WO1998003358A1

WO1998003358A1 - Automotive tyre tread wear indicator

Info

Publication number: WO1998003358A1
Application number: PCT/AU1997/000457
Authority: WO
Inventors: Kerry Bryan Spicer; Paul Anthony Richards
Original assignee: Treadline Innovative Products Pty. Ltd.
Priority date: 1996-07-22
Filing date: 1997-07-21
Publication date: 1998-01-29
Also published as: AUPO113496A0

Abstract

A tyre for a vehicle has a carcass (10) with an upper surface. A tread portion (12) is also provided and which has a tread pattern (14) having a number of tread ribs (24) and tread grooves (22), each tread groove (22) having a bottom. The lower surface (18) of tread portion (12) has a plurality of slots (20) generally aligned with the tread ribs (24) and extending upwardly beyond the bottom of the tread grooves (22), each slot (20) having therein an indicator strip (26) of a colour contrasting to that of the tread portion (12).

Description

AUTOMOT-VE TYRE TREAD WEAR INDICATOR

Field of the Invention

This invention relates to automotive tyres and refers particularly to an automotive tyre having at least one indicator strip of contrasting colour in the tread of the tyre so that upon the tread of the tyre becoming worn the indicator strip is revealed to provide a visual indication on the need to replace the tyre. The invention also provides a method of manufacturing such a tyre, and a method of forming a tread stock for use in retreading a tyre.

Background of the Invention

Tyres for vehicles, be they motor cars, motor cycles, trucks, trailers, aeroplanes, and so forth, wear during and as a result of their use. All such tyres normally have some form of tread pattern with treads and grooves on the radially outermost surface of the tyre. The treads and grooves provide the grip for the tyre, particularly when cornering or in wet weather. As the tread wears, the traction provided by the tyre can significantly reduce. As the tread wears to the stage that the groove is almost lost, most tyres reach a "legal limit", whereby the tyre does not satisfy the regulatory requirements and thus its further use is deemed to be unlawful. That legal limit is quite often difficult for the normal motorist or vehicle owner to measure accurately and consistently around the periphery of a tyre, and across the full width of the tyre. Therefore, quite often such tyres wear beyond the legal limit and this can make the use of the tyre dangerous as well as unlawful. In Australia, the depth of tread on a tyre must be at least 1.6 mm for it to be in compliance with Australian Standard AS1973-1993, paragraph 3.2.2. That standard is the legally defined standard, and any non-complying tyre is deemed to be unlawful, or unroadworthy.

As a result, many owners or drivers of vehicles adopt a failsafe attitude and will replace a tyre far earlier than is required. This results in increased expenditure on tyres over the life of the vehicle. For an average family motorist, this is not significant. For a fleet operator, this increase in expenditure may be quite significant.

There have been many proposals for the construction of, and methods of manufacture of, tyres, particularly tyres for automobiles, wherein the tyre has an indicator built in so that upon the tread of the tyre wearing to the stage that the tyre ought to be replaced, the indicator is revealed to enable the extent of wear to be visually noticeable and thus provide a warning to the vehicle driver that the tyre ought to be replaced. Examples of this include Patent Application AUA 12654/83 which has an indicator mounted within the body of the tread at approximately the level of the bottom of a groove in the tread. Being at the bottom of a groove means that by the time the indicator is visible, the tyre had already worn excessively and, thus, would be dangerous to use. Furthermore, the strip is embedded in the tread portion of the tyre. For the tyre to be made, the tread portion would have to be manufactured in a number of layers. Although vulcanising may assist in the integrating of the tread, such a construction is inherently dangerous in that the various layers of the tread may separate in use to thus cause destruction of the tyre, and a possible fatal accident.

Patent Application AUA23511/88 shows an indicator embedded in the rubber of a solid tyre for use with a pulley wheel. In this particular instance the pulley wheel can wear to that extent and thus it is an acceptable solution. However, it is not applicable to a tyre for road vehicles.

US Patent 3,814,160 has a tyre wear indicator which is a layer adapted to be inserted under the tread. The problem here is that by the time the layer is revealed, the tyre is well beyond the stage of being unsafe and probably would have already disintegrated and/or caused a fatal accident.

