GB2142885A - Tyre tread - Google Patents

Abstract

A tyre tread is described, particularly for use on commercial vehicles, which can be used as a winter pattern and which also has a high mileage capacity. For this purpose, a central row (5) of blocks (10) having a mutually interlocking arrangement is provided adjacent to which are disposed side rows (6) of blocks, separated from the central row by continuous grooves (18) of meandering form, which are also arranged in an interlock arrangement with each other and with the blocks in the central row. in addition, connecting webs (13), with transverse slots (14), are provided between the successive blocks in the central row on the one hand and between successive pairs of blocks in the side rows on the other, on a level which is lower than the surface of the blocks. <IMAGE>

Description

SPECIFICATION Tyre tread The invention concerns a tyre tread. In particular it concerns a tyre tread for a tyre for use on a drive axle of a commercial vehicle comprising blocks arranged in rows extending longitudinally of the tread, and in use, circumferentially of the tyre.

It is known that the properties of vehicle tyres are greatly dependent on the tread. In addition to being capable of transmitting high drive and braking forces with little slip, having good lateral stability in all driving situations and as little rolling resistance as possible, a tyre tread must be quiet and smooth running, have good drainage and self-cleaning properties, be capable of high mileage and adequate for use in any season. These requirements which contradict each other to some extent-are met in the best possible way through the design of the tread pattern in particular.

The object of the invention is to provide a tyre tread, particularly for a tyre for use in a drive axle of a commercial vehicle having optimum winter properties and, at the same time, high mileage. it is also intended to meet the other requirements set out above.

In accordance with the invention a tyre tread comprises a plurality of projecting blocks on that surface of the tread which is intended to contact the ground in use, the blocks being arranged in two side rows, one on each side of the tread, and in up to two central rows, the side and central rows extending longitudinally of the tread, and in use, circumferentially of the tyre, each side row being separated from the adjacent central row by a continuous longitudinal groove having sections which are offset from one another transversely of the tread, each block being polygonal and having a transverse length which is greater than the longitudinal length, the blocks in the up to two central rows being offset alternately and symmetrically with respect to the central longitudinal line of the row in an interlocking arrangement, and the blocks in the side rows being arranged in an interlocking engagement with each other and also with the blocks in the adjacent central row, and connecting webs, each containing a transverse narrow slot, provided between each adjacent block in the up to two central rows and between alternate blocks in the side rows, the surface of each web being below the level of the surfaces of the blocks.

The design and interlock arrangement of the blocks in the longitudinal and transverse directions provides, in conjunction with the flexibility of the individual blocks improved by the deep slots, the best possible winter properties, in particular very good adhesion and other properties on wet, wintery roads, especially on slush and snow. For these reasons a tyre having a tread according to the invention is preferably fitted in autumn.

The longitudinal and transverse grooves between blocks ensure good drainage and selfcleaning and prevent any loading with slush and snow, particularly during winter use, if the tread is still not very worn and the grooves have their original width and their original course.

Preferably each block comprises a central portion which extends diagonally of the tread at an angle of about 55 to the longitudinal direction thereof. Preferably also some of the edges of each block extend at about 55 to the longitudinal direction, the remaining edges extending parallel to the longitudinal direction. The rows of blocks are preferably separated by longitudinal grooves each of which follows a meandering path.

Preferably, further the surface of the webs provided between blocks in the up to two central rows lie alternately on a first level and a second level, both being below the level of the surfaces of the blocks, the second level being closer to the level of the surfaces of the blocks than the first. The surface of each web provided between alternate pairs of blocks may be on said first level, and lying transversely of a web between blocks in the adjacent central row, the surface of which lies on said second level.

The webs, provided in the arrangement as described between the individual blocks, mean that with decreasing tread pattern depth as the tyre wears in use, the size of the ground-contact area of the tread is increased, whilst maintaining the separation of the individual blocks, particularly in the central area, which results in a considerable increase in mileage and increasingly endows the tyre with the tread according to the invention with the character and the desired properties of summer tyres.

