Tire Tread For An Agricultural Vehicle

Abstract

Tire (1) for an agricultural vehicle and more particularly to the tread (2) thereof. The tread has a radial thickness H.sub.max and comprises a middle part (20) and two lateral parts (21, 22), the meridian profile (P.sub.S) of the radially outer surface (31, 32) of each lateral part (21, 22) is radially on the inside of the meridian profile (P.sub.C) of the radially outer surface (30) of the middle part (20) and the radial distance (d) between the midpoint (I.sub.1, I.sub.2) of the meridian profile (P.sub.S) of the radially outer surface (31, 32) of each lateral part (21, 22) and the meridian profile (P.sub.C) of the radially outer surface (30) of the middle part (20) is at least equal to 0.5 times the radial thickness H.sub.max of the tread (2).

Claims

1. A fire for a vehicle for agricultural use comprising a tread, adapted to come into contact with the ground via a tread surface: the tread comprising raised elements separated from one another at least in part by grooves running radially towards the outside from a bottom surface as far as the tread surface over a radial height H at least equal to 30 mm and at most equal to the radial thickness H.sub.max of the tread; the tread having a total width W.sub.T measured between two axial ends of the tread surface; the tread comprising a middle part, symmetrical about an equatorial plane and having a middle width W.sub.C at least equal to 5% and at most equal to 25% of the total width W.sub.T, and two lateral parts, each extending axially inwards from an axial end of the tread surface and each having a lateral width W.sub.S at least equal to 5% and at most equal to 20% of the total width W.sub.T; the middle part comprising a radially outer surface having, in a meridian plane, a meridian profile having a midpoint and a radius of curvature R.sub.C at its midpoint, and each said lateral part comprising a radially outer surface having a meridian profile having a midpoint and a radius of curvature R.sub.S at its midpoint, wherein the meridian profile of the radially outer surface of each said lateral part is radially on the inside of the meridian profile of the radially outer surface of the middle part and wherein the radial distance between the midpoint of the meridian profile of the radially outer surface of each said lateral part and the meridian profile of the radially outer surface of the middle part is at least equal to 0.5 times the radial thickness H.sub.max of the tread.

2. The tire according to claim 1, wherein the radius of curvature R.sub.C at the midpoint of the meridian profile of the radially outer surface of the middle part is at least equal to the radius of curvature R.sub.S at the midpoint of the meridian profile of the radially outer surface of each said lateral part.

3. The tire according to claim 1, wherein the radius of curvature R.sub.C at the midpoint of the meridian profile of the radially outer surface of the middle part is at least equal to 1.1 times the radius of curvature R.sub.S at the midpoint of the meridian profile of the radially outer surface of each said lateral part.

4. The tire according to claim 1, the middle part having a middle voids volume ratio TE.sub.C equal to the ratio between the total volume of the grooves separating the raised elements of the middle part and the total volume of the middle part comprised radially between the bottom surface and the tread surface, wherein the middle voids volume ratio TE.sub.C is at most equal to 30%.

5. The tire according to claim 1, each said lateral part having a lateral voids volume ratio TE.sub.S equal to the ratio between the total volume of the grooves separating the raised elements of the lateral part and the total volume of the lateral part comprised radially between the bottom surface and the tread surface, wherein the lateral voids volume ratio TE.sub.S is at least equal to 50%.

6. The tire according to claim 1, the tread comprising two intermediate parts, each said intermediate part being axially delimited by the middle part and one said lateral part, each said intermediate part having an intermediate voids volume ratio TE.sub.I equal to the ratio between the total volume of the grooves separating the raised elements of the intermediate part and the total volume of the intermediate part comprised radially between the bottom surface and the tread surface, wherein the intermediate voids volume ratio TE.sub.I is at least equal to 50%, and at most equal to 75%.

