Claims:WE CLAIM:

1. A modified agricultural tyre adapted to be employed in non-agricultural areas for road haulage applications, said tyre comprising a tread consisting of a first row of central tread blocks (1) disposed on and upstanding from the circumference of the tyre, said first row of tread blocks (1) being axially centred along the median plane (X-X’) of the tyre, two intermediate rows of tread blocks (2) disposed along the tyre circumference one each on either side of said first row of central tread blocks (1) and disposed axially away from the median plane (X-X’) of the tyre and two outermost rows of shoulder lugs (3) each disposed at either shoulder of the tyre along the tyre circumference and each disposed axially closer to the edge of the shoulder of the tyre,

characterized in that:
- said central row of tread blocks (1), said intermediate rows of tread blocks (2) and said outermost rows of shoulder lugs (3) together constituting a tread band having a width (W) in the transverse direction of the tyre, said tread band being composed of a central portion (L1) disposed along the median plane (X-X’) of the tyre and two lateral portions (L2, L3) disposed each on either side of the central portion (L1) along the axial direction of the tyre, said central row of tread blocks (1) being disposed axially on said central portion (L1) and said intermediate rows of tread blocks (2) and said outermost rows of shoulder lugs (3) being disposed axially on said lateral portions (L2, L3) respectively, said central row of tread blocks (1), said intermediate rows of tread blocks (2) and said outermost rows of shoulder lugs (3) being supported upon and by means of a unitary underlying rubber network (4) which connects the central row of tread blocks (1) along the circumferential direction and each of the two intermediate and outermost rows of tread blocks and lugs (2 and 3) along a lateral direction, said unitary rubber network (4) constituting a binding means for stabilising and holding the said rows of blocks (1, 2, 3) in steady position.

2. A modified agricultural tyre as claimed in claim 1 wherein the sum of the transverse widths of the central portion (L1) and the four lateral portions (L2, L3, L2 and L3) is equal to the transverse width (W) of the tread band.

3. A modified agricultural tyre as claimed in claim 1 or 2 wherein transverse width of the central portion (L1) is twice the transverse widths of each of the lateral portions (L2 or L3), i.e. the transverse width of the central portion (L1) is equal to the sum of the transverse widths of each pair of lateral portions (L2, L3).
4. A modified agricultural tyre as claimed in claim 3 wherein the transverse width of each lateral portion (L2) is equal to the transverse width of each lateral portion (L3).
5. A modified agricultural tyre as claimed in any one of claims 1 to 4 wherein the rubber to void ratio of the central row of tread blocks (1) lies in the range of 40% to 46 % with respect to the central portion (L1) of the tyre.
6. A modified agricultural tyre as claimed in any one of claims 1 to 5 wherein the rubber to void ratio of the intermediate rows of tread blocks (2) lies in the range of 27% to 33 % with respect to the lateral portion (L2) of the tyre and the rubber to void ratio of the the outermost rows of shoulder lugs (3) lies in the range of 27% to 33 % with respect to the outer lateral portion (L3) of the tyre.
7. A modified agricultural tyre as claimed in any one of claims 1 to 6 wherein the linear distance (E) from the leading edge 5 of an outermost block 3 to the trailing edge 6 thereof measured at the shoulder (7) of the tyre represents the width (E) of the outermost block 3, the linear distance (E1) from the leading edge 8 of the outermost block 3 remote from the shoulder 7 to the frontal leading edge 9 of the intermediate block 2 nearest to it represents the amount of near-side offset of the outermost block 3 from the intermediate block 2 and the linear distance (E2) from the trailing edge of the outermost block remote from the shoulder to the trailing edge 10 of the intermediate block 2 remote from the central blocks 1 represents the amount of far-side offset of the outermost block 3 from the intermediate block 2.

8. A modified agricultural tyre as claimed in claim 7 wherein the near-side offset of the two blocks 2, 3 is equivalent to a distance of from 75% to 85% of the width (E) of said outermost block and the far-side offset of the two blocks 2, 3 is equivalent to a distance of from 70% to 80% of the width of said outermost block 3.
Dated this 27th day of May, 2020.

ROBIN MARK GROSER
of GROSER & GROSER
REGD. IND. PA 505
AGENT FOR THE APPLICANTS

, Description:
The present invention relates to an improved tyre adapted for and capable of both agricultural and road haulage applications. In particular, the invention relates to a modified agricultural tractor tyre which is capable of employment during the off-season for road haulage applications and which overcomes the problems encountered when conventional agricultural tractor tyres are employed for road usage.

