Sole Structure for Footwear

TECHNICAL FIELD

The present invention relates generally to a sole structure for footwear including shoes, sandals, boots and the like, and more particularly, to a sole structure that can transmit ground surface information acting on a sole bottom surface (i.e. reactive force from the ground, irregularities of the ground and contact area with the ground) to a foot sole of a shoe wearer accurately.

BACKGROUND ART

Generally, in posture control activities of a human being, it is thought that vision, vestibular sensation, deep sensation of individual muscles and tendons of a body and cutaneous sensation of a foot sole play a vital role. Accordingly, it is very important especially as functions of sports shoes that various information applied from the ground surface to a sole bottom surface of a shoe is accurately transmitted to a foot sole of a shoe wearer.

Conventionally, there have been proposed various kinds of sole structures that transmit a reactive force from the ground surface to a foot sole of a show wearer. For example, US patent application publication No. 2010/0126043 discloses a sole structure in which a plurality of ground contact pads are disposed at the base portion of the outsole and each of the ground contact pads is provided at the base portion via the flex portion so that each of the ground contact pads can be displacable independently relative to the base portion (see FIGS. 3, 4 and 9-11 of the publication).

In the structure shown in the above publication, at the time of striking onto the ground, force from the ground is applied to the ground contact pads that have contacted the ground, and then, the ground contact pads move upwardly relative to the base portion of the outsole due to deformation of the flex portion. Thereby, pressing pressure from the ground contact pads acts on a foot sole of a shoe wearer and thus the shoe wearer can sense the force from the ground.

Also, U.S. Pat. No. 6,082,024 discloses a sole structure in which there are provided a pressure-stimulation element that protrudes downwardly from the bottom surface of the outsole and a midsole that is disposed above the pressure-stimulation element (see FIGS. 2 to 4 of the publication).

In the structure shown in the above publication, when force from the ground is applied to the pressure-stimulation element at the time of striking onto the ground, the pressure-stimulation element moves upwardly to push up the midsole and to cause the midsole to deform convexly (see a dotted line of FIGS. 2 to 3 of the publication). Thereby, pressing pressure from the pressure-stimulation element acts on and stimulates the foot sole of the shoe wearer.

Moreover, Japanese patent application publication No. 2009-172183 discloses a sole structure in which there are provided a plurality of elastic protrusions on the foot sole contact surface of the insole board of the shoe and a plurality of push members and elastic members in the insole board at positions corresponding to the elastic protrusions (see FIG. 1 of the publication).

In the structure shown in the above publication, when force from the ground is applied to the ground contact surface of the insole board at the time of striking onto the ground, the force from the ground is transmitted through the push members and elastic members to the elastic protrusions and the elastic protrusions exert pressing pressure to the foot sole of the shoe wearer. Thereby, pressing pressure stimulus is applied to the foot sole of the shoe wearer during walking.

On the other hand, as a sole structure that transmits irregularities of the ground to the foot sole of the shoe wearer, for example, Japanese patent application examined publication No. 1992-75001 discloses a sole structure in which a plurality of cylindrical rubber pieces or resin pieces are provided inside the sole (see FIG. 1 of the publication).

In the structure shown in the above publication, when the bottom surface of the sole comes into contact with the ground, the bottom surface of the sole deforms upwardly and downwardly according to the irregularities of the ground, thus allowing the rubber pieces or resin pieces to move upwardly and downwardly, so that the top surface (i.e. the foot sole contact surface) of the sole deforms irregularly according to the irregularities of the ground. As a result, the shoe wearer can sense the irregularities of the ground.

In the structure shown in the above-mentioned US patent application publication No. 2010/0126043, as mentioned in para. [0060], the flex portion comprises a material having a lower Young's modulus of elasticity and lower durometer and the ground contact pad comprises a material having a greater Young's modulus of elasticity and greater durometer. Therefore, when a force from the ground acts on the ground contact pad, the flex portion easily deforms, thus allowing the ground contact pad to move upwardly with ease. On the other hand, since the shape of the ground contact pad will not change, the force from the ground is transmitted to the foot sole of the shoe wearer as it is through the ground contact pad.

Accordingly, in the structure shown in the above publication, even if the force from the ground can be transmitted from the ground contact pad to the foot sole of the wearer, since the shape of the ground contact pad will not change and a top surface and a bottom surface of the ground contact pad are formed flat (that will be detailed later), information on contact area with the ground surface at the time of impacting the ground cannot be transmitted to the wearer with accuracy.

In the structure shown in the above-mentioned U.S. Pat. No. 6,082,024, as mentioned in column 3, lines 14 to 21, the midsole needs to be locally deformed convexly by causing the pressure-stimulation element to move upwardly to apply local pressure to the middle at the time of impacting the ground, and for that reason the pressure-stimulation element is elastically supported by the surrounding member via the elastic bellow or the like so that the pressure-stimulation element can easily move upwardly when the pressing force is exerted from below.

