Pneumatic vehicle tire

Abstract

A pneumatic vehicle tire for passenger cars, vans or the like has a radial carcass, a multi-ply belt, and a profiled tread that, as viewed in the axial direction, has a central portion and two shoulder portions. The shoulder portions include a rubber mixture that has a lower dynamic modulus of elasticity E (at 55 C. and 8% elongation according to DIN 53513) than the central portion. The central portion has extensions at the base thereof, running laterally substantially parallel to the tread substructure and radially inside and across the width of the shoulder portions.

Claims

1. A pneumatic vehicle tire comprising: a radial ply casing; a multi-ply belt and a profiled tread which, as viewed in the axial direction, has a central portion and two shoulder portions, wherein the shoulder portions are composed of a first rubber compound that has a lower dynamic modulus of elasticity E at 55 C. and 8% elongation according to DIN 53513 than a second rubber in the central portion of the pneumatic tire profiled tread, and wherein the first rubber compound comprises a solution styrene-butadiene rubber (SSBR) having a glass transition temperature (Tg) of between 24 C. to 17 C. and the second rubber compound comprises an SSBR having a glass transition temperature (Tg) of between 30 C. to 25 C.; and, wherein a base of the central portion has extensions positioned laterally substantially parallel to the tread substructure, wherein the base of the central portion has extensions positioned radially within and over the width of the shoulder portions, wherein separating each shoulder portion from the central portion is a shoulder-side circumferential groove that encircles the tire in a substantially rectilinear manner in the circumferential direction, wherein each shoulder-side circumferential groove is bonded by a first groove flank on an inner side of the tread, a second groove flank on an outer side of the tread, and a third groove flank that is a groove base, wherein the first groove flank and the second groove flank are inclined at an acute angle of up to 10 degrees with respect to the radial direction, and wherein the first rubber compound comprises 40 phr of silica and 14 phr of carbon black, and wherein the second rubber compound comprises 96 phr of silica and 14 phr of carbon black.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will now be described with reference to the drawings wherein:

(2) FIG. 1 shows schematically a cross section through the tread region of a pneumatic vehicle tire; and,

(3) FIG. 2 shows a diagram which illustrates the improvements in the rolling resistance and the cornering stiffness.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(4) Pneumatic vehicle tires configured in accordance with the disclosure are provided or are particularly readily suitable for passenger vehicles, vans and the like. Of the customary components of a tire for passenger vehicles, FIG. 1 shows a tread 1, a belt 2, a radial ply casing 3, and an air-tight inner layer 4. In the example, the belt 2 has two belt plies which, in a known manner, can contain steel cord as a reinforcement. The ply casing 3 is reinforced in the customary manner with textile reinforcements. The belt 2 can be covered by a belt bandage (not shown) including rubberized textile reinforcements encircling the tire in the circumferential direction. Furthermore, the axially outer portions of side walls 5 are illustrated. Bead regions with bead cores, core profiles and the like are not shown.

(5) The tread 1 can be configured as a single part, from a single rubber layer, or can be composed of two rubber layers, namely of a radially outer rubber layer, a tread cap 7, and a radially inner rubber layer, a tread base 8. A lower plate (not illustrated) can be installed radially within the tread base 8. The tread base 8 has a substantially constant thickness of in particular approximately 2 mm and is preferably composed of a rubber compound which is optimized with respect to rolling resistance. Even when the tread 1 is worn out, the tread base 8 does not come into contact with the underlying surface. The tread cap 7 is that part of the tread 1 in which the profiling with grooves, incisions and the like is placed, wherein, in the embodiment shown, the profiling has two shoulder-side circumferential grooves 9, which encircle the tire in an at least substantially rectilinearly manner in the circumferential direction. The circumferential grooves 9 are formed here at the maximum profile depth provided for the tread concerned. The profile can be configured in such a manner that circumferential grooves which reach as far as the maximum profile depth are not provided on the outer side of the tread and to the sides of the two circumferential grooves 9. The profiling of the tread 1 can in principle be configured as desired, wherein a central circumferential groove 13 encircling in the circumferential direction is also illustrated by the example of the profiling of FIG. 1.

(6) Each circumferential groove 9 is bonded by a groove flank 9a on the inner side of the tread and a groove flank 9b on the outer side of the tread and by a groove base 9c, which can be configured in a known manner. The two groove flanks (9a, 9b) can be inclined at an acute angle of several degrees, in particular up to 10, with respect to the radial direction, that is, perpendicular to the profile surface, in such a manner that the groove width becomes larger from the groove base 9c as far as the profile surface. As illustrated, the groove base 9c can be rounded and connects the two groove flanks 9a and 9b to each other. In the embodiment shown, the groove flanks 9b placed on the outer side of the tread bound shoulder portions 11 of the tread cap 7, which shoulder portions are composed of a rubber compound which, as will also be described, differs from the rubber compound of the central portion 10 located between the shoulder portions 11. Extensions 12 of the central portion 10 run radially within the shoulder portions 11, the extensions running along the substructure of the tread cap 7, that is, here along the tread base 8 and over the entire width of the shoulder portions 11, and having an at least substantially constant thickness which is of the order of magnitude of 1.0 mm to 2.0 mm. A portion of the groove base 9c adjoining the groove flanks 9b can at the same time bound the shoulder portions 11. In a differently configured tread profiling, the boundaries between the shoulder portions 11 and the central portion 10 do not run through/at circumferential grooves, but rather, for example, through or in profile bands.

