Stud pin, and pneumatic tire

A stud pin fitted into a tread portion of a pneumatic tire comprises a buried base portion extending in a direction, the buried base portion securing the stud pin in the tread portion by being pressed by a side surface of the stud pin installation hole upon the stud pin being embedded in the stud pin installation hole, and a tip portion connected to an end portion of the buried base portion in the extending direction, the tip portion protruding past the tread portion and coming into contact with a road surface upon the buried base portion being embedded in the stud pin installation hole. A connection portion of the tip portion with the buried base portion has a cross-sectional area in a plane orthogonal to the extending direction of the buried base portion greater than an area of the tip end surface.

TECHNICAL FIELD

The present technology relates to a stud pin fitted to the tread portion of a pneumatic tire, and a pneumatic tire fitted with the stud pin.

BACKGROUND ART

Conventional snow tires provide grip on icy road surfaces via stud pins fitted into the tread portion of the tire.

Typical stud pins are embedded in a stud pin installation hole provided on the tread portion. When stud pins are embedded in a stud pin installation hole, the stud pin installation hole expands in diameter. By inserting stud pins into a stud pin installation hole in this state, the stud pins are firmly embedded in the stud pin installation hole. As a result, stud pins are prevented from falling out from the stud pin installation holes upon receiving forces upon breaking or accelerating or lateral forces from the road surface during rolling motion of the tire.

A spike for a tire (stud pin) that can realize enhanced clawing force against a surface of ice and weight reduction is known (International Patent Publication No. WO/2012/117962). The stud pin is provided with a columnar body to be secured to the tread surface with its one end side in the direction along its central axis fitted into a bottomed hole formed in the tread surface of the tire, and a pin protruding from the other end face of the columnar body in the direction along its central axis. The pin is shaped as an odd-shaped columnar body protruding from the other end face of the columnar body and having recessed portions formed by removing portions straddling the other end face and the peripheral surface of a cylindrical body to extend in the direction along the central axis of the columnar body.

However, snow tires with stud pins travel not only on icy road surfaces, but also on concrete road surfaces and asphalt road surfaces. Concrete road surfaces and asphalt road surfaces are harder than icy road surfaces. On such surfaces, the forces received from the hard road surface cause many stud pins to fall out from the tire when braking, accelerating, or cornering.

SUMMARY

The present technology provides a stud pin that does not easily fall out from a tire that improves the performance on ice of a pneumatic tire and further reduces the number of stud pins that fall out upon traveling on concrete road surfaces and asphalt road surfaces, and a pneumatic tire fitted with the stud pin.

One aspect of the present technology is a stud pin that fits into a stud pin installation hole on a tread portion of a pneumatic tire. The stud pin comprises a buried base portion extending in a direction, the buried base portion securing the stud pin in the tread portion by being pressed by a side surface of the stud pin installation hole upon the stud pin being embedded in the stud pin installation hole, and a tip portion connected to an end portion of the buried base portion in the extending direction, the tip portion protruding past the tread portion and coming into contact with a road surface upon the buried base portion being embedded in the stud pin installation hole. The tip portion comprises a tip end surface perpendicular to the extending direction of the buried base portion, and a connection portion of the tip portion with the buried base portion has a cross-sectional area in a plane orthogonal to the extending direction of the buried base portion greater than an area of the tip end surface.

Here, an area ratio S2/S1is preferably from 1.25 to 7.5, where S1is the area of the tip end surface, and S2is the cross-sectional area of the connection portion.

Preferably, the buried base portion comprises a flat surface from which the tip portion protrudes, the tip portion comprises an inclined side surface extending from the tip end surface to the buried base portion, and an angle of inclination of the inclined side surface with respect to the flat surface of the buried base portion is from 30 to 60 degrees.

The tip end surface is preferably a polygonal shape. For example, a triangular shape, a quadrangular shape, a pentagonal shape, and the like are preferable. In particular, the tip end surface is preferably a 4×n-gon shape (where n is a natural number; examples include a quadrangular shape, an octogonal shape, a dodecagonal shape, and the like). By the tip end surface having a 4×n-gon shape, tire braking performance can be improved due to the sides disposed in, for example, the tire circumferential direction and the tire width direction.

Also, the tip end surface is preferably a concave-polygonal shape. Here, a concave polygon means a polygon with at least one internal angle greater than 180 degrees, for example a cross shaped or a star shaped polygon. The concave polygon preferably has 4n number of vertices (where n is a natural number).

Note that the corners of the polygon may be rounded. Also, part of or the entirety of a side of the polygon may be an arc.

The tip portion is preferably a truncated polygonal pyramid. For example, a truncated triangular pyramid, a truncated pentagonal pyramid, and the like are preferable.

In particular, the tip portion is preferably a truncated quadrangular pyramid.

Preferably, the tip end surface is a rectangular shape, and the tip portion comprises a pair of inclined side surfaces extending from two opposing sides to the buried base portion. The corners of the polygon may be rounded. Also, part of or the entirety of a side of the polygon may be an arc. Preferably, the tip portion comprises a pair of inclined side surfaces extending from sides in the lateral direction of the rectangular shape to the buried base portion. The stud pin is preferably installed in the stud pin installation hole with the longitudinal direction of the rectangular shape aligned with the tire circumferential direction. As a result of this configuration, by the inclined side surfaces facing the tire circumferential direction, the moment acting upon the stud pin can be reduced, and by the sides in the longitudinal direction, the braking performance with respect to the forces in the tire width direction can be improved.