Because of the arrangement of the two web levels, with a residual tread pattern depth of,for example, 8.5mm, pairs of blocks in the central row or rows merge together and a semi-continous rib, which reduces the rolling resistance further, is created from the central row of blocks. With a residual pattern depth of 5.5mm, for example, all the blocks in the central row or rows and pairs of blocks in the side rows merge together resulting in additional ground contacting surface area; again the narrow transverse slots separate the individual pattern blocks.

A further special feature of the tread according to the invention consists of the fact that the majority of the edges of the blocks and the slots run at an acute angle in relation to the transverse direction of the tyre. This ensures quiet, smooth running in particular.

Preferably a plateau, which may be substantially on the level of each web between blocks in the side rows and which extends into the longitudinal groove is formed on at least the inner side of each block in the side rows. The formation of these plateaus in the grooves with a V-shaped cross-section contributes to preventing damage to the base of the groove and also to self cleaning, stabilisation of the blocks and efficient stone ejection and the plateaus contribute to the creation of increased ground contacting surface areas when the tread has worn considerably.

Preferably, the surfaces of all the blocks are provided with at least one slot, and depending on the shape of the block, arranged to follow the block centre line, but with the exception that those areas of the surfaces of the blocks in the side rows adajcent to the tread edges are free from slots. In this way, the necessary rigidity of the pattern is achieved on the shoulder side without having to provide special pattern elements in this area for reinforcement and the mechanical vulnerability is reduced.

The outer edges of each block in the side rows may extend in a longitudinal direction and said edges of the alternate blocks may be displaced transversely towards the tread centre. This feature has an advantageous effect, particularly during winter use.

In accordance with a limited aspect of the invention the tread comprises a single central row of blocks which are substantially Z-shaped and the blocks in the side rows are alternately substantially S-shaped and substantially, Ishaped, when each block is considered in a transverse direction.

Preferably, each block comprises a central portion, the central portions of the blocks in the central row being inclined in the same direction in relation to the longitudinal direction, the central portions of the S-shaped blocks in the side rows also being inclined in the same direction in relation to each other, but in the opposite direction in relation to the central portions of the blocks in the central row, and the central portions of the I-shaped blocks in the side rows inclined in the same direction as the central portions of the blocks in the central row. In this way, a large number of edges are obtained directed differently in the corresponding contact surface of the tread and running at an angle in relation to the longitudinal direction of the tread, which has a particularly favourable effect with regard to the running and power transmission properties.

With regard to retreading, which is very important in connection with commercial vehicle tyres the low shoulder openings represent a further important feature of the tyre tread according to the invention; they lead to the creation of a continuous, recapping edge, also to be identified by a rib if necessary.

Laterally smooth surfaces connect to this recapping edge, i.e. so that there is no risk of the material escaping or of an imprecise impression or an imprecisely defined formation of the outside parts of the ribs in connection with the retreading or recapping process. Further advantageous embodiments of the invention are given in the sub-claims.

One exemplary embodiment of a tyre tread according to the invention is described below in more detail, with reference to the drawings, of which: Figure 1 shows a diagrammatic representation of a partial plan view of a tyre tread according to the invention; Figure 2 shows groove sections along section lines 1-1 to 5-5 in Figure 1; Figure 3 shows a graph for explaining the wear phases of the tread shown in Figure 1; Figures 1 6 show corresponding partial plan views of the tread shown in Figure 1 after various stages of wear; Figure 7 shows a diagrammatic representation of a small partial plan view of a modified form of the tread shown in Figure 1, and Figure 8 shows groove sections along lines 6-6 and 7-7 in Figure 6.

As shown in Figure 1, a tyre tread consists of a central row 5 of substantially Z-shaped blocks 10 when considered transversally to the longitudinal direction and two side tows of blocks 6 separated from the central row by continuous longitudinal grooves 18 each of which follows a meandering path. As can be seen in Figure 1, each longitudinal groove 1 8 comprises sections which extend diagonally of the tread interspersed with sections which extend parallel to the longitudinal direction.

These latter sections are clearly alternately laterally displaced.

The side rows 6 comprise substantially Sshaped blocks 11 and substantially shaped blocks 12, again considered transversally, in alternating sequence and disposed in an interlock arrangement with each other and also with the blocks 10 in the centre row.

In Figure 1 the entire tread width is marked Si and the width of central row of blocks 5 is marked S2, S2 being 41% of tread width S.

