GB1591139A - Tyres for agricultural tractors or like vehicles - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO TYRES FOR AGRICULTURAL TRACTORS OR LIKE VEHICLES (71) We, PNEUMATIQUES, CAOUT CHOUC 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 tyres for the driving wheels of agricultural tractors or like vehicles or machines which are intended for use mainly on unstable ground, and particularly to the tread patterns thereof.

Unlike tyres for road vehicles, the tread pattern of such agricultural tyres is generally formed by heavy bars which extend transversely for slightly more than half the width of the tread at an inclination of approximately 45" to the mid-circumferential plane and which are orientated in opposite directions at the two sides of the tread. These bars are very widely spaced in the circumferential direction with the result that, on unstable ground, they bury themselves completely in the ground. The tractive force is thus transmitted mainly by the rear side-faces of the bars, the bars operating like paddle blades.

One of the problems encountered with tyres of this nature is to prevent the spaces in the tread from becoming clogged with earth on unstable and slippery ground and to prevent the loss of grip which results.

The invention-proposes a tread pattern which endows tyres of this nature with a better self-cleaning action resulting from the expulsion at the exit from the ground contact area of the earth which has become packed into the spaces of the tread. To this end, not only are bars making up each of two lateral series of bars which form the chief part of the tread pattern separated from one another in the circumferential direction, but the series are separated from one another in the axial direction, by spaces which are arranged at the centre of the tread. By making these inter-bar spaces of suitable size, in particular in the axial direction, the gripping ability and self-cleaning action of the pattern are improved when operating on soft and clinging ground.

Specifically, the invention consists of a tyre for the driving wheels of agricultural tractors or like vehicles, of the kind which has a tread pattern comprising two series of transverse bars which are inclined to the mid-circumferential plane with those of one series oppositely inclined to those of the other, each series being located in a respective lateral region of the tread, wherein in each series said bars are separated from one another in the circumferential direction of spaces at least three times the thickness of the bars, and the series are separated from one another in the axial direction by a space whose width is between 10 and 35% of the axial width of the tread.

The bars may be associated with other parts in relief such as slabs located in the central part of the tread, provided that these other parts in relief are themselves separated from the bars by spaces of sufficient size.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, which show some embodiments thereof by way of example andinwhich:- Figures 1 and 2 are schematic views from above of tread patterns having aligned bars and staggered bars respectively.

Figure 3 is a cross-section through a tyre having either of these patterns, Figures 4 and 5 are similar views of tread patterns having bars and central slabs, and Figure 6 is a cross-section through such a tyre.

Referring now to the drawings, in conventional fashion, the tyres in question have a body 1 having axially spaced beads 2, sidewalls 3, and a crown 4 which has a transverse curvature which is more or less pronounced depending upon the type of construction used, namely cross-ply or radial and belted. The crown carries the tread, which is formed by a relatively thin continuous layer 5 generally termed the "treadbase", and by the parts in relief forming the tread pattern proper which project radially from the outer surface of the tread base 5. The surface of the tread base may be smooth rough, or provided with shallow protruberances.

In all cases, the pattern proper is formed by two lateral series a and b of high and thick individual heavy bars 6 which are distributed on respective sides, of the tread. These bars extend transversely in realtion to the tread at an inclination of between 30 and 50 to the mid circumferential plane c-c of the tyre and they are orientated in opposite directions from one another in the two series a and b. Their thickness e is sufficient to enable the tractive force to be transmitted without major deformation and in each lateral series they are separated from one another by spaces 7 whose length d in the circumferential direction is equal to at least three times the thickness e of the bars.

The length d of the spaces is not however greater than the length of the footprint of the tyre on the ground when loaded so that, in operation, at least one bar in each series is always in the area of contact with the ground.

In practice the length d is not generally greater than seven times the thickness e. In addition, the lateral series a, b are separated axially by a space 8 arranged at the centre of the tread. All the bars 6 of the tread pattern are thus spaced appreciably apart from one another and do not interlock with one another. They are connected together at their bases only by the shallow tread-base 5 which is relatively resilient and deformable in the radial direction.

The width "1 " of the open space 8 which separates the series a and b axially may vary with the size of the tyre and in particular with the width of the tread and the longitudinal spacing of the bars. This width "1 " is between 10 and 35% of the width L of the tread.