Preferably, the tip end surface is a quadrangular shape, a cross section of the connection portion of the tip portion with the buried base portion in the plane orthogonal to the extending direction of the buried base portion is cross shaped, and

four inclined side surfaces are provided extending from four sides of the tip end surface to four end portions of the cross shape. Preferably, one pair of the four inclined side surfaces is disposed facing the tire circumferential direction, and the other pair of inclined side surfaces is disposed facing the tire width direction.

Preferably, the tip end surface is cross shaped, and a cross section of the connection portion of the tip portion with the buried base portion in the plane orthogonal to the extending direction of the buried base portion is cross shaped, and

four inclined side surfaces extend from four end portions of the cross shaped tip end surface to the buried base portion. Preferably, one pair of the four inclined side surfaces is disposed facing the tire circumferential direction, and the other pair of inclined side surfaces is disposed facing the tire width direction.

Preferably,the buried base portion comprises, in order from the tip portion side, a body portion, a shank portion having a maximum outer diameter less than that of the body portion, and a bottom portion having a maximum outer diameter greater than that of the body portion and that of the shank portion, and

the body portion comprises on the outer peripheral surface thereof a plurality of recessed portions.

Preferably, the tip portion is a truncated concave-polygonal pyramid, the tip portion comprising four recessed portions separated in the circumferential direction;

the tip end surface and the connection portion of the tip portion with the buried base portion have a cross section in the plane orthogonal to the extending direction of the buried base portion that, as a whole, is a concave polygon shaped like a cross;

the buried base portion comprises, in order from the tip portion side, the body portion, the shank portion having the maximum outer diameter less than that of the body portion, and the bottom portion having the maximum outer diameter greater than that of the body portion and that of the shank portion;

the body portion comprises on the outer peripheral surface thereof four recessed portions separated in the circumferential direction; and

the recessed portions of the tip portion and the recessed portions of the body portion are provided arranged in the same direction with respect to a central axis of the stud pin.

Also, preferably the bottom portion comprises on the outer peripheral surface thereof four recessed portions separated in the circumferential direction; and

the recessed portions of the tip portion and the recessed portions of the bottom portion are provided arranged in the same direction with respect to a central axis of the stud pin.

Also, another aspect of the present technology is a pneumatic tire. The pneumatic tire is fitted with the stud pin described above fitted in the stud pin installation hole on a tread portion of the pneumatic tire.

According to the aspects described above, a stud pin that improves the performance on ice of a pneumatic tire and that does not easily fall out from the pneumatic tire can be provided. Also, a pneumatic tire into which stud pins are fitted can be provided. The pneumatic tire improves performance on ice, and the number of stud pins falling out from the pneumatic tire is less than that of conventional stud pins.

DESCRIPTION OF EMBODIMENTS

Overall Explanation of the Tire

Below, a pneumatic tire of the present embodiment is described.FIG. 1is a tire cross-sectional view illustrating a cross section of a pneumatic tire (hereinafter referred to as “tire”)10of the present embodiment. The tire10is a studded tire with stud pins embedded in a tread portion.

The tire10is, for example, a tire for a passenger vehicle. A tire for a passenger vehicle refers to a tire defined according to Chapter A of the JATMA Yearbook 2012 (standards of The Japan Automobile Tyre Manufacturers Association, Inc.). The tire10can also be a small truck tire as defined in Chapter B or a truck tire or bus tire as defined in Chapter C.

Below, values of the dimensions of various pattern elements are described in detail as an example values for a tire for a passenger vehicle. However, the pneumatic tire of the present technology is not limited to these example values.

The “tire circumferential direction” described below is the direction of rotation (in both directions) of the tread surface when the tire10rotates about the tire rotation axis of the tire. The “tire radial direction” is the direction that extends radially orthogonal to the tire rotation axis. The “outer side in the tire radial direction” is the direction away from the tire rotation axis in the tire radial direction. The “tire width direction” is the direction aligned with the direction of the tire rotation axis. The “outer side in the tire width direction” is the direction away from the tire center line CL of the tire10in both directions.

Tire Structure

The tire10includes a carcass ply layer12, a belt layer14, and bead cores16as skeleton members. The tire10mainly includes a tread rubber member18, sidewall rubber members20, bead filler rubber members22, rim cushion rubber members24, and an inner liner rubber member26, around these skeleton members.

The carcass ply layer12of the tire10illustrated inFIG. 1includes carcass ply members12a,12bextending between the pair of annular bead cores16and wrapped in a toroidal shape. The carcass ply members12a,12bare made from organic fibers covered with rubber. The carcass ply layer12may be formed from a single carcass ply member.

The belt layer14is provided on the outer side in the tire radial direction of the carcass ply layer12, and is constituted by two belt members14a,14b.The belt members14a,14bare members made from steel cords covered in rubber. The belt members14a,14bare disposed inclined at a predetermined angle of, for example, from 20 to 30 degrees, with respect to the tire circumferential direction. The lower layer belt member14ahas a width in the tire width direction greater than the width of the upper layer belt member14b.The steel cords of the belt members14a,14bare inclined in the direction opposite to one another with respect to the tire circumferential direction and cross one another. The belt layer14prevents or minimizes the expansion of the carcass ply layer12caused by the pressure of the air in the tire cavity region formed between the tire10and the rim.

