GB2104011A

GB2104011A - Pneumatic vehicle tyre

Info

Publication number: GB2104011A
Application number: GB08215549A
Authority: GB
Inventors: Dionysius Joseph Poque
Original assignee: Uniroyal GmbH
Current assignee: Uniroyal GmbH
Priority date: 1981-06-19
Filing date: 1982-05-27
Publication date: 1983-03-02
Also published as: DE3124119C2; DE3124119A1; FR2507970A1; GB2104011B; JPH0579521B2; JPS5816903A; FR2507970B1

Abstract

A pneumatic vehicle tyre has a crown reinforcement (7), and a radial carcase comprising an inner ply (12) turned-up around bead cores (4) and an outer, auxiliary, ply (14) which terminates axially outwardly of the bead cores (4) and has at least 20% less tensile strength and fewer filaments than the inner ply (12). The cord density and/or number of filaments per cord may be smaller in the outer ply than in the inner ply, and the cord materials in the two plies may be different. <IMAGE>

Description

SPECIFICATION Pneumatic vehicle tyre The present invention relates to a pneumatic vehicle tyre having a radial carcase, two beads, a tread surface and a belt-like tread surface reinforcement, wherein the carcase is composed of two cord fabric plies, the radially inner ply extending around the bead ring, together with the core reinforcement, from axially internally towards the outside and forming a foided-over end portion and the radially outer ply being located in the bead axially externally of these elements, the carcase being covered internally by a protective rubber layer and externally by a lateral wall strip.

Such belted radial tyres are standard tyres both for private motor cars and for lorries. In such cases, the carcase comprises two identical cord fabric plies, the development of the cord filaments in said plies amounting to substantially 90 + tolerance, measured relative to the central plane of the tyre circumference.

These cord fabric plies are made of proven cord materials, such as rayon, nylon or polyester, and, depending on material, cord filament structure and cord filament packing density, they have a strength which ensures that the carcase positively absorbs the alternating stresses which occur in the cord filaments of the carcase because of pneumatic pressure and loading. A carcase of this type also has a reserve strength which, for protection against local pressure, is a multiple of what is required.

Known carcases, which are formed from two identical equivalent cord fabric plies having full packing density and a rubber coating, make up a considerable portion of the tyre weight. Until now, no changes have been made to alter this carcase weight.

The present-day requirements set for tyres in connection with safety, travel behaviour, economy and comfort always emphasize one factor, namely that they should be made as light-weight as possible, though not at the expense of safety.

Light-weight tyres considerably reduce the rolling resistance, and a reduced rolling resistance means a saving of energy. In times when raw materials are scarce, this is particularly important.

In certain cases, a one-ply carcase will bring about a great weight reduction. However, a belted radial tyre fitted with such a carcase would have the considerable disadvantage of unfavourable travel behaviour. The flexion zone of the tyre, i.e. the portion of the tyre located between the tread surface shoulder and the tyre bead, would be disadvantageously large, and this has a negative effect on lateral stability, on stabilization after a change of travel direction and on travel behaviour round bends in the case of belted radial tyres.

The invention therefore seeks to provide a pneumatic vehicle tyre which is to have a carcase which is considerably reduced in weight, meets the strength requirements and, from the point of view of travel behaviour, provides the tyre with properties comparable with those of a standard tyre having a conventional two-ply carcase.

According to the present invention there is provided a pneumatic vehicle tyre having a radial carcase, two beads, a tread surface and a belt-like tread surface reinforcement, wherein the carcase is composed of two cord fabric plies, the radially inner ply extending around the bead ring, together with the core reinforcement, from axially internally towards the outside and forming a folded-over end portion, and the radially outer ply being located in the bead axially externally of these elements, the carcase being covered internally by a protective rubber layer and externally by a lateral wall strip, in which the radially inner carcase ply, formed from standard-filament cord fabric, is the reinforcing member for the carcase, and in which the radially outer carcase ply serves as an auxiliary ply having fewer filaments and having a minimum of 20% less tensile strength then the inner carcase ply, wherein the strength of the ply is determined by the product of the packing density, the strength of the cord filaments and their rubber coating.