The mutual overlapping of the successive blocks 10 with the central row in the longitudinal direction is marked S3 and preferably this overlapping amounts to 18% of tread width S1. The blocks 10 in the central row 5 are alternately symmetrically displaced in relation to the tread centre line and inter-connected by means of connecting webs 13, 13' which are also disposed symmetrically with respect to this centre line. These connecting webs 13,13' are on two different levels in relation to the surfaces of the blocks. Connecting webs 13, the width B of which is greater than width C of connecting webs 13', are on a higher level i e closer to the surfaces of the blocks than the narrower connecting webs 13' and therefore take effect more. quickly in the course of tread wear by increasing the area cf the ground-contacting surface of the central row of blocks.

Connecting webs 13" are provided between successive pairs of blocks 11,12 in the side rows. As can be seen from the sections 3-3 and 5-5 in Figure 2, the levels of webs 13' and 13" are preferably the same.

A preferably continuous slot 14, which follows the zig-zag path of the web, or the groove in which the web is located, extends through each one of the connecting webs 1 3,1 3'. The depth of the slots more or less corresponds to the maximum pattern depth so that the separation of the successive blocks in the longitudinal direction is guaranteed, irrespective of the corresponding degree of wear of the tread pattern. Thus there can be a mutual supporting action between successive blocks in each row.

The central portions 1 5 of the Z-shaped blocks 10 in the central row 5 all extend in the same direction in relation to the longitudinal direction of the tread. The central portions 1 6 of the S-shaped blocks 11 in the side rows are also inclined in the same direction in relation to each other, but in the opposite direction in relation to the central portions 1 5 of the Z-shaped blocks 10. The central portions 1 7 of the I-shaped blocks 1 2 extend parallel to the central portions 1 5 of the blocks 10 in the central row. In this way, the side rows 6 of blocks 11,12 assume a zig-zag character whilst the centre row 5 of blocks 10 has more the character of a continuous rib.

One characteristic of the tread according to the invention consists of the fact that all the edges of the blocks apart from those edges running in the longitudinal direction, and also all the slots extend at an angle of about 55 to the longitudinal direction. Thus a large number of inclined edges are created by the Z-shaped blocks 10 and the S-shaped blocks 11 in particular, which run at said angle of about 55 . Apart from quiet running, this special feature also brings about very good power transmission properties.The meandering path of the continuous longitudinal grooves 18, created by the interlock arrangement between the Z-shaped blocks 10 in the central row 5 and she S-shaped blocks 11 and I-shaped blocks in the side rows 6, have a width A which is equal to the sum of widths B and C of transverse grooves 21 and 25 which, when the pattern is new, separate the successive Z-shaped blocks 10 in the longitudinal direction from each other.

The Z-shaped blocks 10 have two different widths of their central portions 1 5. This is indicated by references L2 and K2 in Figure 1.

These different widths are related so the tread pattern division or moulding segment length L, K, used. In particular L2 is L x 0.21 and K2 is K X 0.19. The pattern division of moulding segment length is related to tread width S" where L is equal to S1 X 0.43 and L is equal to K X 1.3.

Plateaus 22, extending into the continuous longitudinal grooves 1 8 and which are on the level of connecting webs 1 3" between Sshaped blocks 11 and I-shaped blocks 1 2 are formed on the inner sides of S-shaped blocks 11 and I-shaped blocks 12.

Preferably, and as shown in Figure 1 these plateaus 22 are also formed in the transverse grooves between S-shaped blocks 11 and Ishaped blocks 1 2 of width A, i e particularly in a first section leading away from the longitudinal grooves 18 so that these plateaus can contribute to increasing the ground contacting surface area of the central row 5 of blocks 10 when the tread pattern wears.

The edges of S-shaped blocks 11 and Ishaped blocks 1 2 on the shoulder side extend parallel to the longitudinal direction as do the side edges of Z-shaped blocks 10 and of Sshaped blocks 11 and I-shaped blocks 12, which lie opposite each other in the transverse direction. However, the outer edges of Sshaped blocks 11 i e on the shoulder side are displaced in an inwards direction i e transversely towards the tread centre, thereby forming a shoulder contraction M, i e by dimensions S4 which is preferably equal to width A of continuous grooves 1 8.

