阅读说明：本技术 断路器、液压机构及其低压油箱 (Circuit breaker, hydraulic mechanism and low-voltage oil tank thereof ) 是由 杨海明 曾乔迪 廖伟兴 伍国兴 汪鹏 张繁 于 2019-10-15 设计创作，主要内容包括：本发明涉及一种低压油箱,包括箱体及逆止阀。加注液压油时,先将逆止阀拆下,待加注完成后再将逆止阀安装。液压机构在正常工作的过程中,高压油箱内的液压油通过高压油路回流到箱体时,箱体内液面上升、压强增大,冲开逆止阀排出气体。而当箱体内的液压油通过高压油路压进高压油箱时,箱体的液压油液面下降、压强减小,逆止阀关闭,故空气将无法进入低压油箱。经过液压机构的多个工作循环后,低压油箱内的气体将被排出殆尽,从而实现低压油箱内保持真空的目的。因此,能有效地防止低压油箱内的液压油变质,从而改善液压机构的性能。此外,本发明还提供一种液压机构及断路器。(The invention relates to a low-pressure oil tank which comprises a tank body and a check valve. When the hydraulic oil is filled, the check valve is detached firstly, and the check valve is installed after the filling is finished. When the hydraulic mechanism works normally, when hydraulic oil in the high-pressure oil tank flows back to the tank body through the high-pressure oil way, the liquid level in the tank body rises, the pressure is increased, and the check valve is opened to discharge gas. When the hydraulic oil in the box body is pressed into the high-pressure oil tank through the high-pressure oil circuit, the liquid level of the hydraulic oil in the box body is reduced, the pressure intensity is reduced, the check valve is closed, and therefore air cannot enter the low-pressure oil tank. After a plurality of working cycles of the hydraulic mechanism, the gas in the low-pressure oil tank is exhausted, so that the aim of keeping vacuum in the low-pressure oil tank is fulfilled. Therefore, the hydraulic oil in the low-pressure oil tank can be effectively prevented from being deteriorated, thereby improving the performance of the hydraulic mechanism. In addition, the invention also provides a hydraulic mechanism and a circuit breaker.)

1. A low-pressure fuel tank, comprising:

the side wall of the box body is provided with an oil filling hole communicated with the interior of the box body; and

the check valve is provided with an air inlet and an air outlet, the check valve is conducted in a one-way mode in the direction from the air inlet to the air outlet, the check valve is detachably installed in the oil filling hole, and the air inlet is communicated with the oil filling hole.

2. The low-pressure tank according to claim 1, characterized in that the check valve comprises:

the valve body is of a hollow columnar structure and is provided with an air guide channel, and the two ends of the air guide channel are respectively provided with the air inlet and the air outlet;

the valve core is arranged in the valve body and can stretch and retract along the axial direction of the valve body, the valve core comprises a sleeve extending along the axial direction of the valve body, and an opening of the sleeve faces the air outlet;

the fixing part is positioned on one side of the valve core facing the air outlet and comprises a fixing part and a guide rod, the fixing part is fixed on the valve body, and the guide rod extends along the axial direction of the valve body and penetrates through the sleeve;

the elastic piece is accommodated in the sleeve and abuts against the guide rod so as to apply an elastic force pointing to the air inlet to the valve core, and the valve core abuts against the inner wall of the air guide channel under the action of the elastic force.

3. The low-pressure oil tank is characterized in that the middle of the air guide channel expands along the radial direction of the valve body to form an air guide chamber, the air guide channel further comprises a first guide section and a second guide section which are communicated with two ends of the air guide chamber, a sealing step is formed between the first guide section and the air guide chamber, the valve core comprises a sealing disc and a guide column, the sealing disc is located at one end of the sleeve, the guide column is located on one side, back to the sleeve, of the sealing disc, the guide column penetrates through the first guide section, and the sealing disc is contained in the air guide chamber and abuts against the sealing step under the action of elastic force.

4. The low pressure tank of claim 3, wherein the side wall of the guide post includes a first arcuate wall and a first planar wall, and the first arcuate wall contacts the inner wall of the first guide section.

