Resilient tires and wheels – Tires – resilient – Anti-skid devices
Patent
1992-01-17
1993-09-21
Ball, Michael W.
Resilient tires and wheels
Tires, resilient
Anti-skid devices
B60C 1111
Patent
active
052460487
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the tread of a tire intended to travel on sand or sandy soils, that is to say, soils formed of a mixture of sand and another material in small proportion.
The tread of such a tire is generally formed of blocks of rubber separated from each other in the axial direction of the tire by linear or broken-line longitudinal grooves and/or, in the longitudinal direction of the tire, by transverse grooves which debouch on the edges of the tread. These blocks of rubber are of such a nature that in the contact surface between the tire and hard flat ground they occupy an area of between 40% and 60% of the total area of the contact surface, the tire being mounted on its normal operating rim, bearing the recommended normal load, and being inflated to the corresponding normal pressure recommended for travel on sand.
It is obvious that the conditions of travel recommended for tires of the type in question in the case of travel on sandy tracks or on pure sand are different from the conditions recommended in the case of highway travel: for a given load, it is known that the inflation pressure is lowered, the decrease in inflation pressure possibly amounting to 50% and more of the pressure recommended for highway travel.
Despite this, there are still numerous difficulties encountered by vehicles equipped with such tires when they are confronted by layers of sand of substantial thickness.
SUMMARY OF THE INVENTION
The object of the present invention is to increase the adherence of the tire on sand by modifying the characteristics of the tread, this tire being a tire with radial carcass reinforcement and having a crown reinforcement formed of at least two plies of cords or cables forming small angles of between 10.degree. and 45.degree. with the circumferential direction of the tire.
The tread of the present invention is characterized by the fact that it is provided with closed cells so as to entrap the sandy material or sand without possibility of flow in the contact surface, the area occupied by these cells being at least equal to 20% of the actual area of contact of the tread with hard flat ground, and the maximum depth of the cells being at least equal to 10% of the thickness of the tread.
The area measurements are carried out on flat hard ground to assure reproducibility of the measurements. The actual area of contact of the tread with the ground is the area occupied by the elements in relief which bear on the ground and support the load imposed by the tire. The area occupied by the cells is the area in which there is no contact between the ground and the tread, this lack of contact being due to the presence of the cells alone.
In fact, the tread can possibly be provided with longitudinal and/or transverse grooves in order to impart it a certain flexibility in the longitudinal direction and/or axial direction of the tire, but the area occupied by these grooves in which there is no contact between the tread and the ground is not taken into account.
The cells in accordance with the invention may be of a constant depth, which is then the maximum depth. However, it is advantageous for the cells of the tread to have a variable depth so that the leading walls of the elements in relief which define the cells in the circumferential direction are deeper than their trailing walls, the height of the trailing walls, furthermore, possibly being zero. The filling of the cells by the sand then takes place progressively and more completely. The maximum depth of the cells is advantageously between 20% and 80% of the thickness of the tread, that is to say, the thickness of the rubber above the crown reinforcement.
As seen on the surface of the tread, the cells preferably have the shape of a quadrilateral, with at least two sides parallel to each other and parallel to the axis of rotation of the tire.
As for the surface constituting the bottom of the cells, it is preferably curved in the transverse direction, the curvature facing the ground.
In order to increase the effectivene
REFERENCES:
patent: 3160190 (1964-12-01), Jediny
patent: 3409064 (1968-11-01), Leonard
patent: 3532147 (1970-10-01), Gough et al.
patent: 4311179 (1982-01-01), Hayakawa et al.
patent: 4402356 (1983-09-01), Musy
patent: 4456046 (1984-06-01), Miller
patent: 4664166 (1987-05-01), Benisti
Ball Michael W.
Compagnie Generale des Etablissements Michelin - Michelin & Cie
Krawczyk Nancy T.
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