It is perhaps not known or appreciated that tractors, which are conventionally fitted with tyres adapted to be employed for agricultural purposes, spend less than fifty per cent of their work time on agricultural occupations. This is only natural since the use of tractors for agriculture is dictated by the initial ploughing of fields and the subsequent reaping and harvesting of crops. In between those two periods, the tractors left with fallow time.

As a result, tractors are employed in their downtime or off season for transporting material from one place to another. In fact, if one were to calculate it, tractors spend more than half their work time away from agricultural areas on surfaces such as roads, highways and hard unpaved thoroughfares and are frequently coupled to heavy trailers. When employed in this manner, the tyres of tractors are required for reason of the surfaces they interact with to evince increased traction as well as to provide good ride comfort and substantially even wear throughout the tyre tread. By providing for even wear across the width and circumference of the tyre tread ensures the enhancement of mileage and comfort and the lessening of vibrations and these represent one of the main customer requirements for agricultural tyres which are compelled to operate on hard road surfaces.

When tyres, which are manufactured essentially for agricultural usage, are employed in road haulage applications, they are ill-equipped for the conditions they are forced to face and as a result such tyres suffer from the problems of uneven wear or alternate lug wear which causes the tyre to lose its desired degree of traction. The expression “alternate lug wear” implies the difference in the rate of wear which is visible and can be measured by the difference in tread depth between alternate lugs, i.e. lugs 1 and 3, 2 and 4 , 5 and 7, 6 and 8 and so on, in the same position. By way of explanation, tyre lugs which are also known as a tread blocks are independent freestanding rubber blocks positioned around the circumference of a tyre.

Moreover, tyres intended for employment in road haulage applications are usually tyres with radial construction. Such road haulage tyres require good tread stiffness and contact along the footprint. To explain this, the most important part of tyre design is how the tyre interacts with the surface with which it makes contact. This interaction area is known as the “tyre footprint” or “contact patch” and it is within this area that tyre forces and moments are generated giving rise to tyre wear. Tyres manufactured for agricultural purposes are, therefore, subject to greater deterioration when employed for road haulage applications.

It is thus a primary object of this invention to provide an improved tractor tyre which evinces good tread stiffness and contact along the tyre footprint, affords even and uniform lug wear and maintains the desired degree of traction irrespective of the surface or terrain with which it comes into contact.

It is a more specific object of the invention to provide the requisite modifications to a tractor tyre intended mainly for operation in agricultural areas so as to render it capable of being employed for road haulage applications without the difficulties and problems of uneven wear, alternate lug wear, lack of tread stiffness or improper contact along the footprint as stated above.

It must be appreciated and understood that the provision of lugs or tread blocks on the circumference of a tyre is not merely a design feature or one which is intended to provide a visually pleasing effect to the tyre. On the contrary, the tread blocks and lugs and the manner in which they are set out or arranged on the surface of the tyre circumference provide a technical advantage and great utility. As stated above, tread blocks are individual, freestanding elements arranged circumferentially around the surface of a tyre. Lugs are very large tread blocks which are located on the circumference of the tyre extending from the centre thereof to the shoulder of the tyre and are employed mainly for off-road all-terrain agricultural vehicles such as tractors.

It was discovered several decades ago that the provision of lugs and/or tread blocks on the outer circumference of a tyre greatly improved the traction which a tyre could display. Furthermore, the provision of raised tread blocks and lugs on the circumference of the tyre also resulted in the simultaneous provision of valley-like gaps between the raised tread blocks. These gaps are referred to as a tread voids and these allow the tyre to flex slightly thereby giving it increased traction and handling. Apart from this advantage, the tread void is vital in increasing the tyre’s grip on the road in wet weather since the gaps of such tread voids direct water, mud or snow on the surface of the road away from the tyre and this helps to prevent hydroplaning and maintains the tyre’s grip on the road.

From a very modest beginning following its incorporation on September 28, 1972, the applicant company is now the largest tyre manufacturing company in India and the fourteenth largest tyre manufacturer in the world with an annual consolidated revenue in March, 2019 of US $ 2.48 billion. The applicants are thus extremely well versed in tyre technology and possess a wealth of experience with respect thereto.

