GB1587963A

GB1587963A - Pneumatic tyres

Info

Publication number: GB1587963A
Application number: GB42718/77A
Authority: GB
Original assignee: Pneumatiques Caoutchouc Manufacture et Plastiques Kleber Colombes SA
Current assignee: Pneumatiques Caoutchouc Manufacture et Plastiques Kleber Colombes SA
Priority date: 1976-10-13
Filing date: 1977-10-13
Publication date: 1981-04-15
Also published as: NL7711136A; AT354871B; IT1091437B; SE7712339L; LU78295A1; DE2745265C2; FR2367626A1; DE2745265A1; SE438988B; BE859698A; FR2367626B1; CH618644A5; ATA726277A

Description

(54) IMPROVEMENTS IN OR RELATING TO PNEUMATIC TYRES (71) We, PNEUMATIQUES CAOUTCHOUC MANUFACTURE ET PLASTIQUES KLEBER COLOMBES, a French Bodu Corporate, of Place de Valmy, 92 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 for the driving wheels of agricultural tractors or similar vehicles which are designed generally to move over unstable ground, of the kind having a body with axially spaced boards, a tread having a pattern formed by circumferentially spaced transverse ribs, and a tread width (B) equal to or greater than the axial spacing of the bead heels when the tyre is mounted on the rim for which it is intended, and a belt which reinforces the crown of the tyre over an axial width equal to or less than the axial distance between the bead heels.

There are on the market two main types of tyre of this nature; those having a crossply carcass and those having a radial-ply carcass and a crown belt. The latter are generally admitted to give better grip under the most difficult working conditions and in particular on slippery ground.

However, tractors are now being constructed which are more powerful and heavy and thus capable of drawing much greater loads. Under difficult working conditions tyres constructed to current designs often reach the limit of their capacity for gripping and they do not allow full use to be made of greater tractive ability of these more powerful tractors. The limit mentioned is reached when the tyre "slips"; i.e., turns without moving forward, which it does either because the torque is too great in comparison with the resistance offered by the loose or soft ground, or because its tread pattern becomes clogged with muddy earth which the tyre is unable to eject at the exit from the contact zone.

This limit is also reached when the joint between the tyre and the rim is unable to sustain the driving torque applied to the wheel and the rim turns with respect to the tyre. It hterefore appeared to be necessary to make a fairly thorough revision of the current design of tyres of this nature with a view to extending the limiting values of their chief characteristics and in particular grip, load bearing capacity, the circumferential stiffness of the tyre and the tyre/rim combination, and the ease with which the pattern of the tyre cleans itself, and to do this without thereby detracting from the other characteristics of the tyre or affecting the possibility of manufacturing it with conventional equipment.

Accordingly, the invention consists in a pneumatic tyre for the driving wheels of agricultural tractors or similar vehicles, of the kind having a body with axially spaced beads, a tread having a pattern formed by circumferentially spaced transverse ribs, and a tread width (B) equal to or greater than the axial spacing of the bead heels when the tyre is mounted on the rim for which it is intended, and a belt which reinforces the crown of the carcass of the tyre over an axial width equal to or less than the axial distance between the bead heels, wherein the crown of the tyre has a transverse curvature such that the inner surface of the crown has, under the belt, a radial rise which is equal to or greater than 1/5 of the cross-sectional height (H) of the tyre, and the sidewalls of the tyre each being reinforced from the associated bead to a location spaced from the radially innermost part of the bead by at least half the cross-sectional height (H), so that the flexing of the tyre under load is confined chiefly to the area of the crown of the tyre.

The cross-sectional height H of the tyre is preferably small in comparison with the cross-sectional width G, the ratio H/G being less than 0.6 and preferably between 0.3 and 0.5 whereas in present day tractor tyres this ratio is of the order of 0.9 to 1. With this new design it is possible to produce tractor tyres which, by virtue of their reinforced sidewalls, have a greater load-bearing capacity and greater circumferential stiff ness allowing greater tractive forces to be transmitted. The tyres also have better grip by reason of the fact that flexing under load takes place chiefly at the crown, which thus increases the area in contact with the ground while maintaining a relatively low contact pressure. In addition, the self-cleaning action of th e pattern is improved by greater mobility of the crown in the area of contact with the ground. This mobility may also be helped by forming the pattern with separate spaced ridges which each extend across only approximately half the tread of the tyre.

