Optimized structure of civil engineering type tire

Abstract

A radial tyre for a vehicle of the civil engineering type, intended to be mounted on a nominal rim (1), comprises a hook (122) having a circular portion. A portion of the outer surface (31) of the bead is configured to be in contact with the nominal rim (1) up to a point (311) in contact with the circular portion of the rim hook, the angle (A1) between the radius of the circular portion of the rim passing through said contact point (311) and the axial direction being between 80 DEG and 85 DEG.

Description

Technical Field

[0001] The subject of the invention is a radial tyre intended to be fitted to heavy vehicles of the civil engineering type and it more particularly concerns the beads and the sidewalls of such a tyre. Background Art

[0002] Radial tyres intended to be fitted to heavy vehicles of the civil engineering type are specified within the meaning of the European Tyre and Rim Technical Organisation (or ETRTO) standards.

[0003] For example, within the meaning of the European Tire and Rim Technical Organization (or ETRTO) standards, radial tires for heavy vehicles of the civil engineering type are intended to be mounted on rims with a diameter at least equal to 25 inches. Although not limited to this type of application, the present invention is described for radial tires of large dimensions, intended to be mounted on dump trucks, in particular on vehicles used to transport material extracted from quarries or opencast mines, with rims with a diameter at least equal to 35 inches, possibly up to 57 inches, or even 63 inches.

[0004] The tyre is intended to be mounted on a rim, the geometric details of which are given in technical documents of national or international organisations, such as the European Tire and Rim Technical Organisation (or ETRTO) or the American Tire and Rim Association (or TRA). These documents specify which rim should be used with which size tyre, and for something as technical as a tyre for civil engineering vehicles, there is only one rim size that corresponds to one size tyre, within manufacturing tolerances.

[0005] Since the tire and the rim have geometries that exhibit rotational symmetry about an axis of rotation, which is the same axis once the tire is mounted on the rim, their geometries are usually described in a meridian plane containing the axis of rotation. For a given meridian plane, radial, axial and circumferential directions denote, respectively, directions perpendicular to the axis of rotation of the tire or rim, parallel to the axis of rotation and perpendicular to the meridian plane. The circumferential direction is tangential to the circumference of the tire.

[0006] In the following, the expressions "radially inner / located radially inside" and "radially outer / located radially outside" mean "closer to the rotation axis of the tire / rim" and "further away from the rotation axis of the tire / rim", respectively. The expressions "axially inner / located axially inside" and "axially outer / located axially outside" mean "closer to the equatorial plane of the tire / rim" and "further away from the equatorial plane of the tire / rim", respectively. The equatorial plane or median plane of the tire is the plane passing through the middle of the tread surface and perpendicular to the rotation axis. Likewise, the equatorial plane or median plane of the rim is the plane passing through the middle of the two rim hooks and perpendicular to the rotation axis.

[0007] Typically, a tire comprises a tread intended to come into contact with the ground via a tread surface, the two axial ends of which are connected by two sidewalls to two beads providing a mechanical connection between the tire and the rim on which it is intended to be mounted.

[0008] The radial tire also comprises a reinforcement composed of a crown reinforcement radially on the inside of the tread and a carcass reinforcement radially on the inside of the crown reinforcement.

[0009] The carcass reinforcement of a radial tire for heavy vehicles of the civil engineering type generally comprises a carcass layer, which generally comprises a metal reinforcement or reinforcing element, which is coated with an elastomer or a polymer material of the elastomeric type, which is obtained by blending and is called a coating compound. The carcass layer comprises a main part, which connects the two beads together and is generally wound around a circumferential reinforcing element (called a bead wire) which is generally metal in each bead from the inside to the outside of the tire, thereby forming a bead. The metal reinforcements of the carcass layer are substantially parallel to each other and form an angle between 80 ° and 100 ° with the circumferential direction. In the case of a civil engineering tire, the diameter of the reinforcing element of the carcass layer is at least equal to 1.5 mm.