In the case of Figures 1 and 2 the pattern is formed solely by bars 6 arranged as described above. In Figure 1, the bars in each series a and b are positioned transversely facing one another, that is to say they are arranged in pairs consisting of two bars inclined in opposite directions in the form of a truncated V whose virtual apex F lies on the mid-circumferential plane c-c of the tread. In this embodiment, it may be useful for the length d of the spaces 7 to be sufficiently small that, given that the inclination of the bars and their extent transversely, the longitudinal distances g separating the central ends and the lateral ends of successive bars is small, zero or negative, so as to provide for less jerky or completely smooth movement over soft and hard ground. With this arrangement for the ridges, the width 1 of the space 8 is advantageously relatively large to assist the self-cleaning action of the pattern In Figure 2 the bars in the two series a and b are staggered circumfemetially relative to one another. In the example illustrated, this stagger is equal to half the pitch of the series so that the central end 6a of the bars in one lateral series a are situated opposite the centres of the open spaces 7 separating the central ends 6b of pairs of adjoining bars in the other lateral series b. This stagger could be equal to some other fraction of the pitch of the bars.

however, in this case too the longitudinal spacing d and the angle of inclination of the bars are preferably made such that any axial line or area across the tread intersects the radially outer surface of at least one of the bars of the pattern, so as to ensure smoother move ment over soft ground. With this staggered arrangement for the bars 6, the axial width 1 of the space may be smaller.

In the case of Figures 4 and 5, the inclined bars 6 which form the chief part of the pattern, at least as regards the grip and tractive ability of the tyre on unstable ground, are associated with slabs 9 in relief which are of the same radial height as the bars relative to the tread base 5. These slabs 9 are confined to the cen tral part of the tread and they are of small size transversely, of the order of 10 to 35% of the width L of the tread for example. These slabs 9. are spaced apart from one another and are separated from the bars 6 by spaces 10 which are at least equal to the thickness e of the bars. When the spacing d of the bars is such that a space having a widthg of positive value lies between successive bars, the slabs 9 are ad vantageously arranged at least partly in this space to improve the ride over hard ground.

In Figure 4, the bars 6 are arranged in the form of truncated V's in the case of Figure 1 and the slabs 9 are situated in the vicinity of the apicesfof the arms of the V's. In Figure 5, the bars 6 are staggered as in the case of Figure 2 and the slabs 9 are situated in the inter-bar spaces. In both cases, the slabs 9 project from the outer surface of the tread base 5.

The embodiments illustrated have bar 9 of straight configuration whose thickness e is con stant throughout their length. It would of course be possible to use bars of other configur ations, for example of curved or sloping con figuration. What is taken into account in this case is the general or mean orientation of the bars and their minimum circumferential spac ing d. It is also possible to have bar configura tions where the thickness varies from one end to the other and it will then be the mean thickness of the bars which is taken into con sideration. Finally, as is standard practice, the bars 6 may have sidewalls of sidefaces which are tapered by the same of different amounts on the front and rear faces. They may also merge with the surface of the tread base at their feet via radised or stepped joints. What will be taken into consideration however will be the thickness e of the bars at their radially outer surfaces when the tyre is new. As already indi cated, the transverse dimensions of the slabs 9 are small but they are however of massive build with a thickness at least equal to the thickness e of the bars 6.

WHAT WE CLAIM IS: 1. A tyre for the driving wheels of agri cultural tractors or like vehicles, of the kind which has a tread pattern comprising two series of transverse bars which are inclined to the mid circumferential plane with those of one series oppositely inclined to those of the other, each

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

Claims (8)

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

   extend transversely in realtion to the tread at an inclination of between 30 and 50 to the mid circumferential plane c-c of the tyre and they are orientated in opposite directions from one another in the two series a and b. Their thickness e is sufficient to enable the tractive force to be transmitted without major deformation and in each lateral series they are separated from one another by spaces 7 whose length d in the circumferential direction is equal to at least three times the thickness e of the bars.

   The length d of the spaces is not however greater than the length of the footprint of the tyre on the ground when loaded so that, in operation, at least one bar in each series is always in the area of contact with the ground.

   In practice the length d is not generally greater than seven times the thickness e. In addition, the lateral series a, b are separated axially by a space 8 arranged at the centre of the tread. All the bars 6 of the tread pattern are thus spaced appreciably apart from one another and do not interlock with one another. They are connected together at their bases only by the shallow tread-base 5 which is relatively resilient and deformable in the radial direction.

   The width "1 " of the open space 8 which separates the series a and b axially may vary with the size of the tyre and in particular with the width of the tread and the longitudinal spacing of the bars. This width "1 " is between

   10 and 35% of the width L of the tread.

