IE43773B1 - Vehicle tyres - Google Patents

Description

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

Hitherto known and used studded tyres have been successful in providing an improved grip on ice-,or snowcovered surfaces and have resulted in little loss of grip when operating on road surfaces free of ice and 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 and snow and they cannot therefore be considered entirely satisfactory.

Investigations have been made previously to determine the parameters affecting road surface damage and have been found to include weight of stud, distance between base of stud and tyre reinforcement carcass, length of stud and other shape and dimensional features of the studs. Optimisation of 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 2. 3 7 7 3 of the stud, 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.

The present invention, which is a modification of the invention described in our Patent Specification No. 41978 provides a studded tyre which gives a good grip on snow and ice but which is a considerable improvement on conventional studded tyres in regard to reduced damage to road surfaces in use.

Accordingly the present invention provides a studded tyre having an array of studs secured to and protruding from the tyre tread, in which the studs are disposed in two bands extending circumferentially around the tyre tread and separated by a stud-free circumferential band of tyre tread, the stud-free band bridging the midcircumferential plane of the tyre and having a width of at least 25% of the tread width, and the density of studs in relation to the total tread area (as herein defined) being in the range 1 stud per 4400 mm to 1 stud per 3200 mm .

By total tread area is meant the area of the entire tread region of the tyre - i»e.total tread area = tread width x tread circumference. The tread width is the axial width of the ground-contacting surface of the tread. The tread circumference is as measured at the mid-circumferential plane.

In a preferred embodiment of the invention the 3. studs are disposed in rows extending circumferentialy around the tyre, A convenient total number (S) of studs per row is given by the expression S = 277.8 x 2 x total tread area (mm )/R where R is the number of rows.

The two studded hands are preferably of substantially equal width. Preferably they contain equal numbers of rows of studs resulting in an even number of rows in total. Convenient numbers of rows, given by way of example, for various tread widths are given in the following Table.

TABLE TREAD WIDTH (W) NUMBER OF ROWS OF STUDS mm 75.0 to 113.9 4 114.0 to 167.9 6 168.0 to 214.9 8 215.0 to 262.9 10 263.0 to 311.0 12 Preferably the rows of studs are substantially uniformly spaced across the width of their band.

The studs in each row preferably are uniformly spaced so as to assist in reducing road surface damage, but the pitch between successive studs may, alternatively, he non-uniform so as to assist in reducing road surface noise. 3 7 7 3 4.

The stud-free band bridging the mid-circumferential plane preferably represents at least 33% of the tyre tread widtli.

Several embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:Figures 1 to 4 show the configurations of studs on the tread portions of tyres provided respectively with 4, 6, 8 and 10 circumferential rows of studs. In each case the density of studs in relation to the total tread area (as herein defined) is in the range one stud per 4400 mm 2 to one stud per 3200 mm .

The tread 10 of a tyre having a tread width (W) of 90 mm is shown in Figure 1 and is provided with studs ti arranged in two bands 12, 13 of equal widths A/2 and separated by a central stud-free band 14 bridging the mid-circumferential plane of the tyre. The term stud-free used herein refers to freedom from whole studs. In this respect the halves of the studs of rows 12b and 13a in Figure 1 adjacent band B are to be disregarded. Similar considerations apply to the studs shown in Figures 2, 3 and 4 lying in the rows bordering the stud-free bands B. The tread has four rows 12a, 12b, 13a, 13b, two in each band 12, 13. The width B of the stud-free band represents approximately 40% of the tread width. The centres of the studs in the two outermost rows are inset by a distance C of 10 mm from the edge of the tread. The width of the studded bands is defined respectively, by the distance between neighbouring . stud rows 12a and 12b and 13a and 13b'. '(In this and the following figures, the total width of the studded bands is A and the width of the stud-free band is B, whilst C denotes the distance (10mm) by which the centres of the outermost rows of studs are inset from the adjacent edge of the tread).