The reinforcement of the sidewalls over at least their lower half beginning at the beads may be achieved by various known means and in particular by extending the reinforcements in the beads to at least half the height of the sidewalls. It may also be achieved, or supplemented, by making the bottoms of the sidewalls of increased thickness to form a fillet which bears against the turned-over outer edge of the rim, or by extending the lateral parts of the ridges to the bottoms of the sidewalls to form radial buttresses or pillars which project from the sidewalls of the tyre.

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, 2 and 3, 4 are cross-sectional and partly cut-away plan views respectively of two different embodiments, and Fig. 5 is a cross-section of a third embodiment.

Referring now to the three drawings, the tyres shown each have a body 1 having axially spaced beads 2, a crown 3 which carries a patterned tread 4 and sidewalls 5 which connect the margins of the crown to the beads 2. The body 1 is reinforced by a carcass made up of one or more layers or plies of metal or textile cords which are orientated in radial or substantially radial planes, the edges of these layers being folded over around the wires 7 in the beds 2. The crown of the tyre is confined by a reinforcing belt 8 which restricts the outside diameter of the tyre when inflated, this belt being positioned between the crown of the carcass 6 and the tread 4. The belt 8 is formed for example by two or more layers or plies of metal or textile cords which are orientated at small angles, of the order of 20 , to the equatorial plane of the tyre to form an annular reinforcement which is substantially inextensible in the circumferential direction. This conventional construction for the belt may be replaced by one of the many other known constructions.

When thé tyre is mounted on its rim 10, the axial spacing A of the beads 2 between the edges of the rim is equal to or smaller than the width B of the tread to give the tyre good lateral stability, and the width L of the belt 8 is in turn equal to or slightly less than that of the tread. The belt 8 should be neither too narrow to confine the crown of the tyre effectively nor too wide, so as not to detract from the ability of the crown of the tyre to flex under load. The width of the belt 8 is generally from 0.8 to 1 times the width B of the tread and also of the distance A between the beads.

Since what are involved are tyres for fitting to the driving wheels of agricultural tractors or other vehicles or machines which -operate on similar terrain, the pattern of the tread 4 is a coarse pattern made up in essence of oblique bar-like ribs 9 of substantial height which are spaced apart circumferentially by a distance D equal to at least twice their own thickness E and, generally between 4 and 7 times this thickness.

The ribs 9 preferably each extend transversely from one side of the tyre to approximately the centre of the tread. The ribs are inclined in alternate directions in a socalled open-centred chevron arrangement in which the ends of the ribs situated at the centre of the tread are separated from one another.

In the tyres shown, the complete crown 3, including the tread pattern 4, has a relatively pronounced transverse curvature for a tyre of the belted type, this curvature being such that, in the area of the crown covered by the belt 8 it creates a radial rise a which is at least equal to or greater than 1/5 of the radial cross-sectional height H of the tyre between the beads and the outer face of the tread (not including the height of the ribs 9 which varies depending upon how much wear the tyre has had). In addition, in these tyres the sidewalls 5 are reinforced for at least half the cross-sectional height H beginning from the beads. This overall design for the tyres is particularly suitable and is easier to achieve, when the tyres have a low cross-section in which the ratio of the cross-sectional height H over the width G of the body of the tyre is less than 0.6 and is between 0.3 and 0.5. When this is the case it is possible to meet the condition that there should be adequate radial rise a to allow the flexing, which is confined to the crown of the tyre, to be of large amplitude, while still having a tyre with a wide tread area, which assists in gripping soft ground, and with short sidewalls which give good lateral stability, which sidewalls may more easily be reinforced over a rela timely great height so as to have the radial stiffness required to confine the flexing of the tyre chiefly to the area of the crown.

In the case of Figs. 1 and 2, the rein forcement for the sidewalls 5 is provided chiefly by extending upwards the fillers 11 which normally surmount the bead wires 7, until their height h is greater than half the cross-sectional height H of the tyre. These fillers are made of a hard rubbery mixture to provide the sidewalls with the requisite stiffness. Similarly, rim rubbers 12 of hard rubber are themselves extended upwards to back up the fillers 11.

