Patent Description:
For as long as studded winter tyres have been used on public roads, a constant challenge in stud design has been striking a balance between high grip, low road wear, and reliable attachment of the stud in the tyre.

As a solution, Oy Airam Ab disclosed in FI <NUM> B a stud comprising with a sleeve around a wear resistant pin - a radical solution at the time. The pin was made from a homogenous material, such as pulverized hard metal, suitable for contacting the road surface. The sleeve, which was intended to sit stationary in the tyre tread, was made from a plastic with has good gliding properties for allowing the pin to translate in the pin hole formed into the sleeve. To prevent rotation of the pin about the center axis of the stud, the pin hole and the pin were provided with cooperating grooves and protrusions that extend along the center axis, respectively. According to <CIT> the form-locking grooves and protrusions were necessary to counteract wear of the harsh road conditions subjected to the plastic sleeve.

As elegant as the solution proposed by <CIT> may be, the invention disclosed therein was never used in a commercial product because the practical application was deemed to lack wear resistance. Plastic materials that exhibit satisfactory gliding properties required by the construction of <CIT>, such as polyamide, polyether ether ketone (PEEK), polycarbonate, ABS, blends of polycarbonate and ABS or polyamide and glass fiber, are injection moulded plastics that have transpired as unideal to endure harsh road conditions.

<CIT> discloses a stud having a sleeve made of thermoplastic vulcanisate and a pin made of metal and provided inside the sleeve.

<CIT> discloses a stud having a hard metal pin inside a rubber sleeve via an anchor made of metal, duroplastic or thermoplastic.

<CIT> and <CIT> both disclose a stud having a having a rubber and a cemented carbide pin provided inside the rubber sleeve.

There still remains, however, a need for a stud that is gentle on the road but able to produce enough grip required for passenger vehicle use.

The present invention is defined by the features of the independent claims.

According to a first aspect of the present invention, there is provided a stud for a pneumatic tyre. The stud includes a sleeve, which comprises or is formed of rubber, a thermoplastic elastomer or silicone based material and which comprises a pin hole. The stud also includes a pin being formed as a unitary piece from one or more than one wear resistant material or compound and inserted into the pin hole.

According to a second aspect of the present invention, there is provided a method of manufacturing such a stud. The method involves providing the pin as a unitary piece of one or more than one wear resistant material, providing the sleeve as unitary piece of rubber, a thermoplastic elastomer or silicone based material, and fitting the pin into the pin hole of the sleeve either as an insert placed in an injection mould or after moulding of the sleeve.

According to a third aspect of the present invention, there is provided a pneumatic winter tyre featuring a rubber tread and a plurality of studs according to the first aspect fitted into the tread.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a pneumatic winter tyre according to the first aspect. The method involves providing a tyre with a tread, providing the tread with a plurality of stud holes, providing a plurality of such studs, and fitting the plurality of studs into the corresponding plurality of stud holes.

Certain embodiments of the present disclosure may include one feature or more that one from the following list:.

Considerable benefits may be gained with at least certain embodiments of the present invention. By constructing the sleeve from a relatively soft material, e.g. thermoplastic elastomer, it has been surprisingly found that the stud is able to withstand the environmental impact better than the relatively hard plastic optimized for gliding that was previously preferred. Thermoplastic elastomers and silicone based materials have been found to endure salt and grease as well as fluctuating temperatures without cracking, a problem associated with conventional gliding plastics.

The properties of the proposed sleeve materials have shown properties enabling use as an excellent transitional adaptor between the relatively very soft winter tyre rubber compound used in the tread and the relatively hard and rigid pin used as the working component of the stud. Said adaptation benefits from the ability to match or at least relatively closely imitate the hardness of the sleeve material with that of the hosting rubber compound. Additionally, the sleeve material provides all the benefits found in the original sleeved stud concept, namely ability to support the pin by controlling axial and radial translation as well as tilting in respect to the longitudinal axis of the stud. The sleeve is also able to control vibrations of the stud thus mitigating the risk of the stud becoming loose in the tyre.

