KR101665346B1 - Drilling bit - Google Patents

Abstract

The present invention relates to a drilling bit capable of facilitating the installation of a steel pipe using a foldable wing bit, comprising: a bit body having an advanced excavation surface formed on one side and a guide groove formed on the other side; A wing bit which is formed on one side or both sides of the shaft body and which can be guided along the guide groove of the bit body and which can be assembled with the bit body about the axis projection guided along the guide groove and pivotable; A stopper member provided on the bit body such that the shaft protrusion is not separated from the guide groove; And an inclination supporting member provided on the bit body or the stopper member and supporting the wing bit in an inclined manner so that the wing bit is rotated and is inclined at a supporting angle with respect to the advancing direction.

Description

Drilling bit

The present invention relates to a drilling bit, and more particularly, to a drilling bit capable of facilitating installation of a steel pipe using a wing bit capable of folding.

Generally, the steel pipe grouting method is an underground excavation assist method that improves the water quality while reinforcing the ground. By installing the steel pipe on the ground and injecting the grout material into the inside of the steel pipe, the steel pipe and the ground are integrally It is characterized by increasing the soil and the shear strength of the rock mass. It is very advantageous in terms of workability and economical efficiency because the injection is performed in the steel pipe.

Such a steel pipe grouting method has been established and widely used as a tunnel reinforcement method in recognition of its effect.

Generally, the steel pipe grouting method includes a step of drilling a ground, a step of inserting a steel pipe provided with a strainer (grout reinjecting part) into the perforated hole, a step of injecting a sealing material between the steel pipe and the perforation hole, While injecting cement.

However, since this method proceeds by inserting the steel pipe after the perforation, there is a problem that it is difficult to insert the steel pipe due to collapse of the perforation hole or mixing of foreign materials in the soft soil layer where the perforation hole is not naturally maintained.

In order to solve the above problems, a technique has been developed in which a steel pipe can be easily installed using a foldable wing bit as disclosed in Korean Patent Registration No. 100919628.

However, such a conventional foldable wing bit is a separate component in which the wing bit and the pin are separated from each other by hinging the wing bit to the bit body by assembling the pin, which is a separate component from the bit body, There is a serious problem that the wing bit and the pin are finely collided with each other due to the great external force and impact generated in the excavation process and the gap is widened or the wing bit or pin is broken.

Since the pin is assembled through the bit body, a part of the pin is exposed, and various foreign substances can easily penetrate between the pin and the gap of the bit body caused by a great external force and impact generated during the excavation process. There is a problem in that the durability becomes very weak such as interfering with the folding or even detaching the pin from the bit body.

In addition, the conventional pins are coupled to the bit body in a deteriorated manner, so that it is very difficult to separate the wing bits in order to repair or replace the wing bits.

In addition, the conventional wing bit is spread at 90 degrees in the traveling direction, and has a problem in that it can not withstand a great resistance when the drill bit travels, and is broken or broken.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art, and it is an object of the present invention to provide a wing bit and a shaft protrusion which are integrally formed with the wing bit and the shaft protrusion integrally and are resistant to external force and impact, The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a drilling bit for facilitating repair and replacement of a wing bit by using a stopper member capable of preventing detachment of wing bit and drastically improving durability. However, these problems are exemplary and do not limit the scope of the present invention.

According to an aspect of the present invention, there is provided a drilling bit comprising: a bit body having an advanced excavation surface formed on one side and a guide groove formed on the other side; A wing bit which is formed on one side or both sides of the shaft body and which can be guided along the guide groove of the bit body and which can be assembled with the bit body about the axis projection guided along the guide groove and pivotable; A stopper member provided on the bit body such that the shaft protrusion is not separated from the guide groove; And an inclination supporting member provided on the bit body or the stopper member and supporting the wing bit in an inclined manner so that the wing bit is rotated and is inclined at a supporting angle with respect to the advancing direction.

Further, according to the idea of the present invention, the bit body is composed of two parts which are detachably fastened to each other by a screw projection part and a screw groove part, and the stopper member may be assembled between the parts.