5. The low-pressure fuel tank as claimed in claim 3, wherein a side of the sealing plate facing away from the first guide section is formed with a truncated cone-shaped air guide slope, and a diameter of the air guide slope increases in a direction from the sleeve to the guide post.

6. The low-pressure oil tank as claimed in claim 2, wherein the valve body has an inner wall on which the air outlet is opened, and is formed with an internal thread, the fixing portion has an outer surface formed with an external thread, and the fixing portion is screwed with the inner wall of the valve body.

7. The low pressure fuel tank of claim 6, wherein the side wall of the fixing portion includes a second planar wall and a second arcuate wall, and the external thread of the fixing portion is formed on the second arcuate wall.

8. The low-pressure oil tank as claimed in claim 2, wherein external threads are formed on the outer walls of the two ends of the valve body, internal threads are formed on the wall of the oil filling hole, and the end of the valve body, provided with the air inlet, penetrates through the oil filling hole and is screwed with the oil filling hole.

9. A hydraulic mechanism comprising a low-pressure oil tank according to any one of claims 1 to 8, a high-pressure oil passage, and a high-pressure oil tank communicating with the low-pressure oil tank through the high-pressure oil passage.

10. A circuit breaker comprising a hydraulic mechanism according to claim 9.

Technical Field

The invention relates to the technical field of electricity, in particular to a circuit breaker, a hydraulic mechanism and a low-voltage oil tank thereof.

Background

Hydraulic mechanisms are widely used in various electrical devices, such as circuit breakers, and a vacuum oil injection type is generally used to ensure the performance of the hydraulic mechanism. After the equipment is put into operation, the leakage (tiny or seepage) of the hydraulic oil will cause the loss of the hydraulic oil in the hydraulic mechanism, so the hydraulic oil needs to be supplemented.

An oil filling port and a plug are arranged on a low-pressure oil tank of a common hydraulic mechanism, and hydraulic oil can be supplemented by pulling out the plug. However, since the vacuum oil injection cannot be performed in the operating state of the equipment, the vacuum breaking oil injection can be performed only by opening the oil injection port. Therefore, the quality of the hydraulic oil is affected by the entering air and water vapor, and the performance of the hydraulic mechanism is adversely affected by long-term erosion of various valve bodies in the hydraulic mechanism.

Disclosure of Invention

In view of this, it is necessary to provide a low-pressure oil tank capable of improving the performance of the hydraulic mechanism.

A low-pressure fuel tank comprising:

the side wall of the box body is provided with an oil filling hole communicated with the interior of the box body; and

the check valve is provided with an air inlet and an air outlet, the check valve is conducted in a one-way mode in the direction from the air inlet to the air outlet, the check valve is detachably installed in the oil filling hole, and the air inlet is communicated with the oil filling hole.

In one embodiment, the check valve comprises:

the valve body is of a hollow columnar structure and is provided with an air guide channel, and the two ends of the air guide channel are respectively provided with the air inlet and the air outlet;

the valve core is arranged in the valve body and can stretch and retract along the axial direction of the valve body, the valve core comprises a sleeve extending along the axial direction of the valve body, and an opening of the sleeve faces the air outlet;

the fixing part is positioned on one side of the valve core facing the air outlet and comprises a fixing part and a guide rod, the fixing part is fixed on the valve body, and the guide rod extends along the axial direction of the valve body and penetrates through the sleeve;

the elastic piece is accommodated in the sleeve and abuts against the guide rod so as to apply an elastic force pointing to the air inlet to the valve core, and the valve core abuts against the inner wall of the air guide channel under the action of the elastic force.

In one embodiment, the middle of the air guide channel expands along the radial direction of the valve body to form an air guide chamber, the air guide channel further comprises a first guide section and a second guide section which are communicated with two ends of the air guide chamber, a sealing step is formed between the first guide section and the air guide chamber, the valve core comprises a sealing disc located at one end of the sleeve and a guide column located on one side, back to the sleeve, of the sealing disc, the guide column penetrates through the first guide section, and the sealing disc is contained in the air guide chamber and is abutted to the sealing step under the action of elastic force.

