WO2016083264A1 - Tyre device for agricultural vehicle - Google Patents

Abstract

The present invention relates to a tyre device intended for being provided on an agricultural vehicle. The invention aims to provide a tyre device that makes it possible to guarantee low contact pressure with the ground during use in the field, and thus to minimise soil compaction. According to the invention, the tyre device (1) is made up of a circumferential assembly of cells (4) pressurised independently from one another at a positive or zero relative pressure and secured together two-by-two. Each cell (4) has a hexahedral shape and comprises two meridian surfaces (41, 42) respectively connected to a meridian surface of an adjacent cell, a radially inner surface (43) intended for engaging with the wheel rim (3), and a radially outer surface (44), and two circumferential surfaces (45, 46) that are symmetrical relative to the equatorial plane (XZ) passing through the middle of the tread (2) and perpendicular to the axis of rotation (ΥΥ') of the tyre device (1). Finally, the envelope of each cell (4) — made up of the two meridian surfaces (41, 42), the two radially inner and outer surfaces (43, 44), respectively, and the two circumferential surfaces (45, 46) — is deformable.

Description

 PNEUMATIC DEVICE FOR AGRICULTURAL VEHICLE

 The present invention relates to a pneumatic device, alternating with a conventional tire, intended to equip a vehicle and in particular a vehicle for agricultural use, such as an agricultural tractor or an agro-industrial vehicle. In what follows, the circumferential, axial and radial directions respectively designate a direction tangent to the running surface of the pneumatic device and oriented in the direction of rotation of the pneumatic device, a direction parallel to the axis of rotation of the device. pneumatic and a direction perpendicular to the axis of rotation of the pneumatic device. A meridian or radial plane is a plane containing the axis of rotation of the pneumatic device, defined by the radial direction and the axial direction. A circumferential plane is a plane perpendicular to the axis of rotation of the pneumatic device, defined by the radial direction and the circumferential direction. The equatorial plane of the pneumatic device is the circumferential plane passing through the middle of the tread of the pneumatic device. An agricultural tire is intended to ride on various types of soil such as more or less compact land fields, unpaved access roads to fields and asphalt surfaces of roads. Given the diversity of use, in the field and on the road, an agricultural tire, and in particular its tread, must present a compromise of performance between the traction in the field, the tear resistance, the resistance to road wear, rolling resistance, vibratory comfort on the road.

To meet this set of performance, the tread of an agricultural tire generally comprises a plurality of bars. The bars are elements in relief with respect to a bottom surface of the tread, of revolution about the axis of rotation of the tire, and extending radially to the tread surface.

In addition to the performance described above, an agricultural tire must minimize soil compaction, in field use, to better respect the integrity of the soil and not to damage harvests.

To minimize soil compaction while ensuring traction in the field, agricultural tires called "low pressure", for example inflated to a relative pressure of 0.85 bar, have been proposed. Such tires are described for example in the document WO2004106089. By way of example, a "low pressure" agricultural tire has a maximum radial deflection rate of 25%, the maximum radial deflection rate corresponding to the ratio between the difference between the outside radius of the tire measured opposite the contact area and the crushed outer radius measured in the contact area, and the radial height of the tire measured opposite the contact area.

In contrast a low pressure inflation causes a reduction in the mechanical stiffness of the tire, and in particular its lateral stiffness, which can possibly lead to less good lateral stability and less accurate guidance of the vehicle. Furthermore, because of the low pressure, the high and rigid bars of the tread can punch the carcass reinforcement of the tire, which can lead to a decrease in the endurance of the tire.

An alternative solution to the tire "low pressure" is the rubber or metal crawler. A caterpillar has the advantage of having, compared to a tire, a smaller crushed surface, for example during phytosanitary treatments of cereal plantations, and significantly increases the stability of agricultural machinery, the center of gravity of which is high relative to the ground at high center of gravity, especially on sloping floors, with tilt, but also vis-à-vis pumping in rolling. Moreover, the high radial rigidity of a track also contributes to a good stability of the vehicle. In contrast, a caterpillar is an accumulator of soil, mud or pebbles. In addition, it does not allow an increase in the surface of the contact area when it sinks into the ground it cuts openly. It also does not allow small turning radiuses and tends to pull the surface of the ground during maneuvers. Finally, a caterpillar is associated with expensive and vulnerable mechanical training equipment. The present invention aims to provide an alternative pneumatic device to ensure a low contact pressure on the ground, in field use, and thus minimize soil compaction.