According to an aspect of the present invention, the bit body includes: a cap portion having the tip excavated surface formed at a tip thereof and a screw groove portion provided at a rear end thereof; And a body portion having a screw protruding portion which is screwed to the screw groove portion of the cap portion at a tip end thereof and in which the guide groove is formed in the middle of the screw protruding portion, the stopper member having a cap portion, And the inclined support member may be an inclined body portion provided near the guide groove portion of the body portion.

According to an aspect of the present invention, the body portion is formed with a wing bit receiving groove having a shape corresponding to a part of the wing bit on one side thereof, and a stopper receiving groove having a shape corresponding to a part of the stopper member is formed on the other side Wherein the guide groove is formed in an inner wall surface of the stopper receiving groove toward the advancing direction, the stopper member having a through hole through which the screw projection of the body passes; And a stopper arm protruding from the stopper body in a direction opposite to the advancing direction so as to close the inlet of the guide groove, wherein the inclined jaw of the inclined support member is formed by a step And a concave inclined surface formed so as to protrude toward the first direction.

According to an aspect of the present invention, the bit body includes: a head portion having the tip excavated surface formed at its tip end, the guide groove formed in the middle in a direction opposite to the advancing direction, and a screw protruding portion provided at a rear end thereof; And a tail portion provided at a tip end thereof with a screw groove portion to be screwed with the screw projection portion of the head portion, wherein the stopper member is provided between the head portion and the tail portion, The stopper can be a slope stop provided on the member.

According to an aspect of the present invention, the head portion is formed with a wing bit receiving groove having a shape corresponding to a part of the wing bit on one side, and a stopper receiving groove having a shape corresponding to a part of the stopper member is formed on the other side Wherein the guide groove is formed in an inner wall surface of the stopper receiving groove in a direction opposite to the traveling direction, and the stopper member includes a stopper body having a through hole through which the threaded portion of the head passes; And a stopper arm protruding in the advancing direction from the stopper body so as to close the entrance of the guide groove, wherein the inclined jaw of the inclined support member is formed to protrude from the stopper arm toward the advancing direction And may include concave slopes.

According to an aspect of the present invention, when the wing bit is rotated and folded on the bit body, the screw protruding portion is provided on both sides of the bit body so as to secure a space for the wing bit accommodating groove capable of accommodating the wing bit. A side cutting portion may be formed on the side surface.

In addition, according to the idea of the present invention, the wing bit has axle protrusions formed on both sides thereof, and the wing bit is pivoted so that a wing bit excavation surface facing forward is formed in a state in which the wing bit is inclined at a supporting angle with respect to the advancing direction And a carbide tip is installed on the advanced excavation surface and the wing bit excavation surface.

According to an aspect of the present invention, the bit body may have a working fluid injection hole formed in a central shaft portion and a working fluid discharge groove formed in an outer side surface thereof.

According to some embodiments of the present invention as described above, it is possible to improve the durability, accuracy, reliability and performance of the apparatus by preventing the wing bit from deviating from the external force and shock generated during excavation, Thereby facilitating repair and replacement, thereby facilitating management of the apparatus. Of course, the scope of the present invention is not limited by these effects.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a part exploded perspective view of a drill bit according to some embodiments of the present invention.
2 is a part assembly perspective view of the excavating bit of Fig.
3 is a perspective view showing the body part of FIG.
Fig. 4 is a plan view showing the body of Fig. 3. Fig.
FIG. 5 is a perspective view showing the wing bit of FIG. 1; FIG.
Fig. 6 is a perspective view showing the stopper member of Fig. 1;
7 is a rear view showing the stopper member of Fig.
8 is a perspective view showing the cap portion of FIG.
9 is a plan view showing the cap portion of Fig.
Figure 10 is a part exploded perspective view of a drill bit according to some other embodiments of the present invention.
11 is a part assembly perspective view of the excavating bit of Fig.
12 is a perspective view showing the stopper member and the wing bit of Fig.
13 is a part exploded perspective view showing a drill bit according to still another embodiment of the present invention.
14 is a part assembly perspective view of the excavating bit of Fig.
15 is a perspective view showing the head of Fig.
16 is a rear perspective view showing the head of Fig.
17 is a perspective view showing the head and the wing bit of Fig. 15;

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention are described in order to more fully explain the present invention to those skilled in the art, and the following embodiments may be modified into various other forms, The present invention is not limited to the embodiment. Rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thickness and size of each layer are exaggerated for convenience and clarity of explanation.

