SPIKED TIRES

Description

[0001] The present invention relates to the fields of tires comprising studs which are particularly suitable for driving on ice. These are generally referred to as “studded tires”.

[0002] The invention is suitable for passenger vehicles and commercial vehicles.

[0003] Studded tires have undeniable advantages in terms of behavior in winter driving conditions, such as driving on icy surfaces. Contact with ice, and more specifically the penetration of the stud into the ice, helps compensate for the reduction in grip observed at the level of the tread elements of the tire. Indeed, the studs scrape the ice and allow additional forces to be generated on the ice.

[0004] One of the difficulties in using such studded tires is that these tires, when used on a non-icy or snow-covered road, degrade the condition of the road surface and lead to premature wear of the road surface.

[0005] For this reason, a number of countries have banned studded tires or restricted their use to certain types of vehicles and / or limited winter periods.

[0006] However, an increase in the ice grip efficiency of a studded tire usually results either in a greater abrasive character of each stud with respect to the road surface for a constant number of studs, or in an increase in the number of studs while keeping the abrasive character of each stud constant.

[0007] This generally leads to an increase in the harmful effect of the studded tire on non-icy or snowy roads.

[0008] Also known from the state of the art are documents FR2131913, EP0813981, GB1546780, DE2304036, WO2016 / 045807A1, EP1055509A1, FR2982529A1, EP3524444A1.

[0009] The present invention aims to provide a studded tire having excellent grip on ice while having reduced impact on a non-icy or snowy road surface.

[0010] A pneumatic tire suitable for a passenger vehicle or a utility vehicle comprises a tread having a running surface, and a plurality of studs anchored in the tread and extending projecting from the running surface.

[0011] According to a general characteristic, the average surface density of nails on the rolling surface is at least equal to 6.7 nails per square decimeter (dm 2 < ). According to another general characteristic, the static striking force of each of the nails of only a part of the plurality of nails is in a range from 120 to 170 Newtons (N).

[0012] By "pneumatic" we mean all types of elastic bandages, whether or not subject to internal pressure.

[0013] The term "rolling surface" of a tire means the surface of the tread that comes into contact with the road surface when the tire is inflated to its operating pressure and is considered to be studless.

[0014] The "rolling surface" is calculated from the width and diameter of the tread of the free tire, i.e. not mounted on its rim.

[0015] Here, the term "average surface density" refers to the ratio between the total number of studs and the tire's tread surface expressed in dm 2 < . In other words, the studs are distributed across the tread with an average density of 6.7 studs per 1 dm 2 < of tread surface.

[0016] The "static impact force" of a stud means the vertical force exerted by the stud when the tire is crushed on a flat road surface under an internal inflation pressure of 2 bars and under a load corresponding to 70% of the tire's maximum load capacity. This maximum load capacity is usually indicated by a load index printed on at least one of the tire's sidewalls.

[0017] Tests carried out by the applicant have shown that the particular surface density of studs combined with such a static impact force makes it possible to increase the grip performance of the studded tire on icy roads while limiting its abrasive action on dry roads.

[0018] The increased average stud density compared to conventional studded tires allows for load distribution across a greater number of studs in the tread contact area. The tire's grip on icy roads is improved. In addition, stud wear is limited.

[0019] Furthermore, the static impact force determined by the applicant makes it possible to obtain a good compromise between the improved grip of the tire on ice and the limited abrasive nature of the studs on the road.

[0020] According to the invention, only a portion of the nails each have a static striking force within this range.

[0021] According to an optional feature, the average linear density of studs on the tread surface is at least 115 studs per meter. Here, "average linear density" means the ratio between the total number of studs and the circumference of the tire's tread surface expressed in meters. In other words, the studs are distributed in the tread with an average density of 115 studs per 1 meter of circumference of the tread surface.

[0022] According to another optional characteristic, the protruding height HS of the nails of the plurality of nails is at most equal to 1.6 millimeters (mm), and preferably between 0.8 mm and 1.2 mm. This makes it possible to further limit the abrasive nature of the nails on the roadway.

[0023] The "protrusion height" of a stud means the radial distance between the radially outermost point of the stud and the portion of the tread surface surrounding the stud, for example up to 1 centimeter from the stud axis. A "radial" direction is a direction corresponding to a radius of the tire. The radial direction is therefore a direction that is perpendicular to the tire's axis of rotation. The radially outermost point of the stud is therefore the point of the stud furthest from the tire's axis of rotation.