This object has been achieved according to the invention by a pneumatic device for a vehicle for agricultural use, intended to come into contact with a ground via a rolling surface and to cooperate with a rim, said pneumatic device. having a shape of revolution around the axis of rotation of the pneumatic device, the pneumatic device being constituted by a circumferential assembly of cells pressurized independently of each other at a positive or zero relative pressure and secured in pairs,

each cell having a hexahedral form,

each cell comprising two meridian faces respectively linked to a meridian face of an adjacent cell,

 each cell comprising a radially inner face, intended to cooperate with the rim, and a radially outer face,

 each cell comprising two circumferential faces, symmetrical with respect to the equatorial plane passing through the middle of the running surface and perpendicular to the axis of rotation of the pneumatic device,

 and the envelope of each cell, constituted by the two meridian faces, the two radially inner and outer faces and the two circumferential faces being deformable respectively. The principle of the pneumatic device according to the invention is to have a circumferential assembly of cells, pressurized independently of each other at a positive or zero relative pressure and secured in pairs. In other words, the single cavity cylindrical structure of a tire of the state of the art is replaced, in the invention, by a juxtaposition, in the circumferential direction, of unit cells. Each cell is inflated, using an inflation gas, such as, most often but not exclusively, air. The relative inflation pressure of each cell, most often the same for each cell, is generally positive but may possibly be zero. A zero relative pressure corresponds, for example, to the case where the internal cavity of the cell is in contact with the ambient atmospheric air. In addition, the cells are joined in pairs, which means that each cell is structurally connected to two adjacent cells positioned on either side of said cell.

According to the invention, each cell has a hexahedral shape. By hexahedral form is meant a cell comprising six faces. However, the faces are not flat, but have curvatures. The faces are not connected to each other by rectilinear edges, but by curvilinear connections. Thus the cell is not a real hexahedron in the mathematical sense, but is contained in a hexahedron. The six faces of the hexahedral-shaped cell are respectively two meridian faces, two respectively radially inner and outer faces and two circumferential faces.

Each cell comprises two meridian faces. A meridian face is not strictly contained in a meridian plane, because it is not a priori plane. However, its overall shape can be approximated by a meridian plane. A meridian face of a given cell is structurally bonded to a meridian face of an adjacent cell, for example by gluing.

Each cell also comprises a radially inner face, intended to cooperate with the rim. Most often, this radially inner face is secured to the rim, to avoid any relative displacement between said radially inner face and the rim, which can cause an overall rotation of the pneumatic device relative to the rim. Each cell also comprises a radially outer face, intended either to come into direct contact with a ground, or to interface with a tread, said tread being intended to come into contact with the ground via a running surface.

Finally, each cell comprises two circumferential faces, symmetrical with respect to the equatorial plane passing through the middle of the running surface and perpendicular to the axis of rotation of the pneumatic device. A circumferential face is not strictly contained in a circumferential plane, because it is not a priori plane. However, its overall shape can be approximated by a substantially circumferential plane, forming a weak angle with the equatorial plane, typically at most equal to 20 °.

Finally, the envelope of each cell, constituted by the two meridian faces, the two radially inner and outer faces respectively and the two circumferential faces, is deformable. Deformable means that it is able to undergo deformation levels customary in the field of the tire, with the materials usually used such as elastomeric mixtures and textile reinforcements.

A first advantage of the invention is to limit the pneumatic portion, intended for the recovery of the crushing force of the pneumatic device mounted on the vehicle, the pressurized cells at least partially in contact with the ground. The inflation pressure of these cells, deformed by crushing, will increase significantly, while the inflation pressure of the cells outside the contact area remains substantially constant. By way of comparison, for a conventional single-cavity tire, the inflation pressure remains almost constant during crushing. Thus, for the pneumatic device of the invention, the local overpressure of the cells at least partially in contact with the ground results in a vertical rigidity significantly greater than that of a conventional tire, which contributes to a limitation of the vertical pumping phenomenon of the pneumatic while driving.

