GB2276357A

GB2276357A - Pneumatic tyre

Info

Publication number: GB2276357A
Application number: GB9306345A
Authority: GB
Inventors: Ian Kemp
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1993-03-26
Filing date: 1993-03-26
Publication date: 1994-09-28
Anticipated expiration: 2013-03-26
Also published as: GB2276357B; GB9306345D0

Abstract

A heavy duty pneumatic tyre comprises a carcass 1 reinforced by a ply of radially disposed metal cords extending between two bead regions (2, Fig. 1) and in each bead region turned around a bead core 6 from the axial inside to the outside to form a carcass ply turn-up 7, each carcass ply turn-up being wrapped by a fabric layer 9 comprising parallel cords inclined to the radial direction of the tyre. The part of the fabric layer 9 on the carcass ply surface nearer the bead core 6 extends around the bead core such that it is interposed between the carcass ply 1 and the bead core. The cords of the fabric layer may be organic cords and may be inclined at between 10 and 50 degrees to the radial direction of the tyre. A method of manufacture of the tyre is also described. <IMAGE>

Description

PNEUMATIC TYRE This invention relates to a pneumatic radial tyre and more particularly to a heavy duty radial tyre for trucks and buses and a method of manufacturing such a tyre.

The conventional heavy duty radial tyre comprises a carcass reinforced by a single carcass ply of metal cords extending between two bead regions. In each bead region of the tyre the carcass ply is wrapped or turned around a metallic bead core, which extends in the circumferential direction of the tyre providing a reinforcing bead hoop, from axially inside to outside to form a ply turn-up which serves to anchor the end of the ply in the bead region.

Conventionally the metal carcass ply cords used in heavy duty tyres comprise steel wires which are surface coated with brass to promote adhesion to rubber. A plurality of such cords are arranged in parallel orientation and embedded in a matrix of uncured rubber known as a topping or skim coat to form a sheet of ply fabric. This ply fabric is then cut substantially perpendicularly to the cord direction at a width corresponding to the cord length in the tyre cross-section. Accordingly the ply turn-up edge in each bead region and in particular the cord ends in said ply are sharp resulting from being cut from the fabric sheet and are also devoid of brass coating across the cut face and hence devoid of adequate adhesion to rubber at the tip.

During running of the tyre the bead regions in which the ply turn-ups are formed are subjected to high levels of stress. Such high levels of stress in combination with the above-mentioned features of the ply turn-up edge tend to cause premature failure of the tyre bead region due to ply edge looseness and cracking initiated by the repetitive cutting action of the cord end during flexing of the bead region.

The conventional method employed to combat such premature failure of the tyre bead region is to position axially outward of the ply turn-up a bias cut metal cord fabric, commonly known as a "filler" or "flipper", which extends around the circumference of the bead region and lying with its edges radially inwards and outwards of the ply turn-up edge. Such a filler in the bead region mitigates the effects of high stress by stiffening the bead region in addition to protecting the ply turn-up edge from accidental damage. However, although the metal cords of the filler are conventionally of thinner gauge than the ply cords, the cut ends of the metal filler cords are themselves prone to cause similar failures as those caused by the ply turn-up ends.

It is therefore an object of the present invention to provide a pneumatic heavy duty radial tyre with improved durability in the bead region.

According to one aspect of the present invention a heavy duty pneumatic tyre comprises a carcass reinforced by a ply of radially disposed metal cords extending between two bead regions and in each bead region turned around a bead core from the axial inside to the outside to form a carcass ply turn-up characterised in that each carcass ply turn-up is wrapped by a fabric layer comprising parallel cords inclined at an angle to the radial direction of the tyre.

Preferably the fabric layer comprises organic fibre cords and most preferably it comprises aromatic polyamide cords.

Preferably the cords of the fabric layer are inclined at 10-50 degrees to the tyre radial direction and most preferably they are inclined at 25-35 degrees.

The portion of the fabric layer on the carcass ply surface which is furthest from the bead core may extend axially under the bead core.

Preferably the portion of the fabric layer on the carcass ply surface nearest the bead core extends around the bead core so that it is interposed between the carcass ply and the bead core thus obviating the necessity for a separate bead core wrapping to protect the ply from chafing on the metallic bead core.

The present invention also provides a method of fabricating the tyre utilising a conventional expandable tyre building drum comprising the steps of positioning the fabric layer on the drum such that the axial inner edge of the fabric layer is displaced from the drum circumferential centreline and the axially inner part of the fabric layer is in contact with the drum surface, positioning the carcass ply centrally on the drum such that the axially outer part of the carcass ply overlaps a portion of the fabric layer, folding the remaining axially outer portion of the fabric layer radially outwardly positioning the tyre bead core over the folded fabric portion, expanding the building drum such that the radially outer portion of the folded fabric layer contacts the radially inner surface of the bead core and then folding the portion of the folded fabric portion lying axially outward of the bead core radially outwardly around the bead core to form a fabric wrapped ply turn-up.

