Shoe sole

Abstract

Disclosed is a shoe sole having an upwardly sloped front side and an upwardly rear side so that it has a substantially arch-shaped bottom surface, in which a middle sole made of a rigid material is embedded in an outsole. A non-slip sole is attached over the total bottom surface of the outsole. An arch-shaped groove is formed at a center portion of the bottom surface of the outsole. An elliptical stamping cushion is installed in the arch-shaped groove and it is made of a material that is a softer than the outsole. The middle shoe is rounded at a substantially arch shape such that it is corresponding to the shape of the outsole. A rib-shaped reinforcing portion is provided at a middle portion of the middle sole. An uneven surface is provided on an upper surface and a lower surface of the middle sole, respectively. A plurality of through holes are formed through the middle sole and a plurality of cut-away portions are formed at positions of the front side of the middle sole, thereby forming resilient supporting portions.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a shoe sole having an upwardly sloped front side and an upwardly rear side so that it has a substantially arch-shaped bottom surface, in which a middle sole made of a rigid material is embedded in an outsole. More particularly, the present invention relates a shoe sole capable of allowing a user to walk in such a manner that the total portions of the foot can contact the ground in sequence with absorbing a shock given by a weight of the user while walking, by attaching an elliptical stamping cushion made of a material that is a softer than the outsole in an arch-shaped groove formed at a rear lower portion of the outsole, and which is capable of allowing the stamping cushion to be rapidly compressed and to rapidly expand so as to alleviate the shock by embedding a plate spring having a circular shape in a main body of the stamping cushion, and which is capable of preventing water from penetrating into the main body of the stamping cushion by installing a waterproof cover on an outer surface of the stamping cushion.

A prior art shoe sole structure is shown in Korean Utility Model Registration No. 226048. This shoe sole structure includes a resilient material, which has a U-shape and is embedded in a heel portion of an outsole usually made of polyurethane. If a user putts on a shoe having the shoe sole, the weight of the user tends to concentrate in the heel portion while wearing the shoe. Then, the U-shaped resilient material becomes slightly constricted and it has a function of supporting the weight of the user, thereby absorbing and alleviating a shock given to the sole of the foot to a minimum.

One of the principal problems associated with resilient material is that it cannot firmly being attached to the outsole. The resilient material comprises a U-shaped steel plate having a smooth surface. The outsole is usually made of polyurethane and the resilient material is made of the steel plate, so that they cannot firmly combine with each other.

If a user walks on a street while wearing the shoe, the U-shaped resilient material becomes constricted and restored repeatedly, thereby absorbing and alleviating a shock given to the sole of the foot. Since the outsole and the resilient material are not firmly combined with each other, a nerve-racking noise may be generated there between at the time of contacting the ground. In addition, the outsole usually made of polyurethane tears easily because of the contact with the U-shaped resilient material made of steel plate.

Another prior art shoe sole structure is shown in Korean Patent Registration No. 575875. This shoe sole structure includes an outsole having a rear side slanted upwards. In this shoe structure, an arch-shaped groove is formed at the center of a lower surface of the outsole and a rigid middle sole is installed at an upper surface of the outsole. A cushion material is inserted into the arch-shaped groove. A non-slip sole is attached onto the total bottom surface of the outsole. Additional cushion materials are attached to front and rear upper surfaces of the rigid middle sole.

If a user a user walks on a street while wearing the shoe having this shoe structure, the heel is the first portion of the foot to contact the ground. As the step continues and the remainder of the foot contacts the ground, the weight of the body is carried forward along the lateral side of the foot. This type of walking is what we called Masai walking, which is developed by Karl Mueller. It is well known that this type of walking is good for health.

One drawback of prior art shoe sole is that a shock given through the heel portion given by the weight of the user while walking on the street with wearing the shoe is hardly absorbed and alleviated. In detail, since the total shoe sole is made of some same materials, the shoe may have the same capacity for absorbing the shock over the total weight bearing surfaces of the sole. As a result, the shoe having the shoe sole structure as described above does not fully absorb and sufficiently alleviate the shock given by the weight of the user while walking.