US Patent 4,226,274 also has an indicator built into the tread of the tyre in the raised portions but again would require the tread to be made in a number of layers thus causing considerable safety problems. US Patent 3,929,179 has an indicator device for indicating tread wear which includes a rod-like body embedded in the tyre, which includes within it a hard wear-resistant element at its innermost end. The height of the wear-resistant element is intended to be slightly above or at the height of the minimum thickness of the tread portion of the tyre-the safe wear level. The hard wearing element is adapted to provide an audible indication when the tyre rolls on a hard surface. This is difficult to assemble in manufacture, is not visible, and would not be heard by many people driving with windows closed, radios or other music devices on, or over general conversation. Its audibility would also depend significantly upon the nature of the road surface. It also provides a material of different nature within the tread of the tyre to thus provide a point of weakness. It is therefore the principle object of the invention to provide a tyre having a tread wear indicator which is easily inserted during manufacturing and which will provide a visual indication of tread wear during the normal operation of the tyre.

There is a further object of the present invention to provide a method of manufacturing a tyre incorporating such a tread wear indicator. Summary of the Invention

With the above and other objects in mind the present invention provides a tyre for a vehicle, the tyre having a carcass with a radially outermost surface, and a tread portion having a tread pattern with a number of grooves therein, each groove having a bottom, the tread portion having a lower surface and a top surface; the lower surface of the tread portion having at least one slot therein, each such slot being to receive an indicator strip, the indicator strip being of a contrasting colour to that of the tread portion and extending into the tread pattern above the bottom of the grooves.

Preferably, the slot is semi-circular. Alternatively, it may be triangular, rectangular, or barbed.

The slot should extend into the tread above the bottom of the groove by a height which is a legally-defined minimum height of tread to enable the tyre to be legally used. That minimum height may vary from country-to-country. In Australia it is 1.6 mm.

Furthermore, the slot may extend transversely across the lower surface of the tread portion for at least a part of the width of the tread portion. Alternatively, it may extend longitudinally of the tread portion. If extending transversely, there may be a number of such slots around the perimeter of the tyre. A suggested number is 3 or 4. These would preferably be equally spaced. If extending longitudinally, the slot may be continuous for the length of the tread portion or may be intermittently spaced along the tread portion. Furthermore, there may be a number of such longitudinally-extending slots spaced transversely across the tread portion at, for example, the centre of the tread portion, and one adjacent to each shoulder of the tyre. Also, for tread portions having grooves extending substantially across the width of the tyre, the bottom of the grooves may be provided with a shaft of material in which the indicator strip can be located.

The indicator strip may be made as a solid strip, or may be hollow. The colour may be any suitable colour such as, for example, iridescent orange, white, yellow, or the like. The indicator strip is preferably made of a material of similar density as the tread portion.

It is preferred the height of the slot is such that when the tread wears to the minimum height, the indicator strip is visible for a major part of its length. As the tread wears further, more of the width of the indicator strip becomes visible, thus providing an indication as to how long the tyre has been used when unlawful, or unroad worthy.

The invention also provides a method of making a tyre including forming a carcass of a tyre, extruding a tread portion of a tyre, cutting the tread portion to length, forming at least one slot in the lower surface of the tread portion, the slot being sized and shaped to receive an indicator strip, placing the indicator strip in the slot, the indicator strip being of a contrasting colour to the tread portion, assembling the tread portion on the carcass, and curing the assembly in a curing press. The invention also provides a method of making a tread stock for use in retreading a tyre, the method including extruding the tread stock, cutting the tread portion to length, forming at least one slot in the lower surface of the tread stock, the slot being sized and shaped to received therein an indicator strip, placing the indicator strip in the slot, applying an adhesive layer to the lower surface of the tread stock, and placing a removable cover over the adhesive layer.

The slot may be formed in the tread portion at the time of extrusion and/or cutting to length. Adhesive may be applied to the slot prior to placing the indicator strip in the slot. The indicator strip is preferably inserted progressively along the slot. This may be by extruding the indication strip into the slot. Description of the drawings

In order that the invention may be fully understood there shall now be described by way of non-limitative example only a preferred construction of a tyre, and a method of forming a tyre, incorporating the principal features of the present invention, the description being with reference to the accompanying illustrative drawings in which: Figure 1 is a perspective view of a tyre in partial cutaway showing a first embodiment of the present invention;

Figure 2 is a vertical cross-sectional view of the tyre of Figure 1 along the lines and in the direction of arrows 2-2 of Figure 1 ;

Figure 3 is a partial plan view of a different tyre; Figure 4 is a vertical cross-sectional view along the lines and in the direction of arrows 4-4 of Figure 3;

Figure 5 is a partial plan view of a third tyre; and

Figure 6 is a vertical cross-sectional view along the lines and in the direction of arrows 6-6 of Figure 5. Description of the preferred embodiment

To now refer to Figures 1 and 2 there is shown a tyre which is of normal radial tyre construction, although the present invention is equally applicable to cross-ply construction and other forms of tyre construction.