The construction provides surprising design advantages. The pin may be designed relatively freely to exhibit optimal gripping properties with a minimal bottom flange and/or with a flange that is shaped to cater for orientation of the stud in respect of the rolling direction of the tyre. The sleeve, on the other hand, may be designed to provide some or most of axial grip required to keep the pin in the tread. The sleeve may further be designed to connect the optimized pin to the host rubber tread so as to evenly distribute forces exerted by the pin to the rubber. More generally speaking, the sleeve may be designed to adjust the behaviour of the pin in the rubber. It may be understood that such flexibility in design also conveys modularity benefits.

According to a particular embodiment, the hardness of the sleeve material and the hosting tyre rubber are substantially matched with each other. Contrary to intuition, such a solution creates a virtually sleeveless stud, as the environment experienced by the pin is as if there was no sleeve. However, the sleeve nevertheless provides support that would not be present if the pin was simply inserted into the stud hole of the tyre. Accordingly, the pin may be allowed to move in the rubber even across the longitudinal axis thus minimizing scraping, which is detrimental to the road surface.

In the following certain embodiments of the present invention are discussed in greater detail with reference to the accompanying drawings, in which:.

Various embodiments herein described are based on a novel concept of a stud having a rubber, thermoplastic elastomer or silicone based sleeve on a wear resistant pin that is housed in a through hole of the sleeve. The sleeve acts as an adapted between the pin and the host, i.e. tyre tread. By being made of rubber, thermoplastic elastomer or silicone based material, the sleeve is able to transition the flexibility properties of the surrounding rubber tread and the relatively rigid pin. Also, the pin may be constructed as the body of the stud with the sleeve providing support and vibration control for the pin.

<FIG> illustrates a stud <NUM>, i.e. an anti-skid insert, in accordance with at least some embodiments of the present invention. The stud <NUM> has two main components, namely a pin <NUM> and a sleeve <NUM>. The purpose of the pin <NUM> is to form the effective part of the stud <NUM> meaning that the pin <NUM> defines the grip properties of the stud <NUM>. The purpose of the sleeve <NUM> is to fit the pin <NUM> into the tread of a pneumatic tyre. Let us first consider the details of the pin <NUM>.

The pin <NUM> extends along a longitudinal dimension Y between a flange <NUM> and a tip <NUM>. The pin <NUM> defines the tallness T of the stud <NUM> in the longitudinal dimension Y, i.e. the dimension, in which the stud <NUM> exhibits is greatest extension.

In the illustrated example the flange <NUM> has a circular cross section taken across the longitudinal dimension Y. However, other shapes are foreseeable, such as quadrilateral, trapezoidal, chamfered and/or rounded polygons, oval, and various fused shapes, such as two circles merged with a narrow web. The flange <NUM> has a diameter D<NUM>, which may represent the widest part of the illustrated exemplary stud <NUM>. The relationship between the flange diameter D<NUM> and the tip diameter is directly proportional to the static piercing force exerted by the stud <NUM> on the road. It follows that the flange diameter D<NUM> is optimized for providing sufficient but not excess piercing force. In the present context the expression diameter is not limited to the largest measurement taken across a circle but any largest measurement taken across any cross-sectional shape of the stud.

The tip <NUM> is shaped to interact with the road surface. The illustrated tip <NUM> is cylindrical with a flat distal surface. Other shapes are, however, foreseeable, such as star-like, polygons, chamfered and/or rounded polygons, trapezoidal, etc..

The tip <NUM> may be made of the same, optionally homogenous, material as the rest of the pin <NUM>. Alternatively, the material properties of the tip <NUM> may be improved with a locally applied heat treatment. Alternatively, the tip <NUM> may be constructed from a material that is different to the rest of the pin <NUM>.

The pin <NUM> has a shaft <NUM>, which connects the flange <NUM> to the tip <NUM> by extending along the longitudinal dimension Y. The shaft <NUM> may exhibit a generally cylindrical shape meaning that the shaft <NUM> is elongated along the longitudinal dimension Y and has a circular shape in a cross-sectional plane in respect to the longitudinal dimension Y. Because the shaft <NUM> has a diameter smaller than the flange diameter D<NUM>, the pin <NUM> features a transition <NUM> between the shaft <NUM> and the flange <NUM>, such as a rounded of chamfered shape.

