PNEUMATIC TYRE

Abstract: A tyre comprising a tread portion, sidewalls and a pair of beads each containing a substantially inextensible annular bead core, having a bead seats and an extended toe portion comprising elastomeric material, extending lengthwise from the bead core in a direction radially and axially inwards thereof, the toe of a rigidity in the direction of its length such that in use of the tyre on a wheel rim having a groove complementary to the toe and engaging the toe when an axially inward force is applies to the tread portion a radially and axially outwardly directed force is generated at the bead core to affect bead retention characterised by the toe including a substantially continuous, circumferentially extending toe decoupling means at the junction of the tyre bead seats and the toe so that the toe is effectively decoupled from the bead in bending of the toe axially inwards of the tyre. The decoupling means may be a single cut or a small groove. The resultant tyre may safely be fitted to a normal wheel rim without the usual groove for a TD type of tyre.

Description: This invention relates to tyres and in particular to the bead regions of tyres of the type disclosed in UK Patent Specification Number 1 584 553 (Corresponding to the preamble of claim 1). Such tyres incorporate an axially and radially inwardly projecting toe having two distinct physical properties which provide a unique bead retention feature even when fitted to a one piece wheel rim of the required type. Some tyres of this type are known as "TD" tyres. The physical properties of the toe are:- firstly a substantial form stiffness in the direction of the length of the toe so that the toe resists compressive force applied between the inward end of the bead toe and the bead reinforcement core and secondly a reasonable degree of flexibility perpendicular to its length when not under longitudinal compression to allow fitting and stripping of the tyre to and from its one piece wheel rim. Hitherto tyres with this type of bead have been unusable on normal wheel rims (i.e. wheel rims without the groove provided to accept the bead retaining toe) because the degree of toe flexibility possible without affecting the first property and reducing the degree of bead retention has not been sufficient to allow the tyre bead to be correctly fitted. As a result tyres and wheel rims of this type have been made only with a non-inch standard bead seat diameter to avoid such mismatchment. One object of the present invention is to provide a tyre having the large bead retention toe of UK Patent Specification 1 584 553 but able to be correctly seated on a standard type of wheel rim without the special toe engaging groove. This assembly is of course by no means as safe as when a proper TD type grooved wheel is used but it means that if the "TD" tyre is inadvertently fitted to a standard rim then the assembly is not a dangerous one and is as safe as a normal tyre on a normal wheel rim. This invention is based on the discovery that it is possible to partially 'decouple' the toe from the remainder of the tyre to greatly increase its flexibility for fitting without seriously impairing the "form stiffness". The invention also allows further toe flexibility properties to be introduced which provide four other advantages as will be explained. Luxemburg Patent Specification LU-A-65919 (also corresponding to the preamble of claim 1) discloses a bead retention system wherein the tyre toe extends into a circumferentially extending groove in the wheel rim. However the nature of the tyre toe is such that it does not provide the necessary "form stiffness" to generate sufficient retaining force. According to the present invention a tyre comprises a tread portion, sidewalls and a pair of beads each containing a substantially inextensible annular bead core, having bead seats and an extended toe portion comprising elastomeric materials, extending lengthwise from the bead core in a direction radially and axially inwards thereof, the toe being of a rigidity in the direction of its length such that in use of the tyre on a wheel rim having a groove complementary to the toe and engaging the toe when an axially inward force is applied to the tread portion an axially outwardly directed force is generated at the bead core to affect bead retention wherein a single substantially continuous circumferentially extending cut is arranged at the junction of the tyre bead seats and the toe, the single cut being not more than 1mm in width and extending into the toe axially inwardly and radially outwardly of the tyre whereby the toe is effectively decoupled from the bead in bending of the toe axially inwards of the tyre. Further aspects 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-section of the bead of a TD tyre according to the invention; Figure 2 shows the bead of Figure 1 fitted to a normal wheel rim. The tyre bead shown in Figure 1 is a 185/65R365 and comprises a bead reinforcement core 1, a bead seating region 2 and a wheel rim flange contacting portion 3. A radially and axially inwardly projecting toe 4 is formed of hard rubber compound and this is reinforced by a skin reinforcement of chafer ply 5 of cross woven fabric. This construction is entirely typical of a "TD" type of tyre. The bead seating region 2 is a tapered, substantially straight cross section line and this joins the curved axially outer surface of the toe at a point P. At this point P a knife cut 6 is cut in the bead inclined as shown so that it is effectively perpendicular to the centre line of the toe 4 from bead 1 to toe tip 7. The knife cut has a depth of 3mm. The knife cut 6 is circumferentially continuous around the tyre. The effect of the knife cut 6 is to decouple the main part of the toe 4 from the remainder of the bead when the toe is subject to bending force in the general direction of arrow A. Thus when the tyre bead is fitted to a wheel rim 8 (as shown in Figure 2) which does not have the normally required "TD" tyre groove the toe 4 is able to bend as shown and the bead seats correctly and safely on the bead seat on the wheel rim. The resultant assembly provides a similar degree of bead retention to a normal (non-"TD") tyre on the same wheel rim and so the "TD" tyre may be safely so fitted. The knife cut length may be deeper than 3mm and may be as much as ½ the width of the toe. As a preferred feature the toe reinforcement ply 5 has its axially outer edge 10 positioned at the decoupling point P. An air seal improving component in the form of a narrow strip of soft rubber may be arranged immediately adjacent to the decoupling point P. this is, of course, an optional feature. It is of course important that the decoupling means is positioned at or near the point P to ensure it is only the bending property of the toe which is enhanced so that bead retention by generation of bead core tension as a result of bead rotation and compressive forces being generated in the toe can occur.

Claims: A tyre comprising a tread portion, sidewalls and a pair of beads each containing a substantially inextensible annular bead core (1), having bead seats (2) and an extended toe portion (4) comprising elastomeric materials, extending lengthwise from the bead core (1) in a direction radially and axially inwards thereof, the toe (4) being of a rigidity in the direction of its length such that in use of the tyre on a wheel rim having a groove complementary to the toe (4) and engaging the toe (4) when an axially inward force is applied to the tread portion an axially outwardly directed force is generated at the bead core (1) to affect bead retention characterised in that a single substantially continuous circumferentially extending cut (6) is arranged at the junction (P) of the tyre bead seats (2) and the toe (4), the single cut (6) being not more than 1mm in width and extending into the toe axially inwardly and radially outwardly of the tyre whereby the toe (4) is effectively decoupled from the bead in bending of the toe (4) axially inwards of the tyre. A tyre according to claim 1 characterised in that the cut (6) has substantially no width. A tyre according to claim 1 or 2 characterised in that the cut (6) has depth of not more than ½ of the width of the toe at the point P in the direction of the cut (6). A tyre according to claim 1 characterised in that the toe (4) includes a reinforcement layer (5) extending around and adjacent to the surface of the toe (4) and the continuous cut (6) extends through said reinforcement layer. A tyre according to claim 1 characterised in that the continuous cut (6) is at an edge of a reinforcement layer (5) that begins at the cut and extends around the toe (4) therefrom. A tyre according to any one of claims 1-5 characterised in that the bead seating region (2) of the tyre includes immediately adjacent to the cut (6) a softstrip of elastomeric material to provide more effective air retention when the tyre is fitted to a normal rim.

Inventors: GRIFFITHS, PHILLIP NEWELL, HOLMES, THOMAS
Applicants: SP TYRES UK LIMITED
Application year: 1987
Main classification: B60C15
IPC codes: B60C15