In one embodiment, the side wall of the guide post comprises a first arc-shaped wall and a first plane wall, and the first arc-shaped wall is in contact with the inner wall of the first guide section.

In one embodiment, the side of the sealing disk facing away from the first guide section is formed with a truncated cone-shaped air guide slope, and the diameter of the air guide slope increases in the direction from the sleeve to the guide post.

In one embodiment, an inner wall of the valve body, at which the end of the valve body, at which the air outlet is opened, is provided with an internal thread, the fixing part is an outer surface provided with an external thread, and the fixing part is screwed with the inner wall of the valve body.

In one embodiment, the side wall of the fixing portion includes a second planar wall and a second arc-shaped wall, and the external thread on the fixing portion is formed on the second arc-shaped wall.

In one embodiment, the outer walls of the two ends of the valve body are both provided with external threads, the hole wall of the oil filling hole is provided with internal threads, and one end of the valve body, provided with the air inlet, penetrates through the oil filling hole and is screwed with the oil filling hole.

When hydraulic oil needs to be filled into the low-pressure oil tank, the check valve is detached firstly, and the check valve is installed after the filling is finished. When the hydraulic mechanism works normally, when hydraulic oil in the high-pressure oil tank flows back to the tank body through the high-pressure oil way, the liquid level in the tank body rises, the pressure is increased, and the check valve is opened to discharge gas. When the hydraulic oil in the box body is pressed into the high-pressure oil tank through the high-pressure oil circuit, the liquid level of the hydraulic oil in the box body is reduced, the pressure intensity is reduced, the check valve is closed, and therefore air cannot enter the low-pressure oil tank. After a plurality of working cycles of the hydraulic mechanism, the gas in the low-pressure oil tank is exhausted, so that the aim of keeping vacuum in the low-pressure oil tank is fulfilled. Therefore, the hydraulic oil in the low-pressure oil tank can be effectively prevented from being deteriorated, thereby improving the performance of the hydraulic mechanism.

The invention also provides a hydraulic mechanism, which comprises the low-pressure oil tank, the high-pressure oil path and the high-pressure oil tank communicated with the low-pressure oil tank through the high-pressure oil path.

Furthermore, the present invention also provides a circuit breaker including the hydraulic mechanism as described in the above preferred embodiment.

Drawings

FIG. 1 is a schematic view of a low-pressure fuel tank according to a preferred embodiment of the present invention;

FIG. 2 is a schematic structural view of a check valve in the low-pressure oil tank shown in FIG. 1;

FIG. 3 is a cross-sectional view of the check valve of FIG. 2;

FIG. 4 is a schematic diagram of the engagement between the retaining member and the valve element of the check valve shown in FIG. 2;

FIG. 5 is a schematic structural view of a valve body of the check valve shown in FIG. 2;

FIG. 6 is a schematic diagram of a valve cartridge of the check valve shown in FIG. 2;

fig. 7 is a schematic view showing a structure of a fixing member in the check valve shown in fig. 2.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Referring to fig. 1, the present invention provides a low pressure fuel tank 10. In addition, the invention also provides a hydraulic mechanism (not shown) and a circuit breaker (not shown).

The hydraulic mechanism includes a low-pressure oil tank 10, a high-pressure oil passage (not shown), and a high-pressure oil tank (not shown) communicating with the low-pressure oil tank 10 through the high-pressure oil passage. The low-pressure oil tank 10 can store hydraulic oil and exchange the hydraulic oil with the high-pressure oil tank through a high-pressure oil path. The circuit breaker includes the above-described hydraulic mechanism, and can perform related operations using the hydraulic mechanism.

Referring to fig. 2, the low pressure fuel tank 10 according to the preferred embodiment of the present invention includes a check valve 100 and a tank 200.

The box 200 is used for storing hydraulic oil, and may be made of metal or plastic, and the external contour thereof may be set to be in various shapes such as a cube shape and a cylinder shape according to the requirements of specific application scenarios. An oil hole (not shown) communicating with the inside of the case 200 is formed in a sidewall of the case 200. When the hydraulic oil in the tank body 200 runs off, the hydraulic oil can be filled through the oil injection hole.