It is to be understood that throughout the specification, when an element such as a film, region or substrate is referred to as being "on", "connected to", "laminated" or "coupled to" another element, It will be appreciated that elements may be directly "on", "connected", "laminated" or "coupled" to another element, or there may be other elements intervening therebetween. On the other hand, when one element is referred to as being "directly on", "directly connected", or "directly coupled" to another element, it is interpreted that there are no other components intervening therebetween do. Like numbers refer to like elements. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items.

Although the terms first, second, etc. are used herein to describe various elements, components, regions, layers and / or portions, these members, components, regions, layers and / It is obvious that no. These terms are only used to distinguish one member, component, region, layer or section from another region, layer or section. Thus, a first member, component, region, layer or section described below may refer to a second member, component, region, layer or section without departing from the teachings of the present invention.

Also, relative terms such as "top" or "above" and "under" or "below" can be used herein to describe the relationship of certain elements to other elements as illustrated in the Figures. Relative terms are intended to include different orientations of the device in addition to those depicted in the Figures. For example, in the figures the elements are turned over so that the elements depicted as being on the top surface of the other elements are oriented on the bottom surface of the other elements. Thus, the example "top" may include both "under" and "top" directions depending on the particular orientation of the figure. If the elements are oriented in different directions (rotated 90 degrees with respect to the other direction), the relative descriptions used herein can be interpreted accordingly.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" include singular forms unless the context clearly dictates otherwise. Also, " comprise "and / or" comprising "when used herein should be interpreted as specifying the presence of stated shapes, numbers, steps, operations, elements, elements, and / And does not preclude the presence or addition of one or more other features, integers, operations, elements, elements, and / or groups.

Hereinafter, embodiments of the present invention will be described with reference to the drawings schematically showing ideal embodiments of the present invention. In the figures, for example, variations in the shape shown may be expected, depending on manufacturing techniques and / or tolerances. Accordingly, the embodiments of the present invention should not be construed as limited to the particular shapes of the regions illustrated herein, but should include, for example, changes in shape resulting from manufacturing.

1 is a part exploded perspective view showing a drill bit 100 in accordance with some embodiments of the present invention. 3 is a perspective view showing the body part 10-2 of FIG. 1, and FIG. 4 is a perspective view of the body part 10-2 of FIG. 3 6 is a perspective view showing the stopper member 30 in Fig. 1, and Fig. 7 is a plan view showing the stopper member 30 in Fig. 6, Fig. 8 is a perspective view showing the cap portion 10-1 in Fig. 1, and Fig. 9 is a plan view showing the cap portion 10-1 in Fig.

1 to 9, a drilling bit 100 according to some embodiments of the present invention includes a bit body 10, a wing bit 20, a stopper member 30 And an inclined support member 40, as shown in Fig.

1 and 2, the bit body 10 has an advanced excavation surface 10a formed on one side thereof and a guide groove GD formed on the other side thereof, and the screw protrusion S1, And can be a kind of prefabricated metal block composed of two parts which are detachably fastened to each other by a screw groove S2.

More specifically, for example, as shown in Figs. 1 and 2, the bit body 10 has a tip portion 10a formed at the distal end thereof, and a screw portion S2 provided at the rear end thereof. A threaded protrusion S1 for screwing the threaded portion S2-1 of the cap portion 10-1 to the threaded portion S2 of the cap portion 10-1 is provided at the front end thereof and the guide groove GD And a body portion 10-2.

8 and 9, the cap portion 10-1 is formed with the advanced excavation surface 10a at its tip, and the advanced excavation surface 10a is provided with a cemented carbide tip (T) can be installed.

8 and 9, in the cap portion 10-1, a working fluid injection hole G1 may be formed in the central shaft portion.

More specifically, as shown in FIGS. 1 and 2, the bit body 10 has a working fluid injection hole G1 formed at a central shaft portion thereof, and a working fluid discharge groove G2 .