[0010] In civil engineering, the carcass reinforcement of the prior art (see US5236031) includes a single carcass layer without other reinforcing element layers. The end of the bead is close to the axial outermost point of the tire, or even radially located outside the axial outermost point of the tire, as disclosed in the cited literature. If the end is positioned too close to the bead wire, there is a risk that the reinforcing element of the carcass layer may slide under the bead wire during high-intensity use under the action of pressure and heat, thereby causing a sudden drop in tire pressure. If the end of the bead is located in an intermediate radial position so that its radial distance to the radial innermost point of the tire is less than twice the height of the hook portion of the nominal rim, the end of the bead will be in the compression zone, thereby increasing the risk of cracking of the rubber composition around these ends. Positioning the end of the bead near the axial outermost point of the tire makes it possible to prevent cracking caused by the end of the reinforcing element. However, in the flexure zone, the bead is subjected to tension-compression cycles, which may cause fatigue fracture of the reinforcing element. Prior art (see US5236031) proposes bringing the bead closer to the main part of the carcass layer to reduce the bending stresses due to the bead behaving like a beam. However, the diameter of the reinforcing elements used in the carcass layer of tires for civil engineering vehicles complicates this solution. Considering their bending stiffness, it is difficult to keep them in an ideal position for tire durability throughout the manufacturing process.

[0011] Nevertheless, this solution does not solve all the problems of the durability of the bead and its surrounding carcass layer. Specifically, on uneven terrain where tires of civil engineering vehicles are used, in order to increase their productivity, the ever-increasing speed of the vehicle generates a resonance phenomenon when the tire separates from the ground, followed by a rebound, which means a great dynamic overload, which can be up to 2 times the nominal load. In addition to this, there are some practices that are not conducive to the durability of the bead, such as using it at a pressure lower than the recommended pressure, or increasing the load to exceed the nominal load. Reducing the pressure is a strategy used to improve the durability of the crown with respect to impact loads, but this is accompanied by an increase in the deformation of the carcass layer above the bead. In addition, the electrification of the power unit will also lead to the need to improve the overload durability of the bead, considering the weight of the battery. Summary of the invention

[0012] For a radial tire for civil engineering type vehicles, the inventors set themselves the goal of increasing the durability of the beads.

[0013] According to the invention, this object has been achieved by a tyre for civil engineering type vehicles, the tyre being intended to be mounted on a nominal rim comprising, on each side of a midplane perpendicular to the axis of rotation of the rim, a conical rim seat and a flange, the flange having a radial height G, the flange being formed axially from the inside towards the outside by a radial first portion and a hook, the hook being formed by a circular first portion with a standardized radius R1 and a centre O1, and by a hook tip, the tyre comprising:

[0014] a crown reinforcement radially on the inside of the tread connected to the two beads by means of two sidewalls,

[0015] each bead having an outer surface extending from the outer surface of the sidewall,

[0016] a radial carcass reinforcement extending between two beads and comprising at least one carcass layer, said carcass layer comprising a metal reinforcement making an angle of between 80° and 100° with the circumferential direction and coated with a rubber composition, said carcass layer being anchored in each bead by a turn-up around the bead wires so as to form a main part and a turn-up, said main part extending from one bead wire to the other, said turn-up being axially on the outside of the main part in each bead and having a free end,

[0017] The outer surface of the bead is arranged to be in contact with said nominal rim in each meridian plane, the measurement being made on the tyre mounted on said nominal rim and inflated to the nominal pressure, the contact occurring on the rim seat and the flange up to the last point of contact with the circular portion of the hook of the nominal rim, the last point of contact being the radially outermost point of contact between the nominal rim and the bead, the angle between the radius of the circular portion of the nominal rim passing through said last point of contact and the axial direction being between 80° and 85°.

[0018] The present invention relates to a civil engineering radial tire, which includes a metal carcass layer, the bead of which is configured to have an enlarged contact area with the rim hook portion to maximize the reaction force of the rubber composition to the compressive stress, thereby relieving the stress on the bead and the reinforcing elements of the main part of the carcass layer. The last contact point between the rim and the bead needs to be correctly positioned so that the gain in durability of the carcass layer is not destroyed by the failure of the rubber composition in the bead, which is subjected to a heavier load in the present invention than in the prior art. The pressure load changes the deformation in this area of ​​the bead.

[0019] The external surface of the tire refers to the surface that defines the object. This surface can be radially external, in which case it means the tread surface. It can be axially external, in which case it is the surface of the sidewall or bead intended to come into contact with the rim. It can be internal, in which case it is intended to come into contact with the inflation gas once the tire is mounted on its rim.