Accordingly, in the structure shown in the above publication, even if the force from the ground can be transmitted to the foot sole of the wearer through the pressure-stimulation element, since the force from the ground is applied to the foot sole of the wearer through the midsole, information on contact area with the ground surface at the time of impacting the ground cannot be transmitted to the wearer with accuracy.

In the structure shown in the above-mentioned Japanese patent application publication No. 2009-172183, as mentioned in paras. [0015] and [0017], when the force from the ground is applied to the ground contact surface of the insole board at the time of striking onto the ground, the push members inside the insole board transmit the force from the ground to the elastic protrusions as they are, and the elastic members inside the insole board transmit and partially absorb the force from the ground to the elastic protrusions.

Accordingly, in the structure shown in the above publication, even if the force from the ground can be transmitted to the foot sole of the wearer through the push members and the elastic members, since the push members and the elastic members are disposed inside the insole board, bottom surfaces of the push members and the elastic members are formed flat (that will be detailed later), and top surfaces of the elastic protrusions are formed flat (that will be detailed later), information on contact area with the ground surface at the time of impacting the ground cannot be transmitted to the wearer with accuracy.

In the structure shown in the above-mentioned Japanese patent application examined publication No. 1992-75001, as mentioned in page 1, column 2, lines 20 to page 2, column 3, line 1, when the bottom surface of the sole comes into contact with the ground at the time of striking onto the ground, the rubber pieces or resin pieces inside the sole move upwardly and downwardly as they are without deforming according to the irregularities of the ground, thus allowing the top surface (i.e. the foot sole contact surface) of the sole deforms irregularly according to the irregularities of the ground.

Accordingly, in the structure shown in the above publication, even if the irregularities of the ground can be transmitted to the foot sole of the wearer through upward and downward movement of the rubber pieces or resin pieces, since the shapes of the rubber pieces or resin pieces will not change and the rubber pieces or resin pieces are disposed inside the sole, information on contact area with the ground surface at the time of impacting the ground cannot be transmitted to the wearer with accuracy.

Incidentally, human sense has been generally evolving so that respective senses are correlated with each other. It is known that when plural senses are stimulated at one time recognition is enhanced. That can also be said about sensation of skin. It is known that when perceiving softness of an object perception of softness of the object is enhanced by presenting not only information on sense of force applied to skin but also information on contact area of skin with the object (Ikeda & Fujita: “Presentation of Soft Elastic Object due to Simultaneous Control of Contact Area of Fingertip and Reactive Force”, Research Journal of Japan Virtual Reality Association, Vol. 9, No. 2, 2004).

On the other hand, it is critically important in view of recognition of a brain that information from plural senses is accurately correlated with each other. Because when brain obtains inconsistent information from plural senses it tries to make such information consistent by its very nature and sometimes causes sensation that does not occur in reality (McGurk effect is a good example for that).

Accordingly, it is of importance in view of enhancement of cognition of the shoe wearer that information on force applied to the foot sole of the shoe wearer and information on contact area are accurately transmitted to the foot sole of the shoe wearer with both information correlated with each other. Here, when a relation between the force to the foot sole and the contact area is reviewed, since the foot sole has a curved surface, the contact relation between the foot sole and an object conforms to the Hertz contact theory and it is considered that the greater the applied force becomes the greater the contact area becomes. Therefore, it is necessary to maintain such relation when transmitting information on the force to the foot sole of the shoe wearer and information on the contact area accurately with both information correlated with each other.

The present invention has been made in view of these circumstances and its object is to provide a sole structure that can transmit ground surface information acting on a sole bottom surface (i.e. contact area with the ground as well as reactive force from the ground and irregularities of the ground) correlatedly with each other to a foot sole of a shoe wearer accurately.

DISCLOSURE OF INVENTION

A sole structure for footwear according to the present invention includes a sole body having a sole bottom surface disposed on a ground surface side and a sole top surface disposed on an opposite side thereof, a plurality of first protrusions formed of elastic members and disposed on the sole bottom surface, and a plurality of second protrusions formed of elastic members, disposed on the sole top surface and located at positions corresponding respectively to positions of the plurality of first protrusions. A sectional shape of the first protrusion is formed such that it gradually becomes smaller as it leaves the sole bottom surface and a distal end portion of the first protrusion has a convex surface that protrudes downwardly. A sectional shape of the second protrusion is formed such that it gradually becomes smaller as it leaves the sole top surface and a distal end portion of the second protrusion has a convex surface that protrudes upwardly. An irregular shape of a foot sole contact surface of foot wear is formed by an irregular shape of the plurality of the second protrusions on the sole top surface.