Therefore, during excavation, a working fluid such as air or water is injected into the working fluid inlet hole G1 to reduce the impact or impact, and the excavated foreign matter can be easily discharged to the outside along the working fluid discharge groove G2 .

3 and 4, the body 10-2 has a wing bit receiving groove 11 formed on one side thereof and having a shape corresponding to a part of the wing bit 20, A stopper receiving groove 12 having a shape corresponding to a part of the stopper member 30 is formed in the stopper receiving groove 12 and the guide groove GD is formed on the inner wall surface of the stopper receiving groove 12 toward the traveling direction .

The guide groove GD may have a shape corresponding to the shaft protrusion 21 so as to guide the shaft protrusion 21 of the wing bit 20 and have a rounded end.

1, the wing bit 20 is formed on one side or both sides of an axis projection 21 which can be guided along a guide groove GD of the bit body 10, And may be a kind of metal block that can be assembled with the bit body 10 and pivotable about the axis projection 21 guided along the guide groove GD.

More specifically, for example, as shown in Fig. 5, the wing bit 20 has columnar shaft projections 21 formed on both sides thereof, and the wing bit 20 is rotated, A wing bit excavation surface 20a facing forward is formed in a state of being inclined at a supporting angle A with respect to the base 10a and a carbide tip T is installed on the advanced excavation surface 10a and the wing bit excavation surface 20a .

Here, for example, the support angle A may be 30 degrees to 60 degrees or 45 degrees based on the traveling direction. However, the above-mentioned support angle A is not necessarily limited to this, but can be optimized and designed in accordance with the material, specification, work environment, etc. of the parts.

6 and 7, the stopper member 30 may be a kind of metal structure provided on the bit body 10 so that the shaft protrusion 21 is not separated from the guide groove GD, Lt; / RTI >

More specifically, for example, as shown in FIGS. 1 and 2, the stopper member 30 is installed between the cap portion 10-1 and the body portion 10-2, Shaped stopper body 31 formed with a through hole W through which the threaded protrusion S1 of the stopper body 10-2 passes, and a stopper body 31 for closing the inlet of the guide groove GD, And four stopper arms 32 projecting in a direction opposite to the advancing direction.

Therefore, as shown in Figs. 1 and 2, after the four axial projections 21 of the two wing bits 20 are completely inserted into the four guide grooves GD, the stopper member When the cap portion 10-1 and the body portion 10-2 are assembled together with the stopper arm 30 and the four stopper arms 32 close the mouth of the guide groove GD, Can be folded without detaching from the bit body 10.

Therefore, since the wing bit 20 and the shaft projection 21 are integrally formed as one unit, it is possible to prevent the collision between the components from being originally supported, so that the wing bit 20 can be firmly supported even under the great external force and shock generated during the excavation process. 20 are inserted into the guide groove GD without being exposed to the outside of the bit body 10, the penetration of various foreign substances is blocked to prevent malfunction or malfunction, and the durability is remarkably improved Since the wing bit 20 can be easily repaired or replaced by removing the stopper member 30, the manageability of the apparatus can be greatly improved.

1, 3 and 4, the inclined support member 40 is installed on the body 10-2 of the bit body 10, and the wing bit 20 May be pivoted to support the wing bit 20 in an inclined manner so that the wing bit 20 may be inclined at a supporting angle A with respect to the traveling direction.

More specifically, for example, the inclined support member 40 may be a body part inclined step 41 provided near the guide groove GD of the body part 10-2.

4, the inclined jaws 41 of the inclination supporting member 40 are inclined with respect to the inclined surface 41 formed to protrude from the inner wall surface of the wing bit receiving groove 11 toward the advancing direction, Lt; RTI ID = 0.0 > 41a. ≪ / RTI >

4, the inclined jaw 41 can limit the spread angle of the wing bit 20 to the support angle A, and the wing bit 20 can be inclined with respect to the wing It is possible to widen the contact area of the bit 20 to disperse the force in the event of an external force or various impacts, and to more firmly support the bit 20.

Therefore, two wing bits 20 are provided on the left and right sides of the bit body 10, respectively. The wing bit 20 is extended from the bit body 10 at an inclination angle (A) A large area can be excavated to be inserted.