Because of the design according to the invention, the inner carcase ply essentially constitutes the reinforcing member of the carcase, and the outer carcase ply fulfils the function of ensuring good travel behaviour and guarantees the reduction in weight. The flexion zone of the tyre becomes more advantageous compared with a standard tyre as described. The neutral axis for the bending stress of the lateral wall is advantageously located in the region close to the inner carcase ply.

This may be achieved with an auxiliary ply, the cord having a low packing density and/or a small number of filaments.

For this purpose, the radially outer carcase ply preferably has a cord filament packing density which is from 20% to 70% lower than the packing density of the inner ply made from standard-filament cord fabric. This inner ply preferably has a packing density of from 55% to 95%.

Thus, the auxiliary ply, having fewer filaments, acts as the radially outer carcase ply and may differ from the inner carcase ply, forming the reinforcing member from the point of view of cord filament structure and fabric material.

In addition, the auxiliary ply may also be made from yarn(s) instead of cord filament. There are a number of technical yarns therefor. Thus, for example, single yarn made from polyamide or from aromatic polyamide may be provided in the auxiliary ply due to the advantageous specific weight and the tensile strength which, in the case of aramide, is comparable with metal filaments and because of other physical properties.

In all cases of application, including the mixed structure for carcases, the carcase results in being reduced in weight to a greater or lesser degree, as does the tyre in this respect which therefore has less rolling resistance.

In addition, the thickness of the rubber coating for the auxiliary ply may also be reduced. The thickness may preferably be reduced by up to 50% over the cord or filament diameter. For example, the overall ply thickness D may equal d (cord diameter) + 2 x 0.05 mm. In respect of the rubber coating, the auxiliary ply may also have a higher modulus than the radially inner carcase. The modulus of the auxiliary ply may be considerably higher than the normal values in the region of 10.0 MPa for 300% modulus, namely from 15.0 to 20.0 MPa.

Relatively light-weight carcase plies may be achieved in this manner, the cord filaments thereof being substantially parallel to one another and being spaced in the auxiliary ply at relatively wide lateral distances from one another. Because there are few warp filaments present, they resemble a rubbercoated, wide-meshed net which is arranged above the inner ply forming the reinforcing member.

The present invention will be further illustrated, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view through a pneumatic vehicle tyre; and Fig. 2 is a spatial, partial view of one detail of the carcase.

As illustrated, a pneumatic vehicle tyre 1 has a radial carcase 2 which is composed of two cord fabric plies 12, 14 and two beads 3. The tread strip 6 has a tread surface reinforcement 7.

The reinforcement 7 comprises two or three cord plies 8, 9 which are arrnged in belt-like fashion between the carcase 2 and the tread surface. The carcase 2 is covered internally by a protective rubber layer 10 which, in the case of a tubeless tyre, is composed of a rubber mixture which is impenetrable by air. Halobutyl rubber is an example of suitable material. The carcase 2 is covered externally by a rubber strip 11 which essentially forms the lateral wall of the tyre. The radially inner carcase ply 1 2 extends around the bead ring 4, formed of steel wires, and around the core reinforcement 5, composed of a rubber mixture, from axially internally towards the outside. The ends of the ply form folded-over portions 1 3 in the region of the core reinforcement 5.

The radially inner carcase ply 12 comprises rubber-coated cord filaments which exist as normal filaments, i.e. they are packed relatively tightly. The packing density, i.e. the number of cord filaments per decimetre, measured in the region above the bead ring, is, for example, approximately 100 to 130 cord filaments (epdm = ends per decimetre) in the case of rayon cord of the 1 840/2 yarn type. Instead of rayon, nylon and polyester yarns are also often chosen as carcase cord materials. In addition, aromatic polyamide cords or even flexible thin metal cords are also possible as carcase material. The relatively high packing density of the carcase ply 12 ensures the strength, which is required for the radial tyres to absorb the alternating stresses which are caused by pneumatic pressure and load, and ensures the flexibility which is desirable for good travel behaviour and comfort.At the same time, the relatively high packing density prevents the layer of butyl rubber 10 from being able to penetrate into the carcase.

