GB1586721A

GB1586721A - Pneumatic tyres for agricultural tractors and like machines

Info

Publication number: GB1586721A
Application number: GB413/78A
Authority: GB
Original assignee: Pneumatiques Caoutchouc Manufacture et Plastiques Kleber Colombes SA
Current assignee: Pneumatiques Caoutchouc Manufacture et Plastiques Kleber Colombes SA
Priority date: 1977-01-05
Filing date: 1978-01-05
Publication date: 1981-03-25
Also published as: IT1091645B; BE862660A; ATA921777A; LU78809A1; SE7800128L; CH619402A5; ES465753A1; DE2800308A1; NL7713965A; AT355928B; FR2376763A1; FR2376763B1

Description

(54) IMPROVEMENTS IN OR RELATING TO PNEUMATIC TYRES FOR AGRICULTURAL TRACTORS AND LIKE MACHINES (71) We, PNEUMATIQUES, CAOUTCHOUC MANUFACTURE ET PLASTIQUES KLEBER COLOMBES, a French Body Corporate, of Place de Valmy - 92700 Colombes, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to pneumatic tyres intended for fitting to the driving wheels of vehicles or machines normally intended for use on unstable ground, such as agricultural tractors.

The tread pattern of such tyres is gene rally formed by heavy bar-like ribs which extend for approximately half the width of the crown of the tyre at an inclination to the longitudinal centre plane of approxi mately 45" and which are orientated in opposite directions on the two sides of the tread. These ribs are very widely spaced in the circumferental direction with the re sult that, on unstable ground, they sink com pletely into the ground. The tractive force or drive torque is thus transmitted by the rear side-faces of the ribs so that they operate like paddle blades.

One of the problems encountered with tyres of this kind is to avoid the loss of grip which occurs on soft and clinging ground and whch results from the open spaces in the tread pattern becoming clogged with earth.

The invention consists in a pneumatic tyre for the driving wheels of agricultural tractors or similar machines, of the kind in which tht pattern of the tread is formed by discrete ribs which are widely separated in the circumferential direction, and comprising members for reinforcing the crown of the tyre located beneath the tread, wherein said discrete ribs of the pattern are arranged in two lateral sets each extending from one side of the tread to the central region thereof, and wherein said crownreinforcing members are localised at least mainly in the lateral separated parts of the crown so that said central region of the crown located beneath the corresponding central ends of said ribs has a radial flexibility which is greater than the thus reinforced lateral parts.

The construction according to the invention improves the self-cleaning properties which the tyres have as a result of the expulsion of the earth whch has become packed into the open spaces of the pattern.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, which show certain embodiments thereof by way of example and in which: Figs. 1 and 2 are, respectively, a crosssection of a tyre for agricultural tractors and a partly cut-away view from above showing in particular a typical structure for tyres of this kind, Figs. 3 and 4 are schematic views in cross-section of other constructions of crown reinforcement, Figs. 5 to 9 are schematic views in cross section of other constructions of crown reinforcement, Figs. 10, 11 and 12 are schematic views in cross-section and plan of two other embodiments of such reinforcements, and Figs. 13 and 14 are partly cut-away plan views showng crown reinforcements associated with other tread pattern configurations.

Referring now to the drawings, the tyres to which the invention particularly relates and which are described below comprise, in the conventional fashion, a body 1 having axially spaced beads 2, a crown 3 which carries the patterned tread 4, and side-walls 5 which connect the sides of the crown to the beads 2. The body 1 is generally reinforced by a carcass 6 formed from one or more layers or plies of parallel textile or metal cords whose edges are folded over around the wires 7 in the beads 2. The carcass 6 may be of the radial-ply type, that is to say may be made from cords which form an angle of about 90" (from 70 to 90" for example) with the centre plane x-x' of the tyre at the crown. The tyres described below are of this kind. The invention may however be applied to tyres having carcasses of the bias or cross-ply kind in which the cords of the carcass form more acute angles of the order of 45 to 600 at the crown.