That is, the wing bit 20 is inclined with respect to the traveling direction, and is resistant to external force and impact, and is substantially similar to increasing the thickness of the wing bit 20, so that the durability can be remarkably improved.

At this time, a working fluid such as air or water may be introduced into the working fluid inlet hole G1 during excavation, and excavated foreign matter may be discharged along the working fluid discharge groove G2.

When the excavation is completed, the wing bit 20 is pivoted about the axis projection 21 and folded in the direction of the bit body 10, and can easily escape to the outside through the inner diameter surface of the steel pipe.

10 is a part exploded perspective view showing a drill bit 200 according to some other embodiments of the present invention. 11 is a fragmentary assembled perspective view of the excavating bit 200 of FIG. 10, and FIG. 12 is a perspective view showing the stopper member 30 and the wing bit 20 of FIG.

10-12, the bit body 10 of the excavating bit 200 according to some other embodiments of the present invention is characterized in that the advanced excavation surface 10a is formed at its tip, (10-3) in which the guide groove (GD) facing the direction opposite to the traveling direction is formed and the screw protrusion (S1) is provided at the rear end, and the screw protrusion And a tail portion 10-4 provided with a thread groove S2 threadedly engaged with the threaded portion S1.

Here, as shown in FIGS. 10 to 12, the stopper member 30 may be installed between the head 10-3 and the tail 10-4. At this time, the inclination supporting member 40 may be a stopper slanting step 42 provided on the stopper member 30.

More specifically, for example, the head portion 10-3 is formed with a wing bit receiving groove 11 having a shape corresponding to a part of the wing bit 20 on one side thereof, And the guide groove GD may be formed on an inner wall surface of the stopper receiving groove 12 in a direction opposite to the traveling direction.

10 to 12, the stopper member 30 includes a stopper body 31 having a through hole W through which the threaded portion S3 of the head portion 10-3 passes, And a stopper arm 32 protruding from the stopper body 31 in the advancing direction so as to close the entrance of the guide groove GD. The inclined jaw 42 of the inclined support member 40, May include a concave sloped surface (42a) formed to protrude from the stopper arm (32) toward the traveling direction.

Therefore, as shown in FIG. 12, the inclined jaw 42 can limit the spread angle of the wing bit 20 to the support angle A, and the wing bit 20 can be inclined with respect to the wing It is possible to widen the contact area of the bit 20 to disperse the force in the event of an external force or various impacts, and to more firmly support the bit 20.

Therefore, two wing bits 20 are provided on the left and right sides of the bit body 10, respectively. The wing bit 20 is extended from the bit body 10 at an inclination angle (A) A large area can be excavated to be inserted.

Figures 13-17 are perspective views showing drilling bits 300 in accordance with some further embodiments of the present invention.

13 to 17, the threaded protrusion S5 of the excavating bit 300 according to some further embodiments of the present invention is formed in such a manner that the wing bit 20 is pivoted so that the bit body 10 It is possible to secure a sufficient space for the wing bit accommodating groove 11 capable of accommodating the wing bit 20 and to provide the wing bit accommodating groove 11 with side cutting A portion S5a may be formed.

Therefore, it is possible to secure a sufficient space for the wing bit receiving groove 11 capable of accommodating the wing bit 20 in the cut space due to the side cutting portion S5a.

Here, it is obvious that the threaded protrusion S5 is cut in both sides in an appropriate range so that the threaded portion S5 can be screwed into the threaded groove S6. In addition, the working fluid injection hole G1 passing through the inside due to the side cutting portion S5a may not be exposed.