According to the present invention, when the shoe wearer strikes onto the ground, force applied to the sole structure from the ground surface is transmitted from the first protrusions on the sole bottom surface side through the sole body to the second protrusions on the sole top surface side, and the second protrusions transmit information of the force from the ground surface to the foot sole of the shoe wearer. Also, at that moment, distribution of the force applied to the first protrusions from the ground surface varies according to irregularities of the ground. The state of such variation is transmitted through the sole body to the second protrusions and through the second protrusions information on the irregularities of the ground is transmitted to the foot sole of the shoe wearer.

Moreover, according to the present invention, the sectional shape of the first protrusion is formed in such a way as to gradually become smaller as it leaves the sole bottom surface, the distal end portion of the first protrusion has a convex surface that protrudes downwardly, the sectional shape of the second protrusion is formed in such a way as to gradually become smaller as it leaves the sole top surface, and the distal end portion of the second protrusion has a convex surface that protrudes upwardly. Thereby, as the force applied to the first protrusion from the ground surface at the time of striking the ground increases, a contact area of the first protrusion with the ground surface increases and at the same time, as the force applied from the foot sole of the wearer to the second protrusions corresponding to the first protrusions increases at the time of striking the ground, a contact area of the second protrusion with the foot sole increases. As a result, information on the contact area with the ground surface is transmitted to the foot sole of the shoe wearer accurately.

In such a manner, according to the present invention, ground surface information acting on the sole bottom surface (i.e. contact area with the ground as well as reactive force from the ground and irregularities of the ground) can be transmitted correlatedly with each other to the foot sole of the shoe wearer accurately.

Here, FIG. 15 shows the result of analysis that was performed in order to see the effects of the present invention. In this analysis, as shown in the left column of FIG. 15, four projection structures of different shapes are prepared. Sample 1 is a cylindrical projection; Sample 2 is a spherical projection; Sample 3 is a projection whose top and bottom surfaces have R-shape; and Sample 4 is a projection whose top surface has an R-shape and bottom surface has a flat shape. When each of the projection structures is allowed to fall freely from a certain height with a certain weight placed on a top surface of each of the projection structures, the inventors analyzed a relation between load that a bottom surface of each of the projection structures applies to a fall surface/ground contact surface (i.e. reaction force that the ground contact surface applies to the bottom surface of each of the projection structures) and contact area with a contact surface of each of the projection structures using FEM (Finite Element Method). The weight placed on the top surface of each of the projection structures corresponds to the sole body of the present invention. In addition, a more detailed side shape of each of the element-divided projection structures is shown in FIGS. 16 to 19. In these drawings, a downward arrow mark indicates the falling direction. Also, specific dimensions of each of the projection structures are shown in the middle column of FIG. 15.

Analysis conditions of FEM are as follows:

(i) A weight of each of the projection structures is 1 g, a weight of the weight placed on the top surface of each of the projection structures is 256 g, and the total weight of both of the weights are set to 257 g.

(ii) A fall height, i.e. a height from the fall surface to the bottom surface of each of the projection structures is set to 7.7 mm.

Analysis results of the projection structures are shown in graphs of the right column of FIG. 15. In each of the graphs, a horizontal axis represents a reaction force (kg) and a vertical axis represents a contact area (mm²). As can be seen from each of the graphs, in the case of a flat bottom surface such as shown in the cylindrical protrusion of Sample 1 or the protrusion of Sample 4, the contact area with the ground surface is approximately constant even if the reaction force from the ground increases and thus information of the force from the ground surface and information of the contact area with the ground surface are not accurately correlated to each other. In the sole structures described in the above-mentioned US patent application publication No. 2010/0126043 and JP patent application publication No. 2009-172183, a ground contact pad/pushmember/elasticmember whose bottom surface is formed flat corresponds to Sample 1 or 4.

To the contrary, in the case of a protrusion such as shown in Samples 2 and 3 whose bottom surface is a convex surface (more specifically, a curved shaped surface that curves downwardly convexly, an arcuate shaped surface, or spherical surface) and whose sectional shape becomes gradually small toward the bottom surface, as the reaction force from the ground contact surface increases the contact area with the ground contact surface increases. It is thus found that information of the force from the ground surface and information of the contact area with the ground surface are accurately correlated to each other.