The tread rubber member18is provided on the outer side in the tire radial direction of the belt layer14. The sidewall rubber members20are connected to both end portions of the tread rubber member18to form sidewall portions.

The tread rubber material18is made of two rubber layers: an upper layer tread rubber material18aprovided on the outer side in the tire radial direction and a lower layer tread rubber material18bprovided on the inner side in the tire radial direction.

The rim cushion rubber member24is provided at the end of the sidewall rubber member20on the inner side in the tire radial direction. The rim cushion rubber member24comes into contact with the rim on which the tire10is mounted.

The bead filler rubber member22is provided on the outer side of the bead core16in the tire radial direction so as to be interposed between the carcass ply layer12wound around the bead core16. The inner liner rubber member26is provided on an inner surface of the tire10facing a tire cavity region.

In addition, the tire10is provided with a belt cover layer28that covers the surface of the belt layer14on the outer side in the tire radial direction. The belt cover layer28is made from organic fibers covered with rubber.

The tire10has such a tire structure, but the structure of the pneumatic tire according to the present technology is not limited to the tire structure illustrated inFIG. 1.

Tread Pattern

FIG. 2is a planar development diagram illustrating a portion of the tread pattern of a tread pattern30of the tire10developed on a plane. As illustrated inFIG. 2, the tire10has a first orientation in the tire circumferential direction designated by rotational direction R. The orientation of the rotational direction R is designated by displaying numbers, symbols, and the like on the sidewall surface of the tire10. InFIG. 2, stud pins fitted into the tread portion are omitted. The stud pin (seeFIG. 3) is fitted into the pin installation holes illustrated inFIG. 2.

The tread pattern30is provided with a plurality of first inclined grooves31, a plurality of first lug grooves32, a plurality of second inclined grooves33, a plurality of third inclined grooves34, second lug grooves35, and fourth inclined grooves36. InFIG. 2, the symbol CL indicates the tire center line.

The first inclined grooves31are provided in plurality in the tire circumferential direction. Each of the first inclined grooves31has a position located separated from the center line CL as a starting end, extends from the starting end in the opposite direction to the tire rotation direction R, and extends at an inclination towards the outer side in the tire width direction. The first inclined grooves31have a shape in which the groove width gradually widens towards the outer side in the tire width direction, and the groove width gradually narrows towards the starting end.

The first lug grooves32are provided in plurality in the tire circumferential direction. The first lug grooves32extend from the end portion of the first inclined grooves31on the outer side in the tire width direction in the opposite direction to the tire rotation direction R and extend at an inclination towards the outer side in the tire width direction beyond the ground contact edge.

The second inclined grooves33are provided in plurality in the tire circumferential direction. The second inclined grooves33extend from the end portion of the first inclined grooves31on the outer side in the tire width direction in the opposite direction to the tire rotation direction R and extend at an inclination towards the inner side in the tire width direction reaching an adjacent first inclined groove31.

The third inclined grooves34are provided in plurality in the tire circumferential direction. Each of the third inclined grooves34extends from an intermediate point on the first lug grooves32in the opposite direction to the tire rotation direction R and extends at an inclination towards the outer side in the tire width direction. The third inclined grooves34have a shape in which the groove width gradually narrows towards the outer side in the tire width direction and gradually widens towards the inner side in the tire width direction.

The second lug grooves35extend between two of the first lug grooves32located adjacent to each other in the tire circumferential direction aligned with the first lug grooves32without crossing with the first inclined grooves31and the second inclined grooves33.

The third inclined grooves34extend through the second lug grooves35. The width of portions35aof the second lug grooves35on the inner side in the tire width direction of the crossing sections with the third inclined grooves34is narrower than the width of portions35bon the outer side in the tire width direction of the crossing sections with the third inclined grooves34.

The fourth inclined grooves36extend from an intermediate point on the first inclined grooves31in one direction in the tire circumferential direction and extend at an inclination towards the inner side in the tire width direction.

Sipes43are provided in land portions41that are enclosed by the first inclined grooves31, the first lug grooves32, the second inclined grooves33, and the tread ground contact edge. Also, sipes44are provided in land portions42on the inner side in the tire width direction of the first inclined grooves31and the second inclined grooves33. The sipes44extend substantially parallel to the tire width direction. The sipes43incline with respect to the sipes44. With the sipes43being inclined with respect to the sipes44, it is possible to increase the turning performance of the tire10.

Also, stud pin installation holes45are provided in the land portions41enclosed by the first inclined grooves31, the first lug grooves32, the second inclined grooves33, and the tread ground contact edges, as illustrated inFIG. 2. By fitting stud pins50A, which are described below, into the stud pin installation holes45, the tire10functions as a studded tire, and the performance on ice, namely the braking on ice and the turning on ice performances, is improved.

Stud Pin

FIG. 3is an external perspective view illustrating the stud pin50A of the first embodiment of the present technology.FIG. 4is a side view illustrating the stud pin50A fitted into the stud pin installation hole45provided on the tread rubber material18of the tread portion.

The stud pin50A mainly includes a buried base portion52and a tip portion60A. The buried base portion52is embedded in the tread portion of the pneumatic tire to be mounted. The stud pin50A is secured in the tread portion by the side surface of the buried base portion52being pressed by the tread rubber material18via the side surface of the stud pin installation hole45. The stud pin50A is formed of the buried base portion52and the tip portion60A in the stated order in the X-direction. Note that the X-direction corresponds to the extending direction of the buried base portion52toward the tip portion60, and the normal line direction relative to the tread surface of the tread portion when the stud pin50A is fitted into the stud pin installation hole45.