The pin <NUM> is preferably constructed as a unitary piece. In the present context the expression "unitary" means that the pin <NUM> is constructed as an integral piece without assembly. In other words the pin is not assembled from a shaft and a flange, for example. The pin <NUM> may be constructed as a homogenous unitary piece meaning that is formed of a single wear resistant material. Suitable materials of the pin <NUM> include, for example, hardened steel, hardened aluminium, an alloy comprising hardened steel or hardened aluminium, composites, and ceramics. The pin <NUM> is preferably made with a powder metallurgy manufacturing process, such as sintering.

Alternatively, the unitary piece may be constructed of more than one wear resistant material by a powder metallurgy process, such as sintering several components into a single mold. Generally speaking, the pin <NUM> may provided with a powder metallurgy process so that several raw materials form one unitary pin. Different raw materials may construct respective different sections of the unitary pin. For example, a first wear resistant material may form the tip section of the pin <NUM>, whereas a second, potentially less wear resistant material, may form the flange section of the pin <NUM>. The materials may then be compacted and sintered to one unitary pin. Sintering of more than two raw materials to provide a pin <NUM> is also foreseen, for example by constructing the tip section of a first material, the shaft section from another material, and the flange section for a third material. The first and third material may be the same or different from one another.

The sleeve <NUM> has a body including or made exclusively of, rubber a thermoplastic elastomer or silicone based material. If the sleeve <NUM> is constructed of rubber, the properties of the rubber are preferably matched with the rubber found on the tread, carcass, or inner liner of the host tyre.

The sleeve <NUM> is preferably constructed from a thermoplastic elastomer that has a hardness that is substantially matched with the host tyre. Accordingly, a working hardness range for the sleeve <NUM> is between <NUM> and <NUM> Shore A. According to a more specific embodiment, the hardness is between <NUM> and <NUM> Shore A, preferably between <NUM> and <NUM> Shore A. According to a very specific embodiment, the hardness is between <NUM> and <NUM> Shore A, preferably between <NUM> and <NUM> Shore A. The shore A value may be measured for <NUM> seconds at <NUM> degrees Celsius, such as defined in ISO <NUM>. Accordingly, the sleeve <NUM> may be considered to be well matched with the hardness of the surrounding tyre compound.

Additionally or alternatively, it may be defined that the elastic modulus of tread is equal to or different by <NUM> per cent or less, preferably <NUM> per cent or less, more preferably <NUM> per cent or less, such as <NUM> per cent or less than the elastic modulus of the sleeve <NUM> under similar measurement circumstances.

According to one embodiment, the sleeve <NUM> comprises or is constructed, such as injection moulded, exclusively from a thermoplastic elastomer or thermoplastic elastomer based material. Foreseeable thermoplastic materials include non-hygroscopic thermoplastic vulcanizates (TPV), such as the Santoprene™ TPV, e.g. in a <NUM> Shore A variant measured for <NUM> seconds at <NUM> degrees Celsius according to ISO <NUM>. Other suitable elastomers include fluoro-liquid silicone rubber (F-LSR), fluorosilicone rubber (FSR), high consistency rubber (HCR), liquid silicone rubber (LSR). SILASTIC™ and XIAMETER™ produced by DOW® exemplify some commercially available alternatives of suitable F-LSR, FSR, HCR, and LSR materials. For example, the SILASTIC™ HCR <NUM> or HCE <NUM> are foreseen as applicable options.

According to a particular embodiment, the sleeve <NUM> comprises or is constructed, such as injection moulded, exclusively from silicone rubber, which is a silicone based material. One practical example of a suitable silicone rubber is XIAMETER™ RBL-<NUM>-<NUM> liquid silicone rubber produced by DOW®. The commercial example has a Shore A hardness of approximately <NUM> measured according to ASTM D2240.

By matching the sleeve and tyre tread hardness with each other the attachment of the sleeve <NUM> and the tyre rubber may, according to optimal circumstances, may be reinforced by cross-linking between the sleeve and tyre material.