Accordingly, as in the case of the present invention in which the distal end portion of the first protrusion has a convex surface that protrudes downwardly and the sectional shape of the first protrusion is formed so that it gradually becomes smaller as it leaves the sole bottom surface, as the reaction force from the ground contact surface increases the contact area with the ground contact surface increases and thus information of the reaction force from the ground surface and information of the contact area with the ground surface are accurately correlated to each other. Moreover, in the present invention, the distal end portion of the second protrusion located at a position on the sole top surface corresponding to the first protrusion has a convex surface protruding upwardly and the sectional shape of the second protrusion is formed so that it gradually becomes smaller as it leaves the sole top surface. Thereby, when the contact area of the first protrusion with the ground contact surface increases as the force applied from the ground to the first protrusion at the time of impacting the ground increases, the contact area of the second protrusion with the foot sole increases as the force applied from the foot sole to the second protrusion corresponding to the first protrusion at the time of impacting the ground increases. Thus, information of the contact area with the ground contact surface is accurately transmitted to the foot sole of the shoe wearer.

In the present invention, when impacting the ground, the first protrusion and the second protrusion compressively deform, thereby the contact area of the first protrusion with the ground contact surface increases in accordance with an increase of the load to the first protrusion and at the same time the contact area of the second protrusion with the foot sole of the shoe wearer increases in accordance with an increase of the contact area of the first protrusion with the ground contact surface.

In the present invention, the distal endportion of the first protrusion may have a curved surface shape that curves downwardly convexly and the distal end portion of the second protrusion may have a curved surface shape that curves upwardly convexly.

In the present invention, the distal endportion of the first protrusion or the second protrusion may be formed of an arcuate shaped surface composed of single or a plurality of circular arcs.

In the present invention, an outside surface of the first protrusion may form an obtuse angle relative to the sole bottom surface and an outside surface of the second protrusion may form an obtuse angle relative to the sole top surface.

In the present invention, the distal end portion of the second protrusion may be adapted to directly contact a bottom surface of an upper of footwear or directly constitute the foot sole contact surface of foot wear.

Here, if the distal end portion of the second protrusion directly abuts on the bottom surface of the upper of footwear, the foot sole contact surface is formed of the bottom surface of the upper. Also, in the case that the distal end portion of the second protrusion directly constitutes the foot sole contact surface of footwear, such footwear includes a shoe in which the upper does not have a bottom surface and an outer circumferential edge portion of the upper is fixedly attached to an outer circumferential edge portion of the sole structure by sewing, gluing and the like, or a sandal without an upper.

In the present invention, the first protrusion may have a hardness greater than a hardness of the second protrusion. Thereby, the hardness of the first protrusion that abuts on the ground contact surface is made relatively high to improve wear resistance of the first protrusion, and at the same time the hardness of the second protrusion disposed on the foot sole contact side is made relatively low to improve foot contact feeling in wearing footwear.

In the present invention, the first protrusion or the second protrusion may have a cavity formed therein. Thereby, an increase in weight of the entire sole structure due to provision of the protrusions can be reduced.

In the present invention, the first protrusion and the second protrusion may be provided at a forefoot region and a midfoot region of the sole structure, i.e. a region of the sole structure excluding a heel region. That is because especially in sports shoes a great impact force is applied to the heel region when impacting the ground and the heel region is thus prevented from experiencing an excessive pressure if the protrusions are provided at the heel region.

In the present invention, a distance between the first protrusions adjacent to each other and a distance between the second protrusions adjacent to each other may be greater in a forefoot rear side region and the midfoot region than in a forefoot front side region of the sole structure. Also, in the present invention, in the forefoot rear side region and the midfoot region of the sole structure a distance between the first protrusions adjacent to each other and a distance between the second protrusions adjacent to each other may be greater in a foot length direction than in a foot width direction of the sole structure.

The reason why the first and second protrusions are disposed in the above-mentioned manner is as follows:

Two-point threshold experiments were conducted in order to examine sensing ability of a foot sole of a human being. In the experiments, a test performer gave stimuli to some of foot sole regions of a blindfolded subject with a tip of a toothpick. Stimuli by the toothpick is a case of one toothpick and the other case of two toothpicks that are spaced away from each other. The subjects are given stimuli by randomly combining the case of one toothpick with the other case of two toothpicks. When using two toothpicks, the test performer causes each of the tips of the two toothpicks to contact with the foot sole of the subject at the same time with the toothpicks spaced away from each other and fixed to a scale by a predetermined distance that was read by the scale. A direction in which the two toothpicks are spaced away from each other was a foot width direction and a foot length direction. During the experiments, the subjects respond as to whether stimuli were due to one toothpick or two toothpicks. The distance between the two toothpicks was gradually extended along the scale till the subject can discriminate stimuli by the two toothpicks respectively. When the subject discriminated respective stimuli by two toothpicks three times consecutively, it is judged that he/she could detect two toothpicks. Otherwise it is judged that the subject could not detect two toothpicks respectively.