The radially outer carcase ply 14 extends over the entire circumferential length of the inner ply 12 and is located in the bead region axially externally of the core reinforcement 5 and the carcase folded-over portion 13.

This carcase ply 14 has few filaments. In this respect, it may have a low packing density and/or a small number of filaments per cord filament. The preferred packing density is from 20% to 70% less than the packing density in the inner ply; a 20% packing density is still permissible as a minimum.

Rayon, nylon, polyester and aromatic polyamides may be chosen as cord materials.

A radially outer carcase ply 14, which merely contains 25 to 60 cord filaments per decimetre depending on yarn material and cord type, reduces considerably the weight of the carcase.

The auxiliary ply having fewer filaments fulfils the important function of ensuring good travel behaviour. As shown in Fig. 2, the auxiliary ply 14 rests on the carcase ply 1 2 like a wide-meshed net as a consequence of the existing warp filaments. In this respect, the carcase ply 14 provides an advantageous flexion zone 1 5.

This zone is narrower than a one-ply carcase, but is wider than a two-ply carcase composed of two identical, highly-packed cord fabric plies. Also, because of the arrangement of-the carcase ply 14 which is designed as an auxiliary ply, the neutral axis 1 6 for the bending stresses of the lateral wall is advantageously located in the region close to the radially inner carcase ply 14. The general travel behaviour of the belted tyre is improved by both features. Advantageous rolling resistance is imparted to the tyre because of the reduced weight of the carcase.

Various requirements are set for pneumatic tyres in connection with safety, travel behaviour, economy and comfort. Driving and steering behaviour is included, inter alia, in general travel behaviour.

It includes stability of travel direction, steering precision, stabilization after changes in travel direction, controllability in critical cases and restoring movement behaviour. This travel behaviour is good because of the design and arrangement of the auxiliary ply.

The pneumatic pressure resistance to local pressure contributes towards safety. In addition to reasonable costs, the low rolling resistance which results in reduced energy costs also contributes, inter alia, towards economy.

Suspension, tyre uniformity and quiet-running contribute towards comfort. Good values are achieved for the suspension because of the auxiliary ply.

TABLE Two-ply carcase having a minimum packing density inner carcase ply: Minimum Thickness packing of rubber density Filaments/dm Cord Filaments coating Material Cord type (%) (epdm) 8 (mm) (mm) Rayon 1220/2 65% 108 0.6 1840/2 90 0.72 1840/3 76 0.85 Cord filament Nylon 940/2 55% 104 0.53 + 2 x 0.2 (mm) 1400/2 85 0.65 Polyester 1100/2 55% 100 0.55 1100/3 85 0.65 Aramide 1670/2 55% 78 0.70 and outer carcase ply (auxiliary ply):: Rayon 1220/2 20% 33 0.6 1840/2 28 0.72 1840/3 24 0.85 X Cord filament 1840/1 41 0.48 + 2 x 0.05 (mm) 1220/1 50 0.40 Nylon 940/1 20% 57 0.35 940/2 38 0.53 1400/1 46 0.43 1400/2 30 0.65 Polyester 1100/2 20% 36 0.55 1100/3 31 0.65 1100/1 57 0.35 Aramide 1670/2 20% 28 0.70 1670/1 43 0.46 Packing density (%) = cord filament diameter (mm) x number of cord filaments per dm.

Examples of carcase structures wherein the radially outer ply is an auxiliary ply.

EXAMPLE 1.

The radially inner ply 12 is made from rayon of the 1 840/3x cord type. Filament ends present per decimetre: 76. This corresponds to a packing density of 65%. The tensile force amounts to 25 kp (figure per filament).