The buried base portion52includes a bottom portion54, a shank portion56, and a body portion58. The bottom portion54, the shank portion56, and the body portion58are formed in the stated order in the X-direction.

The bottom portion54is located on an end portion opposite the tip portion60A. The bottom portion54is shaped like a disc-shaped flange. The bottom portion54prevents rotation of the stud pin50A in the stud pin installation hole45when the stud pin50A receives forces from the road surface.

The shank portion56connects the body portion58to the bottom portion54. The shank portion56is a truncated cone. The diameter of the shank portion56is less than the maximum outer diameter of the bottom portion54and that of the body portion58. Consequently, the shank portion56is recessed relative to the body portion58and the bottom portion54, and the bottom portion54and the body portion58are formed like flanges.

The body portion58is cylindrical. The body portion58is located between the shank portion56and the tip portion60A. The body portion58is the flange-shaped portion connected to the tip portion60A. The body portion58is embedded in the tread rubber material18, with an upper end surface58aof the body portion58being exposed, flush with the tread surface when the stud pin50A is fitted into the tire10.

As illustrated inFIG. 4, the tip portion60A protrudes past the tread surface when the stud pin50A is fitted into the tread portion. The tip portion60A is the portion that comes into contact with the road surface and claws into the ice. The tip portion60A is the truncated cone portion protruding from the upper end surface58aof the buried base portion52. The tip portion60A includes a tip end surface60a(an end surface in the X-direction) perpendicular to the extending direction of the buried base portion52(X-direction). The tip portion60A includes an inclined side surface60bextending from the peripheral portion of the tip end surface60ato the upper end surface58aof the buried base portion52. The inclined side surface60bhas an acute angle of inclination θ with respect to the upper end surface58aof the body portion58. The angle of inclination is preferably from 30 to 60 degrees. In the first embodiment of the present technology, as described below, the moment of the normal force the inclined side surface60breceives from the road surface acting upon the stud pin50A can be reduced. As a result, occurrences of the stud pin50A falling out from the tread portion are reduced.

The tip portion60A may be made of the same metal material as that of the buried base portion52or of different metal material. For example, the buried base portion52and the tip portion60A may be made from aluminum. Also, the buried base portion52may be made from aluminum and the tip portion60A may be made from tungsten carbide. In the case that the buried base portion52and the tip portion60A are made from different metal materials, the tip portion60A can be anchored to the buried base portion52by mating a protruding portion (not illustrated) provided on the tip portion60A with a hole (not illustrated) formed in the upper end surface58aof the body portion58of the buried base portion52.

The tip end surface60ais circular. The connection portion of the tip portion60A with the buried base portion52has a circular cross section when sectioned along the plane orthogonal to the X-direction. As illustrated inFIG. 4, the radius r2of the cross section of the connection portion is greater than the radius r1of the tip end surface60a. Thus, S2>S1is satisfied; where S1is the area of the tip end surface60aand S2is the cross-sectional area of the connection portion of the tip portion60A, which connects to the buried base portion52, when sectioned in the direction orthogonal to the X-direction. The side surface of the tip portion60A in the tire circumferential direction is inclined with respect to the tire circumferential direction. As a result, as described below, the moment produced by the forces the tip portion60A receives from the road surface can be reduced. Consequently, occurrences of the stud pins50A falling out from the tread portion can be reduced.

FIG. 5is a schematic view illustrating a tip portion160of a conventional stud pin150clawing into the road surface S. The side surface of the conventional tip portion160is perpendicular to a tip end surface158a.Consequently, the cross sectional area of the tip portion160when the tip portion160is sectioned in the direction orthogonal to the X-direction is a constant value regardless of the position at which the tip portion160is sectioned. When the side surface of the tip portion160receives a force F1from the road surface S, the force F1causes the stud pin150to attempt to rotate about an end point C of a bottom portion154and fall out from the stud pin installation hole45. At this time, the moment N1about the end point C is represented by:

N1=R1×F1; where R1is the distance (vector) from the end point C to the force F1.

The greater the moment N1, the more likely the stud pin is to fall out from the tread portion.

FIG. 6is a schematic view illustrating the tip portion60A of the stud pin50A of the present embodiment clawing into the road surface S. The stud pin50A of the present embodiment has a configuration in which the inclined side surface60bof the tip portion60A is inclined with respect to the upper end surface58a. As a result, the force F1that the inclined side surface60breceives from the road surface S is resolved into a normal force F2and a static friction force F3between the inclined side surface60band the road surface S.

Here, F2=F1sin θ; where θ is the angle formed by the inclined side surface60band the upper end surface58a.

Also, component F1cos θ of the force F1aligned with the inclined side surface60bis equal to the component F1cos θ of the friction force F3when the static friction force between the inclined side surface60band the road surface S is not greater than the maximum static friction force. In other words, F3=F1cos θ

Here, the moment N1of the force F1about the end point C is resolved into moment N2of the normal force F2about the end point C and moment N3of the friction force F3about the end point C. At this time, N1=N2+N3is established.

The moment N2of the normal force F2about the end point C is N2=R2×F2; where R2is the distance (vector) from the end point C to the normal force F2.

The moment N3of the friction force F3about the end point C is N3=R3×F3; where R3is the distance (vector) from the end point C to the friction force F3.