[0024] The protruding height HS of the nails of the plurality of nails may be at most equal to 20% of the total height HC of said nail.

[0025] In one embodiment, the maximum section S max of the nail is at most equal to 35 millimeters squared (mm 2 < ). The term "maximum section" means the maximum section of the nail considered perpendicular to the axis of elongation of the nail. In the case of a cylindrical nail, this maximum section is defined by the diameter of said nail.

[0026] The total height of the studs of the plurality of studs may be between 8 mm and 11 mm, and preferably equal to 10 mm. The studs of the plurality of studs generally comprise a body anchored in the tread and a setting intended to come into contact with the road surface. The body and the setting may be made of different materials. Preferably, the setting is made of tungsten carbide and the body is made of a metal alloy, preferably steel. Alternatively, the body and the setting may be made of the same material.

[0027] The section of the said nail may be between 3 mm 2< and 3.5 mm 2< . The section is considered perpendicular to the axis of elongation of the nail. This further limits the abrasive nature of the nails on the road. The mass of the nails of the plurality of nails may be between 0.7 g and 1.2 g.

[0028] Preferably, the surface notch rate of the tread in the new condition of said tire is between 30% and 50%.

[0029] The term "surface notch ratio" of a tread means the ratio between, on the one hand, the difference between the total surface area of ​​the tread and the area of ​​the parts of the tread elements intended to come into contact with the ground when rolling, and on the other hand, this total surface area of ​​the tread.

[0030] Alternatively or in combination, the volumetric indentation rate of the tread in the new condition of said tire is between 25% and 50%. By "volumetric indentation rate" of a tread is meant the ratio between the volume of the hollow of the tread, consisting of the grooves and incisions, and the total volume of the tread.

[0031] In one embodiment, the height of the tread sculptures may be between 6 mm and 12 mm.

[0032] In one embodiment, the tread comprises a first portion delimiting the tread surface and at least a second portion radially inside the first portion and inside which is anchored a head of each stud, the first portion being formed from a first rubber composition and said second portion being formed from a second rubber composition different from the first rubber composition. Thus, it is possible to provide a first rubber composition having good wear resistance and grip properties. The second rubber composition may be chosen to promote obtaining good mechanical strength of the studs in the tread.

[0033] According to an optional characteristic, the complex dynamic shear modulus G*(-10°C) of the first rubber composition is between 1 MPa and 2 MPa. The complex dynamic shear modulus of said second rubber composition can vary depending on the temperature such that G*(5°C) is greater than or equal to 5 MPa and G*(20°C) is less than or equal to 0.5xG*(5°C).

[0034] The “complex module” G* is defined by the following relation: G * = G ′ 2 + G " 2 in which G' represents the elastic modulus and G" represents the viscous modulus.

[0035] The term viscous elastic moduli refers to dynamic properties well known to those skilled in the art. These properties are measured on a Metravib VA4000 type viscoanalyzer on specimens molded from raw compositions. Specimens such as those described in ASTM D 5992 - 96 (version published in September 2006, initially approved in 1996) in Figure X2.1 (circular embodiment) are used. The diameter "d" of the specimen is 10 mm (it therefore has a circular section of 78.5 mm 2< ), the thickness "L" of each of the portions of rubber composition is 2 mm, which gives a "d / L" ratio of 5 (unlike ISO 2856, mentioned in ASTM, paragraph X2.4, which recommends a d / L value of 2).

[0036] The response of a vulcanized rubber compound sample subjected to sinusoidal alternating simple shear stress at a frequency of 10 Hz is recorded. The specimen is subjected to sinusoidal shear stress at 10 Hz, at an imposed stress (0.7 MPa), symmetrically around its equilibrium position. The specimen is accommodated prior to measurement. The specimen is then subjected to sinusoidal shear stress at 10 Hz, at 100% peak-peak strain, at room temperature.

[0037] The measurement is carried out during an increasing temperature ramp of 1.5°C per minute, from a temperature T min lower than the glass transition temperature T g of the material, up to a temperature T max which can correspond to the rubber plateau of the material. Before starting the scan, the sample is stabilized at the temperature T min for 20 minutes to have a homogeneous temperature within the sample. The result used is the dynamic shear elastic modulus G' and the viscous shear modulus G" at the chosen temperatures (in this case -10°, 5° and 20°C). The glass transition temperature T g of the first rubber composition can be between -50°C and -30°C.