The applicants have brought to bear all their experience in attempting to solve the problems described above when tyres intended essentially for agricultural and off-road employment are compelled to double as tyres employed for road haulage. In attempting to solve the problems and difficulties stated above, the applicants and their inventors would have studied and examined the representative prior art in the form of hundreds of technical publications, patent specifications and reference books.

The research carried out by the applicants has revealed that one of the earliest attempts to convert or modify tyres essentially created for agricultural use for road haulage formed the subject of US Patent No. 3,237,669 of the well-known French tyre manufacturer Michelin. The object of this patent was the modification of tyres employed essentially in agricultural locations on vehicles such as tractors, earth movers, earth working equipment and off-highway trucks for alternative employment on roads, highways and the like.

US Patent No. 3,237,669 provided an all-terrain tyre with a casing having a tread portion including a surface extending circumferentially of said casing, said tread portion comprising a row of spaced apart substantially polygonal blocks projecting outwardly from and disposed centrally of the surface of said casing, said blocks having angularly related leading and trailing faces, a bar extending laterally from one of said trailing faces on each of said blocks and projecting outwardly from said surface, said bars extending alternately in opposite directions and separated from said trailing face by a groove and rib portions of less height than said blocks projecting outwardly from said surface, said rib portions spanning the spaces between said blocks and reinforcing said blocks without unduly stiffening the central portion of said tread.

Michelin were also responsible for the manufacture of another modified tyre (illustrated in greater detail in the accompanying drawings) which that company markets under the brands “Agribib” and “Agribib 2”. These are tyres for a vehicle for agricultural use such as an agricultural tractor or agro-industrial vehicle. The tread surface of these tyres is provided with a number of angularly disposed ribs extending inwardly from the shoulder of the tyre tread towards the central axis of the tread and provided offset from one another.

Other attempts to modify agricultural tyres to facilitate their employment as all-terrain tyres have also been carried out by Michelin as witnessed by their published International Patent Application No. 2019/008257 directed to the provision of a tread for an agricultural vehicle tyre which reduced the risk of damage to the leading faces of the lug wings of such tyre by post-harvest stubble and other non-agricultural terrain while maintaining good traction in the fields. This was the tyre marketed by Michelin under the brand “Roadbib”

Unfortunately, despite the efforts made by Michelin and other tyre manufacturers, when it came to modifying the tread of the tyre for an agricultural vehicle, such efforts still left much to be desired. Thus, such modified tyres suffered from three significant defects or drawbacks. First of all, there was a tendency for the tread blocks and/or lugs to shuffle as a result of improper block stability. This in turn gave rise to improper flat contact between the tyre and the road surface with non-uniform pressure across the tyre footprint. Finally, the shuffling between the tread blocks and the non-uniform pressure across the tyre footprint gave rise to uneven and alternate tread and lug wear and made for a very uncomfortable drive on hard surfaces like roads or highways.

It has, therefore, been the applicant’s concerted effort to overcome these problems, the solution of which they have succeeded in achieving by the present invention which substantially removes the problems, reduces the adverse effect of footprint contact and thereby minimises uneven tread wear.

With all these objectives in mind, the present invention provides an improved agricultural tyre adapted to be employed in non-agricultural areas for road haulage applications without the defects and drawbacks prevalent in earlier modified agricultural tyres.

Accordingly, the present invention provides a modified agricultural tyre adapted to be employed in non-agricultural areas for road haulage applications, said tyre comprising a tread consisting of a first row of central tread blocks disposed on and upstanding from the circumference of the tyre, said first row of tread blocks being axially centred along the median plane of the tyre, two intermediate rows of tread blocks disposed along the tyre circumference one each on either side of said first row of central tread blocks and disposed axially away from the median plane of the tyre and two outermost rows of shoulder lugs each disposed at either shoulder of the tyre along the tyre circumference and each disposed axially closer to the edge of the shoulder of the tyre than to the two intermediate rows of tread blocks,

characterized in that:
said central row of tread blocks (1), said intermediate rows of tread blocks (2) and said outermost rows of shoulder lugs (3) together constituting a tread band having a width (W) in the transverse direction of the tyre, said tread band being composed of a central portion (L1) disposed along the equatorial plane (X-X’) of the tyre and two lateral portions (L2, L3) disposed each on either side of the central portion (L1) along the axial direction of the tyre, said central row of tread blocks (1) being disposed axially on said central portion (L1) and said intermediate rows of tread blocks (2) and said outermost rows of shoulder lugs (3) being disposed axially on said lateral portions (L2, L3) respectively, said central row of tread blocks (1), said intermediate rows of tread blocks (2) and said outermost rows of shoulder lugs (3) being supported upon and by means of a unitary underlying rubber network (4) which connects the central row of tread blocks (1) along the circumferential direction and each of the two intermediate and outermost rows of tread blocks and lugs (2 and 3) along a lateral direction, said unitary rubber network (4) constituting a binding means for stabilising and holding the said rows of blocks (1, 2, 3) in steady position.

