Pneumatic vehicle tire

Abstract

A pneumatic vehicle tire having a radial carcass, an at least single-layer belt and a tread that is composed of two layers, a tread cap and a tread base, which are made from different rubber mixtures, in a radial direction, the tread base having a central portion and two lateral portions that extend at least in a radially outward direction from an axial perspective. The two lateral portions are made from a rubber mixture that has a lower dynamic modulus of elasticity E at 55 C. in accordance with DIN 53513 (measured at an extension of 8%) and a lower hysteresis than the central portion of the tread base for a lower rolling resistance without worsening the handling behavior of the vehicle tire.

Claims

1. A pneumatic vehicle tire comprising: a radial ply carcass; an at least single-layer belt and a tread, which is comprised in the radial direction of two layers made from different rubber compounds; and, a tread cap and a tread base; wherein the tread base viewed in the axial direction has at least directed radially outwardly, a central segment and two lateral segments; wherein the two lateral segments are made from a rubber compound that has a lower dynamic elastic modulus E at 55 C. according to DIN 53513 (measured at 8% extension) and a lower hysteresis than the central segment of the tread base; and, wherein the rubber compound of the two lateral segments has a filler content of less than 50 phr and the rubber compound of the central segment has a filler content of more than 55 phr.

2. The pneumatic vehicle tire as claimed in claim 1, wherein the dynamic elastic modulus E at 55 C. according to DIN 53513 (measured at 8% extension) of the rubber compound of the two lateral segments is 35 to 80% of the dynamic elastic modulus E at 55 C. according to DIN 53513 (measured at 8% extension) of the rubber compound of the central segment of the tread base.

3. The pneumatic vehicle tire as claimed in claim 1, wherein the dynamic elastic modulus E at 55 C. according to DIN 53513 (measured at 8% extension) of the rubber compound of the two lateral segments has a value of from 2.3 to 6.3 N/mm.sup.2.

4. The pneumatic vehicle tire as claimed in claim 1, wherein the dynamic elastic modulus E at 55 C. according to DIN 53513 (measured at 8% extension) of the rubber compound of the central segment has a value of from 5.1 to 9.1 N/mm.sup.2.

5. The pneumatic vehicle tire as claimed in claim 1, wherein the loss factor tan (5) at 55 C. according to DIN 53 513 (maximum value between 0 and 12% extension) of the rubber compound of the two lateral segments is 10 to 70% of the loss factor tan (5) at 55 C. according to DIN 53 513 (maximum value between 0 and 12% extension) of the rubber compound of the central segment of the tread base.

6. The pneumatic vehicle tire as claimed in claim 1, wherein the loss factor tan (5) at 55 C. according to DIN 53 513 (maximum value between 0 and 12% extension) of the rubber compound of the two lateral segments has a value of from 0.02 to 0.12.

7. The pneumatic vehicle tire as claimed in claim 1, wherein the loss factor tan (6) at 55 C. according to DIN 53 513 (maximum value between 0 and 12% extension) of the rubber compound of the central segment has a value of from 0.1 to 0.3.

8. The pneumatic vehicle tire as claimed in claim 1, wherein the width of the central segment of the tread base is 20 to 80% of the total width of the tread base.

9. The pneumatic vehicle tire as claimed in claim 8, wherein the width of the central segment of the tread base is 40 to 70% of the total width of the tread base.

10. The pneumatic vehicle tire as claimed in claim 1, wherein the tread base has a thickness of 0.5 to 5 mm.

11. The pneumatic vehicle tire as claimed in claim 10, wherein the tread base has a thickness of 0.7 to 3 mm.

12. The pneumatic vehicle tire as claimed in claim 1, wherein the rubber compound of the two lateral segments and the rubber compound of the central segment contain polymers with a glass transition temperature (T.sub.g) of less than 55 C.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will now be described with reference to the single FIGURE of the drawing (FIG. 1) which shows schematically a cross section through the tread region of a pneumatic vehicle tire according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(2) FIG. 1 shows, from the usual components of a pneumatic tire for automobiles, a tread 1, a belt 2 preferably with two bracing plies comprising reinforcing components, preferably made of steel cords, embedded in rubber, a radial ply carcass 3, also strengthened with reinforcing components, and an air-tight inner layer 4. The belt 2 is covered with a so-called belt bandage 7 of rubberized textile reinforcing components. Only the axially outer end segments are shown of the side walls of the tire. The chafer zones with bead wires and bead wire profiles are not shown. The tread 1 includes a radially outer rubber layer, the tread cap 5 and a radially inner rubber layer, the tread base 6. A backing, not shown, can also be provided underneath the tread base 6. The tread base 6 has a substantially constant thickness of approximately 2 mm and is divided into three segments in the axial direction, so that it comprises a central segment 6a and two lateral segments 6b. The central segment 6a extends, centrally to the center of the tire, over approximately 50% of the total width of the tread base 6. In the embodiment shown, the two lateral segments 6b are of equal width and are arranged symmetrically to the center of the tire. Between the base of the circumferential grooves and the tread base 6 there is another thin layer of the rubber compound of the tread cap 5, which is caused by the molding and vulcanizing operation, in which the tire blank is pressed into the mold. In FIG. 1, the transition between the lateral segments 6b and the central segment 6a is shown schematically as a vertical line. However, softer transitions between the segments, with diagonal transitions, are also possible. In this case the lateral segments 6b preferably overlap the central segment 6a radially outward.