FIG. 20 shows the results of the experiments. In FIG. 20, a bottom column indicates regions (i.e. big toe, middle toe, thenar, midfoot, arch, and heel region) of the foot soles of the subjects. The experiments were conducted on three subjects A to C. Also, a left column of FIG. 20 indicates the distance between two toothpicks. In FIG. 20, a round mark designates that the subject could detect two toothpicks respectively in the foot length direction as well as the foot width direction, an X mark designates that the subject could not detect two toothpicks in the foot length direction as well as the foot width direction, a triangular mark designates that the subject could detect two toothpicks in the foot width direction but could not in the foot length direction, and a hyphen designates that the experiments were not conducted.

In FIG. 20, as the round marks of the big toe and the middle toe are compared with the round marks of the midfoot and arch, it is found that in the case of the big toe and middle toe if the distance of two toothpicks is 8 to 12 mm all of the subjects A to C could detect two toothpicks in the foot length direction as well as the foot width direction, whereas in the case of the midfoot and arch if the distance of two toothpicks is 16 to 18 mm all of the subjects A to C could detect two toothpicks in the foot length direction as well as the foot width direction. Also, in the case of the thenar, if the distance of two toothpicks is 14 to 16 mm the subjects A and B could detect two toothpicks in the foot length direction as well as the foot width direction. In view of this, it is said that the subjects could discriminate two toothpicks respectively in a forefoot front side region of a foot sole even if the distance of two toothpicks is relatively small, and the subjects could not discriminate two toothpicks in a forefoot rear side region (including the thenar) and a midfoot region of the foot sole if the distance of two toothpicks is not made relatively large. The present invention has been made in view of such experimental results and recites that a distance between the first protrusions adjacent to each other and a distance between the second protrusions adjacent to each other may be relatively small in the forefoot front side region of the sole structure and relatively large in the forefoot rear side region and the midfoot region of the sole structure.

In FIG. 20, as the triangular marks of the midfoot and the arch are compared with each other, in either case of the midfoot and the arch if the distance of two toothpicks is 14 mm all of the subjects A to C could discriminate two toothpicks in the foot width direction but could not discriminate in the foot length direction, whereas if the distance of two toothpicks is 16 to 18 mm all of the subjects A to C could discriminate two toothpicks respectively in the foot width direction as well as in the foot length direction. The present invention has been made in view of such experimental results and recites that in the midfoot region of the sole structure a distance between the first protrusions adjacent to each other and a distance between the second protrusions adjacent to each other is made relatively small in the foot width direction of the sole structure and relatively large in the foot length direction of the sole structure.

In the present invention, the first protrusion and the second protrusion may have a circular shape in the forefoot front side region of the sole structure and an elliptic shape that is long in a substantial foot length direction in the forefoot rear side region to the midfoot region as viewed in a bottom and a plane.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a bottom view of a sole structure for a sports shoe according to an embodiment of the present invention;

FIG. 2 is a top plan view of the sole structure of FIG. 1;

FIG. 3 is a cross sectional view of FIG. 1 taken along line III-III;

FIG. 4 is a cross sectional view of FIG. 1 taken along line IV-IV;

FIG. 5 is a longitudinal sectional view of FIG. 1 taken along line V-V;

FIG. 6 is an enlarged view of a portion of a forefoot foreside region of the sole structure of FIG. 1;

FIG. 7 is an enlarged view of a portion of a midfoot region of the sole structure of FIG. 1;

FIG. 8 is a sectional view of FIG. 6 taken along line VIII-VIII;

FIG. 9 is a sectional view of FIG. 6 taken along line IX-IX;

FIG. 10 is a sectional view of FIG. 7 taken along line X-X;

FIG. 11 is a sectional view of FIG. 7 taken along line XI-XI;

FIG. 12 is a sectional view of a portion of the sole structure of FIG. 1 to explain an assembly method of the sole structure;

FIG. 13 is a sectional view of a portion of a variant of the sole structure of FIG. 1;

FIG. 14 is a sectional view of a portion of another variant of the sole structure of FIG. 1;

FIG. 15 illustrates the way and result of analysis in order to see the effects of the present invention;

FIG. 16 is a side view of a protrusion structure of Sample 1 for use in analysis of FIG. 15;

FIG. 17 is a side view of a protrusion structure of Sample 2 for use in analysis of FIG. 15;

FIG. 18 is a side view of a protrusion structure of Sample 3 for use in analysis of FIG. 15;

FIG. 19 is a side view of a protrusion structure of Sample 4 for use in analysis of FIG. 15; and

FIG. 20 illustrates the result of two-point threshold experiments in order to examine sensing ability of foot soles of human beings.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be hereinafter described in accordance with the appended drawings.