The sleeve <NUM> is elongated along the longitudinal dimension Y of the stud <NUM>. The cross-sectional shape of the sleeve <NUM> may be varied in a plane across and/or along the longitudinal axis of the stud <NUM>, i.e. the center axis extending in the longitudinal dimension Y. According to the illustrated example the sleeve <NUM> extends between a generally planar bottom <NUM> and top <NUM> with a varying thickness. The sleeve <NUM> may have a relatively thick middle portion, i.e. a trunk <NUM>. According to the illustrated example the trunk <NUM> has a diameter D<NUM>, which represents the largest cross-section of the sleeve <NUM>. By varying the longitudinal length of the trunk <NUM> along the longitudinal dimension Y and/or the width along the radial dimension X, the supporting properties of the sleeve <NUM> may be adjusted according to the practical application. According to the illustrated example, the trunk diameter D<NUM> is set smaller than the flange diameter D<NUM> with the trunk <NUM> extending approximately one third of the longitudinal extension of the sleeve <NUM>. The relatively narrow bottom <NUM> may transition to the relatively wide trunk <NUM> through a transition <NUM>, which according to the illustrated exemplary embodiment is a chamfered surface. The relatively narrow top <NUM>, on the other hand, may transition to the relatively wide trunk <NUM> through a transition <NUM>, which according to the illustrated exemplary embodiment is a bell surface. The depicted example is provided only as an illustration of at least one working alternative but, naturally, others are also foreseen.

The sleeve <NUM> is provided with a pin hole <NUM>, which according to the illustrated example is a center hole. Alternatively, offset pin holes are also possible. The pin hole <NUM> extends through the sleeve <NUM> for the purpose of receiving the pin <NUM>. The sleeve <NUM> is shorter than the pin <NUM>, whereby the flange <NUM> and the tip <NUM> are exposed and the shaft <NUM> covered by the sleeve <NUM>. As the shaft <NUM> is generally cylindrical, so is the pin hole <NUM>. Other shapes are, however, foreseeable.

The diameter of the pin hole <NUM> may have a nominal size smaller than the diameter of the shaft <NUM>, whereby the fit between the pin <NUM> and the sleeve <NUM> involves deformation of the sleeve <NUM> resulting in minimal degree of freedom for the pin <NUM> to move in respect to the sleeve <NUM>.

According to an embodiment, the sleeve <NUM> is attached to the pin <NUM> only through a mechanical joint, i.e. without the use of an adhesive. The sleeve <NUM> is thus a distinctly different part than the pin <NUM>. It has been found that by omitting adhesives, which are typically used to attach a metal and elastomer pieces together, is preferable because it surprisingly leads to a more controlled movement of the pin <NUM> in respect to the surrounding tyre.

Relative movement may occur between the sleeve <NUM> and the pin <NUM>. In particular, the sleeve <NUM> may translate in respect to the pin <NUM> along the longitudinal dimension Y of the stud <NUM>. Additionally or alternatively, the sleeve <NUM> may rotate in respect to the pin <NUM> about a rotation axis, which extends along the longitudinal dimension Y of the stud <NUM>. Additionally or alternatively, the sleeve <NUM> may translate in respect to the pin <NUM> in the transversal dimension X of the stud <NUM>, i.e. radially. In other words, the movement of the sleeve <NUM> may be axial or radial translation and/or rotation in respect to the pin <NUM>.

The joint between the pin <NUM> and the sleeve <NUM> may also free of a lubricant. Contrary to the teachings of FI <NUM> B, gliding between the pin <NUM> and sleeve <NUM> may also be discouraged so as to provide pin movement only through elastic deformation of the enveloping sleeve material. Alternatively, movement between the pin <NUM> and the sleeve <NUM> is only minimal.

