GB2336344A - Pneumatic tyre - Google Patents

Abstract

A pneumatic tyre has a carcass reinforced by at least one carcass ply 1 of radially disposed cords extending between two bead regions 2 and anchored therein, wherein in each bead region the carcass ply turns radially outwardly in a first turnround region R1 around a first annular bead core 6 then radially inwardly in a second turnround region R2 around a second annular bead core 7, the second region being outward of the first region. The second bead core may be a continuous ring eg of flat profile or a helical winding of single or multiple layers of eg filaments, cord or wire.

Description

2336344 PNEUNATIC TYRE This invention relates to a pneumatic radial tyre,

and particularly but not exclusively to tyres for motorcycles.

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

The present invention in applicable to any radial tyre having a reinforcing carcass ply or plies which are turned around a bead core.

For example, conventional heavy duty tyres utilise metal carcass ply cords comprising 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 2 form a sheet of ply fabric. This ply fabric is then cut substantially perpendicular 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 particularly 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 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, shown in Figure 2, is to position axially outward of the ply turn-up (9) a bias-cut metal cord fabric (10), commonly known as a "filler" or "flipper", which extends around the circumference of the bead region 3 lying with its edges radially inwards and outwards of the ply turn-up edge. Such a f iller (10) in the bead region mitigates the ef fects of high stress by stiffening the bead region in addition to protecting the ply turn-up edges from accidental damage. However, although the inetal cords of the f iller 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.

In contrast to heavy duty truck and bus tyres, motorcycle and passenger vehicle tyres conventionally comprise carcass ply reinforcing cords of organic materials such as nylon, rayon. polyester, aromatic polyamide or the like. Whilst such organic cords do not suffer from the edge cutting problem associated with steel cords, in use the bead regions are subjected to very high levels of stress and are sixilarly prone to ply turn-up looseness which leads to premature f ailure of the tyre.

A further problem concerning carcass turn-up portions occurs during zuf acture of the tyre when tension induced in the ply during both shaping and 4 moulding of the green tyre can cause the carcass to pull back around the bead core. This process is somewhat uncontrollable and local variations give rise to lack of uniformity in the moulded tyre.

It is therefore an object of the present invention to provide a pneumatic radial tyre which solves the aforementioned problems.

According to one aspect of the present invention a pneumatic tyre comprises a carcass reinforced by at least one carcass ply of radially disposed cords extending between two bead regions and anchored therein, characterised in that in each bead region the carcass ply in a first turnround region is turned in a first turning direction radially outward around a f irst or main annular bead core and in a second turnround region longitudinally outward of the f irst turnround region the ply is turned in a second turning direction radially inwardly around a second or anchoring annular bead core.

The second or anchoring hoop may comprise a continuous ring of for example a strip of flat profile or a helical winding of a single or multiple layers of for example filaments, cord or wire.

The anchoring hoop preferably comprises a substantially inextensible material and may be steel or aromatic polyamide or it may be a heat shrinkable material. The anchoring hoop may comprise a plastics material.

Further aspects of the present invention will become apparent from the following description by way of example only of one eiment 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; Figure 2 is a schematic cross-section drawing showing the details of the bead region of a prior art tyre; and

Figures 3 and 4 are schematic cross-sectional drawings showing further tyre bead regions according to the present invention, Figure 1 shows a radial cross-section of a heavy duty tyre. This tyre 11 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. The carcass ply 1 comprises a fabric of rubber coated cords. In the tread region a reinforcing belt package 5 is disposed 6 radially outside the carcass ply 1. In each bead region 2 the carcass ply is wrapped in a first turnround region R1 radially outwardly around a first or main bead core 6, comprising spiral windings of a steel wire formed into an inextensible hoop, from the axial inside to the axial outside. The carcass ply 1 is wrapped around the bead core 6 for substantially the whole of the cross-sectional periphery of the bead core 6. Thereafter the carcass ply 1 is turned in a second turnround region R1 radially inwardly around an additional second bead core or anchoring hoop 7. The turning direction of the ply around the anchoring hoop is opposite to that around the main bead core 6. This anchoring hoop 7 is a continuous ring comprising in cross-section a flat steel strip tapered outwardly from the axial inside to the outside at the same angle as the radially outer surface of the bead core hoop 6. Disposed axially outward of the main ply portion 1 and radially outwardly of the bead core 6 is a hard rubber apex 8 which extends radially outwardly in an approximately triangular crosssection.

The carcass ply end region le lies adjacent to the carcass ply in the first turnround region R1 around 7 the main bead core 6. The ply end lies radially inward of the main bead core in the region of the tyre bead base.

The anchoring hoop 27 may comprise a continuous ring having a flat crosssection profile as previously described or it may have any suitable profile such as round or square.

Alternatively the anchoring hoop 27 may comprise a spiral or helical winding of a single layer 30 as shown in Figure 3 or multiple layers 40 as shown in Figure 4. The anchoring hoop may be coated with a vulcanisable rubber as conventional in the art to promote adhesion to the ply and other adjacent components of the tyre, or it may be coated with any other adhesive suitable for bonding to rubber.

The anchoring hoop may comprise a heat shrinkable material which permits fabrication of the tyre bead region but which then at the time of fabrication or subsequently in the hot vulcanisation process, is shrunk to anchor the ply by compression between the ring and the bead core hoop.

8 Also the cross-section shape of the main bead core hoop 6 may be such as to accommodate the additional anchoring hoop 7 within its overall shape as shown in Figure 4. In this way the main bead core 6 and the anchoring hoop 7 fit together in a form-matched manner.

Whilst the invention has been described by reference to a tyre in which the carcass ply is wrapped around the bead for substantially the whole of its crosssectional periphery the invention has been found effective when the carcass ply wraps only part of the bead core. However it is preferably that a proportion in excess of 80% of the cross-sectional periphery of the bead core hoop is wrapped by the ply.

The above-described ply anchoring system has been shown to improve the bead regions of tyres and particularly to improve the manufacture and performance of motorcycle tyres wherein large tensions occur in the ply cords 9

Claims (9)

1. A pneumatic tyre comprising a carcass reinforced by at least one carcass ply of radially disposed cords extending between two bead regions and anchored therein, characterised in that in each bead region the carcass ply in a first turnround region (R1) is turned in a f irst turning direction radially outward around a first or main annular bead core and in a second turnround region (R2) longitudinally outward of the f irst turnround region the ply is turned in a second turning direction radially inwardly around a second or anchoring annular bead core.

2. A pneumatic tyre according to claim 1, wherein the first turning direction is the opposite direction to the second turning direction.

3. A pneumatic tyre according to either of claims 1 or 2, wherein the ply end region lies adjacent to the first turnround region.

4. A pneumatic tyre according to claim 3, wherein the ply end region lies radially inward of the radially innermost bead core.

5. A pneumatic tyre according to any of claims 1 to 4, wherein the second annular bead core is radially outward of the first annular bead core.

6. A pneumatic tyre according to any of claims 1 to 5, wherein the first annular bead core is axially inward of the second annular bead core.

7. A pneumatic tyre according to any of claims 1 to 6, wherein the first and second annular bead cores have complementary-shaped adjacent surfaces such that the two fit together in a form-matched manner.

8. A pneumatic tyre according to claim 7, wherein the second annular bead core comprises a helical winding of an inextensible material.

9. A pneumatic tyre according to claim 8, wherein the inextensible material is an aramid cord.