[0038] In the above, the limits indicated for a range of values ​​are included in this range, in particular in the expressions “between” and “ranging from ... to ...”.

[0039] The present invention will be better understood upon reading the detailed description of an embodiment taken as a non-limiting example and illustrated by the appended drawings in which: there figure 1 is a schematic perspective view of a studded tire according to an exemplary embodiment of the invention, the figure 2 is a front view of a tire stud of the figure 1 , and the figure 3 is a partial schematic sectional view of the tire of the figure 1 .

[0040] On the figure 1 A tire 10 is schematically represented comprising a tread 12 having a rolling surface (not referenced) intended to come into contact with a road surface when rolling. The tread 12 comprises a plurality of transverse 14 and circumferential 16 grooves which delimit a plurality of blocks or loaves 18 of rubber. Each block 18 comprises a contact face forming a part of the rolling surface of the tread 12.

[0041] The tire 10 also includes a plurality of studs 20 secured in the tread 12 of the tire and arranged across the entire width of the tread surface in the rubber blocks 18. The arrangement of the studs 20 on the tread 12 as illustrated in figure 1 is only illustrative and not limiting. It is for example possible to provide several studs 20 on the same block 18 of rubber. The tread 12 of the tire here comprises a central rib 22 without studs. Alternatively, it is possible to provide a rib 22 comprising studs.

[0042] The studs 20 are arranged at several positions around the periphery of the tread 12 so that at any time a portion of these studs 20 are in contact with the road surface on which the tire 10 is rolling. The total number of studs 20 projecting from the tread surface of the studded tire and the static impact force of each stud are provided so that this studded tire has excellent grip on ice while having reduced impact on a non-icy or non-snowy road surface.

[0043] The applicant has determined that an average surface density of studs 20 on the rolling surface of the tire 10 at least equal to 6.7 studs per dm 2< combined with a static impact force for each stud 20 in a range from 120 N to 170 N makes it possible to significantly improve the compromise between grip on ice and nuisance of the studs 20 in terms of road wear and interior noise in the vehicle.

[0044] The increase in the number of studs 20 on the tread 12 compared to conventional studded tires makes it possible to increase the efficiency of the tire 10 on icy roads, while the limitation of the static impact force of each stud 20 makes it possible to avoid excessive degradation of the condition of the road surface when it is not covered with ice or snow. This particular combination of the average surface density of studs 20 and the static impact force of the stud thus makes it possible to obtain a good compromise between the improved grip on ice of the studded tire 10 and the limited abrasive nature of the studs 20 on the road.

[0045] Preferably, the average linear density of studs 20 on the tread surface of the tire 10 is at least equal to 115 studs per meter. For information purposes, for a tire of size 205 / 55 R16, the average surface density of studs 20 may be equal to 6.7 studs per dm 2 and the static striking force of each stud 20 may be equal to 152 N. For such a tire, the average linear density of studs 20 may be equal to 115 studs per meter.

[0046] As shown in the figure 2 , each stud 20, with a longitudinal axis XX', comprises a head 24 for anchoring in the tread 12 of the tire, a setting 26 intended to come into contact with the road surface (ice, snow or bare surface) when the tire rolls, and a body 28 connecting the setting and the head. In the illustrated embodiment, the stud 20 has a cylindrical profile. Alternatively, the stud 20 could have any other profile, for example polygonal. In the illustrated embodiment, the setting 26 is centered on the axis X-X'. Alternatively, the setting 26 may be off-center relative to said axis.

[0047] The setting 26 of the nail can advantageously be made using a material distinct from that of the rest of the nail 20. This makes it possible to use for this part a harder material compared to the material of the head 24 and the body 28 insofar as the setting 26 is subject to very high mechanical stresses. This also makes it possible to produce, for certain product families, a body 28 and a head 24 made of molded or injected material, on which the setting 21 is fixed. The body 28 can be made of a metallic material, for example steel. Alternatively, the body can be made of a plastic material. The setting 26 can be made of tungsten carbide. Alternatively, the nail 20 can be made of a single material.