Further aspects of the present invention will become apparent from the following description by way of example only of one embodiment of the invention in conjunction with the following drawings in which: Figure 1 is a schematic drawing of a radial cross-section of a tyre of the present invention; and Figure 2 is a schematic drawing showing the details of the bead region of the tyre of Figure 1; and Figures 3A, 3B, 4A, 4B, 5A, 5B, 6, 7 and 8 are schematic diagrams illustrating steps in the method of fabricating the wrapped ply turn-up of Figures 1 and 2.

Figure 1 shows a radial cross-section of an llR22.5 truck tyre. This tyre comprises a carcass reinforced by a radial carcass ply 1 extending between two bead regions 2, through sidewall regions 3 to a tread region 4. In this embodiment the carcass ply 1 comprises a fabric of rubber coated steel cords. In the tread region a reinforcing belt package 5 is disposed radially outside the carcass ply 1. In each bead region 2 the carcass ply 1 is turned around a bead core 6 comprising spiral windings of a steel wire formed into an inextensible hoop from the axial inside to the axial outside to form a ply turn-up 7.

Disposed between the ply turn-up 7 and the main ply portion 1 and extending radially outwardly from the bead core 6 in an approximately triangular crosssection is a hard rubber apex 8.

The ply turn-up 7 is wrapped by a fabric layer 9.

In this embodiment the fabric layer 9 comprises 2/110 TEX cords of KEVLAR aromatic polyamide (KEVLAR is a Registered Trade Mark of EI Du Pont de Nemours) evenly spaced apart at 90 cords per 10cm and embedded in a vulcanisable rubber compound to give a total fabric thickness of 0.8mm.

Further details of the fabric wrapping are shown in Figure 2 from which it can be seen that the fabric wrapping 9 extends continuously from the carcass ply surface nearest the bead core 6, around the cut end 7c of the ply turn-up 7 and along the carcass ply surface furthest from the bead core 6.

Furthermore in this embodiment that portion 9i of the fabric wrapping 9 which is in contact with the carcass ply turn-up surface nearest the bead core 6 extends around the bead core 6 and thus insulates the carcass ply 1 from chafing against the metallic bead core 6. Accordingly the conventional necessity to fit a separate fabric wrapping around the bead core 6 to prevent such chafing in manufacture and service is removed. Additionally the portion 90 of the fabric wrapping 9 which is in contact with the carcass ply turn-up surface further from the bead core 6 extends axially under the bead core and is terminated in the toe region 10 of the tyre. Accordingly both ends of the fabric wrapping 9 are located in non-critical areas of the tyre, i.e. areas of relatively low stress in service.

The cords in the fabric layer 9 are disposed in the tyre at 300 to the radial direction of the tyre.

Accordingly the cords in the portion 9i of the fabric layer in contact with the carcass ply surface nearest the bead core 6 are oppositely inclined to the cords in the portion 9o of the fabric layer in contact with the carcass ply surface furthest from the bead core 6. In combination with the radially disposed cords of the ply turn-up 7 the oppositely inclined cords of the two portions 9i and 9o of the fabric layer form a triangulated cord structure with superior reinforcing ability to the prior conventional arrangement of single layer of bias cut steel cord fabric disposed axially outside the ply turn-up.

Whilst the above-described embodiment utilises fabric layer cords disposed at 30 degrees to the radial direction any angle within the range 10 to 50 degrees may be used. However preferably the angle is in the range 25 to 35 degrees.

A method of fabricating the wrapped ply turn-up of the present invention is shown in Figures 3 to 8.

This method utilises a conventional expandable cylindrical tyre building drum of a type well known in the art and which therefore requires no further description.

Shown in Figures 3A and 3B is the part left side of a tyre building drum 20 onto the radially outer surface of which is firstly assembled a wrapping fabric layer 9 comprising a rubber covered ply of inclined cords having two edges 13 and 14. The fabric layer 9 is assembled around the whole circumference of the cylindrical building drum 20 and the axially inner edge 14 of the fabric layer is axially displaced from the drum centreline so that the axially inner part of the fabric layer contacts the axially outer part of the building drum surface. In the second step shown in Figures 4A and 4B a tyre carcass ply 1 is assembled centrally on to the building drum so that its axially outer part overlaps the axially inner part of the fabric layer 9. In the third step shown in Figures 5A and 5B the axially outer part of the fabric layer 9 is folded radially outwardly and axially inwardly by suitable means to wrap around the axially outer part of the carcass ply 1.