A connection port 210 for connecting to a high-pressure oil passage or the like is opened in a side wall of the case 200.

The check valve 100 has an inlet 111 and an outlet 113, and the check valve 100 is one-way conductive in a direction from the inlet 111 to the outlet 113. That is, gas can flow only from the gas inlet 111 to the gas outlet 113, but cannot flow from the gas outlet 113 to the gas inlet 111. Further, the check valve 100 is detachably installed in the oil hole, and the air inlet 111 communicates with the oil hole.

Wherein, the check valve 100 can be detachably installed by means of screw connection and the like. When hydraulic oil needs to be filled, the check valve 100 is detached firstly, the hydraulic oil is filled into the tank body 200 through the oil filling hole, and the check valve 100 is installed after the filling is completed.

Because the vacuum can not be realized in the filling process when the circuit breaker works, air and water vapor can enter the box body 200 along with hydraulic oil. In the normal operation process of the hydraulic mechanism, frequent hydraulic oil exchange is performed between the low-pressure oil tank 10 and the high-pressure oil tank. When the hydraulic mechanism is reset, hydraulic oil in the high-pressure oil tank flows back to the low-pressure oil tank through the high-pressure oil way. At this time, the liquid level of the low-pressure tank rises, the space decreases, the pressure increases, and the check valve 100 is opened to discharge the gas.

And when the hydraulic oil mechanism executes relevant operation, hydraulic oil in the low-pressure oil tank is pressed into the high-pressure oil tank through the high-pressure oil circuit. At this time, the hydraulic fluid level of the low pressure tank is lowered, the space is increased, the pressure is reduced, the check valve 100 is closed, and thus the external air cannot enter the low pressure tank 10. After a plurality of working cycles of the hydraulic machine, the gas in the low-pressure oil tank 10 will be exhausted, so that the vacuum is maintained in the low-pressure oil tank 10.

The type of the check valve 100 may be various, and it is sufficient that the check valve can realize one-way conduction in the direction from the air inlet 111 to the air outlet 113. To ensure reliability, the check valve 100 is typically a metal component, i.e., each portion of the check valve 100 is formed of metal.

Referring to fig. 3 and 4, the check valve 100 of the present embodiment includes a valve body 110, a valve core 120, a fixing element 130, and an elastic element 140.

The valve body 110 has a hollow cylindrical structure with both ends open. Wherein, the openings at the two ends are respectively an air inlet 111 and an air outlet 113. Referring to fig. 5, the valve body 110 further has an air guide channel 115 communicating the air inlet 111 and the air outlet 113. The air guide passage 115 generally coincides with the extending direction of the valve body 110.

In this embodiment, the outer walls of the two ends of the valve body 110 are both formed with external threads, the hole wall of the oil filler hole is formed with internal threads, and the end of the valve body 110, which is provided with the air inlet 111, is inserted into the oil filler hole and screwed with the oil filler hole.

Through threaded connection, the check valve 100 can be more conveniently disassembled and assembled. In addition, the external thread of the valve body 110 at the end provided with the air outlet 113 can facilitate the connection of the check valve 100 with external equipment such as a muffler and a filtering device.

Further, in this embodiment, an annular limiting protrusion 117 is formed in the middle of the valve body 110. When one end of the valve body 110 is inserted into the oil filler hole, the end surface of the stopper protrusion 117 abuts against the surface of the case 200.

In order to improve the sealing performance of the connection between the check valve 100 and the housing 200, an annular seal ring receiving groove 1171 is formed on an end surface of the stopper protrusion 117 to receive a seal ring (not shown).

Referring to fig. 6, the valve element 120 is installed in the valve body 110 and is retractable along the axial direction of the valve body 110. The valve core 120 can be extended and retracted to close or open the air guide passage 115. The spool 120 includes a sleeve 121 extending in the axial direction of the valve body 110, and the sleeve 121 opens toward the gas outlet 113.