7. The tire according to claim 1, the raised elements of the middle part and of each said lateral part extending radially outwards from the bottom surface out to the tread surface over a radial height H, wherein any raised element of the middle part comprises a first elastomer compound extending radially towards the inside from the radially outer surface over a radial distance at least equal to 0.5 times and at most equal to 1 times the radial height H and wherein any raised element of each said lateral part comprises a second elastomer compound extending radially inwards from the radially outer surface over a radial distance at least equal to 0.5 times and at most equal to 1 times the radial height H.

8. The tire according to claim 1, wherein the radius of curvature R.sub.C at the midpoint of the meridian profile of the radially outer surface of the middle part is at least equal to 1.2 times the radius of curvature R.sub.S at the midpoint of the meridian profile of the radially outer surface of each said lateral part.

9. The tire according to claim 1, the middle part having a middle voids volume ratio TE.sub.C equal to the ratio between the total volume of the grooves separating the raised elements of the middle part and the total volume of the middle part comprised radially between the bottom surface and the tread surface, wherein the middle voids volume ratio TE.sub.C is at most equal to 20%.

10. The tire according to claim 1, each said lateral part having a lateral voids volume ratio TE.sub.S equal to the ratio between the total volume of the grooves separating the raised elements of the lateral part and the total volume of the lateral part comprised radially between the bottom surface and the tread surface, wherein the lateral voids volume ratio TE.sub.S is at least equal to 60%.

Description

[0047] The present invention will be better understood with the aid of the appended figures which are schematic and not drawn to scale:

[0048] FIG. 1: a meridian section of a tread of a tire according to the invention;

[0049] FIG. 2: a plan view of a tread of a tire according to the invention;

[0050] FIG. 3A: a diagram of contact with firm ground of a tire according to the invention used at high pressure;

[0051] FIG. 3B: a diagram of contact with firm ground of a tire according to the invention used at low pressure.

[0052] FIG. 1 depicts a meridian section, in a meridian plane YZ, of a tire 1 for vehicle for agricultural use, comprising a tread 2 intended to come into contact with the ground via a tread surface 3. The tread 2 comprises raised elements 4 separated from one another at least in part by grooves 5 running radially towards the outside from a bottom surface 6 as far as the tread surface 3 over a radial height H at least equal to 30 mm and at most equal to the radial thickness H.sub.max of the tread 2. The tread 2 has a total width W.sub.T measured between two axial ends (E.sub.1, E.sub.2) of the tread surface 3. The tread 2 comprises a middle part 20, symmetrical about an equatorial plane XZ and having a middle width W.sub.C at least equal to 5% and at most equal to 25% of the total width W.sub.T, and two lateral parts (21, 22), each extending axially inwards from an axial end (E.sub.1, E.sub.2) of the tread surface 2 and each having a lateral width W.sub.S at least equal to 5% and at most equal to 20% of the total width W.sub.T. The tread further comprises two intermediate parts (23, 24), each intermediate part (23, 24) being axially delimited by the middle part 20 and a lateral part (21, 22). The middle part 20 comprises a radially outer surface 30 having, in a meridian plane YZ, a meridian profile P.sub.C having a midpoint I and a radius of curvature R.sub.C at its midpoint I. Each lateral part (21, 22) comprises a radially outer surface (31, 32) having a meridian profile P.sub.S having a midpoint (I.sub.1, I.sub.2) and a radius of curvature R.sub.S at its midpoint (I.sub.1, I.sub.2). According to the invention, the meridian profile P.sub.S of the radially outer surface (31, 32) of each lateral part (21, 22) is radially on the inside of the meridian profile P.sub.C of the radially outer surface 30 of the middle part 20. Also according to the invention, the radial distance d between the midpoint (I.sub.1, I.sub.2) of the meridian profile P.sub.S of the radially outer surface (31, 32) of each lateral part (21, 22) and the meridian profile P.sub.C of the radially outer surface (30) of the middle part (20) is at least equal to 0.5 times the radial thickness H.sub.max of the tread (2). More specifically, this radial distance d is measured between the midpoint (I.sub.1, I.sub.2) of the meridian profile P.sub.S of the radially outer surface (31, 32) of each lateral part (21, 22) and the point (J.sub.1, J.sub.2), of intersection between the radial straight line of direction ZZ passing through the midpoint (I.sub.1, I.sub.2) and the meridian profile P.sub.C of the radially outer surface 30 of the middle part 20.

