Patent Application
20180272810
The present invention relates to a tire for a motor vehicle, comprising a tread comprising at least one block, this block having at least one inclined lateral wall.
The document U.S. Pat. No. 4,884,607 discloses a tire comprising a tread, this tread being provided with a plurality of rubber blocks. The rubber blocks are organized in the tread such that this tread is referred to as directional. The rubber blocks are also organized so as to form, in the tread, circumferential grooves and generally transverse grooves. The transverse grooves notably have the role of evacuating water from the tread when the tire is rolling on a wet road surface. In order to improve this evacuation of water, the document U.S. Pat. No. 4,884,607 specifies that the cross sections of the transverse grooves widen in the direction of the edges of the tread. This widening is notably rendered possible by the inclination of the lateral walls of the blocks that delimit the grooves (see FIG. 2A, FIG. 2B and FIG. 2C of the document U.S. Pat. No. 4,884,607). Specifically, for a given transverse groove, each block lateral wall delimiting this groove has its own inclination angle. The inclination of the lateral walls of the blocks decreases away from the centre of the tread so as to increase the cross sections of the transverse grooves.
However, such an arrangement of rubber blocks, having different inclination angles as a function of the distance with respect to the centre of the tread, appears to contribute towards the development of a non-uniform wear profile on this tread during rolling. Notably, it has been found that the wear to the blocks close to the edge regions of the tread is greater notably when the tire is mounted on a directional axle. Similarly, it has been found that the wear to the blocks close to the centre of the tread is greater notably when the tire is mounted on a driven axle.
Therefore, there is a need to improve the wear profile of a tread of a tire, while maintaining a high grip capacity of this tread on a wet road surface.
A “tire” means all types of resilient tread, whether or not it is subjected to an internal pressure.
The “tread” of a tire means a quantity of rubbery material delimited by lateral surfaces and by two main surfaces, one of which is intended to come into contact with a road surface when the tire is being driven on.
The “edge” of the tread means one of the lateral surfaces delimiting the tread.
The “width W of the tread” means the distance between the two edges flanking the tread. This distance is defined by the ETRTO standard. It is thus equal to +/−10% of a nominal width Wnom, where Wnom is equal to (1.075-0.005ar)*S1.001, where ar is the nominal aspect ratio expressed in base 100 and s is the theoretical section width on the measuring rim expressed in mm.
A “block of a tread” means a raised element delimited by recesses or grooves and comprising lateral walls and a contact face, the latter being intended to come into contact with a road surface during rolling.
A “directional tread pattern” means a tread pattern in which the blocks are specifically arranged to optimize the behavioural characteristics as a function of a predetermined sense of rotation. This sense of rotation is conventionally indicated by an arrow on the sidewall of the tire. In such an architecture, the edges of the blocks which face in the sense of the rolling direction are denoted by the term “leading edges”, while the edges of the blocks which face away from the rolling direction are denoted by the term “trailing edges”.
A “continuous evolution” of the inclination angle of a lateral wall means that the inclination angle is a function of a distance measured from the centre of the tread. The function used is continuous. This function may be, for example, a polynomial, exponential or Gaussian function.
A “sipe” means a cutout in which the distance between the walls of material is appropriate to allow the opposite walls delimiting said sipe to come into at least partial contact when in the contact patch in which the tire is in contact with the ground. This distance for a sipe is in this case at most equal to 2 millimetres (mm).
A “groove” means a cutout in which the distance between the walls of material is such that these walls cannot come into contact with one another under normal rolling conditions. This distance for a groove is greater than 2 millimetres (mm).
A “radial direction” means a direction which is perpendicular to the axis of rotation of the tire (this direction corresponds to the direction of the thickness of the tread).
An “axial direction” means a direction parallel to the axis of rotation of the tire.
A “circumferential direction” means a direction tangential to any circle centred on the axis of rotation. This direction is perpendicular both to the axial direction and to the radial direction.
The invention relates to a tire made of rubbery material comprising a tread of width W that is delimited by at least one edge (3). The tread comprises a plurality of blocks, each block being delimited by at least one lateral wall that extends mainly in an axial direction Y in the direction of the edge. The lateral wall has a length L in this axial direction Y, where L is greater than 35% of the width W of the tread. The lateral wall exhibits an inclination angle with respect to a radial direction, said inclination angle evolving in the axial direction Y, this evolution being continuous.
It has been found that continuous evolution of the inclination angle of the lateral wall of the block makes it possible to obtain a more regular wear profile on the block. In particular, the greater the inclination angle of the lateral wall, the greater the wear to the block at this lateral wall. Thus, by controlling the value of the inclination angle while making this variation in inclination continuous, it is possible to direct the wear to the tread to one part or another of the block with a view to better distribution of this wear. In this way, a situation in which parts of the tire become worn prematurely is avoided and consequently the mileage is improved.