The tyre has a carcass generally designated as 10 which is developed in the normal manner. As is normal in the tyre industry, a tread portion 12 is provided which is manufactured separately and subsequently assembled with the carcass 10. The tread portion 12 is normally of a different rubber compound to the carcass 10 and, after being extruded and cut to length, is subsequently pressed to provide the tread pattern 14 in the upper surface 16.

The carcass 10 has sidewalls 28, radial ply cords 30, inner liner 32, bead wires 34, chafer 36, bead heel 38 and bead toe 40. Belts 42 and protective breaker 44 are also provided.

Formed in the lower surface 18 of tread portion 12 are a number of slots 20 generally aligned with tread ribs 24 and which extend upwardly to be of sufficient height to be above the bottom of tread grooves 22. In this way when tread ribs 24 wear, they will eventually reach the top of slot 20 before the tread ribs 24 are completely worn. Each slot 20 is adapted to receive an insert 26, which completely fills slot 20 and which is of a colour contrasting to that of the tread portion 12. The inserts 26 may be triangular, as shown, or any other suitable shape such as semi-circular, circular, square or barbed. They may be hollow or solid. They must be of a contrasting colour to the tread portion 12 so that as the tread ribs 24 wear to the stage that the insert 26 is revealed to the upper surface 16 of tread portion 12, insert 26 will be easily visible. The insert 26 may be of any suitable material, although it may be of substantially the same material as tread portion 12 so that during the vulcanising or curing of the tyre, the insert 26 will integrate with tread portion 12 to minimise any structural weakness and thus provide for the inherent strength required in the tread portion 12.

In this way, as the tyre wears the indicator 26 will become visible before the tread ribs 24 have worn to the stage that tread grooves 22 are effectively eliminated. Therefore, the depth of slots 20 can be used to ensure that when the wear indicator 26 is first revealed to upper surface 16, the depth of tread grooves 22 has been reduced to the minimum allowed by law and therefore the tyre is no longer roadworthy and is unsafe to use. As the tread ribs 24 wear further, a substantial part of the width of insert 26 is revealed. This reveals to an observer how long the tyre has been used when unroad worthy, and thus the extent of the liability or culpability of the owner, operator and/or driver. When the full width of insert 26 is revealed, the tyre is in danger of disintegration. By having inserts 26 triangular (ie of increasing width as they wear) this is possible.

Slot 20 may extend in the peripheral direction, as shown, or may extend transversely. If peripherally as shown, it may be continuous around the periphery of the tyre or be intermittent strips around the periphery of the tyre. This will very much depend upon the tread pattern of the tyre, as for certain tread patterns it will not be possible to have a continuous slot 20.

It is preferable that there be a slot 20 at the centre of the tyre and one adjacent each shoulder of the tyre so that the three normal places of wear of the tyre can be accurately monitored. By having peripherally extending strips at those three locations, the normal wear strips of the centre of the tyre, and both shoulders will be monitored.

If extending transversely, the insert 26 may be continuous or broken in accordance with the requirements of the tread pattern of the tyre. If extending transversely, it is preferable thai there be a number of slots 20 within inserts 26 around the periphery of the tyre to provide for a regular indication.

By having the insert 26 of a different colour to the tread portion 12, when worn such that at least one of the indicator strips 26 is revealed, as the vehicle drives along, the strip 26 will be revealed. Thus, for example, a policeman driving in the opposite direction or following the vehicle concerned will see the regular pattern of colour revealed from the inserts 26 and thus be aware that at least one tyre of the vehicle concerned is of sufficient wear that the tyre is unsafe and/or unroadworthy. The policeman can then take appropriate action. In this way, the safety of tyres will be increased as it will be quite evident when the tyre has reached its safe wear limit. The strips 26 would also be visible on speed and/or video cameras. Also, an owner or operator of the vehicle will know when to replace the tyre, and thus early or late replacement will be avoided or minimised.

Figures 3 and 4 show an alternative form of insert where like components have like reference numerals with the addition of a prefix number 2.

