IE41978B1 - Improvements in or relating to studded tyres - Google Patents

Abstract

1480929 Tyre treads DUNLOP Ltd 10 Dec 1975 [19 Dec 1974] 55061/74 Heading B7C A tyre has a plurality of anti-skid studs protruding from its tread and distributed over the crown and shoulder regions of the tread at an overall density of less than one stud per 20 sq. cm. of the tread surface area. The studs may be arranged in three, Fig. 3, or more (Figs. 6-14, not shown), circumferential rows, the number of rows being equal to W 24 to the nearest integer, where W is the tread width in millimetres. The spacing between rows may be uniform across the tread, and the spacing between studs in a given row may be uniform or non-uniform. The studs may be so distributed that in use at least one but not more than two studs in each row will be present in the tyre/ ground contact patch at any time.

Description

This invention relates to tyres of a kind which are provided with studs to improve the grip given by the tyre when travelling over ice or compacted snow as compared with the grip by a non-studded tyre.

Hitherto known and used studded tyres have been_successful in providing an improved grip on ice and snow covered surfaces and have resulted in little loss of grip when operating on road surfaces free of ice or snow. They do, however, have the disadvantage of tending to cause considerable road surface damage when operating on a surface which is free of ice or snow ahd they cannot therefore be considered entirely satisfactory.

Investigations have been made previously to determine the parameters affecting road surface damage and these have been found to include weight of stud, distance between base of stud and tyre carcass, length of stud and other shape and dimensional features of the studs. Attempts to optimise these parameters to reduce road surface damage without significantly affecting the grip provided have not however been particularly successful.

There has also been developed a stud having a carbide road-surface contacting pin which moves further into a stud body portion if at any time the protrusion of the stud from the tyre exceeds a critical limit. Since road surface wear is dependent on the protruding length of the studs, the impacting force of a stud on a road surface being a function of stud length, excessive impact force and road wear effects can thus be reduced to some extent but only by using this expensive type of stud.

According to a first aspect of the present invention a studded tyre has a plurality of studs secured in and protruding from the tyre tread and distributed over both shoulder and crown regions of the tyre tread at an overall density of less than one stud per twenty square centimetres of the tyre tread surface area.

Preferably the studs are arranged in three or more rows extending around the circumference of the tyre. Preferably the rows are substantially uniformly spaced and positioned across the width of the tyre tread in at least the crown region thereof, substantially the same number of studs then being provided in each row.

Preferably the number of rows of studs is given by the expression W/24 to the nearest integer,where W is the tread width of the tyre in millimetres.

Where the studs are arranged in rows it is preferable that there spacing in each row is such that in use of the tyre at least one but not more than two studs in each row are situated in the tyre ground contact patch.

The studs in each row may be substantially uniformly spaced, or the spacing between successive studs may be non-uniform so as to assist in reducing road surface noise compared with that resulting from use of uniformly spaced studs.

Whilst the present invention requires that the overall stud density is less than 1 stud per 20 square centimetres of the tread surface area, preferably there is less than one stud per 30 square centimetres of surface area. A distribution density substantially equal to one stud per 36 square centimetres of surface area is considered to be particularly desirable. To 1 provide adequate grip on ice and snow covered surfaces it is, however, desirable to provide more than one stud per 45 square centimetres of said surface area.

According to other aspects of the present invention there is provided a tyre and wheel assembly incorporating a studded tyre of the first aspect of the invention, and a vehicle having fitted thereto a studded tyre of the first aspect of the invention.

Several embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:Figure 1 shows a tyre stud; Figure 2 is a sectional view through part of the tread portion of a studded tyre in accordance with the present invention; Figure 3 shows the configuration of the studs on the tread of the tyre shown in Figure 2; Figure 4 is a table giving the preferred number of circumferential rows of studs appropriate to tyres of different tread width; Figure 5 shows a graph for determining the preferred number of studs to be provided on a tyre; Figures 6, 7 and 9-14 show the configuration of studs on the treads of tyres provided respectively with 4, 5,6,7, 8, 9, and 11 circumferential rows of studs, and Figure 8 shows the number of studs in the tyre of Figure 7 lying in the tyre/ground contact patch under normal operating conditions.

A tungsten tipped stud for use on a vehicle tyre is shown in Figure 1. The stud comprises a stem portion 10 (Figure 2), extending from a flanged end portion 11 which serves to enable the stud to be retained in position in the tread portion of a tyre. The stud is shown in Figure 2 in position in the tread portion 12 of a vehicle tyre, and end portion 13 of the stud opposite the flanged end 11 extending a small distance beyond the tread surface 14, and the flanged end 11 being spaced from the tyre reinforcement structure 15 by the rubber material of the tread portion of the tyre.

Referring to Figure 3, the studs are arranged over the tyre tread surface 14 in three rows extending circumferentially around the periphery of the tyre. One row is positioned centrally of the crown region of the tyre tread, and the other two rows are disposed in respective shoulder regions of the tread symmetrically with respect to the mid-circumferential plane of the tyre and each is inset at a distance of 10 mm from the respective edge of the tyre tread. (In this and the other stud distribution figures the letter Z is used to denote the tread width over which the studs are actually positioned).

As also shown in Figure 3, the studs are arranged in groun pattern units each comprising three studs, each group pattern unit extending along the tread a length indicated as P and substantially equivalent to the length of the normal tyre/ ground contact patch. The three studs of each unit are staggered in the three rows such that they lie in a line extending obliquely relative to the circumferential direction of the tyre tread.