[0048] The maximum section S max of the nail 20 is at most equal to 35 mm 2< , this section corresponding to the largest section of the nail 20 in any plane perpendicular to the axis XX' of the nail, whatever the geometric shape of this section (circular, polygonal, etc.). In the illustrated embodiment, this maximum section S max of the nail corresponds to the maximum section of the head 24 of the nail.

[0049] The maximum section of the stake 26 of the nail is between 3 mm 2< and 3.5 mm 2< , and preferably equal to 3.14 mm 2< . This maximum section corresponds to the largest section of the stake 26 in any plane perpendicular to the axis XX' regardless of the geometric shape of this section (circular, polygonal, etc.). The total height HC of the nail 20 is between 8 mm and 11 mm, and preferably equal to 10 mm. The total height HC is defined by the cumulative height of the head 24, the body 28 and the stake 26. The mass of the nail can be between 0.7 g and 1.2 g, and preferably equal to 1.15 g.

[0050] There figure 3 schematically represents a part of the tread 12 of the tire which is provided with a cell 30 inside which a stud 20 is mounted. The cell 30 opens onto the rolling surface 32 of the tread 12. In a manner known per se, in the free state of the cell 30, i.e. before insertion of the stud 20, the latter may have a cylindrical shape with dimensions smaller than those of the stud so that after insertion the stud 20 is perfectly enveloped by the tread by elasticity and anchored inside it.

[0051] The stud 20 is arranged in the tread 12 so that its axis XX' is substantially parallel to a radial direction. The stud 20 projects outwardly relative to the tread surface 32 of the tread 12 when it is not in contact with the roadway as illustrated in figure 3. The protruding height HS of the stud 20 is at most equal to 1.6 mm, and preferably between 0.8 mm and 1.2 mm, and advantageously equal to 0.9 mm. The protruding height HS of the stud 20 is at most equal to 20% of the total height HC of said stud. In the illustrated embodiment, the upper end of the body 28 and the setting 26 of the stud extend in projection relative to the tread surface 32. According to a preferred variant, only the setting 26 of the stud can extend in projection outside the tread 12. The anchored height HA of the stud 20 inside the tread 12 is at most equal to 9.4 mm.

[0052] In the illustrated embodiment, the tread 12 comprises a first portion 34 delimiting the tread surface 32 and a second portion 36 arranged radially inside the first portion 201. The first portion 34 of the tread 12 is formed from a first rubber composition and the second portion 36 is formed from a second rubber composition different from the first rubber composition. The body 28 of the stud is at least partially in contact with the first portion 34 while the head 24 is entirely anchored in the second portion 36 of the tread 20. The second portion 36 entirely envelops the head 24 of the stud.

[0053] The production of the tread 12 with at least first and second parts 34, 36 is particularly advantageous insofar as this makes it possible to provide a first rubber composition suitable for obtaining good wear resistance and grip on ice properties and a second rubber composition promoting the mechanical anchoring of the studs 20.

[0054] Alternatively or in combination, it is also possible to choose the second rubber composition of the second part to obtain a tire 10 whose mechanical behavior changes according to the temperature of the road on which it rolls. If a second rubber composition is chosen which is rigid at low temperature and softer at high temperature, then the stud 20 will tend to remain protruding from the tread 12 when the road is cold (covered with ice or snow) and to tilt, deforming the second rubber composition which surrounds it when the road is warmer (not covered with ice or snow).This effect is optimized when the complex dynamic shear modulus G*(-10°C) of the first rubber composition is between 1 MPa and 2 MPa and the complex dynamic shear modulus of the second rubber composition changes as a function of temperature such that G*(5°C) is greater than or equal to 5 MPa and G*(20°C) is less than or equal to 0.5xG*(5°C). The glass transition temperature T g of the first rubber composition may be between -50°C and -30°C.

[0055] The invention has been illustrated on the basis of a tire equipped with studs having a particular geometry. It is not outside the scope of the present invention if the studs of the tire have a different geometry.

Claims

1. Tyre for passenger car or utility vehicle comprising a tread (12) having a tread surface (32) and a plurality of studs (20) anchored in the tread (12) and projecting out from the tread surface (32), the mean surface density of studs (20) on the tread surface (32) being at least equal to 6.7 studs per dm2, characterized in that the static striking force of each stud (20) of only a part of the plurality of studs (20) is comprised in a range from 120 N to 170 N, the static striking force of a stud (20) being the vertical load applied by this stud when the tyre is compressed onto a flat roadway under an internal inflation pressure equal to 2 bar and under a load corresponding to 70% of the maximum load capacity of the tyre.