As a modification, it is possible to use instead of or in addition to the strips 11 or 12, reinforcing members of a known kind such as strips of fabric, flippers or partplies which are superimposed on the carcass plies in the lower parts of the sidewalls to be reinforced.

In the case of Figs. 3 and 4, the reinforcement for the sidewalls 5 is provided by continuing the lateral parts of the ribs 9 of the pattern to the bottoms of the sidewalls, the continuations forming radial buttresses or pillars 9b which project out wa.rds from the sidewalls themselves for a distance e which may be of the order of 5 to 50 mm depending on the size of the tyre. These pillars or buttresses 9b also provide protection for the sidewalls against cuts when the tyre is used on broken and stony ground. On soft ground they are able to provide extra grip when the tyre is bogged down. In addition in comparison with the previous embodiment, the ribs 9 themselves extend further outwards and may extend beyond the width of the body of the tyre, which gives a wider tread area which further assists the tyre in gripping and assists its tractive ability. Alternatively, the radial pillars could be provided on the sidewalls between ribs 9, as indicated at 13 on Fig. 4, the ribs not being continued to the beads, or additional pillars 13 could be provided at these points in addition to those 9b formed by the downward extensions of the ribs.

It can also be seen in Fig. 3 that the lower part of the sidewalls 5 is of increased thickness in the vicinity of the beads to form a circular fillet 14 whose lower part is shaped to bear against the turned-over outer edge of the rim 10 around which it partly fits. This fillet 14 contributes to the radial stiffness of the sidewall and for this purpose it may be made at least partly of hard rubber, for example by extending the hard rim rubber 12 into the fillet. In addition, it prevents earth and mud from getting between the rim and the bead and prevents the over-rapid wear on the beads which this might cause.

Other constructions for tyres according to the invention may be derived from the embodiments described above, in particular by associating with the internal sidewall reinforcements shown in Fig. 1 the external reinforcements formed by the radial pillars and/or the rim-support fillets 14 illustrated in Fig. 3. This could possibly result in asymmetrical tyre constructions in which, as in Fig. 5 for example, one of the sidewalls 5 is reinforced in the way indicated in Fig. 1 and the other sidewall is reinforced as indicated in Fig. 3. In this case it would sometimes be preferable to have the projecting pillars on the outer side of the tyre with respect to the vehicle.

WHAT WE CLAIM IS: - 1. A pneumatic tyre for the driving wheels of agricultural tractors or similar vechiles, of the kind having a body with axially spaced beads, a tread having a pattern formed by circumferentially spaced transverse ribs, and a tread width (B) equal to or greater than the axial spacing of the bead heels when the tyre is mounted on the rim for which it is intended, and a belt which reinforces the crown of the carcass of the tyre over an axial width equal to or less than the axial distance between the bead heels, wherein the crown of the tyre has a transverse curvature such that the inner surface of the crown has, under the belt, a radial rise which is equal to or greater than 1/5 of the cross-sectional height aI) of the tyre, and the sidewalls of the tyre each being reinforced from the associated bead to a location spaced from the radially innermost part of the bead by at least half the cross-sectional height (H), so that the flexing of the tyre under load is confined chiefly to the area of the crown of the tyre.

2. A pneumatic tyre as claimed in claim 1, wherein the ratio of the cross-sectional height to the width of the body of the tyre is less than 0.6.

3. A pneumatic tyre as claimed in claim 2, wherein said ratio is between 0.3 and 0.5.

4. A pneumatic tyre as claimed in claim 1, 2 or 3, wherein the sidewalls are reinforced by extending reinforcements in the beads to at least half the cross-sectional height of the tyre.

5. A pneumatic tyre as claimed in any of claims 1 to 4, wherein at least one, of the sidewalls is reinforced by radial buttresses or pillars which project from the sidewalls of the tyre.

6. A pneumatic tyre as claimed in claim 5, wherein the radial buttresses or pillars are created by continuing the outer lateral parts of the ribs forming the pattern of the tyre to the beads.