[0053] FIG. 2 is a plan view of a tread 2 of a tire according to the invention. The tread 2, of total width W.sub.T, comprises raised elements 4 at least partly separated from one another by grooves 5. The tread 2, having a total width W.sub.T, comprises a middle part 20 having a middle width W.sub.C at least equal to 5% and at most equal to 25% of the total width W.sub.T, two lateral parts (21, 22), having a lateral width W.sub.S at least equal to 5% and at most equal to 20%, and two intermediate parts (23, 24) having a lateral width W.sub.I. In the case depicted, the middle part 20 is near continuous. The intermediate parts (23, 24) are partially connected to the middle part 20 by bridges.

[0054] FIGS. 3A and 3B schematically depict contact with firm ground of a tire according to the invention used at high pressure and at low pressure, respectively. In FIG. 3A, in use at high pressure, which means to say at an inflation pressure at least equal to of the recommended pressure, the radially outer surface of the middle part of middle width W.sub.C is fully in contact with the ground, while the radially outer surfaces of the lateral parts of lateral width W.sub.S are not in contact with the ground, the radially outer surfaces of the intermediate parts between each lateral part and the middle part of intermediate width W.sub.I being in partial contact with the ground. In other words, the tread is in partial contact with the ground, essentially via its middle part, and at least partially via its intermediate parts. In FIG. 3B, in use at low pressure, which means to say at an inflation pressure at most equal to the recommended pressure, the respective radially outer surfaces of the middle part of middle width W.sub.C, of the intermediate parts of intermediate width W.sub.I and of the lateral parts of lateral width W.sub.S are fully in contact with the ground. In other words, the tread is fully in contact with the ground.

[0055] The invention has been studied more particularly in the case of an agricultural tire of size IF 710/70R42.

[0056] The design features of the tread of the studied tire according to the invention are set out in Table 1 below.

TABLE-US-00001 TABLE 1 Total width W.sub.T of the tread (mm) 738 mm Middle width W.sub.C of the middle part (mm) 106 mm Lateral width W.sub.S of each lateral part (mm) 236 mm Intermediate width W.sub.I of each intermediate part (mm) 80 mm Radial thickness H.sub.max of the tread (mm) 60 mm Radial distance d between the respective radially outer 40 mm profiles of the middle and and lateral parts (mm) Mean radius of curvature R.sub.C of the radially outer profile 1200 mm of the middle part (mm) Mean radius of curvature R.sub.S of the radially outer profile 900 mm of each lateral part (mm) Middle voids volume ratio TE.sub.C (%) 20% Lateral voids volume ratio TE.sub.S (%) 60% Intermediate voids volume ratio TE.sub.I (%) 75%

[0057] As regards the road-use performance measured on the tire according to the invention described hereinabove, as compared with that of a tire of the prior art, the wearing life, which represents the maximum distance covered, has been increased by 10% and the fuel consumption has been reduced by around 10%, because of the reduction in rolling resistance.

[0058] As regards the field-use performance measured on the tire according to the invention described hereinabove, as compared with that of a tire of the prior art, the traction capability, which represents the maximum load that can be pulled, for a given level of tire slip relative to the ground, has been increased by 20% and the fuel consumption has been reduced by around 10%, because of the reduction in resistance to forward travel.

[0059] The invention may easily be extrapolated to a tire in which, for example and non-exhaustively:

[0060] the tread has a radial thickness H.sub.max of less than 30 mm

[0061] the tread comprises a middle part which is not symmetrical about the equatorial plane and/or has intermediate parts with different intermediate widths W.sub.I and/or has lateral parts with different lateral widths W.sub.S.