The outer ply 14, serving as an auxiliary ply, is made from rayon of the 1220/2 x cord type.

Filament ends present per decimetre: 11 6. This corresponds to a packing density of 70%. The tensile force amounts to 10.2 kp (figure per filament).

Because of the selected cord type, the auxiliary ply has fewer filaments. The tensile force, and hence also the fabric strength, is around 37% less than the radially inner ply.

EXAMPLE 2: The radially inner ply 12 is made from rayon of the 1 840/2 x cord type. Filament ends present per decimetre: 1 30. This corresponds to a packing density of 93.6%.

The filament diameter is 0.72 mm. The ply thickness is 1.38 mm; the rubber coating thickness is therefore 0.33 over the filament diameter.

The tensile force amounts to 1 8.5 kp. The fabric strength is 2405 kp/dm. The 300% modulus of the rubber coating mixture is 9.1 MPa. The fabric weight was found to be 1503 gr/m2.

The outer ply 14, serving as an auxiliary ply, is made from nylon of the 1400/1 x cord type.

Filament ends present per decimetre: 110. This corresponds to a packing density of 47.3%.

The filament diameter is 0.43 mm. The rubber coating thickness is 0.11 mm.

The tensile force amounts to 11.4 kp. The fabric strength is 1254 kp/dm.

The 300% modulus of the rubber coating mixture is 1 9 MPa.

The fabric weight was found to be 750 gr/m2.

The fabric strength of the auxiliary ply is 48% less than the radially inner ply. The weight reduction in the case of the auxiliary ply is 50% compared with the inner ply. The reduction of the rubber thickness over the filament diameter in the auxiliary ply is 67%. The 300% modulus of the rubber coating of the auxiliary ply is 109% higher than the rubber coating of the inner ply.

When the described auxiliary ply is used, the weight of the tyre becomes considerably less. The auxiliary ply improves the stability in respect of travel behaviour, and it constitutes a safety reserve. The auxiliary ply also improves the sprung carcase contour. In turn, the service-life, the high-speed suitability and the rolling resistance are favourably improved because of the advantageous flexion zone which is achieved.

Claims

1. A pneumatic vehicle tyre having a radial carcase, two beads, a tread surface and a belt-like tread surface reinforcement, wherein the carcase is composed of two cord fabric plies, the radially inner ply extending around the bead ring, together with the core reinforcement, from axially internally towards the outside and forming a folded-over end portion, and the radially outer ply being located in the bead axially externally of these elements, the carcase being covered internally by a protective rubber layer and externally by a lateral wall strip, in which the radially inner carcase ply, formed from standardfilament cord fabric, is the reinforcing member for the carcase, and in which the radially outer carcase ply serves as an auxiliary ply having fewer filaments and having a minimum of 20% less tensile strength than the inner carcase ply, wherein the strength of the ply is determined by the product of the packing density, the strength of the cord filaments and their rubber coating.

2. A pneumatic vehicle tyre as claimed in claim 1, in which the radially outer carcase ply has a smaller cord filament packing density than the radially inner carcase ply.

3. A pneumatic vehicle tyre as claimed in claim 1 or 2, in which the radially outer carcase ply has a smaller number of filaments per cord filament than the radially inner carcase ply.

4. A pneumatic vehicle tyre as claimed in any preceding claim, in which the cord fabrics differ in material and filament structure for the radially inner carcase ply and the radially outer carcase ply.

5. A pneumatic vehicle tyre as claimed in any preceding claim, in which the radially outer carcase ply is made from yarn(s) instead of from cord fabric.

6. A pneumatic vehicle tyre as claimed in any preceding claim, in which the radially outer carcase ply has a rubber coating thickness, reduced by up to 50%, over the cord or filament diameter.

7. A pneumatic vehicle tryre as claimed in any preceding claim, in which the rubber coatings differ in modulus for the radially inner and outer carcase plies, the outer ply having the rubber coating with the higher modulus.

8. A pneumatic vehicle tyre, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.