A second advantage of the invention is to increase the membrane tension forces of the meridian faces of the cells in overpressure, which allows a better recovery of the lateral forces exerted on the pneumatic device. A third advantage is to contribute to improving the behavior of the vehicle in terms of lateral stability, thanks to the stiffening of the pneumatic device near the contact area due to the local overpressure.

Moreover the reliability is improved because the loss of pressure of a cell, following, for example, a puncture, does not impact the pressure of other cells, since they are pressurized independently of each other, and the pneumatic device can continue to roll even in degraded mode.

Finally the security is also enhanced because the eventual bursting of a cell is not explosive because of the low volume of air concerned.

The pneumatic device is advantageously constituted by a circumferential assembly of at least 6 cells. A lower cell number would not provide a sufficiently circular periphery of the pneumatic device.

The pneumatic device is also advantageously constituted by a circumferential assembly of at most 36 cells. Beyond this number of cells, the individual management of the pressure of each cell is estimated, by the inventors, too restrictive. The pneumatic device is preferably constituted by a circumferential assembly of identical cells. The advantage of having identical cells is to have an axisymmetric pneumatic device, with identical operation in any part of its circumference, and to allow a standardized manufacture of the constituent cells of the pneumatic device. A meridian section of each cell, by a meridian plane containing the axis of rotation of the pneumatic device, is also preferentially inscribed in a trapezium. of large base B, small base b and height H, B and H respectively being the width and height of a reference tire within the meaning of the ETRTO standard (European Tire and Rim Technical Organization) and b being the width of the rim. The respect of these standardized geometric congestion conditions guarantees the adaptability of the pneumatic device on the targeted vehicles, without prior modification.

The envelope of each cell advantageously comprises a reinforcing layer consisting of reinforcements embedded in an elastomeric mixture. The use of an elastomeric mixture comprising reinforcements, for the realization of the six faces constituting the envelope of each cell, guarantees a good dimensional stability of the cell, a recovery of efforts by the effective envelope and a protection of the envelope against aggression and cuts.

According to a first variant embodiment, the reinforcing layer comprises unidirectional reinforcements. This unidirectional reinforcement makes it possible to obtain an elongation at break in a preferred direction, typically of the order of 20%. The reinforcing layer comprises bidirectional reinforcements. This bidirectional reinforcement, which is most often in the form of a fabric, makes it possible to obtain elongation at break in two directions, typically of the order of 200% to 300%.

According to a preferred embodiment, the reinforcing layer comprises textile reinforcements. Textile reinforcements are commonly used in the tire field for economic reasons and ease of implementation.

According to a first variant of textile reinforcement, the reinforcements of the envelope of each cell are textile reinforcements of aliphatic polyamide type. Aliphatic polyamide or nylon is commonly used in the tire field.

According to a second variant of textile reinforcement, the reinforcements of the envelope of each cell are textile reinforcements of polyethylene terephthalate type. Polyethylene terephthalate or PET is also commonly used in the tire field.

The envelope of each cell is advantageously constituted by a stack of an inner layer of elastomeric mixture, intended to be in contact with an inflation gas and sealed to said inflation gas, an intermediate reinforcing layer, consisting of reinforcements embedded in an elastomeric mixture, and an outer layer of elastomeric mixture, intended to be in contact with the atmospheric air. The three layers of this sandwich structure thus make it possible to ensure different and complementary functions: the inner layer provides the sealing function vis-à-vis the inflation gas, the intermediate layer provides the recovery function efforts and the outer layer ensures the function of protection vis-à-vis the outside. It is advantageous that the pneumatic device comprises a tread whose radially inner face is connected to the radially outer faces of the cells and whose radially outer face constitutes the running surface. Indeed, the radially outer face of each cell having a concave shape, the periphery of the pneumatic device is not rigorously circular but has a flower petal shape, hence the advantage of covering said radially outer faces of the cells by a tread forming a circular ring whose radially outer face is perfectly cylindrical and therefore suitable for uniform rolling.

The invention also relates to a mounted assembly comprising a pneumatic device, according to any one of the embodiments described above, and a rim with which the pneumatic device cooperates via the radially inner faces of the cells.

The radially inner faces of the cells are preferably secured to the rim. The fastening of the cells to the rim makes it possible to avoid any problem of rotation on a rim, which is usual for a vehicle used for agricultural purposes, in particular during the passage of a driving torque.