   In the case of Figures 1 and 2 the pattern is formed solely by bars 6 arranged as described above. In Figure 1, the bars in each series a and b are positioned transversely facing one another, that is to say they are arranged in pairs consisting of two bars inclined in opposite directions in the form of a truncated V whose virtual apex F lies on the mid-circumferential plane c-c of the tread. In this embodiment, it may be useful for the length d of the spaces 7 to be sufficiently small that, given that the inclination of the bars and their extent transversely, the longitudinal distances g separating the central ends and the lateral ends of successive bars is small, zero or negative, so as to provide for less jerky or completely smooth movement over soft and hard ground. With this arrangement for the ridges, the width 1 of the space 8 is advantageously relatively large to assist the self-cleaning action of the pattern In Figure 2 the bars in the two series a and b are staggered circumfemetially relative to one another. In the example illustrated, this stagger is equal to half the pitch of the series so that the central end 6a of the bars in one lateral series a are situated opposite the centres of the open spaces 7 separating the central ends 6b of pairs of adjoining bars in the other lateral series b. This stagger could be equal to some other fraction of the pitch of the bars.

   however, in this case too the longitudinal spacing d and the angle of inclination of the bars are preferably made such that any axial line or area across the tread intersects the radially outer surface of at least one of the bars of the pattern, so as to ensure smoother move ment over soft ground. With this staggered arrangement for the bars 6, the axial width 1 of the space may be smaller.

   In the case of Figures 4 and 5, the inclined bars 6 which form the chief part of the pattern, at least as regards the grip and tractive ability of the tyre on unstable ground, are associated with slabs 9 in relief which are of the same radial height as the bars relative to the tread base 5. These slabs 9 are confined to the cen tral part of the tread and they are of small size transversely, of the order of 10 to 35% of the width L of the tread for example. These slabs 9. are spaced apart from one another and are separated from the bars 6 by spaces 10 which are at least equal to the thickness e of the bars. When the spacing d of the bars is such that a space having a widthg of positive value lies between successive bars, the slabs 9 are ad vantageously arranged at least partly in this space to improve the ride over hard ground.

   In Figure 4, the bars 6 are arranged in the form of truncated V's in the case of Figure 1 and the slabs 9 are situated in the vicinity of the apicesfof the arms of the V's. In Figure 5, the bars 6 are staggered as in the case of Figure 2 and the slabs 9 are situated in the inter-bar spaces. In both cases, the slabs 9 project from the outer surface of the tread base 5.

   The embodiments illustrated have bar 9 of straight configuration whose thickness e is con stant throughout their length. It would of course be possible to use bars of other configur ations, for example of curved or sloping con figuration. What is taken into account in this case is the general or mean orientation of the bars and their minimum circumferential spac ing d. It is also possible to have bar configura tions where the thickness varies from one end to the other and it will then be the mean thickness of the bars which is taken into con sideration. Finally, as is standard practice, the bars 6 may have sidewalls of sidefaces which are tapered by the same of different amounts on the front and rear faces. They may also merge with the surface of the tread base at their feet via radised or stepped joints. What will be taken into consideration however will be the thickness e of the bars at their radially outer surfaces when the tyre is new. As already indi cated, the transverse dimensions of the slabs

   9 are small but they are however of massive build with a thickness at least equal to the thickness e of the bars 6.

   WHAT WE CLAIM IS: 1. A tyre for the driving wheels of agri cultural tractors or like vehicles, of the kind which has a tread pattern comprising two series of transverse bars which are inclined to the mid circumferential plane with those of one series oppositely inclined to those of the other, each

   series being located in a respective lateral region of the tread, wherein in each series said bars are separated from one another in the circumferential direction by spaces at least three times the thickness of the bars, and the series are separated from one another in the axial direction by a space whose width is between 10 and 35% of the axial width of the tread.
2. 2. A tyre as claimed in Claim 1, wherein the bars in the two lateral series are arranged in pairs consisting of two bars which are inclined in opposite directions in the form of a truncated V whose virtual apex lies on the midcircumferential plane of the tread.
3. 3. A tyre as claimed in Claim 1, wherein the bars in the two lateral series are staggered from one another in the circumferential direction.
4. 4. A tyre as claimed in Claim 1,2 or 3, wherein the pattern also includes slabs of the same radial height as the bars and of small transverse size which are located in the central part of the tread and which are spearated from the bars by spaces whose size is at least equal to the thickness of the bars.
5. 5. A tyres substantially as hereinbefore described with reference to Figures 1 and 3 of the accompanying drawings.
6. 6. A tyre substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.
7. 7. A tyre substantially as hereinbefore described with reference to Figures 4 and 6 of the accompanying drawings.
8. 8. A tyre substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.