Improvements to tyres

Abstract: A pneumatic tyre having simplified structure and improved properties has mono-ply carcass (7) having ply turn-ups closely wrapped around the bead hoop (6) and extended to underlie breaker edges and the carcass cord angle in crown region (CR) is substantially radial at 85°-90° to the circumferential direction whereas in the sidewall region (SW) the cord angles of the main carcass ply portion (7M) and the turn-up portion (7T) are at a lower angle of 65°-85° and are crossed with respect to each other.

Description: The present invention relates to pneumatic tyres and particularly to belted tyres having a mono-ply carcass construction. Conventional pneumatic tyres comprise a tyre carcass extending between two wheelrim contacting bead portions, through sidewall portions to a ground contacting tread portion. The tyre carcass is conventionally reinforced by one or more plies of cord reinforced tyre fabric extending continuously from bead to bead. The ground contacting tread region is further reinforced between tread edges by a circumferentially extending annular hoop-like belt or breaker comprising a plurality of plies of cord reinforced rubber fabric disposed radially outwardly of the carcass ply and inwardly of the tread rubber. To provide anchorage in each bead region the carcass ply is turned around an annularly extending inextensible bead hoop, and thereafter is extended radially outwardly towards the mid-sidewall. Disposed between the carcass ply main portion and the thus formed carcass ply turn-up portion is a hard rubber apex. The apex is a radially outwardly tapering triangular-shaped component which is incorporated into the tyre structure as a pre-assembly with the bead core. EP 0 819 554 discloses a tyre according to the preamble of claim 1. It is an object of the present invention to simplify the above-described tyre structure without detriment to its properties. According to the present invention a mono-ply carcass pneumatic tyre comprises a carcass ply extending in a main portion between bead regions through sidewall regions and a crown region radially inward of a ground contacting tread and a tread reinforcing breaker, the carcass ply in each bean region being turned closely around an annularly extending inextensible bead core from the axially inside to the outside and thereafter being extended radially outwardly to form a ply turn-up portion overlying the carcass main portion and extending to underlie the edge of the breaker, the carcass ply being reinforced by a plurality of mutually parallel carcass cords, wherein the carcass ply cords in the crown region are disposed at an angle in the range of 85°-90° to the tyre circumferential direction and the cords in the sidewall regions are disposed at a smaller angle than the cords in the crown region being at an angle in the range of 65°-85° to the tyre circumferential direction and the cords in the carcass main portion and those of the carcass turn-up portion are crossed with respect to each other. Preferably the carcass turn-up portion overlaps the breaker edge by a distance of 5-30% most preferably 10-20% of the axial width of the breaker. The change of angle of the carcass cords from the crown to the sidewall region is in the edge region of the breaker. Further aspects of the invention will become apparent from the following description by way of example only of one embodiment and the following drawing in which: Figure 1 shows a schematic cross-section diagram of one half of a tyre in accordance with the invention. Shown in Figure 1 is a cross-section of one half of a 205/60 R15 passenger car tyre according to the present invention. The tyre has a ground contacting tread 1 extending between tread edges 2 connected to radially inwardly extending sidewalls 3 terminating in bead regions 4 for mounting on a wheelrim (not shown). The tread is reinforced by a belt or breaker assembly 5 comprising two centrally disposed plies 5A and 5B. The radially inner ply 5A has a width of 170 mm and a narrower outer breaker ply 5B of width 160 mm. Both of the breaker plies comprise plural steel cords disposed in parallel arrangement at an angle of 22' to the tyre circumferential direction and crossed with respect to the cords of the other ply. Within each bead region 4 is disposed an annular inextensible bead hoop 6 comprising plural turns of steel wire. Extending fully through the tread and sidewall regions and into the bead region is a reinforcing carcass ply 7 comprising cord reinforced rubber fabric. The cords are polyester but may comprise any of the conventional tyre fabric materials such as rayon, aramid or metal cords. In each bead region, the carcass ply 7 is turned closely around the annular bead hoop 6 from the axial inside to the outside and thereafter is extended in turn-up portions 7T radially outwardly. As can be seen the carcass ply turn-up portions 7T lie immediately adjacent to and axially outward of the carcass ply main portion 7M extending between the beads. The turn-up portions 7T extend radially outwardly through the whole length of the tyre sidewall 3 such that the ply turn-up end 7TE underlies the breaker assembly 5. The end of the turn-up 7T overlaps the breaker edge by a distance L of 30 mm, which is 17.6% of the effective breaker width. The overlap must be in the range of 5 to 30% of the breaker width, preferably 10% to 20%. Turning again to the cords of the carcass ply. In the crown region of the tyre, denoted by CR in Figure 1, the cords of the carcass ply 7 are disposed substantially radially, that is at an angle of 85°-90° to the circumferential direction of the tyre. In contrast, in the sidewall region of the tyre, denoted by SW in Figure 1, the carcass ply cords are disposed at a lower angle than in the crown region CR, being in the range of 65°-85° to the tyre circumferential direction. In this sidewall region both the cords of the carcass ply main portion 7M and the turn-up portion 7T are disposed at this angle but they are crossed with respect to each other. In the region ER of the carcass at the breaker edge between the crown region CR and the sidewall region SW the carcass cord line is curved as the angle of the carcass cords changes progressively from the higher value in the crown CR to the lower value in the sidewall region SW. This transition is positioned in the region of the overlap of the turn-up with the breaker at the breaker edge. As is clearly evident in the bead of the tyre the carcass ply turn-up 7T is wrapped closely around the bead hoop 6 and thereafter overlies the radially outer side of the carcass main part 7M so that there is no conventional bead apex between the two. This gives a relatively narrow bead of reduced sectional area and weight. The bead is also provided with a textile reinforced chafer strip 8 which extends along the bead surface from the inside of the tyre, along the radially inner part of the bead at the bead base and thereafter is wrapped closely around the bead coil 6 overlying the radially outer side of the ply turn-up 7T. In a further feature of the tyre, the sidewall rubber 9 overlying the radially outer portion of the turn-up portion 7M is extended into the tread region to also underlie the breaker edge. The crossed cords in the sidewall regions of the present tyre have proved to give better resistance to the onset of the so-called "standing wave phenomenon" and thus give improved high speed durability of the tyre structure. The tyre of the invention may be readily manufactured in a conventional two-stage process employing firstly an expandable/collapsible cylindrical former and subsequently a toroidal shaping former. In the first stage a cylinder of bias-cut carcass fabric is formed on the expandable former. The ply cylinder has cords extending between the ply edges at an angle of 65°-85° to the former axial direction. In a conventional manner bead hoops are assembled onto the carcass ply cylinder and the edges of the ply fabric are turned up and around the bead hoop to subsequently overlie the radially outer surface of the carcass ply between the hoops. In the second stage of manufacture the cylindrical assembly including carcass ply fabric and bead hoops is deformed into a toroidal shape by expanding the central part of the cylinder assembly radially outwardly and simultaneously drawing the edges of the cylinder axially inwardly. During this process the tension created in the carcass cords is sufficient to deform and reduce the cord angle of the carcass cords in the central region, which are between the turn-up regions, from their original bias angle of 65°-85° to become substantially radially aligned at 85-90°, thus giving the cord angle configuration of the present invention. As described above the tyre of the present invention provides a simplified structure which gives excellent tyre properties.