According to a first mode of securing the cells to the rim, the radially inner faces of the cells are secured to the rim by gluing. The bonding bond is both simple to implement and effective.

According to a second method of securing the cells to the rim, the radially inner faces of the cells are secured to the rim by a mechanical connection. A mechanical connection can be conventionally made by rivets, bolts or any other mechanical device.

The present invention will be better understood with reference to FIGS. 1 to 4 presented below, on which the invention is not represented on the scale:

FIG. 1: perspective view of a pneumatic device according to the invention

FIG. 2: perspective view of a cell of the pneumatic device according to the invention -Figure 3: side view of a pneumatic device according to the invention, subjected to a crushing force on a flat floor.

 FIG. 4: comparative standard curves of the evolution of the pressure ratio P / P; as a function of the deflection rate D / H, for a pneumatic device according to the invention and a reference tire of the state of the art.

FIG. 1 presents a perspective view of a pneumatic device 1 for a vehicle for agricultural use intended to come into contact with a ground via a rolling surface 2 and to cooperate with a rim 3, said pneumatic device having a shape of revolution about the axis of rotation YY 'of the pneumatic device 1. In the present case, the pneumatic device 1 is constituted by a circumferential assembly of 18 identical cells 4 pressurized independently of each other at a relative pressure positive or zero and secured in pairs. Each cell 4 has a hexahedral shape, constituted by two meridian faces (41, 42) respectively connected to a meridian face of an adjacent cell, a radially inner face 43 intended to cooperate with the rim 3, and a radially outer face 44 and finally two circumferential faces (45, 46), symmetrical with respect to the equatorial plane XZ passing through the middle of the running surface 2 and perpendicular to the axis of rotation YY 'of the pneumatic device 1. The envelope 5 of each cell 4, constituted by the two meridional faces (41, 42), the two radially inner and outer faces (43, 44) and the two circumferential faces (45, 46), respectively, are deformable.

Figure 2 shows a perspective view of a cell of the pneumatic device according to the invention. Each cell 4 has a hexahedral shape, constituted by two meridian faces (41, 42) respectively connected to a meridian face of an adjacent cell, a radially inner face 43 intended to cooperate with the rim 3, and a radially outer face 44 , and finally two circumferential faces (45, 46). A hexahedral form, in the sense of the invention, is not a hexahedron in the strict mathematical sense, given the rounded connections between the various faces mentioned above, but rather a form inscribed in a hexahedron.

Figure 3 is a side view of a pneumatic device 1 according to the invention, subjected to a crushing force on a flat floor. Under the action of the crushing force, the pneumatic device is subjected to a radial deflection rate D / H, equal to the ratio between the radial height variation D of the crushed cell 4, in the center of the contact area , and the initial radial height H of the uncrushed cell. Also under the action of the crushing force, the initial inflation pressure Pi increases to a maximum value P in the crushed cell in the center of the contact area. The pressure P decreases in the cells adjacent to the central cell in the contact area, because their volume is greater, and returns to the initial inflation pressure Pi outside the contact area. P. The pressure P of the other cells outside the contact area thus remains substantially constant at the initial inflation pressure Pi.

In Figure 4, the curves referenced I and R represent the evolution of the pressure ratio P / P; as a function of the radial deflection rate D / H, respectively for a pneumatic device according to the invention and a reference tire of the state of the art. It should be noted that this ratio of pressures P / P; increases much more rapidly according to the radial deflection rate D / H, for the pneumatic device, which reaches a very high value, mathematically infinite, for a total crash characterized by an arrow rate equal to 1. Table 1 ci -after shows values of pressure ratio P / P; for various rates of radial boom D / H:

 Table 1

The invention has been more particularly studied as an alternative solution to an agricultural tire of outer diameter equal to 1100 mm mounted on a rim of diameter equal to 500 mm. In the example studied, the pneumatic device consists of a circumferential arrangement of 18 identical cells each inflated to an initial pressure P equal to 0.3 bar. The envelope of each cell comprises a reinforcing layer consisting of unidirectional reinforcements of polyethylene terephthalate (PET) or aliphatic polyamide (nylon) embedded in an elastomeric mixture. In addition, the radially inner faces of the cells are secured to the rim by gluing. When crushing such a tire under a load F equal to 1500 daN the vertical arrow D was measured equal to 150 mm, with a maximum pressure for the crushed cell, in the center of the contact area, equal to 0.5 bars. The invention can be generalized to any vehicle for driving on soft ground, such as a heavy vehicle type civil engineering or off-road.