The tread pattern 214 as shown in Figures 3 and 4 has grooves 222 which not only extend in a general longitudinal direction as shown in the embodiment of Figures 1 and 2, but have transverse portions 223. Due to the relationship between grooves 222 and grooves 223, there is no continuous path of tread ribs 224 in which slot 220 may be located to provide a continuous insert 226, in accordance with embodiment of Figures 1 and 2.

To overcome this, small shafts of material 225 are provided across the bottoms of grooves 222 and 223 wherever the slots 220 intersect with a groove 222 or 223. These shafts 225 extend across the relevant portion of the groove 222 or 223 and are of sufficient height to allow the slot 220 to be formed, and the insert 226 to be placed therein. The height of the shaft 225 is not sufficient to interfere with the general operation of the tyre and the tread pattern 214, but is of sufficient height to provide sufficient thickness of material to accommodate the slots 220 and inserts 226. As the tread ribs 224 wear, the top of shafts 225 will wear at the appropriate time to thus reveal the indicators 226 in accordance with embodiment described in Figures 1 and 2.

Therefore, no matter the tread pattern, by appropriate use of shafts 225 of the required height and thickness, continuous slots 220 and thus inserts 226 may be provided. The shafts 225 are relatively easily formed by a small alteration to the tooling during the formation of the tread portion 212.

Figures 5 and 6 illustrate the more normal form, although somewhat different to that of Figures 1 and 2. Again, like reference numerals are used for like components, but with the addition of the prefix number 3. As shown, there is a tread portion 312 having a tread pattern 314 thereon. The tread pattern 314 is formed in the upper surface 316 of the tread portion 312. The tread pattern 314 has tread ribs 324 and longitudinally extending grooves 322. A plurality of relatively short and terminal transfers grooves 323 are provided. Again, a plurality of slots 320 are formed in the lower surface 318 of the tread portion 312. In the slots 320 are located the inserts 326, in accordance with embodiment of Figures 1 and 2, as well as that of Figures 3 and 4. Therefore, no matter if the tread pattern 314 provides a complex series or continuous path of tread ribs 324, appropriate grooves 320 may be placed therein to enable the indicators 326 to be inserted.

Naturally, the grooves 320 may be somewhat curved to pass between the innermost limits of the transverse grooves 323, if required. Therefore, the grooves 320 (and similarly for the grooves in the embodiments of Figures 1 and 2, and Figures 3 and 4) may not of necessity be straight and thus the indicator strips 326 may correspondingly be curved rather than straight.

Again, with all embodiments, although the inserts 26, 226 and 326 have been shown as being triangular, any appropriate shape may be used. This may be circular, semi-circular, square, barbed, or other appropriate shape. Again, they may be hollow or solid. The principal requirement is that they can be adhered into the slots by appropriate adhesive and/or vulcanising action. They must be of a colour contrasting to that of the tread portion and must extend upwardly into the tread portion beyond the bottoms of the grooves in the tread. Naturally, this is only the major grooves in the tread portions and does not concern micro-grooves which may form part of the tread pattern.

To manufacture a tyre such as that of Figures 1 and 2, the normal tyre manufacturing process can be used. This is well known, and well documented. As part of the tyre manufacturing process, the tread portion 12 is extruded in an extruder in a normal manner. It is then cut to length. At that time it will be possible for the slots 20 to also be pressed into or cut from the lower surface 18 of tread portion 12. In accordance with the normal process, the tread portion then passes to a tyre building machine which assembles all components into the one entity, which is called the green or unvulcanised tyre. At that stage, the indicators 26 may be inserted in the slots 20 prior to the tread portion 12 being assembled with the carcass 10. The assembly can then be placed into the curing or vulcanising press for curing in the normal way. If the indicators 26 are of the same material, or of a material of the same density, as the tread portion 12, integration of the surfaces will be made at that time to enable the inherent strength of the tread portion 12 to be retained. Furthermore, it is to be noted that the slot 20 should be of the same dimensions and shape as the indicator 26 inserted therein. In that way, by inserting the indicator 26 progressively along its length, the risk of air bubbles or the like will be reduced. This requires one end of the insert 26 to be placed in the slot 20 and the insert progressively placed in slot 20 along its actual length.

Preferably, an adhesive is placed in slot 20 prior to insertion of insert 26. Also, the insert 26 may be extruded into slot 20.

