Abstract
A rubber caterpillar track (1) has an interior surface (5) intended to collaborate with drive means, and a tread (2) comprising a tread pattern (21) formed of N relief elements made of an elastomeric material which are intended to come into contact with the ground in order to give the caterpillar track (1) traction, each element of the tread pattern (21) comprising a leading face (212) intended to transmit force, characterized in that: a. the leading face of n tread pattern elements, the number n being at least equal to 0.2×N, is inclined with respect to a direction (OZ) normal to the bearing surface by an angle α comprised between 45 degrees and 75 degrees; and b. the tread is notably made of an elastomeric material of which the shore A hardness, measured in accordance with the standard ASTM D2240, is greater than or equal to 65.
Claims
1.-11. (canceled)
12. A rubber caterpillar track (1) forming a closed loop in a longitudinal direction (OX) having a given width in a transverse direction (OY) and having an interior surface (5) intended to collaborate with drive means, and a tread (2) of which an exterior surface (10) is intended to come into contact with a ground, the tread (2) comprising a tread pattern (21) formed of N relief elements made of an elastomeric material which are intended to come into contact with the ground in order to give the caterpillar track (1) traction, each element of the tread pattern (21) extending outward from a bearing surface (22) as far as the exterior surface (10) and comprising a contact face (211) intended to be in contact with the ground and a leading face (212) intended to transmit force, wherein the leading face of n tread pattern elements, the number n being at least equal to 0.2×N, is inclined by an angle α between 45 degrees and 75 degrees with respect to a direction (OZ) normal to the bearing surface, and wherein the tread is made of an elastomeric material of which a shore A hardness, measured in accordance with standard ASTM D2240, is greater than or equal to 65.
13. The rubber caterpillar track (1) according to claim 12, wherein the angle α is between 55 degrees and 70 degrees.
14. The rubber caterpillar track (1) according to claim 12, wherein the number n is at least equal to 0.4×N.
15. The rubber caterpillar track (1) according to claim 12, wherein the leading face (212) is made up mainly of two surfaces, a first surface (212a) being adjacent to the contact face (211) and a second surface (212b) being adjacent to the bearing surface (22), the angle of inclination α being that of a linear regression line (DRL) of a profile of the leading face, the first surface (212a) forming an angle α1 with a vertical direction Z, al being greater than α and between 45 degrees and 75 degrees, a height h of the first surface (212a) being at least equal to one third of a height H of the tread pattern block.
16. The rubber caterpillar track (1) according to claim 12, wherein the tread pattern blocks have a quadrilateral base and form, between one another, rows that are inclined with respect to the transverse direction (OY).
17. The rubber caterpillar track (1) according to claim 16, wherein the tread pattern blocks within each row are disposed such that the leading faces (212) are aligned with one another.
18. The rubber caterpillar track (1) according to claim 16, wherein the tread pattern blocks within each row are disposed such that the leading faces of adjacent blocks (215, 216, 217) are offset with respect to one another in the longitudinal direction (OX).
19. The rubber caterpillar track (1) according to claim 18, wherein the tread pattern blocks within each row are disposed such that, starting from a most central block of the tread, front edge corners of the successively adjacent blocks (215, 216, 217) are offset in the longitudinal direction and in the opposite direction to a direction of running by an offset “a” of between 45% and 65% of a pitch spacing “p” of the tread pattern.
20. The rubber caterpillar track (1) according to claim 12, wherein the tread pattern blocks further comprise transverse sipes (218).
21. The rubber caterpillar track (1) according to claim 12, wherein the tread pattern elements of the tread (1) are lugs having a leading face (212) which extends across an entire width of the track, in the transverse direction (OY).
22. The rubber caterpillar track (1) according to claim 12, wherein the tread pattern elements of the tread (1) are curved lugs distributed in the longitudinal direction (OX) in two rows that are symmetrical with respect to a transverse plane (XOZ), the lugs being inclined with respect to the longitudinal direction (OX) so as to form chevron patterns oriented toward the center of the tread of the rubber caterpillar track (1).
Description
BRIEF DESCRIPTION OF THE FIGURES
[0053] FIGS. 1-A, and 1-B, depict a first embodiment of the invention. The tread pattern of the tread is made up of aligned blocks. FIG. 1-A is a perspective view, and 1-B is a view in the transverse plane (OXZ).
[0054] FIGS. 2-A and 2-B depict a second embodiment of the invention in a perspective view 2-A, and in a view 2-B in the plane of contact with the ground (XOY).
[0055] FIG. 3 is a partial perspective view showing a detail of a tread according to a third embodiment of the invention.