The dimensions of the successive contractions 1 9 in the longitudinal direction are related to moulding segment lengths L and K.

This dimension, which can also be defined as the shoulder outlet, changes periodically according to the segment lengths over the length of the tread, when preferably a shoulder outlet is 68% of segment length L and the connecting shoulder outlet is 65% of segment length K.

In addition to showing the pattern of tread blocks, Figure 1 also shows a diagrammatic side view of shoulder openings 24 between two I-shaped blocks 1 2. The bottom edge of this shoulder opening 24 forms a component of a continuous, enclosed recapping edge and it can, if necessary, be clearly identified by a rib which can be applied. This continuous recapping edge is of particular advantage for the retreading or rebuilding process as there are no more recesses in the side wall area bordering on this recapping edge and therefore there is no problematic escape of material during the rebuilding process.

The sectional views in accordance with Figure 2 show the shape, wall angle and level of the various grooves, when example dimensions are given to provide a better means of comparison.

Section 1-1 passes through continuous groove 1 8 and shows plateau 22 which lies on a level which only reaches the tyre tread surface after wear of the winter pattern portion. The width of the plateau is less than half the groove width in the plateau level.

Section 2-2 shows a transverse groove 20 between an S-shaped block 11 and an 1 shaped block 12, when neither a plateau nor a connecting web is present.

Section 3-3 passes through a transverse groove, having a connecting web 13', between successive Z-shaped blocks 10 in the centre row 5. It can be seen that slot 14 extends as far as the deepest point of the pattern, i e as deep as a groove, as can be seen in section 2-2, for example.

Section 4-4 passes through the transverse groove, having width B, and a connecting web 1 3 between two successive Z-shaped blocks 10 in the centre row 5. It can be seen here, too, that slot 1 4 extends almost to the deepest point of the pattern.

Section 5-5 passes though the transverse groove having width B and a connecting web 13" between an S-shaped block 11 and an Ishaped block 12 in the side rows 6. As can be seen the level of connecting web 13" is the same as web 13', but it need not necessarily be so.

The level of connecting web 1 3 is clearly higher compared with the level of connecting web 13' in section 3-3 and web 1 3" in section 5-5. The wall angle of the transverse grooves between Z-shaped blocks 10 in the centre row 5 is considerably smaller than the wall angle of the V-shaped continuous grooves 18.

The slots 23 in tread blocks 10, 11 and 12 shown in Figure 1 indicate only general possibilities. Some slots 23 have been omitted from Figure 1 for clarity. The actual arrangement of these slots for the invention can be seen in detail in Figures 1 6.

Because of the design and arrangement of connecting webs 13, 13' and 13" a pattern is obtained within the different rows of blocks which can be used in an optimun manner with regard to seasonal requirements.

The graph in Figure 3 illustrates in diagram form the wear or operating phases for a possible case as a function 5 of the corresponding pattern depth.

If a tyre with a tyre tread according to the invention is fitted and used in autumn then the normal wear which happens in the running-in stage will first occur. For example with a pattern depth of 12 mm, a range is reached in which the specific wear remains more or less constant until a first stabilisation has been obtained. The tyre, which, till then, was ideally suited as a winter tyre, reaches a state where, because of the reducing groove widths and because the level of connecting webs 1 3 is reached, the first merger of parts of the tread pattern takes place and therefore the ground contacting surface area of the pattern is increased considerably, particularly in the central area of the tyre. This results in a considerable reduction in the specific wear, and therefore to the increased mileage wanted and aimed for.There is a second stabilisation in the area of a pattern depth of 4 mm, following which the levels of the lower-lying connecting webs 13',13" and plateaus 22 are reached and there is a second merger of some of the tread pattern.

The graph shown in Figure 3 is included for a better understanding of the working principle of the tyre tread described. However, it has no limitative significance.

The various phenomena or functions of the tyre tread pattern obtained during its life described are illustrated on the basis of the plan views in Figure 4-6.

Figure 4 again shows the centre row 5 of blocks 10 and also the two side rows 6 of blocks 11 and 12, separated from the central row of blocks by continuous grooves 1 8 each of which follows a meandering path.