[0020] The current dimensions of the axially outer external surface of the bead of civil engineering tires are therefore such that, in the mounted and inflated position, the contact reaches approximately the middle of the circular portion of the rim hook, which is the most reliable way to have mechanical continuity between the bead and the sidewall. The upper part of the rim hook is then used to accompany the deformation of the sidewall when the portion of the tire situated near the footprint is compressed. This solution is even more advantageous when the carcass reinforcement comprises a single carcass layer.

[0021] In the present invention, the rim hook reacts to some of the compressive loads, resulting in a better distribution of the contact loads between the bead and the rim. For this purpose, it is important that the last contact point between the rim hook and the outer surface of the bead is in a specific position relative to the rim hook, i.e. the angle (A1) between the radius of the circular part of the rim passing through the last contact point and the axial direction needs to be between 80° and 85°. Up to this angle, the operation of the bead remains the same, while above this angle, the continuity of the connection of the bead with the sidewall implies a suboptimal geometry of the tire. The angle (A1) between the radius of the circular part of the rim passing through the last contact point and the axial direction is determined from the intersection of the rim with the axial axis until the last contact point between the rim hook and the outer surface of the bead.

[0022] The position of the last contact point relative to the rim hook can be determined by any relevant measuring means, such as using a thickness gauge or using optical or contact profilometry. These measuring methods can also determine the values ​​of other characteristics of the outer surface of the tire described in the present invention.

[0023] In order to avoid stress concentrations in the area where the sidewall meets the bead, a preferred solution is that, axially outside the bead and the sidewall, the outer surface of the bead should be connected to the outer surface of the sidewall by a radially innermost portion of the outer surface of the sidewall, said radially innermost portion being substantially circular over a portion of radial height at least equal to 0.2 times and at most equal to 0.4 times the radius R1 of the rim hook, the center of curvature of said radially innermost portion of the outer surface of the sidewall being axially located inside said radially innermost portion of the outer surface of the sidewall. The curvature of said radially innermost portion of the outer surface of the sidewall is thus dimensioned and positioned with its center of curvature positioned relative to the outer surface towards the plane of symmetry of the tire, making it possible to avoid the presence of significant discontinuities on the outer surface of the sidewall or the need to dimension the sidewall thicker than necessary. Substantially circular means that, in each meridian plane, between the last point of contact and a point on the outer surface radially located between 0.2 and 0.4 times R1, the outer surface lies on a curve comprised between two circles having radii differing by 10%.

[0024] A preferred solution for optimizing the stresses at the junction of the sidewall and the bead is that, when the tire is mounted on a nominal rim and inflated, the radially innermost part of the outer surface of the sidewall is substantially circular along a circle, the center of which is located on a straight line passing through the center of the circular part of the hook of the rim and the last contact point, and the radius R2 of the circle is between 0.25 and 0.4 times the radius R1 of the circular part of the hook of the rim.

[0025] An advantageous solution for ensuring optimal continuity of the outer surface of the sidewall, and in particular continuity between the radially innermost circular portion and the portion adjacent thereto, is that, with the tyre mounted on a nominal rim and inflated, the radially innermost portion of the outer surface of the sidewall is substantially circular over an angular portion comprised between 65° and 75° and measured from the radius formed by the last point of contact and the centre of said circle.

[0026] In order to optimize the shape of the sidewall and in particular its thermal behavior, the outer surface of the sidewall radially located on the outside and adjacent to the substantially circular radially innermost portion of its outer surface, at a radial height equal to the radial height G of the hook of the nominal rim, has, with the tire mounted on a nominal rim and inflated, a center of curvature axially on the outside of the bead and preferably with a mean radius of curvature at least equal to 400 mm. In tires according to the prior art, the center of curvature of this area of ​​the sidewall is axially on the inside of the bead in the continuation of the connection between the bead and the sidewall. The invention requires a reconfiguration of this entire area in order for it to work properly.

[0027] This reconfiguration of the bead and the adjacent parts of the sidewall has the effect of moving the compression point of the carcass ply turn-up towards a point radially outwards compared to the solutions of the prior art. This point is located between 2 and 2.5 times the height G of the hook of the rim with respect to the axially outermost point of the rim seat. Therefore, in order to minimize the compression of the turn-up at this point, the turn-up needs to be closer to the main part of the carcass ply. Compared to the solutions of the prior art, this convergence at this point is easier to achieve because there is a greater length of turn-up available to achieve it. Therefore, a preferred solution is that when the tire is mounted on a nominal rim and inflated, the distance between the main part of the carcass ply and its turn-up is minimum at a radial height from the axially outermost point of the seat of the nominal rim, which height is between 2 and 2.5 times the height G of the hook of the nominal rim.