In. a preferred form of the invention the total number of studs per row is given to the nearest integer —6 2 by the expression 277.8 x 10 x total tread area (mm )/R where R is the number of rows of studs. Preferably the studs in each row are uniformly spaced around the circumference of the tyre at a pitch denoted by P. Studs in successive rows across the width of the tyre are staggered by one third of the pitch P as illustrated, the studs in the two outer rows thus being positioned at similar angular positions around the periphery of the tyre.

In another embodiment of the invention, illustrated in Figure 2 of the accompanying drawings, a tyre tread 20 has a width such that#in accordance with the expression given above and the Table^it is provided with studs 21 disposed in six rows, three rows in each of two bands symmetrically disposed with respect to the mid-circumferential & plane of the tyre. The stud-free band/defined by the space between the studded bands has a width of approximately 30% of the tread width.

In this embodiment the studs in each row are uniformly spaced at a pitch P and the studs in successive rows across the tread width are staggered relative to each other by a 6. distance of 2P/5 such that the studs in the two outermost rows are positioned at similar angular positions around the periphery of the tyre.

In the construction shown in Figure 3 a tyre tread 30 has 8 rows of studs 31, arranged in two studded bands symmetrically disposed with respect to the midcircumferential plane of the tyre, the studs in each row being uniformly spaced at a pitch P.

The studs of the four successive rows in each band are positioned such that the studs in the neighbouring rows are staggered by distance of 3P/7, and 2P/7 and 3P/7 successively, and studs in the two outermost rows over the width of tread are positioned at similar angular positions around the periphery of the tyre.

A tyre tread having two studded bands symmetrically disposed with respect to the mid-circumferential plane of the tyre, each band containing 5 rows of studs is illustrated in Figure A. The studs of the rows in each band are staggered relative to each other and unlike the abovedescribed stud configurations the staggering of the studs in one band is different from that of the studs in the other band. The studs in the two outermost rows over the width of the tread are, however, located at similar angular positions around the periphery of the tyre.

As with the construction shown in Figure 2, the constructions of each of Figures 3 and A have stud-free bands 3 representing approximately 30/ of the tread width.

Claims (16)

1. A studded tyre having an array of studs secured to and protruding from the tyre tread, in which the studs are disposed in two hands extending circumferentially around the tyre tread and separated by a stud-free circumferential band of tyre tread, the stud-free band bridging the mid-circumferential plane of the tyre and having a width of at least 25% of the tread width, and the density of studs in relation to the total tread area (as herein defined) being in the range 1 stud per 4400 mm^ to 1 stud per 3200 mm^.

2. A tyre according to claim 1 in which the stud-free band separating the two studded bands has a width of at least 33% of the tyre tread width.

3. A tyre according to claim 1 or 2 in which the studs are disposed in rows extending circumferentially of the tyre.

4. A tyre according to claim 3 in which the studs in each row are substantially uniformly spaced.

5. A tyre according to claim 3 or.4, in which each studded band contains two, three, four or five parallel rows of studs.

6. A tyre according to claim 3, 4 or 5, in which the rows in each band are-uniformly spaced across the width of the band.

7. A tyre according to any of claims 3 to 6, which has a tread width in the range from 75.0 to 113.9 mm and the studs are arranged in four circumferential rows. 8.

8. A tyre according to any of claims 5 to 6, which has a tread width in the range from 114.0 to 167.9 mm and the studs are arranged in six circumferential rows.

9. A tyre according to any of claims 3 to 6, which has a tread width in the range from 168.0 to 214.9 mm and the studs are arranged in eight circumferential rows.

10. A tyre according to any of claims 3 to 6, which has a tread width in the range from 215.0 to 262.9 mm and the studs are arranged in ten circumferential rows.

11. A tyre according to any of claims 3 to 6, which has a tread width in the range from 263.0 to 311.0 mm and the studs are arranged in twelve circumferential rows.

12. A tyre according to any of claims 7 to 11 in which the number of studs in each row, to the nearest integer, is 277.8 x 10“^ times the total tread area, in square millimetres, divided by the number of rows.

13. A studded tyre substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

14. A studded tyre substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

15. A studded tyre substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

16. A studded tyre substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.