For example, the distance from the center of the threaded projection S5 of the side cutout S5a may be 10 to 40 percent of the radius of the threaded projection S5. However, the present invention is not limited thereto.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

10: bit body
10a: Advanced excavation surface
10-1:
10-2:
10-3: head portion
10-4: tail
11: Wing bit accommodating groove
12: Stopper housing groove
GD: Guide groove
20: Wing beat
21: Axial projection
30: Stopper member
31: Stopper body
32: Stopper arm
40: inclined support member
41: body part inclined chin
41a: Concave slope
42: Stopper inclined chin
42a: Concave slope
S1: Screw protrusion
S2: Screw groove portion
W: Through hole
S5a: side cutting portion
A: Support angle
20a: Wing bit excavation surface
T: carbide tips
G1: Working fluid injection hole
G2: Working fluid discharge groove
100, 200, 300: excavation bit

Claims (9)

A bit body having an advanced excavation surface formed on one side and a guide groove formed on the other side;
A wing bit which is formed on one side or both sides of the shaft body and which can be guided along the guide groove of the bit body and which can be assembled with the bit body about the axis projection guided along the guide groove and pivotable;
A stopper member provided on the bit body such that the shaft protrusion is not separated from the guide groove; And
An inclination supporting member installed on the bit body or the stopper member and supporting the wing bit in an inclined manner so that the wing bit is rotated and is inclined at a supporting angle with respect to the advancing direction;
Lt; / RTI >
The bit body is composed of two parts which are detachably fastened to each other by a screw projection portion and a screw groove portion,
Wherein the stopper member is assembled between the parts,
The supporting angle (A) is 30 to 60 degrees with respect to the traveling direction,
The bit body comprises:
A cap portion having the tip excavated surface formed at its tip end and a screw groove portion provided at a rear end thereof; And
A body portion having a screw protruding portion screwed to the screw groove portion of the cap portion at a tip thereof and having the guide groove facing the traveling direction in the middle;
Lt; / RTI >
Wherein the stopper member is disposed between the cap portion and the body portion,
Wherein the inclined support member is a body portion inclined jaw provided near the guide groove of the body portion,
Wherein the cap portion has a working fluid discharge groove disposed on the outer surface at least at three equal angles. delete delete The method according to claim 1,
The body portion is formed with a wing bit receiving groove having a shape corresponding to a part of the wing bit on one side and a stopper receiving groove having a shape corresponding to a part of the stopper member on the other side,
Wherein the guide groove is formed on an inner wall surface of the stopper receiving groove toward the traveling direction,
The stopper member
A stopper body having a through hole through which the screw protrusion of the body passes; And
A stopper arm protruding from the stopper body in a direction opposite to the advancing direction so as to close the inlet of the guide groove;
/ RTI >
Wherein the inclined jaw of the inclined support member includes a concave inclined surface formed so as to protrude from the inner wall surface of the wing bit receiving groove toward the advancing direction. The method according to claim 1,
The bit body comprises:
A head portion formed with the advanced excavation surface at its tip end, the guide groove formed in the middle in a direction opposite to the traveling direction, and a screw projection portion provided at a rear end thereof; And
And a tail portion provided at a tip thereof with a screw groove portion screwed into the screw projection portion of the head portion,
Wherein the stopper member is provided between the head portion and the tail portion,
Wherein the inclined support member is a stopper inclined jaw provided on the stopper member. 6. The method of claim 5,
The head portion is formed with a wing bit receiving groove having a shape corresponding to a part of the wing bit on one side and a stopper receiving groove having a shape corresponding to a part of the stopper member on the other side,
Wherein the guide groove is formed on an inner wall surface of the stopper receiving groove in a direction opposite to the advancing direction,
The stopper member
A stopper body having a through hole through which the screw projection of the head penetrates; And
A stopper arm protruding from the stopper body in the advancing direction so as to close the inlet of the guide groove;
/ RTI >
Wherein the inclined jaw of the inclined support member includes a concave inclined surface formed to protrude from the stopper arm toward the advancing direction. The method according to claim 1,
Wherein the screw protrusions are formed with side cuts on both sides thereof to sufficiently secure a space for the wing bit accommodating groove capable of accommodating the wing bit when the wing bit is turned and folded to the bit body, Excavating bit. The method according to claim 1,
Wherein the wing bit is formed with axle protrusions on both sides thereof and the wing bit is rotated to form a forward wing bit excavation surface in a state in which the wing bit is inclined at a supporting angle with respect to the advancing direction, And a carbide tip is installed on the bit excavation surface. The method according to claim 1,
Wherein the bit body has a working fluid injection hole formed at a central shaft portion and a working fluid discharge groove formed at an outer side surface thereof.

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