GB2141676A - Tyre bead reinforcement - Google Patents

Abstract

The bead reinforcing structure comprises an annular bead core (1), an apex strip (5) extending radially outwards from the bead core and a filler strip or chafer (6) comprising a strip of fabric formed by a single continuous reinforcement member (11) which extends continuously back and forth from side-to-side of the strip of fabric so that the filler strip reinforcement includes looped edges and no cut ends at either side. <IMAGE>

Description

SPECIFICATION Tyre bead reinforcement This invention relates to the reinforcing structure for tyre beads. Tyre beads are reinforced by an inextensible hoop or bead core usually formed by steel wires which may be cabled.

The tyre carcass reinforcement ply or piies are folded or wrapped around the bead core to provide a secure anchorage for the carcass.

Additional rubber and textile components are also used in the bead to reinforce and stiffen the bead region.

Particularly in heavy duty tyres it has become usual to provide a filler strip and/or a chafer strip extending around the bead region.

These components have hitherto been made of cut-edged fabric which is usually cut so that the reinforcement material is at a bias angle and the fabric edges, which lie radially outside the bead core, can be a source of tyre failure due to edge looseness in the cords caused both by the filaments or strands being loose and the lack of the usual brass plating at the cut ends and the consequent loss of adhesion to rubber and this causes resultant structural failure in use of the tyre.

It is an object of the present invention to provide a tyre bead having a filler strip, which may be utilised radially inside or outside the carcass ply or plies, which avoids the above problem.

According to the present invention a tyre bead is provided having a reinforcement structure comprising an annular bead core, an apex strip extending radially outwards from the bead core and a filler strip wherein the filler strip comprises a strip of fabric formed by a single continuous reinforcement member which extends continuously back and forth from side-to-side of the strip of fabric so that the filler strip reinforcement includes no cut ends at either side.

The reinforcement member may comprise twisted tyre cord which may be textile or steel. The reinforcement member may also comprise a narrow band comprising a small number of parallel reinforcement cords which band extends continuously back and forth from side-to-side of the strip of fabric.

Preferably the reinforcement member lies in a single plane such that the filler strip is substantially the same thickness at all point across its width and the said thickness is substantially the diameter of the reinforcement member. The reinforcement member thus lies in a zig-zag configuration in the filler strip.

The cord is preferably laid with each successive traverse close to the previous one. The cords may be laid substantially touching one another or at a spacing of between 0.2 and 1.2 times the cord diameter. It will be appreciated that at the edges of the strip the cord is bent through 180" about a vertical axis and this may advantageously be done with a small radius so that the cord filaments are moved to align themselves so that each has the same bend radius. The zig-zag assembly of cords may be retained in position by means of a sheet of elastomeric material pressed onto one side of the assembled cords.

Alternatively the reinforcement member may lie in two planes such that the filler strip is substantially twice as thick as the reinforcement member. The construction is then that of a flattened tubular winding where the cords lie on top of one another. A sheet of elastomer may be positioned within the winding to retain the cord in position in the flattened strip.

In all cases the filler strip is weftless and has no cut edges. The reinforcement members may be perpendicular to the length of the strip or at a bias angle thereto.

The filler strip may be positioned in the tyre bead in the conventional positions inboard or outboard of the centre of the bead core with one edge radially outwards of the bead wire and the other edge beneath the bead core or arranged in other positions, for example with both edges radially outside the centre of the bead core and the filler wrapped underneath the bead. Furthermore the filler strip may be folded back on itself adjacent to one edge to provide still further stiffness in that region and again do so without there being a line of cut cord ends anywhere in the filler strip.

Further as ects of the present invention will be apparent from the following description, by way of example only, of some embodiments in conjunction with the attached diagrammatic drawings in which: Figure 1 is a cross-sectional view of one bead of a radial ply truck tyre; Figure 2 is a cross-sectional view of an alternative to Fig. 1; Figure 3 is a plan view of a short section of filler strip; Figure 4 is a cross-section of the filler strip of Fig. 3 on Ill-Ill; Figure 5 is a plan view of a second type of filler strip, and Figure 6 is a cross-section of the filler strip of Fig. 5 on V-V.

The tyre bead of Fig. 1 comprises an annular bead core 1 which is formed by steel wires wound closely together and a main carcass ply 2 of steel cord tyre carcass fabric. The carcass ply 2 is positioned axially inwards of and is wrapped around the bead core 1 and continues for a short turn-up section 3 where the ply ends with the conventional cut edge 4. A hard rubber apex strip 5 is positioned over the bead core to provide support for the ply to bead core wrap all in the usual manner.

The bead is further stiffened by a filler strip 6 which extends from a point 7 beneath the axially outer edge of the bead core to a second point 8 radially outwards from the cut edge 4. The filler strip thus stiffens the bead, overlaps the cut edge and also provides improved seating of the tyre bead on the wheel rim bead seat and flange in service.