Since the tyres are intended for fitting to the driving wheels of agricultural tractors or similar machines which operate on unstable ground, the pattern of the tread 4 is a pronounced one which is formed mainly by high, thick and heavy bar-like ribs 8 which project from the relatively thin continuous layer 9 known as the base of the tread. These ribs extend axially for approximately half the width of the tread at an inclination to the central longitudinal plane x-x' of the order of 45" and they are orientated in opposite directions on the two sides of the tread, thus forming two separate lateral sets of ribs. In each lateral set, the ribs are spaced apart circumferentially by a distance D equal to at least twice their own thicknesses e and generally between 4 and 7 times the thickness e, the distance D however being less than the length of the footprint of the tyre on the ground when under normal load. In the kind of pattern in current use, the ribs 8 in one lateral set are displaced circum fercntially from the ribs in the other set and their central ends project slightly beyond the central longitudinal plane x-x' so that, in the central part of the tyre, the ribs partly overlap for a width E which may vary but which is not more than 35% of the width L of the tread.

The tyre illustrated in Figs. 1 and 2 conforms to the general description given above for the tyres concerned but it is distinguished from them by the fact that the crown 3 of the tyre 1 is reinforced by means of two annular lateral belts 10 which are spaced apart by an axial distance "A" in the central region of the crown. These belts form two confining members which are substantially inextensible in the circumferential direction and which restrict radial expansion of the body 1 of the tyre when it is inflated. They are confined to the lateral parts of the crown and extend axially outwards to a point close to the shoulders which are situated level with the edges of the tread. The crown 3 of the tyre is thus reinforced firstly by the carcass 6 itself which extends continuously for the whole width of the crown and secondly by the lateral belts 10, whose thickness adds to the thickness of the carcass 6 at these points but which leave between them a central area of width "A " which is more flexible in the radial direction than the lateral parts of the crown.

The lateral belts 10 may be formed in any suitable fashion to give them the circumferential inextensibility needed to confine the crown of the tyre. They may for example each be formed from two superimposed plies 10.1 and 10.2 made of rubber-coated flexible metal or textile cords which are orientated at a small opposing angles of the order of 10 to 30". They may also be formed by one or more plies made from circumferentially orientated cords or by strips of rubbery mixture reinforced with short fibres which are dispersed through the rubber and orientated, if desired, or by using any other kind of known construction for making tyre belts.

The spacing A of the lateral belts 10, which corresponds to the width of the more flexible central area of the crown 3, may be approximately 10 to 35% of the width L of the tread. This spacing A is preferably equal to or slightly greater than the width E for which the ribs 8 of the tread pattern overlap so that the central ends of the said ribs are supported only by the more flexible central area of the crown which is not reinforced by the belts 10.

Figs. 3 to 9 show other embodiments of crown reinforcement which have lateral portions which are thicker and stiffer than the central portion. In Figs. 3 and 4 the reinforcement for the crown comprises one or more crown plies 11 which extend continuously for approximately the width L of the tread and pairs of the lateral belts 10 which are spaced apart by the axial distance "A " The edges of the crown plies 11 and the edges of the plies of the lateral belts 10 may be aligned or stepped. The crown ply or plies 11 are superimposed on the carcass 6 for the entire width of the crown and they may themselves form an jnextensible heft: of the normal kind in which the cords are orientated at small angles to the longitudinal plane of the order of 10 to 30".

In Figs. 5 and 6, the reinforcement for the crown is made in the from of a belt of approximately the same width L as the tread. This belt is formed by a flat ply 12 of this width L and a wider ply 13 whose edges 13.1 are folded over around the flat ply and flattened against the upper (Fig. 5) or lower (Fig. 6) opposite face. The extremities of the edges 13.1 which have been folded thus are spaced apart by a distance A in order to leave a thinner and radially more flexible central area of belt.

The plies 12 and 13 may be formed from cords which are orientated in opposite directions at small angles of the same -or different sizes in order in the latter case to create a triangulation which provides further stiffening for the lateral parts covered by the folded edges 13.1 of the wide ply. A possible modification of these constructions consists in using two crown plies 14, 15 whose developed width is greater than the width L and in folding the edges of these superimposed plies either upwards or downwards (Fig. 7) together, the extremities of the said folded edges still being spaced apart by a distance A in order to leave a thinner and more flexible central zone in the reinforcement for the crown.

In Figs. 8, the reinforcement for the crown is gnce again in the form of a belt whose width is approximately equal to L and which is formed from one or more superimposed crown plies 16 made from cords and two lateral belts for example, which are formed in the present case by plies 17 which are folded around the edges of the crown plies 16 to form two thicker lateral zones. The extremities of the edges of these folded plies 17 are spaced apart by distances A and A' which may be equal, or unequal as shown. In Fig. 9 the superimposed crown plies 16 of approximate width L are bordered by lateral plies 18 whose inner edges are spaced apart by a distance A and whose outer edges extend beyond the edges of plies 16.