FIGS. 1 to 12 show a sole structure for a sports shoe according to an embodiment of the present invention. In the following description, upper, lower, forward, and rearward indicate upper, lower, forward, and rearward of the shoe, respectively. That is, for example, in FIGS. 3 and 4, upper and lower indicate upper and lower of these drawings respectively. In FIG. 1, forward and rearward indicate upward and downward of the drawing. Also, in FIGS. 1 and 2, reference H designates a heel region of the sole structure, M designates a midfoot region, and F designates a forefoot region.

As shown in FIGS. 1 to 5, Sole structure 1 includes a sole body 2 of an elastic material that extends from the heel region H through the midfoot region M to the forefoot region F. The sole body 2 has a sole bottom surface 20 that is disposed on a ground surface side (i.e. lower side of FIGS. 3 and 4) and a sole top surface 21 that is disposed on a foot sole contact side opposite the ground surface side.

There are provided a plurality of first protrusions 3 of elastic material on the sole bottom surface 20. Similarly, there are provided a plurality of second protrusions 4 of elastic material on the sole top surface 21. In this exemplification, the first and second protrusions 3, 4 are provided mainly on the forefoot region F and the midfoot region M of the sole structure 1 and are not provided on the heel region H. The first protrusions 3 and the second protrusions 4 are disposed oppositely to each other in a vertical direction on opposite sides of the sole body 2. Preferably, the first protrusion 3 and the second protrusion 4 corresponding to the first protrusion 3 have centers that are aligned with each other in the vertical direction.

The first protrusions 3 are provided discretely from and unoverlappingly with the adjacent first protrusions 3. Likewise, the second protrusions 4 are provided discretely from and unoverlappingly with the adjacent second protrusions 4. Each of the first and second protrusions 3, 4 has a round shape in planar and bottom views on a foreside of the forefoot region F of the sole structure 1 and an elliptic shape elongating substantially in a longitudinal direction (i.e. foot length direction) in planar and bottom views on a rear side (including a thenar) of the forefoot region F to the midfoot region M of the sole structure 1 (see FIGS. 1 and 2).

In the thenar, each of the elliptic shaped protrusions 3, 4 has a major axis (see an arrow mark a of FIG. 2) that is inclined toward the lateral side by 5 to 12 degrees relative to the longitudinal direction (i.e. foot length direction) of the sole structure 1. In the midfoot region M, each of the elliptic shaped protrusions 3, 4 has a major axis (see an arrow mark b of FIG. 2) that is inclined toward the lateral side by −5 to 25 degrees (that is, 5 degrees toward the medial side to 25 degrees toward the lateral side) relative to the longitudinal direction (i.e. foot length direction) of the sole structure 1. That is based on consideration of shearing direction relative to the sole structure 1 during running activities.

The distance or center distance between the adjacent second protrusions 4 (similar for the distance or center distance between the adjacent first protrusions 3) in the foot width direction as well as in the foot length direction is greater on the rear side of the forefoot region F and the midfoot region M than on the foreside of the forefoot region F. That is, as shown in FIG. 2, regarding a distance of the adjacent second protrusions 4,

S₁′>S₁, S₁″>S₁, S₂′>S₂, S₂″>S₂

wherein S₁: the distance in the foot width direction on the foreside in the forefoot region F; S₁′: the distance in the foot width direction on the rear side in the forefoot region F; S₁″: the distance in the foot width direction in the midfoot region M; S₂: the distance in the foot length direction on the foreside in the forefoot region F; S₂′: the distance in the foot length direction on the rear side in the forefoot region F; S₂″: the distance in the foot length direction in the midfoot region M.

Also, in the rear side of the forefoot region F and the midfoot region M of the sole structure 1, the distance or center distance between the adjacent second protrusions 4 (similar for the distance or center distance between the adjacent first protrusions 3) is greater in the foot length direction than in the foot width direction. That is, as shown in FIG. 2,

S₂′>S₁′, S₂″>S₁″

The reason why the distance between the adjacent first protrusions 3 and the distance between the adjacent second protrusions 4 are adjusted in such a manner is due to the above-mentioned result of two-point threshold experiment using toothpicks.

In the sole structure 1 shown in this embodiment, for example, the distances of the protrusions are set as follows:

S₁≈10 mm, S₂≈10 mm, S₁′≈12 mm S₁″≈12 mm, S₂′≈15 mm, S₂″≈15 mm

As shown in FIGS. 3 and 4, a sectional shape of the first protrusion 3 is formed such that it becomes gradually small as it leaves the sole bottom surface 20. A distal end portion of the first protrusion 3 has a convex surface that protrudes downwardly (in this exemplification, a curved surface shape that curves downwardly convexly). A sectional shape of the second protrusion 4 is formed such that it becomes gradually small as it leaves the sole top surface 21. A distal end portion of the second protrusion 4 has a convex surface that protrudes upwardly (in this exemplification, a curved surface shape that curves upwardly convexly). The curved surface of each of the distal end portions of the first and second protrusions 3, 4 may be formed of an arcuate shaped surface composed of single circular arc. Alternatively, it may be formed of a plurality of arcuate shaped surfaces composed of a plurality of circular arcs. In this example, not only in the round shaped protrusions on the foreside of the forefoot region F but also in the elliptical shaped protrusions on the rear side of the forefoot region F to the midfoot region M (for the elliptical shaped protrusions, in the foot width direction as well as foot length direction), the distal end portion of the second protrusion 4 is formed of single circular arc of grater radius of curvature, and the distal end portion of the first protrusion 3 is formed of a central circular arc of grater radius of curvature disposed in the center of the first protrusion 3 and a side circular arc of smaller radius of curvature disposed around and connected to the central circular arc.

The amount of projection of the second protrusion 4 relative to the sole top surface 21 is made smaller than the amount of projection of the first protrusion 3 relative to the sole bottom surface 20 (see FIGS. 3 to 5). As a result, a surface on a foot sole contact side of the sole structure 1 has an irregular shape of shallow steps that is combined with convex portions of the second protrusions 4 and concave portions of the sole top surface 21. Additionally, in FIGS. 3 to 5, an upper U is provided on the sole structure 1 (only a portion of the upper U is shown in the drawings) and a bottom surface Ua of the upper U is bonded to the distal end portions of curved shapes of the second protrusions 4. Thereby, an irregular shape of shallow steps is formed on the bottom surface Ua of the upper U. Ina sports shoe employing the sole structure 1, preferably, an insole is not used, and a foot sole of a shoe wearer is adapted to directly contact the bottom surface Ua of the upper U.

As shown in FIGS. 6 and 7 that are partially enlarged view of FIG. 1, the first protrusions 3 on the sole bottom surface 20 are coupled to the diagonally adjacent first protrusions 3 through connections 30 of elastic material. The first protrusions 3 are elastically supported in the vertical direction by these connections 30, but the connections 30 are optional. In FIG. 1, a region g in which connections 30 are not provided extends along the foot width direction and the region g corresponds to a position of the Metatarsophalangeal joints of a foot. Such region g without connections 30 is more easily bendable than the other regions, so that satisfactory bendability of the forefoot region F during running can be secured.

As shown in FIGS. 8 and 9 that are sectional views of FIG. 6 and in FIGS. 10 and 11 that are sectional views of FIG. 7, a mesh sheet 5 made of synthetic resin such as nylon or the like is attached on the bottom surface 20 of the sole body 2. The first protrusions 3 and the connections 30 are formed on a lower surface of the mesh sheet 5. In this example, the first protrusions 3 on the lower side and the second protrusions 4 on the upper side are formed separately from each other. That is, as shown in FIG. 12, the mesh sheet 5 and the sole body 2 are separately prepared, the mesh sheet 5 having the first protrusion 3 formed on the bottom surface thereof, and the sole body 2 having the second protrusion 4 integrally formed therewith in a different process. Then, a top surface of the mesh sheet 5 is bonded to the sole bottom surface 20 of the sole body 2. The reason why such mesh sheet is used is that forming the first protrusions 3 is facilitated, a bonding surface to the sole bottom surface 20 of the sole body 2 is secured, and alignment of the first and second protrusions 3, 4 disposed opposite each other in the vertical direction is facilitated with the entire weight of the sole structure 1 lightened.

The first protrusion 3 is formed of synthetic resin or foamed synthetic resin such as polyurethane (TPU) and the like. The second protrusion 4 is formed of synthetic resin or foamed synthetic resin such as ethylene-vinyl acetate copolymer (EVA) and the like. A hardness of the first protrusion 3 is made relatively higher in consideration of wear resistance, and a harness of the second protrusion 4 is made relatively lower in consideration of foot contact feeling. Specifically, the hardness of the first protrusion 3 is set at 40 to 80 A in Asker A, and the hardness of the second protrusion 4 is set at 30 to 70 c in Asker C.

In addition, as shown in FIG. 13, the first and second protrusions 3, 4 and the sole body 2 are integrally formed with each other. In this case, accurate and secure alignment of the first and second protrusions 3, 4 is achieved. Also, it eliminates the necessity for aligning the first and second protrusions 3, 4 after forming of the protrusions thus simplifying an assembly process of the sole structure. As shown in FIG. 19, the sole body 2 may have a hollow 2h inside, alternatively, a lightweight elastic member provided separately may be inserted into the hollow 2h at a position corresponding to the first and second protrusions 3, 4. Such structure can make the entire structure lighter in weight.