[0056] FIGS. 4-A to 4-C are schematic detail views of the profile of a tread pattern block of the tread of the invention.
[0057] FIGS. 5 to 7 are schematic views of further examples of profiles of a tread pattern block of the tread of the invention.
[0058] FIGS. 8 and 9 are schematic views of further examples of profiles of a tread pattern block of the tread of the invention.
[0059] FIGS. 10-A, 10-B relate to a caterpillar-track tread made up of transverse lugs. FIG. 10-A is a perspective view, and 10-B is a view in the transverse plane (OZX).
[0060] FIG. 10-C depicts an enlarged view of the tread of the caterpillar track. FIGS. 10-A, 10-B and 10-C illustrate a fourth embodiment of the invention, with tread pattern blocks in the form of lugs.
[0061] FIG. 11 depicts performance results for two embodiments of the invention in comparison with the prior art.
DESCRIPTION OF THE FIGURES
[0062] FIGS. 1-A and 1-B depict a rubber caterpillar track denoted by the general reference 1, comprising a tread 2, forming a closed loop in a longitudinal direction (OX), with a given width in a transverse direction (OY), having an interior surface 5 and an exterior surface 10. Said tread 1 is provided with a tread pattern 21 made up of a plurality of raised elements intended to come into contact with the ground to provide good traction to the vehicle equipped with this caterpillar track 1 of which the preferred direction of running is indicated by the arrow 15.
[0063] Each element of said tread pattern 21 extends outwards from a bearing surface 22 and comprises a contact face 211, intended to be in contact with the ground, a leading face 212, intended to transmit the motive torque from the vehicle during running, said leading face 212 being inclined, with respect to the direction normal to the bearing surface 22, by an angle α comprised between 45 degrees and 75 degrees.
[0064] In FIG. 1-A, the tread pattern 21 of the tread 1 comprises in total a number “N” of blocks separated from one another by longitudinal cuts 23. Each block has in particular a contact face 211, a leading face 212 and a trailing face 213. The contact face is the face at the crown of the block that is intended to run and to bear the load on firm ground. On loose ground, the blocks can sink into the ground. In the preferred direction of running of the caterpillar track, the leading face 212 is thus the face that is the first to enter the contact patch and can transmit a driving force, while the trailing face is the face that is the last to leave the contact patch. The trailing face 213 can only transmit force to the ground during a braking or reversing phase.
[0065] FIG. 1-B is a depiction of the cross section of the caterpillar track in the plane (OXZ). The geometric centre of the caterpillar track is indicated by the reference 3. This view makes it possible to clearly see the orientation of the leading faces of the blocks. The leading faces are inclined backwards with respect to the direction normal to the bottom surface 22 according to the preferred direction of running indicated by the arrow 15 and make an angle α with this normal direction. According to the invention, the angle α is between 45° and 75°. In this example, the angle α is 60°.
[0066] In this first embodiment, all of the blocks of the tread 2 have leading faces inclined at an angle α of between 45° and 75°, meaning that the number n of blocks that comply with this inclination characteristic of their leading face is equal to N. However, the invention can also be implemented when only some of the tread pattern blocks of the tread comply with this inclination characteristic. For example, when the number n of these blocks is at least equal to 0.2×N, that is to say when at least 20% of the blocks comply with this inclination characteristic of their leading face, the benefit in terms of traction on loose ground is already substantial.
[0067] Still in this first embodiment, the blocks are disposed across the width of the tread in a four-block pattern. Within each row, the blocks are disposed such that their leading faces are aligned with one another, meaning that together they are almost continuous, only being interrupted by the cuts 23. The tread shown here is perfectly symmetric with respect to the median transverse plane of the caterpillar track. In a variant that is not shown, the patterns of the two halves of the tread that are situated on either side of the median transverse plane can, by contrast, be offset with respect to one another in the longitudinal direction, as is often the case for lug tread patterns of prior art agricultural tyres.
[0068] FIGS. 2-A and 2-B depict a second embodiment of a tread according to the invention. The blocks are disposed across the width of the tread in a five-block pattern. The central blocks 215 have a dual leading face, each part of this dual leading face complying with the inclination characteristic set out above. The other blocks are similar to those in the previous embodiment and likewise comply with the inclination described with an angle α close to 60°.