Fig. 10 is a schematic view of another embodiment of the invention in which the radial flexibility required in the central zone of the crown of the tyre is achieved by interrupting the carcass 6 for a width A underneath the crown belt proper. The latter is formed in this embodiment by two superimposed plies 20 which extend axially for a width approximately equal to the width of the tread. The result is that in the lateral zones the crown is reinforced by the edges of the interrupted plies 6.1 of the carcass and by the belt plies 20 which are connected together, while the central zone is reinforced only by the belt plies 20 which form a reinforcement of smaller thickness. When the carcass plies 6.1 and the belt plies 20 are formed from differently oriented cords (for example a radial carcass and belt plies consisting of cords which are symmetrically inclined at small angles of approximately 10 to 30 ), the arrangement means that the reinforced lateral zones of the crown are triangulated and thus relatively stiff whereas the reinforced central zone is not triangulated and is thus relatively more flexible.

Figs. 11 and 12 show a modification derived from Fig. 10 in which the lateral zones of the crown are additionally reinforced by lateral belts 10 which form with the belt a combination similar to that illustrated in Figs. 3 and 4. Other modifi cations may be made by associating a carcass formed from plies 61 which are interrupted at the crown for a width A as in other constructions of crown belts having reinforced lateral zones, for example the belt constructions which have been described with reference to Figs. 3 to 9. It is understood that the crown reinforcements having relatively thin and flexible central zones as shown in Figs. 3 to 12 are- used in the tyres now being considered which have the kind of tread patern formed from spaced ribs of the kmd which is illustrated in Figs. 1 and 2.

Fig. 13 however shows another embodiment in which the reinforcement for the crown having a thin and flexible central zone is associated with a tread pattern of the "agricultural tractor" kind which is made to a slightly different design in which the tractive ribs 8 are arranged axially at substantially 90" to the central longitudinal plane x-x' instead of being obliquely inclined in opposite directions. The ribs are however divided into two lateral sets which partially overlap with one another for a distance E.

In addition, these tractive ribs 8 are associated with slabs 22 of the same height and of small axial dimensions which are situated at the centre of the tread in the inter-ridge spaces in order to improve the movement of the vehicle over hard ground.

With the same object, Fig. 14 shows the invention applied in a case where the pattern consists of ribs 8 which are inclined in opposite directions in the shape of V's or open-centred chevrons, the central ends 8.1 of the ribs stopping short of the central longitudinal plane x-x' and being separated from one another in the axial direction by spaces 23 whose width E may be of the order of 10 to 35 O of the width L of the tread. The crown reinforcement which is associated with this tread pattern may be any of those described above provided that it has relatively thick lateral parts which leave a relatively thinner and more flexible central part of width A, the said width A preferably being equal to or greater than that of the space E' separating the ribs 8.

Associating this kind of crown reinforcement with an open centred pattern of this kind is of particular assistance to the selfcleaning action of the tyre when it is used on shifting and clinging ground.

The accompanying drawings also bring out another feature of the invention which is that, when the lateral belts 10 are separate and formed from plies of cables or fibres inclined to the central longitudinal plane x-x', the inclination of the cords in the upper plies may be selected in such a way that it intersects with the direction of the ribs 8 of the pattern. This feature can be seen in Fig. 2 where the inclined cords in the upper plies 10.2 of the lateral belts are so orientated as to intersect with the direction of inclination of the adjacent ribs 8 of the pattern which are situated above the lateral belts. To this end the upper plies 10.2 are so positioned that their cords are inclined in opposite directions. This feature can also be seen in Fig. 13 although in this case the cords of plies 10.2 of the lateral belts are orientated in the same direction, which intersects with the direction of the ribs, which are orientated at 90", and also in Fig. 14 where the cords in the lateral belts 10 are inclined in opposite directions from one another with respect to the inclined ribs.

This latter feature is advantageous to prevent mis-positioning of the reinforcing plies from occurring during moulding. In effect, when the tyre is being moulded there is considerable movement in the rubber forming the tread, due to the bulk and considerable projection of the ribs 8.