Suitable means to accomplish this third step include manual means, suitably shaped mechanical rollers or pneumatically operated rolling bags all of which are conventional in the art. In the fourth step shown in Figure 6 the bead core hoop 6, which optionally may have a triangular-shaped hard rubber apex 8 pre-assembled to it, is positioned radially outside the wrapped ply end. The fifth step shown in Figure 7 involves expanding the building drum 20 so that the drum surface and the assembled components move radially outward such that the radially outer surface of the wrapping fabric layer 9 contacts the radially inner part of the bead core 6. In the final step the wrapped ply end is turned radially outward around the bead core 6 to form the wrapped ply turn-up as shown in Figure 8. Again this final step may be accomplished using conventional means such as rollers, rolling air-bags or manual means.

Accordingly the present invention provides a wrapped heavy duty tyre carcass ply turn-up and its method of fabrication which prevents the cutting action of the steel cord cut end and thereby improves the durability of the bead region of the tyre and prevents premature failure.

Claims

1. A heavy duty pneumatic tyre comprising a carcass reinforced by a ply of radially disposed metal cords extending between two bead regions and in each bead region turned around a bead core from the axial inside to the outside to form a carcass ply turn-up characterised in that each carcass ply turn-up is wrapped by a fabric layer comprising parallel cords inclined at an angle to the radial direction of the tyre.

2. A pneumatic tyre according to claim 1 wherein the part of the fabric layer on the carcass ply surface nearest the bead core extends around the bead core such that it is interposed between the carcass ply and the bead core.

3. A pneumatic tyre according to claim 1 or 2 wherein the part of the fabric layer on the carcass ply surface further from the bead core extends axially under the bead core.

4. A pneumatic tyre according to any of claims 1 to 3 wherein the cords of the fabric layer are inclined at an angle of between 10 and 50 degrees to the radial direction of the tyre.

5. A pneumatic tyre according to any of claims 1 to 3 wherein the cords of the fabric layer are inclined at an angle of between 25 and 35 degrees to the radial direction of the tyre.

6. A pneumatic tyre according to any of claims 1 to 5 wherein the cords of the fabric layer are organic cords.

7. A pneumatic tyre according to any of claims 1 to 6 wherein the cords of the fabric layer are aromatic polyamide cords.

8. A pneumatic tyre substantially arranged and constructed as described .herein and shown in Figures 1 and 2.

8. A method of fabricating the tyre of claim 1 utilising an expandable cylindrical tyre building drum comprising the steps of positioning the fabric layer on the drum such that the axial inner edge of the fabric layer is displaced from the drum circumferential centreline and the axially inner part of the fabric layer is in contact with the drum surface, positioning the carcass ply centrally on the drum such that the axially outer part of the carcass ply overlaps a portion of the fabric layer, folding the remaining axially outer portion of the fabric layer radially outwardly positioning the tyre bead core over the folded fabric portion, expanding the building drum such that the radially outer portion of the folded fabric layer contacts the radially inner surface of the bead core and then folding the portion of the folded fabric portion lying axially outward of the bead core radially outwardly around the bead core to form a fabric wrapped ply turn-up.

9. A pneumatic tyre substantially arranged and constructed as described herein and shown in Figures 1 and 2.

Amendments to the claims have been filed as follows 1. A heavy duty pneumatic tyre comprising a carcass reinforced by a ply of radially disposed metal cords extending between two bead regions and in each bead region turned around a bead core from the axial inside to the outside to form a carcass ply turn-up wherein each carcass ply turn-up is wrapped by a fabric layer comprising parallel cords inclined at an angle to the radial direction of the tyre and the part of the fabric layer on the carcass ply surface nearest the bead core extends around the bead core such that it is interposed between the carcass ply and the bead core.

2. A pneumatic tyre according to claim 1 wherein the part of the fabric layer on the carcass ply surface further from the bead core extends axially under the bead core.

3. A pneumatic tyre according to claim 1 or 2 wherein the cords of the fabric layer are inclined at an angle of between 10 and 50 degrees to the radial direction of the tyre.

4. A pneumatic tyre according to any of claims 1 to 3 wherein the cords of the fabric layer are inclined at an angle of between 25 and 35 degrees to the radial direction of the tyre.

5. A pneumatic tyre according to any of claims 1 to 4 wherein the cords of the fabric layer are organic cords.

6. A pneumatic tyre according to any of claims 1 to 5 wherein the cords of the fabric layer are aromatic polyamide cords.

7. A method of fabricating the tyre of claim 1 utilising an expandable cylindrical tyre building drum comprising the steps of positioning the fabric layer on the drum such that the axial inner edge of the fabric layer is displaced from the drum circumferential centreline and the axially inner part of the fabric layer is in contact with the drum surface, positioning the carcass ply centrally on the drum such that the axially outer part of the carcass ply overlaps a portion of the fabric layer, folding the remaining axially outer portion of the fabric layer radially outwardly positioning the tyre bead core over the folded fabric portion, expanding the building drum such that the radially outer portion of the folded fabric layer contacts the radially inner surface of the bead core and then folding the portion of the folded fabric portion lying axially outward of the bead core radially outwardly around the bead core to form a fabric wrapped ply turn-up.