Another drawback of prior art shoe sole is that the user of the shoe inconvenience oneself while walking on the street with wearing the shoe. In detail, since the rigid middle sole is installed at an upper surface of the outsole so as to maintain the arch shape of shoe, it gives a feel that the user steps some hard object while walking.

Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, an object of the present invention is to provide a shoe sole capable of allowing a user to walk in such a manner that the total portions of the foot can contact the ground in sequence with absorbing a shock given by a weight of the user while walking, by attaching an elliptical stamping cushion made of a material that is a softer than the outsole in an arch-shaped groove formed at a rear lower portion of the outsole, and which is capable of continuously maintaining the arch shape of the shoe sole so as to providing the user with safe walking by embedding a middle sole in the outsole, and which is capable of allowing the stamping cushion to be rapidly compressed and to rapidly expand so as to alleviate the shock by embedding a plate spring having a circular shape in a main body of the stamping cushion, and which is capable of preventing water from penetrating into the main body of the stamping cushion by installing a waterproof cover on an outer surface of the stamping cushion.

SUMMARY OF THE INVENTION

To accomplish the above object, the present invention provides a shoe sole, of the type consisting of an outsole having a front side and a rear side of a bottom surface thereof, which are sloped upwards, a middle sole being made of a rigid material and being installed in the outsole, and a non-slip sole being attached over the total bottom surface of the outsole,

characterized in that it comprises an arch-shaped groove formed at a center portion of the bottom surface of the outsole, an elliptical stamping cushion installed in the arch-shaped groove, the stamping cushion being made of a material that is a softer than the outsole, in which the non-slip sole is attached over the total bottom surface of the outsole and the exposed surface of the stamping cushion, in which the middle shoe is rounded at a substantially arch shape such that it is corresponding to the shape of the outsole, in which the thickness of a front end of the middle sole is smaller than those of other portions thereof, in which a rib-shaped reinforcing portion is provided at a middle portion of the middle sole, in which an uneven surface is provided on an upper surface and a lower surface of the middle sole, respectively, in which a plurality of through holes are formed through the middle sole and a plurality of cut-away portions are formed at positions of the front side of the middle sole, which are corresponding to the toe, thereby forming resilient supporting portions.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a shoe sole according to the present invention;

FIG. 2 is an exploded sectional view of the shoe sole as shown in FIG. 1;

FIG. 3A is a plan view of a middle sole made of a rigid material according to the present invention, and FIG. 3B is a sectional view of the middle sole according to the present invention;

FIG. 4 is a sectional view of a stamping cushion according to the present invention;

FIG. 5A is a perspective view of a plate spring according to a first preferred embodiment of the present invention, FIG. 5B is a sectional view of the plate spring according to the first preferred embodiment of the present invention; and

FIG. 6 is a perspective view of a plate spring according to a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the shoe sole according to the present invention will be explained in more detail with reference to the accompanying drawings FIGS. 1 to 6.

As shown in FIGS. 1 and 2, the shoe sole comprises an upwardly sloped front side and an upwardly rear side so that it has a substantially arch-shaped bottom surface. A middle sole 30 made of a rigid material is embedded in the outsole 10. An arch-shaped groove 11 is formed at a rear lower portion of the outsole 10. At this time, the position of the arch-shaped groove 11 is corresponding to one's heel. An elliptical stamping cushion 20 is installed in the arch-shaped groove 11. Preferably, the stamping cushion 20 is made of a material that is a softer than the outsole 10. A non-slip sole 40 is attached over the total bottom surface of the outsole 10 and the exposed surface of the stamping cushion 20.

The outsole 10 of the walking shoe according to the present invention is made of soft foam polyurethane and thereby it has a cushion effect. As described above, the stamping cushion 20 is made of a material such as a compressed sponge, which is a softer than the outsole 10. Preferably, the softness of the stamping cushion 20 is typically about half the degree of soft that would do all the outsole 10.

As best seen in FIGS. 2 and 4, the stamping cushion 20 is provided with a waterproof cover 21 for preventing water from penetrating into a main body 20a of the stamping cushion 20. The waterproof cover 21 is made of a soft material such as a sponge, EVA, etc. and it is attached to an outer surface of the stamping cushion 20. Alternatively, the waterproof cover 21 can comprise a vinyl that may be wound around or applied onto the total outer surface of the main body 20a of the stamping cushion 20.