When the cords in the crown plies adjacent the tread have the same orientation as the ribs it is found that some of these cords are drawn into the ribs, particularly at the margins of the crown belts. By arranging the cords in these plies with an orientation which intersects with that of the ribs it is possible to overcome such faults and to obtain properly positioned crown plies in the finished tyre.

WHAT WE CLAIM IS:- 1. A pneumatic tyre for the driving wheels of agricultural tractors or similar machines, of the kind in which the pattern of the tread is formed by discrete rib which are widely separated in the circumferential direction and comprising members for reinforcing the crown of the tyre located beneath the tread, wherein said discrete ribs of the pattern are arranged in two lateral sets each extending from one side of the tread to the central region thereof, and wherein said crown-reinforcing members are localised at least mainly in the lateral separated parts of the crown so that said central region of the crown located beneath the corresponding central ends of said ribs has a radial flexibility which is greater than the thus reinforced lateral parts.

2. A tyre as claimed in claim 1, wherein the width of the flexible central part of the crown is between 10 and 35% of the width of the tread.

3. A tyre as claimed in claim 1 or 2, wherein the ribs of the pattern partly overlap for a width which is not more than 35% of the width of the tread, and wherein the flexible central zone of the crown is relatively thin and its width is equal to or greater than the width of overlap.

4. A tyre as claimed in claim 3, wherein the ribs of the pattern are inclined in opposite directions in said two lateral sets.

5. A tyre as claimed in claim 3, wherein the ribs of the pattern are orientated axially.

6. A tyre as claimed in claim 1 or 2, wherein the two lateral sets of ribs of the pattern are inclined in opposite directions and are spaced apart axially in the central part of the crown of the tyre.

7. A tyre as claimed in claim 6, wherein the ribs are axially spaced by a width equal to or less than the width of the flexible central part of the crown.

8. A tyre as claimed in any of claims 1 to 7 wherein the reinforcement for the crown comprises two spaced lateral belts.

9. A tyre as claimed in claim 8, wherein the reinforcement for the crown comprises at least one crown ply which extends over the width of the tread and two spaced lateral belts.

10. A tyre as claimed in claim 9, wherein the reinforcement for the crown comprises at least two superimposed crown plies of which at least one has its lateral edges folded over and turned down against the other ply, the extremities of the folded edges being spaced apart in the central part of the crown.

11. A tyre as claimed in any of the preceding claims, wherein the reinforcement for the crown comprises at least one ply which extends axially for the width of the tread and two half carcass-plies which are each associated with one lateral part of the crown ply, the corresponding edges of these half-carcass plies being spaced apart in the central part of the crown.

12. A tyre as claimed in claim 9, 10 or 11, wherein the lateral belts are formed from plies of cords or fibres which are orientated in directions which intersect with the directions in which the ribs of the pattern, located above said plies, are orientated.

13. A pneumatic tyre substantially as hereinbefore described in any one of the Figures of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. are inclined in opposite directions. This feature can also be seen in Fig. 13 although in this case the cords of plies 10.2 of the lateral belts are orientated in the same direction, which intersects with the direction of the ribs, which are orientated at 90", and also in Fig. 14 where the cords in the lateral belts 10 are inclined in opposite directions from one another with respect to the inclined ribs. This latter feature is advantageous to prevent mis-positioning of the reinforcing plies from occurring during moulding. In effect, when the tyre is being moulded there is considerable movement in the rubber forming the tread, due to the bulk and considerable projection of the ribs 8. When the cords in the crown plies adjacent the tread have the same orientation as the ribs it is found that some of these cords are drawn into the ribs, particularly at the margins of the crown belts. By arranging the cords in these plies with an orientation which intersects with that of the ribs it is possible to overcome such faults and to obtain properly positioned crown plies in the finished tyre. WHAT WE CLAIM IS:-

1. A pneumatic tyre for the driving wheels of agricultural tractors or similar machines, of the kind in which the pattern of the tread is formed by discrete rib which are widely separated in the circumferential direction and comprising members for reinforcing the crown of the tyre located beneath the tread, wherein said discrete ribs of the pattern are arranged in two lateral sets each extending from one side of the tread to the central region thereof, and wherein said crown-reinforcing members are localised at least mainly in the lateral separated parts of the crown so that said central region of the crown located beneath the corresponding central ends of said ribs has a radial flexibility which is greater than the thus reinforced lateral parts.