Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-10-29
2002-04-23
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C156S114000
Reexamination Certificate
active
06374886
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to vehicle tires comprising a tire carcass and side walls, wherein at least one layer of rubber forms a tire tread with a tread surface on top of the carcass. A tread pattern is provided in said tread rubber layer comprising a plurality of blocks at least in the circumferential direction of the tire and separated by grooves, and anti-skid stud holes within at least some of said blocks. Anti-skid studs are inserted in said stud holes, said studs comprising having a flat lamellar configuration with a stem portion and a basal portion. The diameter or the main and minor dimensions of said stud holes has/have a predetermined relationship to the respective dimensions of said studs. The invention further relates to vehicle tires of said type with a tire tread comprising at least two layers of rubber, wherein the base of the tread consists of a first harder rubber layer next to the tire carcass and the cap of the tread consists of a second more resilient rubber layer forming the tread surface, and elastic cushions disposed at the interior of the anti-skid stud holes.
DESCRIPTION OF THE RELATED ART
There have lately been various attempts to enhance the grip of winter tires in particular. The grip can be increased with a pattern on the tread of the tire especially with a view to driving on snow. However, in driving on a snowy or icy roadway, the properties of the rubber forming the tread and the anti-skid studs fixed to the tread will have a more notable impact. The friction between the road surface covered with ice and/or compacted snow and the tread of the tire can be increased with the use of special friction rubber qualities in the tread. Such rubber qualities are very soft, i.e. they have high elasticity and a hardness typically in the range from 55 to 65 sh° A.
They are commonly called “cap rubbers”. If, however, the rubber layer on top of the tire carcass is throughout formed of such soft cap rubber alone all the way to the tread surface, the tire will sway too much during driving to be apt for many purposes of use, precisely due to this excessive elasticity. This is why the treads of tires have lately been formed of a combination of such soft cap rubber and a harder rubber layer as disclosed in publication US-4 603 721. The harder rubber quality, placed closer to the tire carcass, is commonly called “base rubber”, and its hardness is typically in the range from 65 to 75 sh° A. The surface pattern being pressed into this kind of a rubber layer composite within a tire mold for vulcanization, the major part of the height of the blocks for the surface pattern, i.e. the vertical dimension of the grooves from the tread surface, will consist of the more elastic cap rubber, whereas the portion between the surface pattern and the carcass and a part of the height of the surface pattern will be chiefly of the harder base rubber. This design yields a “friction tire”, having a high friction coefficient with regard to a hard driving surface, while the roadholding and driving properties of the tire still remains good owing to the harder base rubber layer. This kind of “friction tires” are expressly intended to be used and are used without any kind of additional anti-skid elements, in order to avoid wearing of roads.
The use of a harder base rubber layer between the surface pattern and the tire carcass, and partly within the surface pattern blocks, entails the same drawbacks as in the case of more conventional tires, in which the tire tread is entirely made of a harder rubber than the cap rubber mentioned above. When such a tire is provided with conventional anti-skid studs in the stud holes, the bottom flange of the stud within the tire tread opposite to the stud tip will be located in and against this hard rubber, and as a consequence of this, a relatively great force will be required on a road to press the tip of the stud to the plane of the tread. This will occur in any case under the weight of the vehicle, but the great penetrating force of the stud will entail considerable wear of the road surface and also considerable tire noise. What is more, this great penetrating force will prevent studs from being placed in the central parts of the tire, where the grip of the stud would otherwise be utilized at maximum. Current regulations explicitly forbid placing studs in the central parts of tires and allow studs to be placed close to the tire shoulder alone, where surface pressure between tire and road is lower, reducing wear of the road but also impairing the grip of the studs.
Publication JP-61-18506 discloses a tire with a supporting ring-band of a soft rubber quality extending in the circumferential direction of the tire and embedded in the tire tread between the carcass and outer parts of the tread. The width of this supporting ring-band is smaller than the total width of the tire and the supporting ring-band is positioned in the area of studs only. This construction of the tire tread destroys the at least the driving properties of the tire, making it to sway if the ring-band is made broad enough to allow a proper positioning of studs. If the supporting ring-band is kept so narrow that the acceptable driving properties are maintained the studs can be placed within so narrow an area that their effectiveness is considerably lowered.
Publication U.S. Pat. No. 3,831,655 discloses a special anti-skid spike for vehicle tires with at least one individual elastic member between the foot portion of the spike and the bottom of the hole in the tire tread. The individual elastic member may be prepared from a rubber material or a plastic material or it can be a metallic spring or a combination thereof. This disclosed elastic member is in each case fixed to the underside of the foot portion of the spike and preferably adhered either with glue or vulcanization thereto. The disclosed spike construction with an elastic member requires fabrication of tiny springy elements whether of rubber, plastic or metal, and an elaborate adhering of these elements to spikes, and/or a complicated insertion method to retain a proper mutual position of each of the springy elements and the respective spike bodies. The arrangement is impractical and the tires produced would be too expensive.
The well-known anti-skid studs are typically made up of a round pin of a cemented carbide, so called “hard-metal” composed of mainly tungsten carbide as the hard component and cobalt in small amounts—generally from 5% to 10%—as the binder, placed in a larger round body of steel, having a stem portion towards the tread surface of the tire and a flange-like basal portion towards the carcass of the tire. The manufacturing is relatively complicated and expensive, because the steel body has to be machined, the cemented carbide pin has to be moldpressed and sintered, and finally these parts shall be soldered together. These anti-skid elements are pressed into holes which are preformed in the tire tread. They are known to have the disadvantages of a relatively large weight—density of WC is 15.7 g/cm
3
—and a tendency to increase their projection measured outwards from the tread surface during use, thus causing studs to become detached during the wear of the tire. The high stud weight and the large stud projection cause severe wear of the road surface and high tire noise. The tendency of the studs to become detached is also increased by the tilting of the stud, made possible by this known structure. Efforts have been made to reduce this tendency of the studs to become detached by using a stud design described in publication DE-28 04 939, in which the stud is V-shaped in cross-sectional planes parallel to the tread surface and which has, over the stud length, dovetail-like projections pointing outwards from the inside of the tire, but no actual basal flange. This design very effectively prevents the tilting of the stud and possibly thus, together with the dovetail projections, reduces the tendency of the studs to become detached. However, since studs of the type described have in the orientation of the
Klarquist & Sparkman, LLP
Maki Steven D.
Nokian Tyres Plc.
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