According to an alternative embodiment, the sleeve <NUM> is constructed from more than one material. For example, the sleeve <NUM> may be constructed from a first material forming the inner core of the sleeve and another material forming the outer body surrounding the sleeve. The inner core may comprise a material that is relatively hard compared to the outer body material. For example, the outer material, which engages the surrounding rubber, may have a hardness of between <NUM> and <NUM> Shore A, such as between <NUM> and <NUM> Shore A, preferably between <NUM> and <NUM> Shore A, more preferably between <NUM> and <NUM> Shore A, particularly between <NUM> and <NUM> Shore A. The shore A value may be measured for <NUM> seconds at <NUM> degrees Celsius, such as defined in ISO <NUM>. Accordingly, the outer body is well matched with the hardness of the surrounding tyre compound. The inner core, on the other hand, may comprise a more durable and wear resistant material. Such a two-component construction may be achieved with a two-component injection moulding.

The stud <NUM> may be manufactured by, on the one hand, producing the pin <NUM> from a wear resistant material with an additive manufacturing technique, such as sintering, as a homogenous piece and, on the other hand, producing the sleeve <NUM> from a thermoplastic elastomer or silicone based material with an additive manufacturing technique, such as injection moulding, as a homogenous piece. The wear resistant material preferably has a Riley-Stoker value of <NUM> or more, typically between <NUM> and <NUM>. With the pieces produced, the pin <NUM> may simply be inserted into the pin hole <NUM> preferably without using a lubricant or adhesive.

Alternatively, the sleeve <NUM> may be injection moulded onto a pre-fabricated pin <NUM>, which is placed in the mould as an insert.

As already implied, the proposed stud <NUM> finds industrial applicability in winter tyres, particularly pneumatic winter tyres. Both passenger and commercial vehicles or various weight classes may benefit from such tyre both for road and off-road use. The tread of the tyre may comprise a plurality of such studs <NUM> distributed according to the particular practical application.

The manufacturing of such a tyre is relatively straight forward. First, the tyre body is produced with conventional means resulting in a tread pattern on a carcass formed from a relatively soft material suitable for winter tyre use. The tread rubber compound may have a hardness ranging between <NUM> and <NUM> Shore A, preferably between <NUM> and <NUM> Shore A, at <NUM> degrees Celsius. The tread is provided with a plurality of generally cylindrical stud holes for receiving a corresponding plurality of studs with conventional means. Next, a plurality of studs <NUM> herein proposed are installed into the stud holes flange first preferably with an automated stud gun such that the top <NUM> of the sleeve <NUM> is aligned with the tread surface of the tyre leaving the tip <NUM> of the pin <NUM> exposed and protruding from the tread surface by less than <NUM>, e.g. between <NUM>,<NUM> and <NUM>,<NUM>. With the hardness of the sleeve <NUM> and the tread material selected to substantially match each other, the pin <NUM> is housed in the tread as if the shaft <NUM> was interfaced directly with the tyre. However, the sleeve <NUM> is there between the pin <NUM> and the tread to provide support as well as orientation and vibration control for the pin <NUM>.

According to a preferred embodiment, preceding the studding stage, the stud holes are primed with a cross-linking catalyst, such as a water-based soap solution, for facilitating cross-linking between the sleeve <NUM> and the tyre tread rubber compound. The soap solution will not only facilitate studding but, subsequently, also promote firm attachment of the sleeve <NUM> to the tread through cross-linking between the thermoplastic elastomer or silicone based material of the sleeve and the rubber compound of the tyre.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure.

In addition, various embodiments and example of the present disclosure may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present disclosure.

In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the disclosure can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosure.

While the forgoing examples are illustrative of the principles of the present disclosure in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention.

Claim 1:
A stud (<NUM>) for a pneumatic tyre, comprising:
- a sleeve (<NUM>) comprising a pin hole (<NUM>), wherein the sleeve (<NUM>) comprises or is formed of rubber, a thermoplastic elastomer or silicone based material, and
- a pin (<NUM>) being formed as a unitary piece from one or more than one wear resistant material or compound and inserted into the pin hole (<NUM>),
wherein the stud (<NUM>) exhibits a tallness (T) in a longitudinal dimension (Y),
- the tallness (T) of the stud (<NUM>) is defined by the extension of the pin (<NUM>) in the longitudinal dimension (Y), characterized in that
- the sleeve (<NUM>) is configured to allow rotational movement of the pin (<NUM>) in respect to the sleeve (<NUM>) about a rotation axis, which extends in the longitudinal dimension (Y).