A pair of plate springs 22 is embedded in the main body 20a of the stamping cushion 20. The plate springs 22 are made of an elastic metal plate and are disposed in the main body 20a in such a manner that they are opposite to each other. As shown in FIGS. 5A and 5B, the plate spring 22 according to the first preferred embodiment of the present invention has a circular-shaped tension portion 23 and two resilient portions 25, which are integrally formed with each other. One end of the resilient portion 25 is integrally connected with one side of the circular-shaped tension portion 23, respectively. This structure widens the space between two resilient portions 25. A support pin 24 is inserted into an opening of the circular-shaped tension portion 23. A reinforcing portion 26 is added to an outer surface of the resilient portion 25 in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern. At positions adjacent to the reinforcing portion 26, a plurality of through holes 27 are formed through the resilient port ion 25. A rounded portion 28 is formed at a free end of the resilient portion 25, respectively.

As shown in FIGS. 2 and 3, the middle sole 30 is rounded at a substantially arch shape such that it is corresponding to the shape of the outsole 10. At this time, the thickness of a front end of the middle sole 30 is smaller than those of other portions thereof. A rib-shaped reinforcing portion 33 is provided at a middle portion of the middle sole 30. An uneven surface 31 is provided on an upper surface and a lower surface of the middle sole 30, respectively. A plurality of through holes 32 are formed through the middle sole 30. A plurality of cut-away portions 34 are formed at positions of the front side of the middle sole 30, which are corresponding to the toe, thereby forming resilient supporting portions 35.

FIG. 6 shows a plate spring 22a according to the second preferred embodiment of the present invention. The plate springs 22a are made of an elastic metal plate. The plate spring 22a has circular-shaped tension portions 23 and rounded resilient portions 25, which are integrally formed with each other. Both ends of the resilient portion 25 are integrally connected with one side of the circular-shaped tension portion 23, respectively. The resilient portion 25 extends between the circular-shaped tensions portions 23. The resilient portion 25 is radially outwardly rounded between the circular-shaped tension portions 23. This structure widens the space between two resilient portions 25. A reinforcing portion 26 is added to an outer surface of the resilient portion 25 in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern. At positions adjacent to the reinforcing port ion 26, a plurality of through holes 27 are formed through the resilient portion 25.

MODE FOR INVENTION

Having described shoe sole according to the preferred embodiment of the present invention in detail, the operational relationship of the shoe sole can be understood as follows with reference to accompanying drawings FIGS. 1 to 6.

In a process for manufacturing a shoe, the shoe sole according to the present invention may be attached to a bottom surface of a shoe sheath. If a user walks on a street while wearing the shoe having this shoe structure, the heel is the first portion of the foot to contact the ground. That is, if the user walks on a street to Masai's manner of walking, the heel portion of the foot contacts the ground earliest of all.

As shown in FIG. 1, in the shoe sole according to the present invention, a front side and a rear side of the bottom surface of the outsole 10 of which the middle sole 20 is attached to the upper surface of the outsole 10 are sloped upwardly, thereby forming a substantially arch shape of the shoe.

If a user walks on a street while wearing the shoe having this shoe structure, the heel is the first portion of the foot to contact the ground. As the step continues and the remainder of the foot contacts the ground, the weight of the body is carried forward along the outer circumferential side of the foot. If the heel leaves the ground, the weight of the body shifts back towards the medial side of the foot. Continuously, if the medial side leaves the ground, the weight of the body shifts back towards the toe, especially a great toe of the foot.

As shown in FIGS. 1 to 5, the elliptical stamping cushion 20 is installed in the arch-shaped groove 11 formed at a rear lower portion of the outsole 10, which is corresponding to the hill portion contacting the ground at first. Since the stamping cushion 20 is made of a material that is a softer than the outsole 10 and a pair of plate springs 22 is embedded in the main body 20a of the stamping cushion 20, the stamping cushion 20 can primarily absorb the shock given by a weight of the user while walking.