Referring to fig. 7 and again to fig. 4, the fixing element 130 is located on a side of the valve element 120 facing the air outlet 113. The fixing member 130 includes a fixing portion 131 and a guide rod 133. The fixing portion 131 is fixed to the valve body 110, and the guide rod 133 extends in the axial direction of the valve body 110 and is inserted into the sleeve 121.

Specifically, the fixing portion 131 can be fixed by various methods such as screw connection and clamping connection, the guide rod 133 is generally cylindrical, and the outer diameter of the guide pipe 133 is equal to the inner diameter of the sleeve 121. Thus, the outer wall of the guide rod 133 can contact with the inner wall of the sleeve 121 to prevent a gap between the two.

The elastic element 140 is accommodated in the sleeve 121 and abuts against the guide rod 133 to apply an elastic force to the valve element 120 towards the air inlet 111. The elastic member 140 may be a spring, a spring plate or an elastic pad, a foam pad, or the like. The elastic member 140 in this embodiment is a compression spring. The valve core 120 is pressed against the inner wall of the air guide channel 115 by the elastic force. Therefore, in a natural state, the valve body 120 abuts against the inner wall of the air guide passage 115, thereby closing the air guide passage 120.

When the air pressure at one end of the air inlet 111 rises and the pressure difference between the air inlet 111 and the air outlet 113 exceeds the elastic force provided by the elastic member 140, the valve core 120 will move back to open the air guide channel 115; when the air pressure at one end of the air inlet 111 is reduced until the pressure difference between the air inlet 111 and the air outlet 113 is smaller than the elastic force provided by the elastic member 140, the valve element 120 will be pressed against the inner wall of the air guide channel 115 again under the elastic force to close the air guide channel 115. Thus, unidirectional conduction is realized.

Moreover, the sleeve 121 can limit the elastic member 140, and the elastic member 140 is prevented from being jammed due to deflection to the periphery when being stretched. Meanwhile, the guide rod 133 is matched with the sleeve 121, so that the valve core 120 can be guided to limit the movement direction of the valve core to the axial direction along the valve body 110, the check valve 100 is prevented from being failed due to jamming when the valve core 120 stretches and retracts, and the reliability of the check valve 100 is improved.

Specifically, in the embodiment, an inner wall of the valve body 110 at the end opened with the air outlet 113 is formed with a female screw, the fixing portion 131 is an outer surface formed with a male screw, and the fixing portion 131 is screwed with the inner wall of the valve body 110.

The fixing portion 131 may have a disk shape or a cylindrical shape having a diameter smaller than that of the guide rod 133. The threaded connection is convenient to assemble. Further, by rotating the fixing portion 131, the fixing member 130 can be moved in the axial direction of the valve body 110, so that the compression amount of the elastic member 140 is adjusted, and the preload of the elastic member 140 (i.e., the elastic force) is adjusted. Specifically, when the fixing element 130 is screwed out toward the air outlet 113, the pre-tightening force of the elastic element 140 is reduced, and the check valve 100 can be opened only by a small pressure difference between the air inlet 111 and the air outlet 113. When the fixing member 130 is screwed in toward the direction away from the air outlet 113, the pre-tightening force of the elastic member 140 is increased.

Further, referring to fig. 7 again, in the present embodiment, the side wall of the fixing portion 131 includes a second planar wall 1312 and a second arc-shaped wall 1314, and the external thread on the fixing portion 131 is formed on the second arc-shaped wall 1314.

Specifically, the second arc-shaped wall 1314 achieves the purpose of installing the fixing part 131 by the holding force between the external thread and the inner wall of the valve body 110. The second planar wall 1312 does not fit well against the inner wall of the valve body 110, so that a gap exists between the two walls, which allows the air guide channel 115 to be unblocked.

Obviously, in other embodiments, the sidewall of the fixing portion 131 may be configured to completely fit the inner wall of the valve body 110, and the air guide channel 115 may be ensured not to be blocked by forming a through hole on the fixing portion 131.