[0069] In this second embodiment, the disposition of the blocks differs from that of the first embodiment mainly in that the blocks are no longer aligned within each row but rather are disposed such that the leading faces of adjacent blocks are offset with respect to one another in the longitudinal direction. One way of characterizing this offset is best visible in the view of FIG. 2-B. Looking at the pitch spacing “p” between two successive patterns, the intermediate block 216 adjacent to a central block 215 and which in the direction of running of the caterpillar track enters the contact patch after this central block is offset by a distance “a” in the opposite direction to the direction of running (arrows 15). As a preference, this offset “a” is comprised between 45% and 65% of the pitch spacing “p”. As depicted in FIG. 2-B, the distance “p” between two blocks is measured between the front edge corner of the most central block (the edge corner being defined by the intersection of the leading face and the contact face) and the front edge corner of the adjacent block which, in the rolling direction of the tyre, enters the contact patch after said central block. The same measurement principle applies for each successively adjacent block and for the two sides of the tread. A similar offset is thus also observed between the intermediate block 216 and the shoulder block 217. Since the tread pattern is in this case symmetric with respect to the equatorial mid-plane of the caterpillar track, the same rule applies for the two sides of the tread.
[0070] FIG. 3 depicts a third embodiment of the invention, in which the blocks also have transverse sipes 218. Similar sipes are of course compatible with other embodiments of the invention.
[0071] FIGS. 4-A to 4-C show, on a larger scale, an example of a block profile in which the leading face 212 is connected to the contact face 211 and to the bearing surface 22 by fillets. A point C is defined at the intersection of the continuations of the leading face and of the contact face and a point E is defined at the intersection of the continuations of the leading face 212 and of the bearing surface 22. The angle of inclination α of the leading face is thus the angle that the straight line passing through C and E makes with the direction normal to the bearing surface 22.
[0072] FIGS. 5, 6 and 7 show examples of cases in which the leading face 212 is not flat. In this case, the angle of inclination α of the linear regression line DRL of the profile of the leading face between the points C and E at which the leading face meets the contact face 211 and the bearing surface 22, respectively, will be considered. Preferably, the distance d between the profile and the linear regression line DRL thereof remains less than 15 mm. FIG. 5 depicts a so-called sawtooth profile for the leading face.
[0073] FIGS. 8 and 9 show cases in which the leading face 212 is made up mainly of two surfaces, a first surface 212a adjacent to the contact face 211 and a second surface 212b adjacent to the bearing surface 22. As explained above for FIGS. 5 to 7, the angle of inclination α is that of the linear regression line DRL of the profile of the leading face between the points C and E where the first surface 212a meets the contact face 211 and the second surface 212b meets the bearing surface 22, respectively. The angle α is between 45° and 75°, and preferably between 55° and 70°. The first surface 212a itself makes an angle α.sub.1 with the direction normal to the bearing surface 22. This angle α.sub.1 is greater than α while likewise remaining comprised between 45° and 75°. The vertical height h of the first surface 212a in the thickness direction of the caterpillar track represents at least one third of the height of the tread pattern block H.
[0074] FIGS. 10-A, 10-B depict a simplified embodiment of the invention in which the blocks are in actual fact lugs extending across the entire transverse width of the tread 1.
[0075] FIG. 10-C illustrates an enlargement of a tread pattern with curved lugs. This is a variant of the fourth embodiment of the invention. In the case depicted, there are three patterns of lugs, with grey, dark and dotted infill, distributed in pairs of lugs that are symmetrical with respect to the transverse plane (XOZ). The leading faces 212 make the angle α of between 45 degrees and 75 degrees with the direction normal to the bearing surface 22. The direction of rotation of the caterpillar track is indicated by the arrow 15 oriented along the longitudinal axis (OX).
[0076] The traction versus slip performance as defined above was evaluated on test specimens indicative of the embodiment with lugs, as illustrated in FIGS. 10, and of the embodiment as depicted in FIG. 5 having a so-called sawtooth tread pattern. These tread patterns according to the invention were compared with a lugged tread pattern of the prior art. FIG. 11 depicts the two results curvesC1 and C2. Curve C1 in discontinuous line with broad strokes corresponds to the results of the prior art, and curve C2 in discontinuous line with closely spaced strokes represents the results for the tread pattern of the embodiment of FIGS. 10-A and 10-B. The abscissa axis represents the level of slip G as a %, and the ordinate axis represents the traction in newtons T(N). The results show that upwards of 5% slip, the lugged tread pattern according to the embodiment of FIGS. 10-A and 10-B of the invention performs 51% better than the tread pattern of the prior art. The improvement still being by 28% at 15% slip.
[0077] According to the inventors, a tread pattern voids volume ratio of the tread greater than or equal to 30% guarantees the invention good functionality. Likewise, a voids area ratio lower than 70% makes it possible to obtain optimal grip on made-up (asphalted) roads.
[0078] The invention is not intended to be limited to just these described exemplary embodiments, and various modifications can be made thereto while remaining within the scope as defined by the claims.
