CN116906220A - A gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device and method thereof - Google Patents

Abstract

The invention provides a gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device and a method thereof, and relates to the technical field of gas fuel pressure reducing and flow limiting devices. The body is provided with an air inlet and an air outlet. A decompression and flow-limiting mechanism is installed inside the body. The lower cavity is from the air inlet to the lower side of the top of the decompression and flow-limiting mechanism, and from the upper side of the top of the decompression and flow-limiting mechanism to the air outlet. It is an upper chamber with an opening above the body. An elastomer diaphragm is installed above the body and seals the opening. A lower pressure column is installed below the diaphragm. The valve hole of the pressure reducing and limiting mechanism is located below the lower pressure column. The valve hole is installed A sealing valve disc used to close the valve hole. This application adopts a purely mechanical structure to automatically control the on-off and pressure-reducing flow limit of gaseous fuel according to negative pressure conditions. It is suitable for both pipeline gas supply and gas tank gas supply. It has good versatility, has over-pressure shutdown and flameout protection functions, and is highly safe. , automatic pressure reduction and flow limiting enables gas equipment to maintain optimal working conditions and effectively improves the power and economy of gas equipment.

Description

A gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device and method thereof

Technical field

The invention relates to the technical field of a gas fuel pressure reducing and flow limiting device, and in particular to a gas fuel automatic switch, automatic pressure reducing and automatic flow limiting device and a method thereof.

Background technique

Because gaseous fuel is flammable and explosive, when existing internal combustion engines use gaseous fuel, they usually install a secondary pressure reducing valve in the front stage, and use a pressure switch flow meter and a solenoid valve to realize valve switching and pressure reduction and flow limiting. Specifically, The basic method is to install a pressure switch, a flow meter and a solenoid valve on the front and back sides of the secondary pressure reducing valve, and control the switching frequency and duty cycle of the solenoid valve after obtaining the sensor signal and processing it to achieve pressure reduction and current limiting. Using the electronic control method, in addition to the safety certification of the solenoid valve, how to enable the internal combustion engine to achieve optimal working conditions is also a technical problem to be solved.

Existing internal combustion engines use gaseous fuel, and there are two main gas supply modes: pipeline gas supply and gas tank gas supply. When using pipeline gas supply, the front-stage pressure and flow can be regarded as basically constant values. When using the existing two-stage pressure reducing valve, due to its simple working conditions, the solenoid valve can control the pressure and flow and open and close by switching at a fixed frequency. Gas supply, piped gas supply is common in or near homes. Gas tanks are often used to supply gas in the wild. Using gas tanks to supply gas is different from using pipes to supply gas near homes. The pressure in the gas tank gradually decreases, and the flow rate also decreases simultaneously. The current technical solution usually samples the pressure and flow signals of the front stage to adjust the switching frequency and duty ratio of the solenoid valve. This not only increases the complexity of the supply device structure, but also increases the size and occupies a larger space. , and it will also reduce the safety, and the reliability of its operation needs to be checked frequently.

Contents of the invention

The invention provides a gas fuel automatic switch, automatic pressure reduction and automatic current limiting device and a method thereof, which adopts a pure mechanical structure to automatically control the on-off and pressure reducing current limiting of gas fuel according to negative pressure conditions to solve the above technical problems.

The specific technical solution is a gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device, which includes: a body. The body is provided with an air inlet and an air outlet. A pressure reducing and flow limiting mechanism is installed inside the body, from the air inlet to the pressure reducing device. The lower side of the top of the flow-limiting mechanism is the lower chamber, and the upper chamber is the upper chamber from the upper side of the top of the pressure-reducing flow-limiting mechanism to the air outlet. There is an opening above the body. A diaphragm made of elastomer is installed above the body and seals the opening. A lower chamber is installed below the diaphragm. The valve hole of the pressure column and pressure reducing and limiting mechanism is located below the lower pressure column, and a sealing valve plate for closing the valve hole is installed at the valve hole.