Whilst the stud configuration shown in Figure 3 may be employed on tyres of any size, this configuration of studs arranged in three rows is particularly suitable for tyres having tread widths in the region 65 to 83.9 mm. The number of rows of studs most appropriate for tyres of other widths are given by the table shown in Figure 4, The spacing of the studs in each row of the configuration shown in Figure 3 is such that in operation of the tyre at least one but not more than 2 studs in each row lie within the tyre ground contact patch at any one time. The total number of studs provided on the tyre is thus dependent on the number of rows, spacing of the studs in each row and circumferential length of each row. The number of studs may conveniently be determined by use of the graph shown in Figure 5 of the. accompanying drawings, the number of studs per tyre being determined by the 'Q' factor of the tyre,which is.a factor dependent on the tread surface area of the tyre. That is, the Q factor is the product of the tyre tread width and the circumferential length of the tread surface, this latter being π x tread diameter.

Shown inset on the graph of Figure 5 is the formula which representsthe preferred relationship given by the graph between the Q factor and number of studs which it is preferable to provide on a tyre. Having determined the required number of studs, a suitable number per row is then found by dividing the number of rows into the total number of studs and correcting to the nearest integer.

Figures 6, 7 and 9 to 14 give the stud configurations which are preferable for use where tyres are provided respectively with 4, 5, 6, 7, 8, 9, 10 and 11 circumferential rows of studs.

Studded tyres in accordance with the present invention assist in reducing road surface damage compared with conventional studded tyres whilst also ensuring a good grip on both snow and ice covered surfaces as well as clear road surfaces.

Known studded tyres depend on a high concentration of studs in shoulder regions of the tyre tread in order to obtain a good grip, and where, as is usual, ti^studs are arranged in circumferentially extending rows around the tyre tread the studs in each row must be close spaced.

This close spacing of studs has however been found to cause considerable road surface damage. Where more than two studs in any one row contact the road surface at any one moment, relative movement of successive studs due to flexing of the tyre under the action of traction loads and vehicle weight tends to cause a scuffing movement which cuts away at the road surface. This may be substantially avoided by the present invention; by providing studs spaced across both the shoulder and crown regions of the tread surface the overall grip provided by the tyre is maintained at a level comparable with that of a conventional studded tyre despite a reduction in number of studs in the shoulder regions of the tread.

Claims (21)

1. A studded tyre having a plurality of studs secured in and protruding from the tyre tread and distributed over both shoulder and crown regions of the tyre tread at an overall density of less than one stud per twenty square centimetres of the tyre tread surface area. 2. A studded tyre according to claim 1 wherei n there is less than one stud per thirty square centimetres of said surface area. 3. A studded tyre according to claim 2 wherein the distribution density of the studs is substantially equal to one stud per thirty six square centimetres of said surface area.

2. 4. A studded tyre according to claim 1 or 2 wherein the distribution density of the studs is greater than one stud per forty five square centimetres of said surface area.

3. 5. A studded tyre according to any one of the preceding claims wherein the studs are arranged in three or more rows extending around the circumference of the tyre.

4. 6. A studded tyre according to claim 5 wherein the spacing between successive studs in a row is non-uniform.

5. 7. A studded tyre according to claim 4 or claim 6 wherein the rows are substantially uniformly spaced across the width of the tyre in at least the crown region thereof.

6. 8. A studded tyre according to any one of claims 5 to 7 wherein substantially the same number of studs are provided in each row.

7. 9. A studded tyre according to any one of claims 5-8 wherein the number of rows of studs is given by the expression W/24 to the nearest integer z where W is the tread width of the tyre in millimetres.

8. 10. A studded tyre constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

9. 11. A studded,tyre having a tread width in the range 55.0 to 83.9 mm, whose studs are arranged in the repeating pattern shown in Figure 3 of the accompanying drawings.

10. 12. A studded tyre having a tread width in the range 84.0 to 107.9 mm, whose studs are arranged in the repeating pattern shown in Figure 6 of the accompanying drawings.

11. 13. A studded tyre having a tread width in the range 108.0 to 131.9 mm, whose studs are arranged in the repeating pattern shown in Figure 7 of the accompanying drawings.

12. 14. A studded tyre having a tread width in the range 132.0 to 155.9 mm, whose studs are arranged in the repeating pattern shown in Figure 9 of the accompanying drawings.

13. 15. A studded tyre having a tread width in the range 156.0 to 179.9 mm, whose studs are arranged in the repeating pattern shown in Figure 10 of the accompanying drawings.

14. 16. A studded tyre having a tread width in the range 180.0 to 202.9 mm, whose studs are arranged in the repeating pattern shown in Figure 11 of the accompanying drawings.

15. 17. A studded tyre having a tread width in the range 203.0 to 226.9 mm, whose studs are arranged in the repeating pattern shown in Figure 12 of the accompanying drawings.

16. 18. A studded tyre having a tread width in the range 227.0 to 250.9 mm, whose studs are arranged in the repeating pattern shown in Figure 13 of the accompanying drawings.

17. 19. A studded tyre having a tread width in the range 251.0 5 to 275.0 mm, whose studs are arranged in the repeating pattern shown in Figure 14 of the accompanying drawings.

18. 20. A tyre and wheel assembly incorporating a Studded tyre according to any one of the preceding claims.

19. 21. A vehicle having fitted thereto a tyre according to any 10 one of claims 5 to 19 wherein the studs are spaced in each row such that in use not more than two studs in each row are situated in the tyre ground patch.

20. 22. A vehicle having fitted thereto a tyre according to any one of claims 5 to 19 wherein the studs are spaced in each 15 row such that in use at least one stud in each row is situated in the tyre ground patch.

21. 23. A vehicle having fitted thereto any one of claims 1 to 19.