As shown in FIGS. 12 and 13, a base surface 3B of the first protrusion 3 and a base surface 4B of the second protrusion 4 have identical shapes and sizes and are disposed opposite each other in the vertical direction with the sole body 2 therebetween, the base surface 3B being a mating surface of the first protrusion 3 with the mesh sheet 5 or an intersecting plane (see a dotted line) of the sole bottom surface 20 relative to the first protrusion 3, and the base surface 4B being an intersecting plane (see a dotted line) of the sole top surface 21 relative to the second protrusion 4. The outer surface of the first protrusion 3 forms an angle of a with the lower surface of the mesh sheet 5 or the sole bottom surface 20, the angle being obtuse along the entire periphery. Likewise, the outer surface of the second protrusion 4 forms an angle of β with the sole top surface 21, the angle being obtuse along the entire periphery.

In this example, wherein the protruding amount of the first protrusion 3 from the lower surface of the mesh sheet 5 or the sole bottom surface 20 is d₁, the protruding amount of the second protrusion 4 from the sole top surface 21 is d₂, and a thickness of the sole body 2 is t, the values of d₁, d₂and t are set as follows:

d₁=0.5 mm, d₂=1.5 mm, t=4.5-7.5 mm

Next, an action and effect of this embodiment will be explained.

when a shoe wearer strikes onto the ground, force applied to the sole structure 1 from the ground surface is transmitted from the first protrusions 3 on the side of the sole bottom surface 20 through the sole body 2 to the second protrusions 4 on the side of the sole top surface 21, and the second protrusions 4 transmit information of the force from the ground surface to the foot sole of the shoe wearer. Also, at that moment, distribution of the force applied to the first protrusions 3 from the ground surface varies according to irregularities of the ground. The state of such variation is transmitted through the sole body 2 to the second protrusions 4 and through the second protrusions information on the irregularities of the ground is transmitted to a foot sole of the shoe wearer.

Moreover, in the sole structure 1, the sectional shape of the first protrusion 3 is formed in such a way as to gradually become smaller as it leaves the sole bottom surface 20 and the distal end portion of the first protrusion 3 has a convex surface that protrudes downwardly (in this example, an arcuate shaped surface). Thereby, as can be seen from the above-mentioned analysis by FEM (see Samples 2, 3 of FIG. 15), as the force applied to the first protrusion 3 from the ground surface at the time of striking the ground increases, the first protrusion 3 elastically deforms compressively and the contact area of the first protrusion 3 with the ground surface increases. On the other hand, the sectional shape of the second protrusion 4 as well corresponding to the first protrusion 3 is formed in such a way as to gradually become smaller as it leaves the sole top surface 21 and the distal end portion of the second protrusion 4 has a convex surface that protrudes upwardly (in this example, an arcuate shaped surface). Thereby, similarly, as can be seen from the above-mentioned analysis by FEM (see Samples 2, 3 of FIG. 15), as the force applied from the foot sole of the shoe wearer to the second protrusions 4 corresponding to the first protrusions 3 at the time of striking the ground increases, the second protrusion 4 elastically deforms compressively and the contact area of the second protrusion 4 with the foot sole increases. As a result, information on the contact area with the ground surface at the time of striking the ground is transmitted to the foot sole of the shoe wearer accurately.

In such a manner, according to this embodiment, ground surface information acting on the sole bottom surface 20 (i.e. contact area with the ground as well as reactive force from the ground and irregularities of the ground) can be transmitted correlatedly with each other to the foot sole of the shoe wearer accurately.

In the above-mentioned embodiment, an example was shown in which the distal end portion of the second protrusion 4 was provided in such a way as to directly abut on the upper bottom surface Ua that constitutes the foot sole contact surface, but an application of the present invention is not limited to such an example. The present invention is also applicable to an example in which the distal end portion of the second protrusion 4 directly constitutes the foot sole contact surface. The following footwear is given as such an example:

Footwear in which a bottom surface of an upper has an annular shape that extends along an outer perimeter of a top surface of a sole body and such an annular shaped bottom surface of the upper is fixedly attached only to the outer perimeter of the top surface of the sole body by an adhesive, sewing or the like; footwear in which an upper is not provided at a large portion of footwear, e.g. footwear in which a band-shaped upper is provided at only a portion of footwear; and footwear having no upper provided, e.g. a sandal and the like.

In the above-mentioned embodiment, the sole structure was applied to sports shoes such as running shoes and the like, but the present invention also has application to footwear in general including walking shoes, sandals, boots and the like.

INDUSTRIAL APPLICABILITY

As mentioned above, the present invention is of use to a sole structure for footwear, and it is especially suitable for a sole structure that requires accurate transmissibility of ground surface information acting on a sole bottom surface (i.e. reactive force from the ground, irregularities of the ground and contact area with the ground) to a foot sole of a shoe wearer.

Sole Structure for Footwear

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