The tyre bead of Fig. 2 is basically the same as that of Fig. 1 except that the filler strip 6 is wider than previously and is folded at the point 9. The fold defines the radially outermost extent of the filler strip which again is such that the cut edge 4 is overlapped by the filler strip 6. The folded region 10 is axially outwards from the main part of the filler strip 6 as shown.

The above two examples of filler strip are only two of the many configurations known in the art for cut edge filler strip fabric and the novel filler strip material of the present invention may be used in other configurations including multiple strip arrangements and strips axially inwards of the bead core.

The novel filler strip material is shown in the remaining Figures and there are two basic arrangements. The first, shown in Figs. 3 and 4 is formed by a single steel tyre cord 11 made up from twisted steel filaments in the usual way which is laid in a zig-zag path. The cord 11 is laid at a bias angle A across the width of the strip and at the first edge 1 2 it is bent in a 180 bend about a vertical axis 1 3 through the plane of the strip. The cord 11 is then laid parallel to the previous lay across the strip to the other edge 14 with a spacing which is usually between 0.1 and 2.0 times cord diameter.At the next edge the cords again bend through 180 about a second vertical axis 1 5. The zig-zag cord laid is embedded in unvulcanised rubber compound to provide a handleable filler strip material for building into tyre beads as above.

The resultant filler strip material has looped edges without any cut cord ends to fray and cause problems in finished tyres and the filler strip material, as shown in Fig. 4 is one cord diameter thick plus a small amount of topping rubber compound. It should be noted that the cord spacing increases on assembly of the filler strip into a tyre in the radially outer portions of the strip but successive traverses of cord are adjacent.

The alternative filler strip fabric arrangement is shown in Figs. 5 and 6 where a single steel tyre cord is wound in the form of a flattened tube. Thus on one traverse 16 across the top of the fabric the cord shown solid in Fig. 5 is at a bias angle of B and on the return traverse 1 7 the cord is at a slightly greater bias angle C. The strip corss-section is thus more than two cord diamter thick and the edge loops are 180 bends about axes in the plane of the strip. A central core 18 of unvulcanised rubber may be provided or alternatively the strip may be further flattened so that the cords are substantially together.

Instead of winding a single cord the filler strip may be made from a narrow strip comprising a few cords arranged parallel and embedded in rubber compound. The strip is then wound in the same way as the single cord of the second arrangement above.

The cord may be steel or textile depending on the tyre application (i.e. car, truck or earthmover etc.) and any cord construction may be used. Single continuous filaments of material may also be used. In all cases the important advantage of the filler strip of the present invention is the absence of cut ends to the cords or filaments which avoids cord filament separation and corrosion and fretting problems. The looped edges at the edges of the filler strip also reduce the stress concentrations in the rubber to reinforcement cord bead at the ends of the cut cords. Furthermore air trapped in the cord is believed to remain in the continuing cord and not to be expelled from the cut cord ends when the tyre is vulcanised and thus air bubbles do not form in the upper bead regions.

It should be noted that each traverse of reinforcement is substantially straight between the edge loops so that the reinforcement material is used efficiently. Furthermore at the edge of the loops formed by the 180 bends the cord is in many arrangements re-arranged in that the filaments or strands leave their normal cord positions and take up positions around the bend axis such that they all have the same bend radius. This avoids any one filament or strand being over-stressed at the sharp 180 bend and thus avoids filament or strand breakage when the filler strip is flexed in use.

It will be seen that the filler strip can be handled for tyre building conventional means using normal butt joints.

Claims (9)

1. A tyre bead having a reinforcing structure comprising an annular bead core, an apex strip extending radially outwards from the bead core and a filler strip wherein the filler strip comprises a strip of fabric formed by a single continuous reinforcement member which extends continuously back and forth from side-to-side of the strip of fabric so that the filler strip reinforcement includes looped edges and no cut ends at either side.

2. A tyre bead according to claim 1 wherein the reinforcement member lies in a single plane such that the filler strip is substantially the same thickness at all points across its width and the reinforcement member lies in a zig-zag configuration.

3. A tyre bead according to claim 2 wherein the cords extending across the strip on successive traverses are laid at a spacing of between 0.1 and 2.0 times the cord diameter prior to assembly onto the tyre.

4. A tyre bead according to any one of claims 1 to 3 wherein the cord is retained in position in the filler strip by means of a sheet of elastomeric material pressed onto one side of the assembled cords.

5. A tyre bead according to claim 1 wherein the reinforcement member lies in two planes and the reinforcement member is in the form of a flattened tubular winding with the single cord having loops at the filler or strip edges.

6. A tyre bead according to claim 5 wherein the cord of the winding is retained in position by means of a sheet of elastomeric material fitted within the winding and into which the winding is flattened.

7. A tyre bead according to any one of claims 1 to 6 wherein the filler strip when assembled in the bead is folded longitudinally near to one edge and is positioned in the bead so that the folded edge is radially outwards from the bead core.

8. A tyre bead constructed and arranged substantially as described herein and illustrated in Fig. 1 of the accompanying drawings.

9. A tyre bead constructed and arranged substantially as described herein and illustrated in Fig. 2 of the accompanying drawings.