[0028] The distance between the main part of the carcass layer and its turn-up can be measured in a meridian cross section. The distance is measured from the neutral axis of the carcass layer to the neutral axis of the turn-up perpendicular to the neutral axis of the main part of the carcass layer.

[0029] For good distribution of the stiffness within the bead, it is advantageous if the distance between the main part of the carcass layer and its turn-up decreases continuously from the geometrical centre of the bead wire until a point where said distance reaches its minimum value.

[0030] For optimal operation of the beads and sidewalls, it is advantageous if a single rubber composition, called bead filler, fills the volume between the main part of the carcass layer and its turn-up, this rubber composition having a secant tensile modulus MA10 at 10% strain measured at 23°C according to standard ASTM D 412 that is at least equal to 5 MPa.

[0031] In order to avoid excessive deformation gradients between the bead filler and the rubber composition of the reinforcing elements coating the carcass layer, it is advantageous if a single rubber composition fills the volume between the main part of the carcass layer and its turn-up and has a secant tensile modulus MA10 at 10% strain measured at 23°C according to standard ASTM D 412 that is at least equal to 90% of the same modulus of the rubber composition of the reinforcing elements coating the carcass layer and preferably at most equal to 110%.

[0032] Likewise, for optimal operation of the sidewall when bending, it is preferred that the rubber composition is adjacent to and axially outside the bead of the carcass layer, the rubber composition being arranged at least radially outside the said last contact point on the outer surface of the bead, and having a secant tensile modulus MA10 at 10% strain measured at 23°C according to standard ASTM D 412, which is at least equal to 90% of the tensile modulus MA10 of the bead filler and preferably at most equal to 110%. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The features of the present invention are shown schematically in Figures 1 to 3 It is shown in Figures 1 to 3 Not drawn to scale and references a tire size 24.00R35. DETAILED DESCRIPTION

[0034] Figure 1 The profile of a tapered seat rim (1) for tires of sizes 25, 29, 33, 35, 49, 51, 57 and 63 inches as described in the document "The Tire and Rim Association" is depicted. The profile represents a cross section through the rim, said rim comprising, on each side of a midplane perpendicular to the axis of rotation (OY) of the rim, a tapered rim seat (11) and a flange (12) having a radial height G, said flange (12) being formed axially from the inside towards the outside by a radial first portion (121) and a hook (122) having a standardized radius R1 and a center O1 (see Figure 2 and Figure 3 ) and the hook tip. The figure also shows the axially outermost point (111) of the rim seat (11) on the surface intended for contact with the tyre. In the case where the seat (11) of a nominal rim is attached to the flange (12) by a fillet radius, the fillet radius will be considered to be the starting point of the flange (12).

[0035] Figure 2Detail of a meridian section through a tyre for a heavy vehicle of the civil engineering type, mounted on its rim (1) and inflated, and showing in particular the sidewalls (2) and the beads (3). The beads (3) have an outer surface (31) extending from the outer surface (21) of the sidewalls. The radial carcass reinforcement comprises a carcass layer (4) anchored in the beads by a beading around bead wires (5) to form a main part (41) and a beading (42), the main part (41) extending from one bead wire to the other bead wire, the beading (42) being axially located in each bead (3) on the outside of the main part (41) and having a free end (421). The outer surface (31) of the bead is configured to contact the nominal rim (1) until a radially outermost contact point (311) on a circular portion of the rim hook having a center (O1), the angle (A1) between the radius of the circular portion of the rim passing through said last contact point (311) and the axial direction being between 80° and 85°. Figure 2 and Figure 3 The angle (A1) between the radius of the circular portion of the rim passing through the last contact point and the axial direction is determined from the intersection of the rim and the axial axis to the last contact point between the rim hook and the outer surface of the bead. Figure 2 Also shown is the distance (d) between the main part (41) of the carcass layer (4) and its turn-up (42), which distance decreases continuously until its minimum value (dm), which is located at a radial height hm from the axially outermost point (111) of the rim seat, said height hm being between 2 and 2.5 times the height G of the rim hook. A single rubber composition, called bead filler (32), fills the volume between the main part (41) of the carcass layer (4) and its turn-up (42), said single rubber composition being adjacent to the rubber composition (22) and axially located on the inner side of the rubber composition (22). Figure 2 Also shown is the profile (21') of a tyre according to the prior art.