When force F1increases and the component F1cos θ exceeds the maximum friction force, the inclined side surface60bslides a small degree against the road surface S. Note that the amount of slippage by the inclined side surface60bagainst the road surface S is minimal compared to the length of the inclined side surface60bin the tire circumferential direction. At this time, the friction force F4is F4=μF2=μF1sin θ (<F3).

Here, μ is the dynamic coefficient of friction between the road surface S and the inclined side surface60b.

However, when the force F1increases and the component F1cos θ exceeds the maximum friction force, the friction force F4described above becomes less than the component of force F1aligned with the inclined side surface60b(F3=F1cos θ).

The moment N4of the friction force F4about the end point C is N4=R3×F4, thus N4<N3.

As a result, when a force great enough to make the stud pin50A fall out acts upon the stud pin50A, because the component F1cos θ exceeds the maximum friction force, the moment N2+N4of the forces received from the road surface can be reduced to less than the moment N1the conventional stud pin150receives. Consequently, occurrences of the stud pin50A falling out from the tread portion can be reduced.

Note that the area ratio S2/S1is preferably from 1.25 to 7.5. S1is preferably from 2.5 to 7.0 mm2. The height from the upper end surface58ato the tip end surface60ais preferably from 0.8 to 1.5 mm. In this case, when the area ratio S2/S1is less than 1.25, the moment of the forces the tip portion60A receives from the road surface acting upon the stud pin50A increases and the stud pin50A becomes apt to fall out from the tread rubber material18. On the other hand, for S2/S1to be greater than 7.5, S1must be decreased. By decreasing S1, the clawing force gained through the tip portion60A coming into contact with the road surface becomes insufficient. To obtain sufficient clawing force through contact between the tip portion60A and the road surface, S2/S1is preferably less than 3.0.

The edges of the tip end surface60amay be filleted. In this case, the area S1of the tip end surface60arefers to the area of a portion having a height equal to or greater than 95% of the maximum height of the tip portion60A protruding from the upper end surface58aof the buried base portion52.

Also, θ is preferably an acute angle and preferably from 30 to 60 degrees. When θ is less than 30 degrees, the clawing force obtained through the contact of the tip portion60A with the road surface decreases. On the other hand, when θ is greater than 60 degrees, the moment of the forces the tip portion60A receives from the road surface acting upon the stud pin50A increases.

In such a manner, according to the stud pin50A of the first embodiment of the present technology, the moment of the forces received from the road surface acting upon the stud pin50A can be reduced to a greater degree than with a conventional stud pin. As a result, occurrences of the stud pin50A falling out from the tread portion can be reduced.

FIG. 7is a perspective view illustrating a stud pin50B according to a second embodiment of the present technology. The buried base portion52of the stud pin50B of the present embodiment has the same shape as the stud pin50A according to the first embodiment. However, the shape of a tip portion60B is different from that of the tip portion60A.

The tip portion60B is a truncated quadrangular pyramid. The tip portion60B includes a tip end surface60a(an end surface in the X-direction) perpendicular to the extending direction of the buried base portion52(X-direction) and four inclined side surfaces60bthat extend at an inclination from respective edges of the tip end surface60ato the upper end surface58aof the body portion58. The four inclined side surfaces60bmay all have the same angle of inclination or may each independently have different angles of inclination. The stud pin50B may be fitted into a stud portion so that the extending direction of a pair of the inclined side surfaces60bextending from a pair of opposing sides of the tip end surface60aand the tire circumferential direction are aligned.

S2>S1is satisfied; where S1is the area of the tip end surface60aand S2is the cross-sectional area of the connection portion of the tip portion60B with the buried base portion52, when sectioned along the plane orthogonal to the X-direction. As a result, the side surface of the tip portion60B in the tire circumferential direction is inclined with respect to the tire circumferential direction, in a similar manner to that of the tip portion60A of the first embodiment. As a result, in a similar manner to that of the tip portion60A of the first embodiment, the moment of the normal force the tip portion60B receives from the road surface can be reduced. Thus, occurrences of the stud pins50B falling out from the tread portion can be reduced.

Note that the shape of the tip portion60B is not limited to a truncated cone or a truncated quadrangular pyramid and may be a truncated triangular pyramid, a truncated pentagonal pyramid, or any truncated polygonal pyramid having a cross-sectional area perpendicular to the extending direction of the buried base portion52(X-direction) that tapers from the connection portion towards the tip end.

FIG. 8is a perspective view illustrating a stud pin50C according to a third embodiment of the present technology. The buried base portion52of the stud pin50C of the present embodiment has the same shape as the stud pin50A according to the first embodiment. However, the shape of a tip portion60C is different.