In a preferred embodiment, the evolution of the inclination angle is in accordance with a Gaussian curve.
With an evolution in accordance with a Gaussian curve, the inclination angle has a maximum value half-way along the length L of the block. When the block extends across half the width of the tread, the invention favours wear in a region centred on the half-tread. By favouring such wear, the mileage of a tire is improved regardless of whether it is mounted on a driven axle or on a directional axle.
In another embodiment, the evolution of the inclination angle is in accordance with a polynomial function.
In another embodiment, the evolution of the inclination angle is in accordance with an exponential function.
In another embodiment, the tread having a centre, the block extends from the centre of said tread to the edge along a curve C.
In this way, the evacuation of water in the direction of the edge of the tread is favoured. This improves the grip of the tire on a wet road surface.
In another embodiment, each block is divided into a plurality of block segments.
In another embodiment, the lateral wall delimits a groove that extends towards the edge of the tread, the groove having a cross section, the cross section of said groove increasing in the direction of this edge.
By widening the cross section of the groove, the evacuation of water from the tread is improved there, too.
In another embodiment, the values of the inclination angle are between −10° and 30°.
With an inclination angle close to −10°, good grip on a wet and/or snow-covered road surface is ensured. With an inclination angle close to 30°, the grip on a dry road surface is improved. Thus, by providing a relatively wide range of inclination angle values, it is possible to easily adapt the characteristics of the tread to the type of grip desired.
In a preferred embodiment, the inclination angle being able to have a maximum value and a minimum value, the difference between this maximum value and this minimum value is at least 10°.
The inventors have found that there needs to be at least a difference of 10° between the maximum value and the minimum value in order for the effect on the wear to the thread to be appreciable.
The maximum value of the inclination angle is 15° and its minimum value is 5°.
The inventors have found that, with such a characteristic of the inclination angle, the retention of stones in the groove delimited by the lateral wall is limited.
In a preferred embodiment, the block is delimited by another lateral wall, this other lateral wall exhibiting an inclination angle that evolves continuously.
This makes it possible to obtain a regular wear profile on the block, both in its leading part and in its trailing part.
In a preferred embodiment, the tread is directional and the block has a leading edge belonging to the lateral wall of this block. The block also has a trailing edge belonging to the other lateral wall of the block. The maximum value of the inclination angle of the lateral wall that forms the trailing edge is greater than the maximum value of the inclination angle of the lateral wall that forms the leading edge.
This optimizes the function of the tread as a function of its rolling sense. When the vehicle accelerates, it is the leading edge of the block that comes into contact with the ground first. On a wet road surface, when accelerating, the aim is thus to favour the evacuation of water from the tread. By contrast, when the vehicle brakes, it is the trailing edge of the block which acts. By giving this trailing edge a greater inclination angle value, braking is favoured, notably on a dry road surface.
In a preferred embodiment, the block has a chamfered part at its lateral wall.
Transverse grip, notably when cornering, on a snow-covered and/or wet road surface is thus favoured.
In a preferred embodiment, the lateral wall of the block has one or more discontinuities.
The discontinuities in the lateral wall further favour the transverse grip on a snow-covered and/or wet road surface.
Further features and advantages of the invention will become apparent from the following description, given by way of non-limiting example, with reference to the attached drawings in which:
In the following description, elements which are substantially identical or similar will be denoted by identical references.
The tread 1 also comprises a plurality of raised rubber blocks 5. These rubber blocks 5 are organized in the tread so as to form a particular tread pattern design. In the embodiment in
Each block is delimited by at least one lateral wall 7. This lateral wall 7 delimits a groove 8 which extends mainly in an axial direction Y in the direction of the edge region 3. It will be noted that the lateral wall 7 has a length L in this axial direction Y, where L is greater than 35% of the width W of the tread. It will also be noted that, in a preferred embodiment, the cross section of the groove 8 increases in the direction of the edge 3. In the example in
In a preferred embodiment, the evolutions of the inclination angles α, β are in accordance with a Gaussian curve 10, as is shown in
In a variant embodiment shown in
In an alternative embodiment, the block 5 has a chamfered part 23 at its lateral wall, as can be seen in
In another embodiment, which can be seen in
In another embodiment, which can be seen in
The invention is not limited to the examples described and shown and various modifications can be made thereto without departing from its scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1560941 | Nov 2015 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2016/052939 | 11/14/2016 | WO | 00 |