[0036] Figure 3 is an enlarged detail of the bead to show the transition between the bead and the sidewall around the last contact point (311) between the outer surface (31) of the bead (3) and the nominal rim (1). The outer surface (21) of the sidewall (2) is substantially circular in its radially innermost portion (211) along a circle over an angular portion (A2), the center (O2) of which is located on a straight line passing through the center (O1) of the circular portion of the hook (122) and the last contact point (311), the radius R2 of which is between 0.25 and 0.4 times the radius R1 of the circular portion of the hook (122) of the rim (1), the angular portion (A2) being between 65° and 75° and measured from the radius formed by the last contact point (311) and the center (O2) of the circle.

[0037] The invention was tested on tires of size 24.00 R 35. The tires according to the invention were compared with reference tires of the same size.

[0038] The reference tire and the tire according to the invention have a single carcass layer below the bead wires, the metal reinforcement of which is 7 strands of cords, said strands comprising 7 wires of 23 percent of a diameter of 2.24 mm and laid at a twist of 2.6 mm. The turns of the two tires have their free ends (421) near the axially outermost point of the tire. The rubber composition used is identical for both solutions. The geometry of the outer surface of the bead has been modified so that in the case of the reference tire, the last point of contact (311) passes at an angle A1 close to 60° and in the case of the tire according to the invention, at an angle equal to 81.3°. In the case of the reference tire, the junction at the point of contact is in the form of a curve that is substantially circular over the entire portion of the sidewall between the last point of contact (311) and the axially outermost point of the tire, the center of curvature of which is axially located on the inside of the bead. In the case of a tire according to the invention, the bead meets the sidewall at a circular portion extending over an angular portion of 69°, the center of which is located on a straight line extending the radius of the circular portion of the rim hook, which radius passes through the last point of contact (311) between the outer surface (31) of the bead (3) and the rim (1). The radius of this circular portion is equal to 0.3 times the radius R1 of the circular portion of the rim (1). The distance (d) between the main part (41) of the carcass layer (4) and its turnup (42) is minimum at a radial height hm from the axially outermost point (111) of the seat of the rim, this height hm being equal to 2.1 times the height G of the rim hook in the case of the invention and 1.0 times the height G in the case of the reference tire.

[0039] The other components (crown structure, rubber compound, etc.) of the control tire and the tire according to the invention are identical.

[0040] The tires were tested on a machine. They were first planed to the bottom of the tread pattern in order to concentrate the stress loads in the sidewalls and beads. The profile of the planed tire tread corresponded to the new tread profile. At a pressure of 6.2 bar, i.e. 1.05 bar below the nominal pressure, the two tires were pressed against each other with a force of 25 000 daN, which corresponds to the nominal load plus an overload of 25%. The tires were run relative to each other at a speed of 15 km / h. The tire according to the invention continued to run without damage for more than 1000 hours, while the tire according to the prior art stopped running after 600 hours due to a break in the rubber compound in the part of the sidewall close to the rim hook.

[0041] Thus, the present invention does improve the durability of the sidewall and bead by at least 66% when used under overload and underinflation conditions.