Claims

1 - Pneumatic device (1) for a vehicle for agricultural use, intended to come into contact with a ground via a running surface (2) and to cooperate with a rim (3), said pneumatic device having a shape of revolution about the axis of rotation (ΥΥ ') of the pneumatic device (1), characterized in that the pneumatic device (1) is constituted by a circumferential assembly of cells (4) pressurized independently of one another at a pressure relative positive or zero and secured in pairs, in that each cell (4) has a hexahedral shape, in that each cell (4) comprises two meridional faces (41, 42) respectively linked to a meridian face of a cell adjacent, in that each cell (4) comprises a radially inner face (43), intended to cooperate with the rim (3), and a radially outer face (44), in that each cell (4) comprises two circumferential faces (45, 46) , symmetrical with respect to the equatorial plane (XZ) passing through the middle of the running surface (2) and perpendicular to the axis of rotation (ΥΥ ') of the pneumatic device (1), and in that the envelope of each cell (4), constituted by the two meridional faces (41, 42), the two radially inner and outer faces (43, 44) and the two circumferential faces (45, 46), respectively, is deformable. 2 - pneumatic device (1) according to claim 1, wherein the pneumatic device (1) is constituted by a circumferential assembly of at least 6 cells (4). 3 - Pneumatic device (1) according to one of claims 1 or 2, wherein the pneumatic device (1) is constituted by a circumferential assembly of at most 36 cells (4). 4 - pneumatic device (1) according to any one of claims 1 to 3, wherein the pneumatic device (1) is constituted by a circumferential assembly of cells (4) identical. 5 - pneumatic device (1) according to any one of claims 1 to 4, wherein a meridian section of each cell (4), by a meridian plane (YZ) containing the axis of rotation (ΥΥ ') of the pneumatic device (1), is inscribed in a trapezium of large base B, small base b and height H, B and H respectively being the width and height of a reference tire within the meaning of the ETRTO standard (European Tire and Rim Technical Organization) and b being the width of the rim (3). 6 - Pneumatic device (1) according to any one of claims 1 to 5, wherein the envelope of each cell (4) comprises a reinforcing layer consisting of reinforcements embedded in an elastomeric mixture. 7 - pneumatic device (1) according to claim 6, wherein the reinforcing layer comprises unidirectional reinforcements. 8 - pneumatic device (1) according to claim 6, wherein the reinforcing layer comprises bidirectional reinforcements. 9 - pneumatic device (1) according to any one of claims 6 to 8, wherein the reinforcing layer comprises textile reinforcements. 10 - Pneumatic device (1) according to any one of claims 6 to 9, wherein the reinforcements of the envelope of each cell (4) are aliphatic polyamide type textile reinforcements. 11 - Pneumatic device (1) according to any one of claims 6 to 9, wherein the reinforcements of the envelope of each cell (4) are polyethylene terephthalate textile reinforcements. 12 - pneumatic device (1) according to any one of claims 1 to 11, wherein the envelope of each cell (4) is constituted by a stack of an inner layer of elastomeric mixture, intended to be in contact with a inflation gas and sealed to said inflation gas, an intermediate reinforcing layer consisting of reinforcements embedded in an elastomeric mixture, and an outer layer of elastomeric mixture, intended to be in contact with the atmospheric air. 13 - Pneumatic device (1) according to any one of claims 1 to 12, wherein the pneumatic device (1) comprises a tread whose radially inner face is connected to the radially outer faces (44) of the cells (4). and whose radially outer face constitutes the running surface (2). 14 - mounted assembly comprising a pneumatic device (1), according to any one of claims 1 to 13, and a rim (3) with which the pneumatic device (1) cooperates via the radially inner faces (43) of the cells (4). 15 - mounted assembly according to claim 14, wherein the radially inner faces (43) of the cells (4) are secured to the rim (3). 16 - assembly mounted according to claim 14, wherein the radially inner faces (43) of the cells (4) are secured to the rim (3) by gluing.  17 - mounted assembly according to claim 14, wherein the radially inner faces (43) of the cells (4) are secured to the rim (3) by a mechanical connection.