a mean depth of a few millimeters. In this particular instance, the maximum height of material to be worm away, which corresponds to a thickness referred to as “PMU” is, in the new state, equal to 20 mm (which corresponds to the groove depth of 17 mm plus a thickness of 3 mm designed to allow the regrooving operation).

(10) The intermediate rows 11, 12, 13 are provided with transverse cuts arranged at a mean pitch Pi equal to 22 mm as can also be seen in FIG. 4. These cuts comprise both transverse grooves 111, 121, 131—of a width of 10.5 mm—these grooves opening onto the tread surface in the new state and with the circumferential main grooves delimiting tread blocks 110, 120, 130, and sipes 6, 6′, 7, 7′, 8, 8′—of a width of 0.4 mm—of which there are two per block. The mean pitch Pi of the transverse cuts on the intermediate rows is evaluated over a complete turn, taking all of the transverse cuts (both the transverse grooves and the transverse sipes) into consideration.

(11) The mean depth Di of the transverse cuts on the intermediate rows 11, 12, 13 is equal to the mean of the maximum depths of all the transverse cuts; in this particular instance it is equal to 15.3 mm.

(12) The edge rows 14, 15 are provided with transverse cuts arranged at a mean pitch Pe equal to 33 mm as can also be seen in FIG. 3. These cuts comprise both transverse grooves 141, 151—of a width of 10.5 mm—delimiting with the circumferential main grooves tread blocks 140, 150, and sipes 5, 9—of a width of 0.4 mm—of which there is one sipe per block. The mean pitch Pe of the transverse cuts is evaluated over a full turn taking all of the said transverse cuts of each edge row (both the transverse grooves and the transverse sipes) into consideration.

(13) The mean depth De of the transverse cuts on the edge rows is equal to the mean of the maximum depths of all the transverse cuts; in this particular instance it is equal to 14.7 mm.

(14) The tread pattern with which the tread of the alternative form described here is provided is asymmetric with respect to the equatorial plane, this asymmetry being obtained by having the inclination of the transverse cuts the same on one edge row and two intermediate rows and the transverse cuts on the last intermediate row and the other edge row inclined in the opposite direction.

(15) FIG. 2 shows a view in section of part of the tire, this section being made in an oblique plane substantially parallel to the inclination of the transverse cuts, this plane being identified by its line II-II in FIG. 1.

(16) This FIG. 2 shows part of the crown reinforcement 20 extending on each side of the equatorial plane P that divides the tire into two parts. This equatorial plane P intersects the blocks 110 of the central row. The tread has a thickness E measured on the equatorial plane between the radially outermost point of the crown reinforcement 20 and the radially outermost point of the tread. The maximum thickness of tread to be worn away during running is identified by the thickness PMU measured between the tread surface and a regrooving thickness radially on the inside of the bottom of the groove 2.

(17) Surmounting this reinforcement 20 radially on the outside is the tread 10 comprising a groove 2 oriented circumferentially and a sipe 4, these two cuts opening onto the tread surface 100 in the new state. The sipe 4 is extended by a channel 42. The maximum depths of the cuts 2 and 4 are, in this particular instance, identical.

(18) FIG. 3 shows a view in section on a plane sectioning an edge rib and perpendicular to the axis of rotation and identified on the tread shown in FIG. 1 by its line III-III.

(19) As can be seen in FIG. 3, the transverse cuts are either grooves 151 extended towards the inside of the tread by zigzag sipes 152, each of the said sipes 152 itself being extended by a channel 153, or sipes 9 formed of a zigzag first part 91 extended by a channel 92. The maximum depth of the sipes 9 is equal to 13.0 mm, whereas the depth of the channel 153 is equal to 16.5 mm (the latter depth corresponds to the distance separating the bottom of the channel 153 from the tread surface in the new state). This leads to a mean depth Di equal to 14.7 mm. The grooves 151 delimit the blocks 150 in which the sipes 9 are formed.

(20) The sipes 9 have a width of 0.4 mm and a zigzag geometry to encourage mechanical blocking of opposing walls. These sipes 9 are able to close up at least in part as they pass through the contact patch during running Each sipe 9 is extended towards the inside of the tread by a channel 92 of a height equal to 6 mm and a width equal to 4 mm. Each channel 92 is designed to open onto the tread surface after 6 mm of tread wear in order to form new grooves.

(21) The grooves 151 have a width equal to 10 mm and a depth equal to 4.0 mm; these grooves 151 are extended by a sipe 152 of a width of 0.4 mm, this sipe itself being extended by a channel 153 which is 6 mm wide and 4 mm deep.

(22) FIG. 4 shows a view in section on a plane sectioning an intermediate row and perpendicular to the axis of rotation and identified on the tread shown in FIG. 1 by its line IV-IV.

(23) This section shows a groove 121 opening onto the tread surface 100 and extended by a sipe 122, this sipe being extended by a channel 123 of the following dimensions: 3 mm wide and 1.5 mm deep. The maximum depth of the channel 123 is equal to 16.5 mm (the latter depth corresponds to the distance separating the bottom of the channel 123 from the tread surface in the new state).

(24) Between two grooves 121 can be seen two cuts 7, 7′ comprising a first part formed of a zigzag sipe 71, 71′ in the depth of the tread, these sipes 71, 71′ being extended by channels 72, 72′ of identical dimensions. In order to keep tread wear even, it is sensible for the new grooves formed by the channels not all to appear at the same time (namely beyond one and the same degree of partial wear). Furthermore, the sipes 7 have a maximum depth equal to 13 mm whereas the sipes 7′ have a maximum depth equal to 16.5 mm.

(25) The mean of the depths Di of the transverse cuts in each intermediate row is, in this particular instance, equal to 15.3 mm.

(26) In this particular instance, all of the circumferential grooves and transverse cuts together constitute, in the new state, a total void volume Vco open to the tread surface which is equal to 1900 cm.sup.3. This total volume Vco does not include the volumes of hidden voids (namely the volume of the channels which are intended to form new grooves following partial wear) nor does it include the volume of the sipes formed under the tread surface.

(27) The channels form a hidden void of total volume Vcc equal in this particular instance to 720 cm.sup.3 (namely 37% of the total void volume Vco open to the tread surface in the new state).

(28) The total volume Vt is equal to the sum of the volumes of material to be worn away Vmu and of all the voids, whether these be open or hidden. In this particular instance, the total volume Vt is equal to 14 640 cm.sup.3.

(29) In consequence, the hidden volume Vcc represents around 5% of the total volume Vt of the tread as defined above, and the open-voids volume Vco is equal to 13% of that same total volume Vt.

(30) In this example of a tire according to the invention, the recommended relationships are satisfied because: on the edge rows, the ratio Pe/De is equal to 2.24, and on the intermediate rows, the ratio Pi/Di is equal to 1.44. Furthermore, the mean pitch Pe of the cuts on the edge rows is equal to 1.5 times the mean pitch Pi on the intermediate rows.

(31) With the invention having been described in general terms and by means of one alternative form, it must be appreciated that this invention is not in any way restricted to the single alternative form described alone. It is clear that various modifications can be made thereto without departing from the overall scope of the present invention. In particular, the geometries of the channels and sipes may be adapted as need be. Grooves such as those described in patent application WO 2011/039194-A1 may advantageously be employed within the context of the present invention.