7. A pneumatic tyre as claimed in any of the preceding claims, wherein the bottoms of the sidewalls form a fillet of increased thickness which projects axially with respect to the beads to bear against the turned-over outer edge of the rim.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. forcement for the sidewalls 5 is provided chiefly by extending upwards the fillers 11 which normally surmount the bead wires 7, until their height h is greater than half the cross-sectional height H of the tyre. These fillers are made of a hard rubbery mixture to provide the sidewalls with the requisite stiffness. Similarly, rim rubbers 12 of hard rubber are themselves extended upwards to back up the fillers 11. As a modification, it is possible to use instead of or in addition to the strips 11 or 12, reinforcing members of a known kind such as strips of fabric, flippers or partplies which are superimposed on the carcass plies in the lower parts of the sidewalls to be reinforced. In the case of Figs. 3 and 4, the reinforcement for the sidewalls 5 is provided by continuing the lateral parts of the ribs 9 of the pattern to the bottoms of the sidewalls, the continuations forming radial buttresses or pillars 9b which project out wa.rds from the sidewalls themselves for a distance e which may be of the order of 5 to 50 mm depending on the size of the tyre. These pillars or buttresses 9b also provide protection for the sidewalls against cuts when the tyre is used on broken and stony ground. On soft ground they are able to provide extra grip when the tyre is bogged down. In addition in comparison with the previous embodiment, the ribs 9 themselves extend further outwards and may extend beyond the width of the body of the tyre, which gives a wider tread area which further assists the tyre in gripping and assists its tractive ability. Alternatively, the radial pillars could be provided on the sidewalls between ribs 9, as indicated at 13 on Fig. 4, the ribs not being continued to the beads, or additional pillars 13 could be provided at these points in addition to those 9b formed by the downward extensions of the ribs. It can also be seen in Fig. 3 that the lower part of the sidewalls 5 is of increased thickness in the vicinity of the beads to form a circular fillet 14 whose lower part is shaped to bear against the turned-over outer edge of the rim 10 around which it partly fits. This fillet 14 contributes to the radial stiffness of the sidewall and for this purpose it may be made at least partly of hard rubber, for example by extending the hard rim rubber 12 into the fillet. In addition, it prevents earth and mud from getting between the rim and the bead and prevents the over-rapid wear on the beads which this might cause. Other constructions for tyres according to the invention may be derived from the embodiments described above, in particular by associating with the internal sidewall reinforcements shown in Fig. 1 the external reinforcements formed by the radial pillars and/or the rim-support fillets 14 illustrated in Fig. 3. This could possibly result in asymmetrical tyre constructions in which, as in Fig. 5 for example, one of the sidewalls 5 is reinforced in the way indicated in Fig. 1 and the other sidewall is reinforced as indicated in Fig. 3. In this case it would sometimes be preferable to have the projecting pillars on the outer side of the tyre with respect to the vehicle. WHAT WE CLAIM IS: -

1. A pneumatic tyre for the driving wheels of agricultural tractors or similar vechiles, of the kind having a body with axially spaced beads, a tread having a pattern formed by circumferentially spaced transverse ribs, and a tread width (B) equal to or greater than the axial spacing of the bead heels when the tyre is mounted on the rim for which it is intended, and a belt which reinforces the crown of the carcass of the tyre over an axial width equal to or less than the axial distance between the bead heels, wherein the crown of the tyre has a transverse curvature such that the inner surface of the crown has, under the belt, a radial rise which is equal to or greater than 1/5 of the cross-sectional height aI) of the tyre, and the sidewalls of the tyre each being reinforced from the associated bead to a location spaced from the radially innermost part of the bead by at least half the cross-sectional height (H), so that the flexing of the tyre under load is confined chiefly to the area of the crown of the tyre.

8. A pneumatic tyre as claimed in any

of the preceding claims, wherein the ribs of the pattern are inclined in alternating directions in a chevron arrangement with their central ends separated from one another.

9. A pneumatic tyre substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

10. A pneumatic tyre substantially as hereinbefore described with reference to Figs. 3 and 4 of the accompanying drawings.

11. A pneumatic tyre substantially as hereinbefore described with reference to Fig. 5 of the accompanying drawings.