Preferably, the pressure reduction and flow limiting mechanism includes: a sealing valve plate, a bracket and an elastic piece. A clamping table is provided above the air inlet. The elastic piece is placed on the clamping table. The bracket is installed above the elastic piece, and the sealing valve piece is fixed on the clamping table. Above the bracket, bolts are installed through threads at the air inlet branch inside the body. The sealing valve plate is placed below the bolts to control the opening and closing of the threaded holes on the bolts. The outer contour size of the sealing valve plate is smaller than the lower cavity of the corresponding installation location. Inner dimension.

Preferably, in the bracket, the upper middle of the plate-shaped frame protrudes upward to form a frame column, and a clamping platform for fixing the sealing valve plate is provided above the frame column; the lower middle of the frame surface protrudes downward to form a leg, and the leg is embedded in the bracket. inside the elastic piece.

Preferably, in the bracket, the upper middle of the plate-shaped shelf surface protrudes upward to form a frame column, and the sealing valve plate is fixedly installed above the frame column; the lower middle of the frame surface protrudes downward to form a leg, and the leg is embedded in the elastic member. .

Preferably, the edge of the frame protrudes outward to form a convex rib, and the convex rib rests on the elastic member.

Preferably, the elastic member is a spring.

Preferably, an upper aluminum sheet and a lower aluminum sheet for fixing the lower pressure column are fixedly installed in the middle of the diaphragm. The upper aluminum sheet and the lower aluminum sheet are symmetrically located on the upper and lower sides of the diaphragm.

Preferably, the upper cover is fixedly installed on top of the body through screws, the diaphragm is located between the body and the upper cover, a plurality of edge convex films are evenly distributed on the edge of the diaphragm, and the upper cover has holes.

Preferably, the body is provided with more than two air outlets.

Method for automatic gas fuel automatic switch, automatic pressure reduction and automatic current limiting. The working process of the above-mentioned gas fuel automatic switch, automatic pressure reduction and automatic current limiting device in this application is described:

When the gas equipment is started, a negative pressure is formed in the upper chamber. The negative pressure drives the diaphragm down. The lower pressure column moves downward with the diaphragm and presses down the sealing valve plate to open the valve hole of the pressure reduction and flow limiting mechanism. The upper chamber and the lower chamber are connected to transport gas. Fuel, this is an automatic opening process;

When the gas equipment is working, when the inlet pressure P1 of the gas equipment is always greater than the inlet pressure P2 of the gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device, the valve hole of the pressure reducing and flow limiting mechanism is always open, and the valve hole The opening changes with the difference between P1 and P2. The opening of the valve hole becomes larger as ^△ P becomes larger, and becomes smaller as ^△ P becomes smaller, thereby automatically controlling the gas fuel output pressure and flow rate at the air outlet, P1 The difference with P2 is P1-P2 = ^△ P, ^△ P is a positive value;

Turn off the gas equipment, reduce the negative pressure in the upper chamber to zero, and move the diaphragm back to the initial position, that is, the position when it is not working. At this position, the valve hole is closed, and the upper chamber and lower chamber are not connected. This is the process of automatic closing. .

Compared with the existing technology, the present invention has the following technical advantages:

1. The gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device in this application adopts a purely mechanical structure to automatically control the on-off and pressure reducing flow of gas fuel according to the negative pressure. It is applicable to both pipeline gas supply and gas tank gas supply, without the need for Solenoid valve safety certification,

2. In this application, the gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device dynamically controls the output gas pressure and flow according to the pressure difference between the two ends, so that the internal combustion engine can maintain the best working condition when using different gas fuels.

3. The gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device in this application can automatically increase the valve opening to increase the flow when the gas pressure at the gas supply end decreases during use, which can improve the power and economy of the gas equipment. It has been effectively improved. When the air intake pressure is too small, the flow is not enough to support the combustion of the engine. The valve can be automatically closed after the gas equipment is turned off, preventing the risk of gas overflow caused by the accidental failure of the gas equipment during use. It is highly safe.

4. The gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device in this application can automatically cut off the gas supply when the pressure at the gas supply end is too high, avoiding the risk of gas overflow and achieving zero pollution to the atmosphere with high safety.

To sum up, the gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device in this application adopts a pure mechanical structure to automatically control the on-off and pressure reducing flow limiting device of gas fuel according to the negative pressure condition. It has a compact structure and takes up little space. It is suitable for both gas supply and gas tank supply. It has good versatility, has over-pressure shutdown and flameout protection functions, and is highly safe. The automatic pressure reduction and flow limiting enables the gas equipment to maintain its best working condition, and the power and economy of the gas equipment are improved. Effective improvement.