Preferably, the sum of the transverse widths of the central portion (L1) and the four lateral portions (L2, L3, L2 and L3) is equal to the transverse width of the tread portion (W).

More preferably, the transverse width of the central portion (L1) is twice the transverse widths of each of the lateral portions (L2 or L3). In other words, the transverse width of the central portion (L1) is equal to the sum of the transverse widths of each pair of lateral portions (L2, L3).

Still further, the transverse width of each lateral portion (L2) is equal to the transverse width of each lateral portion (L3).
According to a preferred embodiment, the rubber to void ratio of the central row of tread blocks (1) lies in the range of 40% to 46 % with respect to the central portion (L1) of the tyre while the rubber to void ratio of the intermediate rows of tread blocks (2) lies in the range of 27% to 33 % with respect to the lateral portion (L2) of the tyre and the rubber to void ratio of the the outermost rows of shoulder lugs (3) lies in the range of 27% to 33 % with respect to the outer lateral portion (L3) of the tyre.

According to a preferred feature of the present invention, each of the blocks of the centre, intermediate and outermost rows is approximately polygonal in shape. The linear distance from the leading edge of an outermost block to the trailing edge thereof measured at the shoulder of the tyre represents the width (E) of the outermost block. The linear distance (E1) from the leading edge of the outermost block remote from the shoulder to the frontal leading edge of the intermediate block nearest to it represents the amount of near-side offset of the outermost block from the intermediate block. The linear distance (E2) from the trailing edge of the outermost block remote from the shoulder to the trailing edge of the intermediate block remote from the central blocks represents the amount of far-side offset of the outermost block from the intermediate block.

The near-side offset of the two blocks is equivalent to a distance of from 75% to 85% of the width (E) of said outermost block. The far-side offset of the two blocks is equivalent to a distance of from 70% to 80% of the width of said outermost block.

It has been found that when the tyre according to present invention makes contact with the tyre footprint on the engaging road surface, the amount of rubber making contact with the road surface in the footprint is in the range of 28% to 42% with respect to the total area of the footprint.

The invention will now be described in greater detail with reference to the accompanying drawings in which:

Figure 1 is a plan view of the tyre tread of prior Michelin US Patent No. 3,237,669;

Figure 2 shows photographic representations of the treads of the tyres forming the subject of Michelin’s published International Patent Application No. 2019/008257 marketed by them under the brands “Agribib” and “Agribib 2”;

Figure 3 is a photographic representation of the tread of the tyre produced and marketed by Michelin under the brand “Roadbib”;

Figure 4 is a plan view of the tread of the tyre of the present invention; and

Figure 5 is a further more detailed plan view of the tread of the tyre of the present invention identifying preferred embodiments thereof.

Referring now to Figure 1, a typical all-terrain tyre 10 has a tread surface 11 which in the central region is provided with outwardly extending tread blocks 12, 13, 14, 15 arranged in a row extending circumferentially of the tread. Each of the blocks, as illustrated, is of a polygonal shape and may be of an irregular hexagonal shape having a wider leading edge 16 and a narrower leading edge 17, both disposed at an angle between about 40° and 80° to the median plane of the tyre casing. Similarly, the trailing edge of each block, for example the block 12, is provided with a narrow edge 18 and a wider edge 19, these edges likewise being disposed at an angle between about 40° and 80° relative to the median plane of the tyre casing.

In a typical tyre, the inclination of the surfaces 16, 17, 18 and 19 is approximately 60°. While the edges 16 to 19 are shown as straight, they may be curved, if desired. The side edges 20 and 21 of each block may be parallel with the median plane of the tyre or inclined at an angle up to about 15°. These sides and 21 may also be curved somewhat, if desired. Further, as shown in Figure 1, the blocks 12, 13, 14 and 15 are offset alternately with respect to the centre line or median plane of the tyre casing. The amount of offset should be between about 40% and 50% of the width of the blocks in order that a relatively wide centre band of blocks is provided affording a better distribution of the load carried by the tyre and resulting in decrease of the wear of the tyre. In order to reinforce the blocks without unduly stiffening the centre section of the tyre, all of the blocks are connected by means of a rib 22 which extends circumferentially around the tyre.