The tip end surface60aof the tip portion60C of the stud pin50C according to the present embodiment is shaped like a rectangle. The connection portion of the tip portion60C with the buried base portion52has a rectangular cross section when sectioned along the plane orthogonal to the X-direction. The tip portion60C has a trapezoidal shape when viewed from the longitudinal direction of the tip portion60C and the direction perpendicular to the X-direction. The tip end surface60aof the tip portion60C may be a rectangle with the pair of sides in the lateral direction curved in an outwardly convex manner. Two inclined side surfaces60bextend at an inclination in the tire circumferential direction from the pair of sides in the lateral direction to the upper end surface58aof the body portion58. The inclined side surfaces60bhave edges that extend at an inclination between the tip end surface60aand the upper end surface58a. Trapezoidal side surfaces60dof the tip portion60C are defined by the edges of the inclined side surfaces60b, the pair of sides in the longitudinal direction of the tip end surface60a, and the upper end surface58a. The side surface60dmay be substantially perpendicular to the upper end surface58aor may be inclined with respect to the upper end surface58ain a similar manner as that of the inclined side surface60b. The stud pin50C is preferably installed in the stud pin installation hole45with the extending direction of the side surface60d, in other words the longitudinal direction of the base of the truncated rectangular pyramid tip portion60C (the cross section of the connection portion of the tip portion60C with the buried base portion52when sectioned along the plane orthogonal to the X-direction), aligned with the tire circumferential direction. In other words, the stud pin50C is preferably installed in the tread portion with the pair of inclined side surfaces60bfacing the tire circumferential direction. With this configuration, the moment of the forces the inclined side surface60breceives from the road surface acting upon the stud pin50C can be reduced to a greater degree than with a conventional stud pin. As a result, occurrences of the stud pin50C falling out from the tread portion can be reduced.

In the present embodiment, S2>S1is satisfied; where S1is the area of the tip end surface60a, and S2is the cross-sectional area of the connection portion of the tip portion60C with the buried base portion52, when sectioned along the plane orthogonal to the X-direction. Also, the tip portion60C is a trapezoid when viewed from the tire width direction, and the side surface of the tip portion60C in the tire circumferential direction is inclined with respect to the tire circumferential direction. Consequently, the moment of the normal force this inclined side surface receives from the road surface can be reduced, and occurrences of the stud pin50C falling out from the tread portion can be reduced.

FIG. 9is a perspective view illustrating a stud pin50D according to a fourth embodiment of the present technology. The buried base portion52of the stud pin50D of the present embodiment has the same shape as the stud pin50A according to the first embodiment. However, the shape of a tip portion60D is different.

The tip end surface60aof the tip portion60D is substantially quadrangular with each side curved to be outwardly convex. Four inclined side surfaces60bextend out in the radial direction of the body portion58at an inclination from the sides of the tip end surface60ato the upper end surface58aof the body portion58. The tip portion60D is, as a whole, substantially cross shaped when viewed from the tire radial direction. The connection portion of the tip portion60D with the buried base portion52has, as a whole, a concave-polygonal cross section shaped like a cross when sectioned along the plane orthogonal to the X-direction. The four inclined side surfaces60bmay all have the same angle of inclination or may each independently have different angles of inclination. The stud pin50B may be fitted into a stud portion so that the extending direction of one pair of inclined side surfaces60bextending from a pair of opposing sides of the tip end surface60ais aligned with the tire circumferential direction. With this configuration, the moment of the forces the inclined side surfaces60breceive from the road surface acting upon the stud pin50D can be reduced to a greater degree than with a conventional stud pin. As a result, occurrences of the stud pin50D falling out from the tread portion can be reduced.

The side surfaces60dare formed extending from the edges that extend at an inclination between the tip end surface60aand the upper end surface58aof the inclined side surfaces60bto the upper end surface58a. Recessed portions60care defined by adjacent side surfaces60d. The side surfaces60dmay be provided substantially perpendicular to the upper end surface58a, or, in a similar manner to that of the inclined side surface60b, the side surfaces60dmay be inclined with respect to the upper end surface58a. By forming the recessed portions60c, the number of edges of the tip portion60D that claw into the road surface can be increased. As a result, the clawing force the stud pin50D receives from the road surface can be enhanced.

Also, in the present embodiment, S2>S1is satisfied; where S1is the area of the tip end surface of the tip portion60D, and S2is the cross-sectional area of the connection portion of the tip portion60D with the buried base portion52, when sectioned along the plane orthogonal to the X-direction. As a result, the side surface of the tip portion60D in the tire circumferential direction is inclined with respect to the tire circumferential direction. Consequently, in a similar manner to that of the stud pin50A according to the first embodiment, the moment of the normal force the tip portion60D receives from the road surface acting upon the stud pin50D can be reduced. As a result, occurrences of the stud pin50D falling out from the tread portion can be reduced.

FIG. 10is a perspective view illustrating a stud pin50E according to a fifth embodiment of the present technology. The buried base portion52of the stud pin50E of the present embodiment has the same shape as the stud pin50A according to the first embodiment. However, the shape of a tip portion60E is different.

The tip portion60E is the portion that, as illustrated inFIG. 4, protrudes past the tread surface when the stud pin50E is fitted into the tread portion, comes into contact with the road surface, and claws into the ice. The tip portion60E is a truncated concave-polygonal pyramid, protruding from the upper end surface58aof the buried base portion52with a trapezoidal cross section. The tip portion60E includes a tip end surface60a(an end surface in the X-direction) perpendicular to the extending direction of the buried base portion52(X-direction).

Note that the tip end surface60a, as well as the cross section of the connection portion of the tip portion60E with the buried base portion52when sectioned along the plane orthogonal to the X-direction are preferably concave polygons with at least one internal angle greater than 180 degrees. In particular, the tip end surface60a, as well as the cross section of the connection portion of the tip portion60E with the buried base portion52when sectioned along the plane orthogonal to the X-direction is preferably, as a whole, a concave polygon shaped like a cross. As concave polygons have a greater sum of the lengths of the sides than circles or convex polygons with the same area, by the tip end surface60abeing shaped like a concave polygon, the number of edges of the tip portion60E that claw into the road surface can be increased. As a result, the clawing force the stud pin50E receives from the road surface can be enhanced. For example, the tip end surface60acan be cross shaped or star shaped.