Claims: A mono-ply carcass pneumatic tyre comprising a carcass ply (7) extending in a main portion between bead (7m) regions (4) through sidewall regions (3) and a crown region (CR) radially inward of a ground contacting tread (1) and a tread reinforcing breaker (5), the carcass ply (7) in each bead region (4) being turned closely around an annularly extending inextensible bead core (6 from the axially inside to the outside and thereafter being extended radially outwardly to form a ply turn-up portion (7T) overlying the carcass main portion (7m) the ply turn-up portion (7T) extending outwardly to underlie the axial edge of the breaker, the carcass ply (7) being reinforced by a plurality of mutually parallel carcass cords, characterised in that the carcass ply cords in the crown region (CR) are disposed at an angle in the range of 85°-90° to the tyre circumferential direction and the cords in the sidewall regions (SW) are disposed at a smaller angle than the cords in the crown region (CR) being at an angle in the range of 65°-85° to the tyre circumferential direction and the cords in the carcass main portion (7m) and those of the carcass turn-up portion (7T)are crossed with respect to each other. A tyre according to claim 1, characterised in that the ply turn-up (7T) underlies the edge of the breaker by between 5 and 30% of the width of the breaker. A tyre according to claim 1, characterised in that the ply turn-up (7T) underlies the edge of the breaker (5) by between 10 and 20% of the width of the breaker. A tyre according to claim 1, 2 or 3, characterised in that the transition zone between the carcass cord angle in the crown region (CR) and the carcass cord angle in the sidewall region (SW) is in the edge region (ER) of the breaker. A tyre according to any of claims 1 to 4, characterised in that the carcass turn-up portion (7T) lies adjacent to the carcass main portion (7m) over the whole length of the turn-up portion (7T) such that no bead apex component is present between the two. A tyre according to any of claims 1 to 5, characterised in that a textile reinforced chafer (9) is disposed in the bead region (4) extending from the axially inside of the bead, along the radially innermost bead base and overlying the ply turn-up portion (7T) on its axially outer side. A tyre according to any of claims 1 to 6, there being a sidewall rubber component (9) overlying the ply turn-up portion of its radially outer side extends to underlie the breaker edge.

Inventors: SECONDARI FRANCESCO, SECONDARI, FRANCESCO
Applicants: DUNLOP TIRE CORP, DUNLOP TIRE CORPORATION
Application year: 2000
Main classification: B60C9
IPC codes: B60C15, B60C9, B60C13