Without any steadying support for the complex combination of outwardly extending tread blocks 12, 13, 14, 15 and laterally extending bars 24, 25, 26, 27, the tyre of US Patent No. 3,237,669 was unable to control the “shuffle” of the tyre blocks which gave rise to improper contact between the tyre and the road surface resulting in non-uniform pressure across the tyre footprint which in turn gave rise to uneven tread wear.

Each of the tyres of published International Patent Application No. 2019/008257 illustrated in Figure 2 is actually an unmodified agricultural tractor tyre which experienced all the shortcomings and drawbacks of earlier unmodified and even some modified agricultural tyres.

What would appear to be a modified version of the tyres illustrated in Figure 2 is the “Roadbib” tyre illustrated in Figure 3 of the drawings. This tyre represents an improvement over some of the predecessor tyres but still suffered from the drawback of absence of a steadying influence such as the supporting network of the tyre of the present invention.

The improved and modified tyre of the present invention is described with reference to Figure 4 of the drawings which shows a plan view of a part of the tread of such tyre. The tread consists of a first row of central tread blocks 1 disposed along the median plane X-X’ of the tyre. Such central row of tread blocks 1 is disposed upon and are upstanding from the surface of the circumference of the tyre. On either side of the first row of the central tread blocks 1 are two intermediate rows of tread blocks 2. These rows of tread blocks 2 are disposed axially away from the median plane X-X’ of the tyre.

Finally, there are two outermost rows of shoulder lugs 3, each such row being disposed at either edge of the shoulder of the tyre along the circumference thereof. Moreover, such rows of shoulder lugs 3 are disposed axially closer to the edge of the shoulder of the tyre than to the intermediate rows 2.

The essential novel feature of the tyre of the present invention resides in its ability to prevent shuffle or movement from occurring between the tread blocks of the tread. This leads to numerous advantages and overcomes a number of problems as will be seen from the following description. The invention achieves its objectives by providing means in the form of a unitary underlying rubber network 4. This network connects the central row of tread blocks 1 along the circumferential direction of the tyre as well as each of the two intermediate and outermost rows of the tread blocks and lugs 2, 3 along a lateral direction. The said unitary rubber network 4 constitutes a binding force which establishes and holds the said rows of blocks 1, 2 and 3 in steady position.

The tread blocks and lugs 1, 2, 3 of the centre, intermediate and outermost rows of the tread of said tyre can be of any preferred shape but have been found most conveniently to be approximately polygonal. The embodiments shown in Figures 4 and 5 of the drawings disclose an approximate polygonal shape for the several blocks which the applicants have found particularly convenient.

With reference particularly to the embodiment shown in Figure 5, the linear distance (E) from the leading edge 5 of an outermost block 3 to the trailing edge 6 thereof measured at the shoulder (7) of the tyre represents the width (E) of the outermost block 3. The linear distance (E1) from the leading edge 8 of the outermost block 3 remote from the shoulder 7 to the frontal leading edge 9 of the intermediate block 2 nearest to it represents the amount of near-side offset of the outermost block 3 from the intermediate block 2. The linear distance (E2) from the trailing edge 10 of the outermost block 3 remote from the shoulder 7 to the trailing edge 11 of the intermediate block 2 remote from the central blocks 1 represents the amount of far-side offset of the outermost block 3 from the intermediate block 2.

The near-side offset of the two blocks 2, 3 is equivalent to a distance of from 75% to 85% of the width (E) of said outermost block. The far-side offset of the two blocks 2, 3 is equivalent to a distance of from 70% to 80% of the width of said outermost block 3.

Furthermore, by maintaining tread blocks with the offsets indicated, the applicants have found that it is possible to enhance the advantages of providing desired support to the blocks and reducing the deflection thereof by increasing block stiffness which also helps in ensuring even wear.

The description of the invention contained herein includes the best mode known to the inventors for carrying out the invention. Variations of the preferred embodiments disclosed will be apparent to those of ordinary skill in the art upon reading the foregoing description and the accompanying drawings. Accordingly, the invention described includes all modifications and equivalents of the subject matter recited in the claims appended hereto.