As the stamping cushion 20 contacts the ground and then it begins to be compressed, the plate springs 22 embedded in the stamping cushion 20 is also compressed, thereby absorbing the shock given by a weight of the user while walking. As the stamping cushion 20 leaves the ground, the plate springs 22 restores its original state due to the elastic force thereof and the stamping cushion 20 restores its original oval shape.

Meanwhile, if the stamping cushion 20 contacts the wet ground and then it is compressed while walking, water can flow into the main body 20a of the stamping cushion 20, which is made of a material belonging to the sponge system. Because of the waterproof cover 21 is attached to an outer surface of the stamping cushion 20 or is wound around or applied onto the total outer surface of the main body 20a of the stamping cushion 20, it is possible to prevent water from flowing into the stamping cushion 20 while it being compressed.

If water flows into the main body 20a of the stamping cushion 20, the main body 20a made of a material belonging to the sponge system hydrolyzes and thereby it is apt to corrode. Since the waterproof cover 21 for preventing water from penetrating into the main body 20a of the stamping cushion 20 is attached to the total outer surface of the stamping cushion 20, it is possible to prevent water from flowing into the main body 20a of the stamping cushion 20 while it being compressed. Accordingly, there is nothing to worry about the corrosion of the main body 20a of the stamping cushion 20.

As described above, the main body 20a of the stamping cushion 20 is made of a material belonging to the sponge system and a pair of plate springs 22 embedded in the main body 20a of the stamping cushion 20 is made of the steel plate. That is, since the main body 20a is usually made of polyurethane and the plate springs 22 are made of the steel plate, they cannot firmly combine with each other.

To solve this problem, the reinforcing portion 26 is added to the outer surface of the resilient portion 25 in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern. At positions adjacent to the reinforcing portion 26, a plurality of through holes 27 are formed through the resilient portion 25. A rounded portion 28 is formed at a free end of the resilient portion 25, respectively. Due to this structure, the plate springs 22 are firmly combined with the main body 20a. Since the outwardly projected portions, the recessed portions and the through holes 27 in the reinforcing portion 26 are filled with the materials of the main body 20a, the materials of the main body 20a are integrally formed together. In addition, the rounded portion 28 is combined with the materials of the main body 20a in such a manner that it is driven into the materials of the main body 20a. Consequently, the plate springs 22 are firmly combined with the materials of the main body 20a.

Meanwhile, the support pin 24 is inserted into the opening of the circular-shaped tension portion 23 of the plate spring 22. If the plate spring 22 is continuously compressed and restores its initial state, the circular-shaped tension portion 23 is apt to cause breakage owing to the fatigue accumulated thereon. At this time, the support pin 24 inserted into the opening of the circular-shaped tension portion 23 prevents the circular-shaped tension portion 23 from being compressed and restoring its initial state, thereby minimizing the breakage of the circular-shaped tension portion 23.

If the plate spring 22 is continuously compressed and restores its initial state, the main body 20a made of soft materials belonging to the sponge system is apt to cause breakage by means of the distal end of the resilient portion 25 made of steel plate. To solve this problem, the rounded portion 28 is provided at the distal end of the resilient portion 25 so that it is possible to minimize the breakage of the main body 20a of the plate spring 22.

The plate spring 22 has a relatively wide width of 40 mm or so. If a user walks on a street while wearing the shoe, the plate spring 22 is not always equally stepped on by means of the heel. Since different persons have different manners of walking and the road is not always smooth, the plate spring 22 is unevenly inwardly or outwardly stepped on by means of the heel.

If the plate spring 22 is continuously stepped on to one side by means of the heel, it is apt to cause transform of the plate spring 22. According to the present invention, the reinforcing portion 26 is added to the outer surface of the resilient portion 25 in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern. Due to this structure, if the plate spring 22 is continuously stepped on to one side by means of the heel, the reinforcing portion 26 supports the plate spring 22 so as to prevent the plate spring 22 from being transformed. As a result, the stamping cushion 20 can be equally stepped on and restore its initial state while walking.

Hereinafter, the operational relationship of the middle sole 30 can be understood as follows with reference to accompanying drawings FIGS. 1 to 3.