The cross section of the tip portion60E in the direction orthogonal to the X-direction may have a different shape to the tip end surface60a, however a similar shape to the tip end surface60ais preferable.

In the present embodiment, S2>S1is satisfied; where S1is the area of the tip end surface60a, and S2is the cross-sectional area of the connection portion of the tip portion60E with the buried base portion52, when sectioned along the plane orthogonal to the X-direction. As a result, the side surface of the tip portion60E in the tire circumferential direction is inclined with respect to the tire circumferential direction. Consequently, in a similar manner to that of the embodiments described above, the moment of the normal force the tip portion60E receives from the road surface can be reduced, and occurrences of the stud pin50A falling out from the tread portion can be reduced.

Twelve inclined side surfaces60bextend at an inclination from the sides of the tip end surface60ato the upper end surface58aof the body portion58.

The recessed portions60care defined by at least one pair of the inclined side surfaces60bextending from the sides of the tip end surface60athat form an internal angle greater than 180 degrees. By forming the recessed portions60c,the number of edges of the tip portion60E that claw into the road surface can be increased. As a result, the clawing force the stud pin50E receives from the road surface can be enhanced.

FIG. 11is a perspective view illustrating a stud pin50F according to a sixth embodiment of the present technology. A tip portion60E of the stud pin50F of the present embodiment has the same shape as the tip portion60E of the stud pin50E according to the fifth embodiment. However, the shape of a buried base portion52F is different.

The buried base portion52F of the stud pin50F includes a bottom portion54F, a shank portion56F, and a body portion58F. The bottom portion54F, the shank portion56F, and the body portion58F are formed in the stated order in the X-direction.

A recessed portion54ais formed in the outer peripheral surface of the bottom portion54F that comes into contact with the side surface of the stud pin installation hole45. Specifically, the cross section of the bottom portion54F is substantially quadrangular with filleted corners. The four sides of the substantially quadrangular shape are recessed to form four of the recessed portions54a. The cross section of the bottom portion54F may not be substantially quadrangular with filleted corners and may be substantially triangular, pentagonal, hexagonal, or any substantially polygonal shape. By the bottom portion54F being substantially polygonal, rotational motion of the stud pin50F about the central axis thereof that is aligned with the X-direction is prevented or minimized. Note that the dull corners of the bottom portion54achieved by filleting the corners can prevent damage to the side surface of the stud pin installation hole45. In this case, the recessed portion54ais preferably formed by at least one side of the substantially polygonal shape being recessed. Of course, a plurality of recessed portions54amay be formed by a portion of or all of the sides of the substantially polygonal shape, for example two sides, three sides, four sides, five sides, six sides, and the like, being recessed. By forming the recessed portion54a, the surface area per unit volume of the bottom portion54F can be increased. As a result, the surface contact area with the tread rubber material18of the tread portion is increased and the friction force preventing the stud pin50F from moving can be increased. Also, by the tread rubber material18filling the recessed portion54a, rotational motion about the central axis of the stud pin50F, which is aligned with the X-direction, is prevented or minimized.

The shank portion56F is the portion that connects the body portion58F to the bottom portion54F. The shank portion56F is cylindrical with a diameter less than the maximum outer diameter of the bottom portion54F and that of the body portion58F. As a result, the shank portion56is formed as a recessed portion relative to the body portion58and the bottom portion54F, and the bottom portion54F and the body portion58F are formed like flanges. Recessed portions are not formed in the outer peripheral surface of the shank portion56F.

The body portion58F is located between the shank portion56F and the tip portion60F and is the flange portion connected to the tip portion60F. A recessed portion58bis formed on the outer peripheral surface of the body portion58F which is pressed by the side surface of the stud pin installation hole. By the tread rubber material18of the tread portion being brought into contact with and pressing the outer peripheral surface, movement of the stud pin50F is prevented or minimized by friction force.

Explaining the body portion58F in detail, the body portion58F has a cross section perpendicular to the X-direction that is substantially quadrangular having filleted corners with four of the recessed portions58bformed by the four sides being recessed. In the present embodiment, four of the recessed portion58bare provided on the outer peripheral surface. However, at least one recessed portion58b, in other words one, two, three, and the like, may be provided. The cross section of the body portion58F may not be substantially quadrangular with filleted corners and may be substantially triangular, pentagonal, hexagonal, or any substantially polygonal shape. By the body portion58F being substantially polygonal, rotational motion of the stud pin50F about the central axis thereof that is aligned with the X-direction is prevented or minimized. Note that the dull corners of the body portion58F of the stud pin50F achieved by filleting the corners can prevent damage to the side surface of the stud pin installation hole45.

In this case, the recessed portion58bis preferably formed by at least one side of the substantially polygonal shape being recessed. Of course, a plurality of recessed portions58bmay be formed by a portion of or all of the sides of the substantially polygonal shape, for example two sides, three sides, four sides, five sides, six sides, and the like, being recessed. By forming the recessed portion58b, the surface area per unit volume of the body portion58F can be increased. As a result, the surface contact area with the tread rubber material18of the tread portion is increased and the friction force preventing the stud pin50F from moving can be increased. Also, by the tread rubber material18filling the recessed portion58b, rotational motion about the central axis of the stud pin50F, which is aligned with the X-direction, is prevented or minimized.