2. Tyre according to Claim 1, in which the mean linear density of studs (20) on the tread surface (32) is at least equal to 115 studs per metre.

3. Tyre according to Claim 1 or 2, in which the projecting height Hs of each stud (20) of the plurality of studs (20) is at most equal to 1.6 mm, and preferably comprised between 0.8 mm and 1.2 mm.

4. Tyre according to any one of the preceding claims, in which the projecting height HS of each stud (20) of the plurality of studs (20) is at most equal to 20% of the total height HC of the said stud (20).

5. Tyre according to any one of the preceding claims, in which the maximum cross section Smax of each stud (20) considered perpendicular to the axis of elongation of said stud of the plurality of studs is at most equal to 35 mm2.

6. Tyre according to any one of the preceding claims, in which the total height HC of each stud (20) of the plurality of studs (20) is comprised between 8 mm and 11 mm, and preferably equal to 10 mm.

7. Tyre according to any one of the preceding claims, in which each stud of the plurality of studs (20) comprise a jacket (28) anchored in the tread (32) and a stud pin (26) intended to come into contact with the roadway, the jacket (28) and the stud pin (26) being made from different materials.

8. Tyre according to Claim 7, in which the maximum cross section of the pin of each stud of the plurality of studs is comprised between 3 mm2 and 3.5 mm2.

9. Tyre according to any one of the preceding claims, in which the mass of each stud (20) of the plurality of studs is comprised between 0.7 g and 1.2 g.

10. Tyre according to any one of the preceding claims, in which the surface void ratio of the tread of the said tyre when new is comprised between 30% and 50%.

11. Tyre according to any one of the preceding claims, in which the volume void ratio of the tread of the said tyre when new is comprised between 25% and 50%.

12. Tyre according to any one of the preceding claims, in which the tread comprises a first part (34) delimiting the tread surface (32) and at least one second part (36) radially on the inside of the first part and in which a base (24) of each stud (20) is anchored, the first part being formed from a first rubber composition and the said second part (34) being formed from a second rubber composition different from the first rubber composition.

13. Tyre according to Claim 12, in which the complex dynamic shear modulus G*(-10°C) of the first rubber composition is comprised between 1 MPa and 2 MPa, the complex modulus G*(-10°C) being defined by the following relationship: G * − 10 ° C = G ′ 2 + G " 2 in which G' represents the elastic modulus and G" represents the viscous modulus measured at a temperature of -10°C under simple alternating sinusoidal shear stress at a frequency of 10 Hz with a stress of 0.7 MPa on test specimens moulded from uncured compositions such as those described in the standard ASTM D 5992-96 in Figure X2.1 where the diameter of the test specimen is 10 mm and the thickness of each of the portions of rubber composition is 2 mm.

14. Tyre according to Claim 12 or 13, in which the complex dynamic shear modulus of the said second rubber composition changes with temperature such that G*(5°C) is greater than or equal to 5 MPa and G*(20°C) is less than or equal to 0.5xG*(5°C), the complex modulus G*(5°C) being defined by the following relationship: G*(5°C) = G ′ 2 + G " 2 in which G' represents the elastic modulus and G" represents the viscous modulus measured at a temperature of 5°C under simple alternating sinusoidal shear stress at a frequency of 10 Hz with a stress of 0.7 MPa on test specimens moulded from uncured compositions such as those described in the standard ASTM D 5992-96 in Figure X2.1 where the diameter of the test specimen is 10 mm and the thickness of each of the portions of rubber composition is 2 mm et, the complex modulus G*(20°C) being defined by the following relationship: G * 20 ° C = G ′ 2 + G " 2 in which G' represents the elastic modulus and G" represents the viscous modulus measured at a temperature of 20°C under simple alternating sinusoidal shear stress at a frequency of 10 Hz with a stress of 0.7 MPa on test specimens moulded from uncured compositions such as those described in the standard ASTM D 5992-96 in Figure X2.1 where the diameter of the test specimen is 10 mm and the thickness of each of the portions of rubber composition is 2 mm.

15. Tyre according to any one of Claims 12 to 14 in which the glass transition temperature (Tg) of the first rubber composition is comprised between -50°C and -30°C.