The middle sole 30 made of a rigid material is embedded in the outsole 10. This middle sole 30 has an arch shape that is substantially the same as the shape of the outsole 10 so as to continuously maintain the arch shape of the outsole 10. The rib-shaped reinforcing portion 33 is provided at a middle portion of the middle sole 30. This rib-shaped reinforcing portion 33 has a function of preventing the middle portion of the middle sole 30 from unfolding so that the middle portion 30 is not transformed.

Since the middle sole 30 of the walking shoe according to the present invention is made of soft foam polyurethane and is embedded in the outsole 10, it is possible to attenuate the oppressive feeling and to alleviate the pain applied to the sole of the foot. The shoe sole of the present invention has significant advantages over previously known shoe sole.

At the joint between the middle sole 30 and the outsole 10, the uneven surface 31 is provided on an upper surface and a lower surface of the middle sole 30, respectively. In addition, a plurality of through holes 32 are formed through the middle sole 30 and a plurality of cut-away portions 34 are formed at positions of the front side of the middle sole 30. Due to this structure, the middle sole 30 is firmly combined with the outsole 10 so that it is possible to prevent the middle sole 30 from being released from the outsole 10.

The pluralities of cut-away portions 34 are formed at positions of the front side of the middle sole 30, which are corresponding to the toe, thereby forming resilient supporting portions 35. When a user wears the shoes according to the present invention, the toe is corresponding to the resilient supporting portions 35. At this time, the user feels at ease due to operation of the resilient supporting portions 35.

Since the pluralities of cut-away portions 34 are formed at both sides of the front portion of the middle sole 30, this front portion of the middle sole 30 can be easily bent so that the user can move the toe with easy.

Hereinafter, the operational relationship of the plate spring 22a can be understood as follows with reference to accompanying drawing FIG. 6.

The plate spring 22a according to the second embodiment of the present invention operates in the same manner as the plate spring 22 according to the first embodiment of the present invention, except for partial operation.

In the plate spring 22a according to the second preferred embodiment of the present invention, the rounded resilient portions 25 are integrally formed with the circular-shaped tension portions 23 and extend between the circular-shaped tensions portions 23. Between the circular-shaped tensions portions 23, the resilient portions 25 are radially outwardly rounded and they exhibit an elastic force. Accordingly, the plate spring 22a is formed as a substantially oval shape. Due to this structure, when the plate spring 22a is continuously compressed and restores its initial state, it is possible to prevent the plate spring 22a from being damaged.

In addition, the reinforcing portion 26 is added to an outer surface of the resilient portion 25 in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern. Accordingly, the degree of strength of the resilient portion 25 is enhanced due to operation of the reinforcing portion 26. If the resilient portion 25 is pressed down at its outer side or inner side, it is possible to minimize the excessive compression of the resilient portion 25 due to operation of the reinforcing portion 26. As a result, it is possible to prevent the user from getting sprained due to operation of the reinforcing portion 26.

In the description of the operation according to the present invention as described above, it should be noted that, for the sake of clarity and understanding of the invention, the detailed description relative to the non-slip sole 40 attached to the lower surfaces of the outsole 10 and the stamping cushion 20 is omitted. As shown in FIG. 1, the non-slip sole 40 is attached over the total bottom surface of the outsole 10 and the exposed surface of the stamping cushion 20 in a state that an elliptical stamping cushion 20 is installed in the arch-shaped groove 11.

INDUSTRIAL APPLICABILITY

As described above, the shoe sole according to the present invention is capable of allowing a user to walk in such a manner that the total portions of the foot can contact the ground in sequence due to absorbing a shock given by a weight of the user while walking, by attaching an elliptical stamping cushion made of a material that is a softer than the outsole in an arch-shaped groove formed at a rear lower portion of the outsole, and which is capable of continuously maintaining the arch shape of the shoe sole so as to providing the user with safe walking by embedding a middle sole in the outsole, and which is capable of allowing the stamping cushion to be rapidly compressed and to rapidly expand so as to alleviate the shock by embedding a plate spring having a circular shape in a main body of the stamping cushion.

In addition, the shoe sole according to the present invention is capable of preventing water from penetrating into the main body of the stamping cushion by installing a waterproof cover on an outer surface of the stamping cushion.