Claims

1. A tyre for civil engineering type vehicles, intended to be mounted on a nominal rim (1), said nominal rim comprising, on each side of a midplane perpendicular to the axis of rotation of said rim, a conical rim seat (11) and a flange (12), said flange (12) having a radial height G, said flange (12) being formed axially from the inside towards the outside by a radial first portion (121) and a hook (122), said hook (122) being formed by a circular first portion with a standardized radius R1 and a centre O1, and by a hook tip, said tyre include: a crown reinforcement radially on the inside of the tread connected to the two beads (3) by means of the two sidewalls (2), Each bead (3) has an outer surface (31) extending from the outer surface (21) of the sidewall, a radial carcass reinforcement extending between two beads and comprising at least one carcass layer (4), said carcass layer (4) comprising a metal reinforcement forming an angle of between 80° and 100° with the circumferential direction and coated with a rubber composition, said carcass layer (4) being anchored in each bead by turning around a bead wire (5) so as to form a main portion (41) and a turnup (42), said main portion (41) extending from one bead wire to the other, said turnup (42) being axially outside the main portion (41) in each bead (3) and having a free end (421), · Characterized in that the outer surface (31) of the tire bead is configured to contact the nominal rim (1) in each meridian plane, the measurement being carried out on a tire mounted on the nominal rim (1) and inflated to the nominal pressure, the contact occurring on the seat and flange of the rim up to a last point (311) of contact with the circular part of the hook of the nominal rim, the last contact point (311) being the radially outermost contact point between the nominal rim and the tire bead, the angle (A1) between the radius of the circular part of the nominal rim passing through the last contact point (311) and the axial direction being between 80° and 85°.

2. The tire according to claim 1, in, Axially outside the tire bead (3) and the sidewall (2), the outer surface (31) of the tire bead is connected to the outer surface (21) of the sidewall through the radially innermost portion (211) of the outer surface (21) of the sidewall, the radially innermost portion (211) being substantially circular over a portion of a radial height at least equal to 0.2 times and at most equal to 0.4 times the radius R1 of the rim hook (122), and the center of curvature (O2) of the radially innermost portion (211) of the outer surface (21) of the sidewall is axially located inside the radially innermost portion (211) of the outer surface (21) of the sidewall.

3. The tire according to claim 2, in, The radially innermost portion (211) of the outer surface (21) of the sidewall (2) is substantially circular along a circle, the center (O2) of the circle is located on a straight line passing through the center of the circular portion of the hook portion (122) of the rim (1) and the last contact point (311), and the radius R2 of the circle is between 0.25 and 0.4 times the radius R1 of the circular portion of the hook portion (122) of the rim (1).

4. The tire according to claim 3, in, The radially innermost portion (211) of the outer surface (21) of the sidewall (2) is substantially circular over an angular portion (A2) comprised between 65° and 75° and measured from a radius formed by the last contact point (311) and the center (O2) of the circle.

5. A tyre according to any one of the preceding claims, in, The outer surface (21) of the sidewall (2) is radially located outside and adjacent to a substantially circular radially innermost portion (211) of the outer surface (21) of the sidewall (2) at a radial height equal to the radial height G of the hook portion (122) of the nominal rim (1), and has a center of curvature axially located outside the tire bead (3).

6. A tyre according to any one of the preceding claims, in, The distance (d) between the main part (41) of the carcass layer (4) and its turn-up (42) is minimum at a radial height (hm) from the axially outermost point of the seat (111) of the nominal rim, said radial height being between 2 and 2.5 times the height (G) of the hook of the nominal rim.

7. A tyre according to any one of the preceding claims, in, The distance (d) between the main part (41) of the carcass layer and its turn-up (42) decreases continuously from the geometrical centre of the bead wire (5) until a point where said distance (d) reaches a minimum value (dm).

8. A tyre according to any one of the preceding claims, in, A single rubber composition, called bead filler (32), fills the volume between the main part (41) of the carcass layer (4) and its turn-up (42), the rubber composition having a secant tensile modulus MA10 at 10% strain measured at 23°C according to standard ASTM D 412, which is at least equal to 5 MPa.

9. A tyre according to any one of the preceding claims, in, A single rubber composition (32) fills the volume between the main part (41) of the carcass layer (4) and its turn-up (42) and has a secant tensile modulus MA10 at 10% strain measured at 23°C according to standard ASTM D 412, which is at least equal to 90% of the same modulus of the rubber composition of the reinforcing elements coating the carcass layer (4) and preferably at most equal to 110%.

10. The tire according to any one of the preceding claims, in, The rubber composition (22) is adjacent to the bead (42) of the carcass layer and is axially located on the outside of the bead (42) of the carcass layer. The rubber composition is at least radially arranged on the outside of the said last contact point (311) on the outer surface of the tire bead, and has a secant tensile modulus MA10 at 10% strain measured at 23°C according to standard ASTM D 412, and the secant tensile modulus MA10 is at least equal to 90% of the tensile modulus MA10 of the tire bead filling rubber (32) and preferably at most equal to 110%.

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