(7) The central portion 10 of the tread cap 7 extends with a constant or substantially constant axial width and preferably symmetrically with respect to the tire center over a width B.sub.z of 30% to 70% of the width B.sub.A of the tread 1 in the ground contact area which is determined with a tire mounted on a rim and placed under nominal pressure and nominal load (in accordance with the E.T.R.T.O. standard). In the case of wider tires, the central portion is relatively wider, and in the case of narrower tires is relatively smaller. The width of the two shoulder portions 11 can coincide, but the shoulder portions 11 can also differ in widthin the case of asymmetrically designed tread profiles, in which the circumferential grooves 9 do not run symmetrically with respect to the center of the tire. In each case, the minimum width of the shoulder portions is 10% of the ground contact area B.sub.A.

(8) The two shoulder portions 11 of the tread cap 7 are composed of a rubber compound, the rebound resilience of which, at 70 C. according to DIN 53512 at least corresponds to, and is preferably greater than, the rebound resilience of the rubber compound of the central portion 10 and of the two extensions 12. The rubber compound of the shoulder portions 11 furthermore has a lower dynamic modulus of elasticity E, at 55 C. according to DIN 53513 (at 8% elongation), than the rubber compound of the central portion 10 and of the extensions 12 of the latter. It is particularly advantageous if the rubber compound in the shoulder portions 11 has a modulus of elasticity E, at 55 C., which is 2.0 N/mm.sup.2 to 6.4 N/mm.sup.2, in particular 3.0 N/mm.sup.2 to 5.7 N/mm.sup.2. The rubber compound in the central portion 10 has a modulus of elasticity E which is 3.9 N/mm.sup.2 to 8.1 N/mm.sup.2, in particular 5.2N/mm.sup.2 to 7.7 N/mm.sup.2.

(9) The rebound resilience of the rubber compound in the shoulder portions 11, at 70 C., is 40% to 90%, in particular 50% to 80%, and the rebound resilience of the rubber compound of the central portion 10 and of the extensions 12 thereof is 15% to 70%, in particular 20% to 60%.

(10) Examples of typical rubber compounds for the central portion 10 and the two extensions 12 and for the shoulder portions 11 of the tread cap 7 can be gathered from Table 1. The portions of the compound components are stated in phr. SSBR 1 is a rubber with a glass transition temperature T.sub.g of between 25 C. and 30 C., SSBR 2 is a rubber with a glass transition temperature T.sub.g of between 17 C. and 24 C. The compound M.sub.1 is an example of a compound for the central portion 10 and the extensions 12, and the compound M.sub.2 is an example of a compound for the shoulder portions 11.

(11) TABLE-US-00001 TABLE 1 Components M.sub.1 M.sub.2 NR 15 15 SSBR 1 85 SSBR 2 85 Carbon black 14 14 Silica 96 40 Silane 8 3 Adhesive resin 14 7 DPG 2 1.5 accelerator CBS 2 2 accelerator Sulfur 1.7 1.7

(12) A test program was carried out with passenger vehicle tires of size 205/55 R 16 with differing construction of the tread and the rolling resistance and the cornering stiffness determined. The rolling resistance of the tires was determined according to ISO 28580, and the cornering stiffness according to TIME (measuring method, see VDI-Berichte (VDI reports), issue number: 1494, publisher: VDI Verlag GmbH, ISSN: 0083-5560). Table 2 below contains the four used tread variants of the tested tires and the measuring results. FIG. 2 graphically reproduces the measured values for the rolling resistance and the cornering stiffness. The tires of variant V.sub.1 had a tread with a uniform tread cap composed of a single compound, the compound M.sub.1, the tires of variant V.sub.3 had a tread with a uniform tread cap composed of the compound M.sub.2. The values for rolling resistance and cornering stiffness, determined with tires of variant V.sub.1 were set to 100%. The tires of variant V.sub.E had a tread cap configured according to the present disclosure, the tires of variant V.sub.3 had a tread cap composed of a central portion and two shoulder portions, but without extensions of the central portion. In FIG. 2, a straight line in the form of a dashed line is drawn between the measuring results of variants V.sub.1 and V.sub.3, the two measuring points of variants V.sub.E and V.sub.2 above the dashed line therefore both show an improvement, wherein the measuring point of variant V.sub.E is at a greater distance from the dashed line than the measuring point of variant V.sub.2. Tires of variant V.sub.E, which are configured according to the disclosure, therefore best reach the set target of particularly readily resolving the conflict of objectives between the rolling resistance and the good cornering stiffness.

(13) TABLE-US-00002 TABLE 2 Variant V.sub.1 V.sub.E V.sub.2 V.sub.3 Central portion M.sub.1 M.sub.1 M.sub.2 without extensions Central portion M.sub.1 with extensions Shoulder portion M.sub.1 M.sub.2 M.sub.2 M.sub.2 Portion of M.sub.1 100% 69% 49% 0% Rolling 100.0% 105.6% 107.0% 111.2% resistance Cornering 100.0% 98.2% 96.6% 92.3% stiffness

(14) 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.

REFERENCE NUMBERS

(15) 1 Tread 2 Belt 3 Radial ply casing 4 Inner layer 5 Side wall 7 Tread cap 8 Tread base 9 Circumferential groove 9a Groove flank 9b Groove flank 9c Groove base 10 Central portion 11 Shoulder portion 12 Extension 13 Circumferential groove