While the present invention has been particularly shown and described with reference to the particular embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be effected therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A shoe sole comprising an outsole having a front side and a rear side of a bottom surface thereof, which are sloped upwards, a middle sole being made of a rigid material and being installed in the outsole, and a non-slip sole being attached over the total bottom surface of the outsole,

wherein an arch-shaped groove is formed at a center portion of the bottom surface of the outsole, an elliptical stamping cushion is installed in the arch-shaped groove, the stamping cushion being made of a material that is a softer than the outsole, the non-slip sole is attached over the total bottom surface of the outsole and an exposed surface of the stamping cushion and the shoe sole further comprises a waterproof cover attached to an outer surface of the stamping cushion.

2. A shoe sole according to claim 1, wherein the middle sole is rounded at a substantially arch shape such that it is corresponding to the shape of the outsole, the thickness of a front end of the middle sole is smaller than the thickness of other portions thereof, a rib-shaped reinforcing portion is provided at a middle portion of the middle sole, an uneven surface is provided on an upper surface and a lower surface of the middle sole, respectively, a plurality of through holes are formed through the middle sole and a plurality of cut-away portions are formed at positions of the front side of the middle sole, which are corresponding to the toe, thereby forming resilient supporting portions.

3. A shoe sole according to claim 1, further comprising a pair of plate springs that are made of an elastic metal plate and are disposed in the stamping cushion in such a manner that the plate springs are opposite to each other, each the plate spring having a circular-shaped tension portion and resilient portions, which are integrally formed with each other, one end of the resilient portion being integrally connected with one side of the circular-shaped tension portion, respectively, a space between the resilient portions thereby being widened, a support pin being inserted into an opening of the circular-shaped tension portion, a reinforcing portion being situated on an outer surface of the resilient portion in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern, at positions adjacent to the reinforcing portion, a plurality of through holes being formed through the resilient portion, and a rounded portion being formed at a free end of the resilient portion, respectively.

4. A shoe sole according to claim 2, further comprising a pair of plate springs that are made of an elastic metal plate and are disposed in the stamping cushion in such a manner that the plate springs are opposite to each other, each the plate spring having a circular-shaped tension portion and resilient portions, which are integrally formed with each other, one end of the resilient portion being integrally connected with one side of the circular-shaped tension portion, respectively, a space between the resilient portions thereby being widened, a support pin being inserted into an opening of the circular-shaped tension portion, in a reinforcing portion being situated on an outer surface of the resilient portion in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern, at positions adjacent to the reinforcing portion, a plurality of through holes being formed through the resilient portion, and a rounded portion being formed at a free end of the resilient portion, respectively.

5. A shoe sole according to claim 1, further comprising a pair of plate springs that are made of a metal plate and are disposed in the stamping cushion in such a manner that the plate springs are opposite to each other, in the plate spring having circular-shaped tension portions and rounded resilient portions, which are integrally formed with each other, both ends of the resilient portion being integrally connected with one side of the circular-shaped tension portion, respectively, the resilient portion extending between the circular-shaped tension portions, the resilient portion being radially outwardly rounded between the circular-shaped tension portions, a space between the resilient portions thereby being widened, a reinforcing portion being situated on an outer surface of the resilient portion in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern, in which at positions adjacent to the reinforcing portion, a plurality of through holes are formed through the resilient portion.

6. A shoe sole according to claim 2, further comprising a pair of plate springs that are made of a metal plate and are disposed in the stamping cushion in such a manner that the plate springs are opposite to each other, the plate spring having circular-shaped tension portions and rounded resilient portions, which are integrally formed with each other, both ends of the resilient portion being integrally connected with one side of the circular-shaped tension portion, respectively, the resilient portion extending between the circular-shaped tension portions, the resilient portion being radially outwardly rounded between the circular-shaped tension portions, a space between the resilient portions thereby being widened, a reinforcing portion being situated on an outer surface of the resilient portion in a cylindrical embossing pattern thereon, respectively, thereby forming an X-shaped pattern, in which at positions adjacent to the reinforcing portion, a plurality of through holes are formed through the resilient portion.