For tread stock for retreading of a tyre, after the insert 26 is inserted the lower surface of the tread stock is buffed, and the adhesive layer applied subsequent to buffing. The uncured indicator strip 26 may be used with cured or uncured tread stock; or the indicator strip 26 may be cured and used with cured or uncured tread stock. The invention is applicable to pneumatic tyres, as well as solid tyres, and recaps. Also, the reference to colour is to be taken as including a number of different colours. Finally, the slot and insert may extend at an angle to the peripheral axis and/or may be a combination of lateral and peripheral slots and inserts.

Whilst there has been described in the foregoing description, a tyre incorporating the principle features of the present invention, as well as the method of manufacturing the tyre with those features, it will be realised by those skilled in the technology concerns that many variations or modifications and details of the design or construction may be made without departing from the essential features of the present invention, as we understood from the foregoing description. It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

It will also be understood that where the term "comprises" or its grammatical variants, is employed herein, equivalent to the term "includes" and is not to be taken as excluding the presence of other elements or features.

Claims

CLAIMS*.

1. A tyre for a vehicle, the tyre having a carcass with a radially outermost surface, and a tread portion having a tread pattern with a number of grooves therein, each groove having a bottom, the tread portion having a lower surface and a top surface; the lower surface of the tread portion having at least one slot therein, each such slot being to receive an indicator strip, the indicator strip being of a contrasting colour to that of the tread portion and extending into the tread portion above the bottom of the grooves.

2. A tyre as claimed in claim 1, wherein the slot is semi-circular, triangular, rectangular, or barbed.

3. A tyre as claimed in claim 1 or claim 2, wherein the slot extends transversely across the lower surface of the tread portion for at least a part of the width of the tread portion.

4. A tyre as claimed in claim 1 or claim 2, wherein the slot extends longitudinally of the tread portion.

5. A tyre as claimed in any one of claims 1 to 4, wherein there are a plurality of slots.

6. A tyre as claimed in any one of claims 1 to 5, wherein the slot is continuous.

7. A tyre as claimed in claim 5, wherein there are longitudinally-extending slots spaced transversely across the tread portion at the centre of the tread portion, and one adjacent to each shoulder of the tyre.

8. A tyre as claimed in anyone of claims 1 to 7, wherein the bottom of grooves are provided with a shaft of material in which the indicator strip can be located.

9. A tyre as claimed in any one of claims 1 to 8, wherein the indicator strip is solid or hollow.

10. A tyre as claimed in any one of claims 1 to 9, wherein the slot extends into the tread portion above the bottom of the grooves by a height which is a legally defined minimum height of tread to enable the tyre to be legally used.

1 1. A tyre as claimed in claim 10, wherein the legally defined minimum height is 1.6 mm.

12. A tyre as claimed in claim 10 or claim 11, wherein the indicator strip is initially visible when the tread portion has worn to the legally defined minimum height.

13. A tyre as claimed in any one of claims 1 to 12, wherein the indicator strip is of material of the same density as the tread portion.

14. A tyre as claimed in any one of claims 1 to 13, wherein the indicator strip is of the same material as the tread portion.

15. A method of making a tyre including forming a carcass of a tyre, extruding a tread portion of a tyre, cutting the tread portion to lengths, forming at least one slot in the lower surface of the tread portion, the slot being sized and shaped to receive an indicator strip, placing the indicator strip in the slot, the indicator strip being of a contrasting colour to the tread portion, assembling the tread portion on the carcass, and curing the assembly in a curing press.

16. A method of making a tread stock for use in retreading a tyre, the method including extruding the tread stock, cutting the tread portion to length, forming at least one slot in the lower surface of the tread stock, the slot being sized and shaped to receive therein an indicator strip, placing the indicator strip in the slot, applying an adhesive layer to the lower surface of the tread stock, and placing a removable cover over the adhesive layer.

17. A method as claimed in claim 15 or claim 16, wherein the slot is formed in the tread portion at the time of extrusion and/or cutting to length.

18. A method as claimed in any one of claims 15 to 17, wherein an adhesive is applied to the slot prior to insertion of the indicator strip.

19. A method as claimed in any one of claims 15 to 18, wherein the insert strip is progressively placed in the slot from one end of the slot to the other end of the slot.

20. A method as claims in any one of claims 15 to 19, wherein the indicator strip is extruded into the slot.

21. A tyre for a vehicle substantially as hereinbefore described with reference to the accompanying illustrative drawings.

22. A method of manufacturing a tyre for a vehicle substantially as hereinbefore described with reference to the accompanying drawings.

23. A method of making a tread stock for use in retreading a tyre substantially as hereinbefore described with reference to the accompanying drawings.