Referring again to fig. 5, in the present embodiment, the middle portion of the air guide channel 115 expands in the radial direction of the valve body 110 to form an air guide chamber 1151, the air guide channel 115 further includes a first guide section 1153 and a second guide section 1155 communicating with both ends of the air guide chamber 1151, and a sealing step 1157 is formed between the first guide section 1153 and the air guide chamber 1151.

That is, the inner diameters of the first and second guide segments 1153 and 1155 are smaller than the inner diameter of the gas directing chamber 1151. Wherein the first guide section 1153 is located at an end of the valve body 110 near the gas inlet 111, and the second guide section 1155 is located at an end of the valve body near the gas outlet 113.

Further, referring to fig. 6 again, the valve element 120 includes a sealing plate 123 at one end of the sleeve 121 and a guiding post 125 at a side of the sealing plate 123 opposite to the sleeve 121. The guide post 125 penetrates through the first guide section 1153, and the sealing disc 123 is accommodated in the air guide chamber 1151 and abuts against the sealing step 1157 under the action of elastic force.

Specifically, the outer diameter of the guide post 125 may be comparable to the inner diameter of the first guide section 1153. Thus, the side walls of the guide post 125 may contact the inner wall of the first guide section 1153. When the valve core 120 extends and contracts, the guide post 125 cooperates with the first guide section 1153 to guide the valve core 120 so as to limit the movement direction thereof to the axial direction of the valve body 110. The movement directions of both ends of the spool 120 are restricted by the guiding action of the sleeve 121 and the guide rod 133, so that the reliability of the check valve 100 is further improved.

Sealing disk 123, when abutted against sealing step 1157, can "jam" first guide 1153, thereby closing air guide channel 115. Further, to improve the sealing performance, an O-ring 150 is fitted over the guide post 125. The O-ring 150 may be clamped between the sealing disk 123 and the sealing step 1157.

Further, in the present embodiment, the side of the seal plate 123 facing away from the first guide section 1153 is formed with a truncated cone-shaped air guide slope 1232, and the diameter of the air guide slope 1153 increases in the direction from the sleeve 121 to the guide post 125.

The provision of the air guide ramp 1232 provides for the sealing disk 123 to be generally inverted conical in shape. In this manner, when the valve body 120 is retracted to open the air guide passage 115, the sealing disk 123 is prevented from covering the second guide section 1155, thereby ensuring the smoothness of the air guide passage 115.

Further, in the present embodiment, the side wall of the guiding post 125 includes a first arc-shaped wall 1252 and a first plane wall 1254, and the first arc-shaped wall 1252 contacts with the inner wall of the first guiding section 1153.

Specifically, the first arc-shaped wall 1252 contacts with the inner wall of the first guide section 1153, so as to limit the moving direction of the guide post 125. Similar to the function of the second planar wall 1312, the first planar wall 1254, because it does not conform well to the inner wall of the first guide section 1153, has a gap between them that allows the air guide channel 115 to be unobstructed.

Obviously, in other embodiments, the side wall of the guiding post 125 may be configured to completely fit the inner wall of the first guiding segment 1153, and the guiding channel 115 may be ensured not to be blocked by forming a through groove on the guiding post 125.

When the low-pressure oil tank 10 needs to be filled with hydraulic oil, the check valve 100 is firstly detached, and the check valve 100 is installed after the filling is completed. When the hydraulic mechanism works normally, when hydraulic oil in the high-pressure oil tank flows back to the low-pressure oil tank 10 through the high-pressure oil path, the liquid level of the tank body 200 rises, the pressure is increased, and the check valve 100 is opened to discharge gas. When the hydraulic oil in the tank 200 is pressed into the high-pressure oil tank through the high-pressure oil path, the liquid level of the hydraulic oil in the tank 200 is lowered, the pressure is reduced, the check valve 100 is closed, and therefore air cannot enter the low-pressure oil tank 10. After a plurality of working cycles of the hydraulic machine, the gas in the low-pressure oil tank 10 will be exhausted, so that the vacuum is maintained in the low-pressure oil tank 10. Therefore, the hydraulic oil of the low-pressure oil tank 10 can be effectively prevented from being deteriorated, thereby improving the performance of the hydraulic mechanism.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.