The illustration in Figure 4 corresponds to the new condition of the tyre tread, i e the individual blocks 10, 11, 1 2 in rows 5, 6, are separated from each other by clearly defined transverse grooves 20, 21, 25, 26. The marked interlock arrangement of the blocks in the longitudinal and transverse directions and also the transverse arrangement of the individual blocks give the tread in this condition excellent winter properties, with low-slip transmission of high drive and braking forces.

The proportion of the ground-contacting surface area of the blocks, compared to a plain tread i e if there were no grooves or slots, is 64%. It is also important that through the arrangement and design of the blocks, a tyre tread pattern is obtained which is not subject to the direction of travel.

If a tyre with a tread pattern in accordance with Figure 4 is in use over a long period and if a residual pattern depth of 8.5 mm, for example, is reached, then the pattern changes to that illustrated in Figure 5.

It can be seen, that because of the Vshaped cross-section of the longitudinal and transverse grooves, the width of the grooves has become less throughout. However, it can also be seen that two neighbouring blocks 10 in the centre row 5, have merged together, except for the narrow slot 14, and that as a result of wear, the level of the connecting webs 1 3 illustrated in Figure 1 has been reached. Consequently, the proportion of the ground contacting surface area is increased in the centre of the tyre tread, which has a quite considerable effect with regard to the mileage of tyres used on drive axles which can be achieved. The stage of the first merger illustrated in Figure 3 now exists.

After further wear, the level of the connecting webs 13',13" is now finally achieved between the centre pairs of blocks which have already merged and an I-shaped block 12 and a S-shaped block 11.

This results in a more or less continuous central row 5 of blocks closer to the side rows 6, which also have an increased surface area.

However, in this stage, the individual pattern blocks are still separated by the deep slots 14.

If the tyre has reached the condition shown in Figure 6, the tread pattern can be particularly easily re-profiled if required, although reprofiling can wait and can later be done without any problem. The reason why reprofiling is easier is that even in the case of a tyre which has travelled many miles, the groove contours, because of the slots in particular, are still clearly visible and can be used as a guide for the re-profiling tool. Through the re-profiling process, the pattern can even be given certain winter properties once more by cutting transverse grooves according to the path of the slots in the connecting webs.

The above described tyre tread may be modified as shown in Figures 7 and 8. The overall tyre tread pattern and block shape is the same as the tyre tread shown in Figure 1 and the modification relates only to the webs between alternate blocks in the side rows 6.

As can be seen in Figure 7 the web is in two parts; an inner part 25 provided with a transverse slot 24, which only extends over some of the length of the inner part, and an outer part 26, which is devoid of any transverse slot. For convenience part 26 is shaded with horizontal lines.

As can be seen in Figure 8 the level of the inner part 25 is the same as that of web 13" shown in Figure 1, but the level of the outer part 26, which extends to the outer edge of the S-shaped block is higher than that of webs 13, 13' and 13". This means that as the tread wears, the surface of part 26 of the web becomes part of the ground-contacting surface area of the tread before the surfaces of webs 1 3, 1 3', 13" and plateaus 22. The part 26 thus joins an I-shaped block to an Sshaped block early in the tread life providing mutual support between the blocks and lessening the occurrence of cracking.

Although the tyre tread described and illustrated has Z-shaped blocks in the central row, and S- and I-shaped blocks in the side rows, the tread pattern could be the "mirror image" in the tread centre line and as a result the Zshaped blocks would be S-shaped, and the Sshaped blocks would be Z-shaped. The overall performance of the tread would remain the same.

Claims (26)

1. Tyre tread comprising a plurality of projecting blocks on that surface of the tread which is intended to contact the ground in use, the blocks being arranged in two side rows, one on each side of the tread, and in up to two central rows, the side and central rows extending longitudinally of the tread, and in use, circumferentially of the tyre, each side row being separated from the adjacent central row by a continuous longitudinal groove having sections which are offset from one another transversely of the tread, each block being polygonal and having a transverse length which is greater than the longitudinal length, the blocks in the up to two central rows being offset alternately and symmetrically with respect to the central longitudinal line of the row in an interlocking arrangement, and the blocks in the side rows being arranged in an interlocking engagement with each other and also with the blocks in the adjacent central row, and connecting webs, each containing a transverse narrow slot, provided between each adjacent block in the up to two central rows and between alternate blocks in the side rows, the surface of each web being below the level of the surfaces of the blocks.