(3) The two lateral segments 6b are made from a rubber compound with a lower dynamic elastic modulus E at 55 C. according to DIN 53513 (measured at 8% extension) than the rubber compound of the central segment 6a. The compound of the lateral segments 6b also has a lower hysteresis than that of the central segment 6a.

(4) Table 1 shows FEM calculations for the arrangement of compounds with different elastic modulus and different hysteresis in the different zones of the tread base with the resultant percentages for the rolling resistance and the cornering stiffness, wherein the values for the rolling resistance and the cornering stiffness with a tread base consisting of a uniform compound were set equal to 100%. Values above 100% signify an improvement of the corresponding property. The FEM calculations were based on the elastic moduli E, for determination of which the stress-strain curves are adapted so that viscous effects are excluded. Purely elastic stress-strain curves are used.

(5) TABLE-US-00001 TABLE 1 Compound of the Compound of the Rolling Cornering central segment 6a lateral segments 6b resistance [%] stiffness [%] A A 100 100 B B 102.4 99.7 B C 104.8 99.4 B D 105.9 99.1 C C 104.8 97.3
With
Compound A: elastic modulus (without viscous effects)
E=6.29 N/mm.sup.2 (E=7.2 N/mm.sup.2, tan =0.22)
Compound B: elastic modulus (without viscous effects)
E=5.98 N/mm.sup.2 (E=6.9 N/mm.sup.2, tan =0.15)
Compound C: elastic modulus (without viscous effects)
E=4.09 N/mm.sup.2 (E=4.5 N/mm.sup.2, tan =0.07)
Compound D: elastic modulus (without viscous effects)
E=3.15 N/mm.sup.2 (E=3.6 N/mm.sup.2, tan =0.044)

(6) It can be seen from Table 1 that the best results with respect to reduced rolling resistance, and cornering stiffness as constant as possible, can be achieved if compounds with high elastic modulus are used for the central segment 6a and compounds with a lower elastic modulus are used in the lateral segments 6b. This is shown by the combinations of compound B in the central segment 6a with the compounds C or D in the lateral segments 6b.

(7) Moreover, tires of size 205/55R16 were built, wherein the compounds for the central segment 6a (compound 1) and the lateral segments 6b (compound 2) of the tread base have the compositions and material properties given in Table 2. The central segment 6a of the tires extended over 50% of the total width of the tread base.

(8) Tires of the same size were also made, for which the tread base was formed completely on the one hand of compound 1 and on the other hand completely of compound 2. The results of the tire tests carried out with these tires are shown in Table 3, wherein the values for the cornering stiffness and the rolling resistance of the tire with compound 1 as tread base were set equal to 100%. Values above 100% signify an improvement of the corresponding property.

(9) The compounds were prepared in the usual conditions, making a base compound and then the finished compound in a laboratory tangential mixer. The Mooney viscosities ML (1+4) at 100 C. were determined using a rotorless curemeter (MDR=moving disk rheometer) according to DIN 53 523. From all the compounds, test specimens were prepared by optimal vulcanization under pressure at 160 C. and material properties that are typical for the rubber industry were determined on these test specimens by the following test methods. Shore-A hardness at room temperature and 70 C. according to DIN 53 505 Rebound elasticity at room temperature and 70 C. according to DIN 53 512 Tensile strength at room temperature according to DIN 53 504 Extension at break at room temperature according to DIN 53 504 Stress value (modulus) at 300% extension at room temperature according to DIN 53 504 Dynamic elastic modulus E at 55 C. according to DIN 53 513 at 8% extension Loss factor tan at 55 C. from dynamic-mechanical measurement according to DIN 53 513 as maximum value between 0 and 12% extension

(10) TABLE-US-00002 TABLE 2 Compound 1 for Compound 2 for central segment lateral Unit 6a segments 6b Ingredients Natural rubber phr 70 100 BR.sup.a phr 30 Carbon black N339 phr 75 25 Silica phr 5 Plasticizer oil phr 15 4 Antiaging agent phr 4 4 Antiozonant wax phr 1 1 Adhesive resin phr 4 2 Stearic acid phr 2 2 Zinc oxide phr 3 3 Accelerator phr 2.5 2 Sulfur phr 2.5 2 Properties Hardness at RT ShoreA 73 55 Hardness at 70 C. ShoreA 67 49 Rebound elast. at RT % 37 61 Rebound elast. at 70 C. % 50 73 Tensile strength at RT MPa 16 16 Extension at break at RT % 330 450 Stress value 300% MPa 15 9 E N/mm.sup.2 7.2 4.0 tan 0.22 0.04 .sup.aHigh-cis polybutadiene

(11) TABLE-US-00003 TABLE 3 Tires with compound 1 in the central Tires with Tires with segment and compound 1 as compound 2 as compound 2 in the lateral tread base tread base segments Cornering 100 94 99 stiffness Rolling 100 106 106 resistance

(12) The tires according to the invention are characterized by improved rolling resistance, without notable impairment of handling.

(13) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.