The body portion58F is embedded in the tread rubber material18, with the upper end surface58aof the body portion58being exposed, flush with the tread surface when the stud pin50F is fitted into the tire10.

According to the present embodiment, a similar result to that of the stud pin50E according to the fifth embodiment can be achieved, and rotational motion about the central axis of the buried base portion52F, which is aligned with the X-direction, can be prevented or minimized. As a result, occurrences of the stud pin50F falling out from the tread portion can be reduced.

Note that, as illustrated inFIG. 11, the recessed portion54a, the recessed portion58b, and the recessed portion60care preferably provided arranged in the same direction with respect to the central axis of the stud pin50F.

EXAMPLES

To test the effects of the stud pins of the embodiments, stud pins of a Comparative Example and Working Examples 1 to 9 described below were installed in the tires10having the configuration illustrated inFIG. 1andFIG. 2. For each stud pin, the surface area S1of the tip end surface60aof the tip portion60was 4.0 mm2, and the height from the upper end surface58aof the buried base portion52to the tip end surface60awas 1.2 mm. The shape of the buried base portion52was the same for each stud pin (the shape illustrated inFIG. 3,FIG. 7, andFIG. 10).

Next, the tires10described above were mounted on a passenger vehicle, and the braking performance on ice, representing performance on ice, and stud pin resistance to falling out (difficulty to fall out) was tested.

The size of each manufactured tire was 205/55R16. The passenger vehicle used was a front wheel drive sedan type passenger vehicle with an engine displacement of 2000 cc. The internal pressure condition of the tires was 230 (kPa) for both the front wheels and rear wheels. The load condition of the tires was a 450 kg load on the front wheels and a 300 kg load on the rear wheels.

The stud pins of the Comparative Example and Working Examples 1 to 6 had a varied cross-sectional area S2of the connection portion of the tip portion with the buried base portion, and thus S2/S1varied.

Comparative Example

The cylindrical tip portion illustrated inFIG. 5was used in the stud pin of the Comparative Example. In other words, the shape of the tip end surface (hereinafter referred to as “tip end shape”) was circular. Also, S2/S1was set to S2/S1=1.00.

Working Examples 1 to 9

The truncated conical tip portion illustrated inFIG. 3was used in the stud pins of Working Examples 1 to 9. In other words, the shape of the tip end surface (hereinafter referred to as “tip end shape”) was circular.

S2/S1was set to 1.10 in Working Example 1, 1.25 in Working Example 2, 1.50 in Working Example 3, 2.50 in Working Example 4, 3.00 in Working Example 5, 3.25 in Working Example 6, 6.50 in Working Example 7, 7.00 in Working Example 8, and 7.5 in Working Example 9.

Working Examples 10 to 12

In Working Examples 10 to 12, S2/S1was set to a constant value (2.00) and the tip end shape was varied. Specifically, in Working Example 10, the tip end shape was circular, as illustrated inFIG. 3; in Working Example 11, the tip end shape was quadrangular, as illustrated inFIG. 7; and in Working Example 12, the tip end shape was a cross shape, as illustrated inFIG. 10. In Working Example 11, the stud pins were installed in the tread portion so that a pair of the inclined side surfaces60bfaced the tire circumferential direction. In Working Example 12, the stud pins were installed in the tread portion so that any one of the pairs of the inclined side surfaces60bfaced the tire circumferential direction.

Braking Performance on Ice

The braking performance on ice of each Example was obtained as follows:

the distance (breaking distance) the passenger vehicle travelling at 40 km/hour takes to stop when the brake pedal is pushed to the maximum travel point with a fixed force was measured a plurality of times (five times) and the average value of the measurement values was obtained.

The inverse value of the average value of the measurement values of the braking distance was indexed based on the inverse value of the average value of the measurement values of the braking distance of the Comparative Example (index of 100).

The results are shown in Tables 1 and 2.

Stud Pin Resistance to Falling Out

The stud pin resistance to falling out for each Example was obtained as follows:

the proportion of the number of stud pins remaining in the tread portion to the total number of fitted stud pins was obtained after the vehicle had travelled 1000 km on a dry road surface including asphalt road surfaces or concrete road surfaces.

The proportion of remaining stud pins was indexed based on the proportion of remaining stud pins in the Comparative Example (index of 100).

The results are shown in Tables 1 to 3.

As can be seen by comparing the Comparative Example and Working Examples 1 to 9 shown in Table 1 and Table 2, when S2/S1>1 is satisfied, the braking performance on ice increases and the resistance to falling out of the stud pins increases. In particular, when 1.25≤S2/S1≤7.00 is satisfied, the braking performance on ice and the resistance to falling out of the stud pins can be further increased. Also, when 1.25≤S2/S1≤3.00 is satisfied, the braking performance on ice and the resistance to falling out of the stud pins can be even further increased.

As can be seen by comparing Working Examples 10 to 12 shown in Table 3, a quadrangular tip end shape achieves greater braking performance on ice and resistance to falling out of stud pins than a circular tip end shape. Also, a cross shaped tip end shape achieves even greater braking performance on ice and resistance to falling out of stud pins than a quadrangular tip end shape.

The foregoing has been a detailed description of the stud pin and pneumatic tire of the present technology. However, the pneumatic tire of the present technology is not limited to the above embodiments, and may be enhanced or modified in various ways within the scope of the present technology.