2. Tyre tread according to claim 1 wherein each block comprises a central portion which extends diagonally of the tread.

3. Tyre tread according to claim 2 wherein the central portion of each block extends at an angle of about 55 to the longitudinal direction of the tread.

4. Tyre tread according to any one of the preceding claims wherein some of the edges of each block extend at about 55 to the longitudinal direction of the tread and the remaining edges extend parallel to the longitudinal direction.

5. Tyre tread according to any one of the preceding claims wherein the rows of blocks are separated by longitudinal grooves each of which follows a meandering path.

6. Tyre tread according to any one of the preceding claims wherein transverse zig-zag grooves extend between blocks in each longitudinal row.

7. Tyre tread according to claim 6 wherein the width of each transverse groove between alternate blocks in each side row is equal to the width of the longitudinal grooves.

8. Tyre tread according to claim 6 or 7 wherein the width of each transverse groove between adjacent blocks in the up to two central rows is less than the width of the longitudinal grooves.

9. Tyre tread according to any one of the claims 6-8 wherein each transverse narrow slot is as deep as a transverse groove.

10. Tyre tread according to any one of the preceding claims wherein the surfaces of the webs provided between blocks in the up to two central rows lie alternately on a first level and a second level, both being below the level of the surfaces of the blocks,the second level being closer to the level of the surfaces of the blocks than the first.

11. Tyre tread according to claim 10 wherein the surface of each web provided between alternate pairs of blocks in the two side rows is on the said first level.

1 2. Tyre tread according to claim 10 wherein the webs between alternate pairs of blocks in the side rows each lie transversely of a web between blocks in the adjacent central row the surface of which lies on said second level.

1 3. Tyre tread according to any one of the preceding claims wherein the narrow slots provided in the webs extend transversely in zig-zag formation.

14. Tyre tread according to any one of the preceding claims wherein a plateau is formed on at least the inner edge of each block in the side rows, each plateau extending into one of the longitudinal grooves.

1 5. Tyre tread according to any one of the preceding claims wherein the surfaces of all the blocks are provided with at least one slot and, depending on the shape of the block, arranged generally to follow the block centre line.

1 6. Tyre tread according to claim 15 wherein those areas of the surfaces of the blocks in the side rows adjacent the tread edges are free from slots.

1 7. Tyre tread according to claim 1 5 or 1 6 wherein the slots formed in the blocks are as deep as the longitudinal grooves.

18. Tyre tread according to any one of the preceding claims wherein only one central row of blocks is provided, the width of the central row being about 41% of the tread width.

19. Tyre tread according to any one of the preceding claims wherein the outer edges of each block in the side rows extend longitudinally of the tread and said edges of alternate blocks are displaced transversely towards the tread centre.

20. Tyre tread according to any of the preceding claims comprising a single central row of blocks which are substantially Z-shaped and the blocks in the side rows are alternately S-shaped and I-shaped, when each block is considered in a transverse direction.

21. Tyre tread according to claim 20 wherein each block comprises a central portion, the central portions of blocks in the central row being inclined in the same direction in relation to the longitudinal direction, the central portions of the S-shaped blocks in the side rows being inclined in the same direction in relation to each other but in the opposite direction in relation to the central portions of blocks in the central row, and the central portions of the I-shaped blocks in the side rows being inclined in the same direction as the centre portions of the blocks in the central row.

22. Tyre tread according to claim 20 or 21 wherein the longitudinal distance between Ishaped blocks has one of two values, the first value being equal to 43% of the tread width, and the second value being 77% of the first value.

23. Tyre tread according to any one of claims 20-22 comprising shoulder openings formed between each I-shaped block and the next in one of the two side rows, the depth of each opening being substantially the same as the longitudinal groove depth.

24. Tyre tread according to any one of claims 20-22 with the modification that the shape of each tread block is the mirror image of the corresponding block in the longitudinal tread centre-line, the S-shaped blocks being Zshaped and vice-versa.

25. A tyre comprising a tread according to any one of the preceding claims.

26. A tyre for use on a drive axle of a commercial vehicle comprising a tread according to any one of claims 1-24.