Description of the drawings

The drawings forming a part of this application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached picture:

Figure 1 is a front view of the present invention,

Figure 2 is an exploded view of the invention,

Figure 3 is a cross-sectional view A-A in Figure 1,

Figure 4 is a schematic diagram of the state in which the valve hole is opened to transport gaseous fuel according to the present invention.

Figure 5 is a schematic diagram of the structure of the bracket in the present invention.

Figure 6 is a schematic structural diagram of the present invention.

in:

1. Body, 2. Upper cover, 3. Diaphragm, 4. Bolts, 5. Sealing valve plate, 6. Bracket, 7. Elastic parts, 8. Screws,

101. Air inlet, 102. Air outlet, 103. Lower chamber, 104. Upper chamber,

301. Upper aluminum sheet, 302. Lower aluminum sheet, 303. Lower pressure column, 304. Edge convex film,

601. Legs, 602. Frame surface, 603. Frame column, 604. Clamping platform, 605. Raised edge.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the embodiments and drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not used to limit the present invention.

In the description of the present invention, it should be noted that the terms "inner", "outer", "left" and "right" indicate the orientation or positional relationship based on the positional relationship shown in the drawings, and are only for convenience of description. The present invention and simplified description are not intended to indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore are not to be construed as limitations of the present invention.

Combining Figure 1 and Figure 3, a gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device includes: a body 1, the body 1 is provided with an air inlet 101 and an air outlet 102, and a pressure reducing and flow limiting mechanism is installed inside the body 1 , from the air inlet nozzle 101 to the lower side of the top of the decompression and flow limiting mechanism is the lower cavity 103, from the upper side of the top of the decompression flow limiting mechanism to the air outlet nozzle 102 is the upper cavity 104, the upper part of the body 1 is open, and the elastomer material diaphragm 3 It is installed above the body 1 and seals the opening. A lower pressure column 303 is installed below the diaphragm 3. The valve hole of the pressure reduction and flow limiting mechanism is located below the lower pressure column 303. A sealing valve plate 5 for closing the valve hole is installed at the valve hole. .

Working process: The assembly is completed, the valve hole of the pressure reduction and flow limiting mechanism is closed, the upper chamber 104 and the lower chamber 103 are independent of each other and are not connected. They are in the closed state at this time, the diaphragm 3 is in the original position and the pressure on both sides is the same. The pressure column 303 has no force on the sealing valve plate 5; when the gas equipment is started, a negative pressure is formed in the upper chamber 104, and the negative pressure drives the diaphragm 3 to drop. The lower pressure column 303 moves downward with the diaphragm 3 and presses down the sealing valve plate 5. The valve hole of the pressure reduction and flow limiting mechanism is opened, and the upper chamber 104 and the lower chamber 103 are connected to transport gaseous fuel. This is an automatic opening process; during the operation of the gas equipment, when the inlet pressure P1 of the gas equipment is always greater than the gaseous fuel automatic switch automatically When the inlet pressure of the pressure reducing automatic flow limiting device is P2, the valve hole of the pressure reducing flow limiting mechanism is always open, and the opening of the valve hole changes with the difference between P1 and P2. The opening of the valve hole changes with ^△ P becomes larger as ^△ P becomes smaller, thereby automatically controlling the gas fuel output pressure and flow rate at the air outlet 102. The difference between P1 and P2 is P1-P2 = ^△ P, ^△ P is a positive value; close For gas equipment, the negative pressure at the upper chamber 104 is reduced to zero, and the diaphragm 3 moves upward to return to the initial position, that is, the position when not working. At this position, the valve hole is closed, and the upper chamber 104 and the lower chamber 103 are not connected. This is automatic closing process.

The device in this application is suitable for both pipeline gas supply and gas tank gas supply, and has good versatility. When applied to pipeline air supply, the air inlet pressure and flow rate of the air inlet nozzle 101 remain basically unchanged. When used to supply air to a gas tank, the air inlet pressure and flow rate of the air inlet nozzle 101 decrease over time. When the gas pressure decreases during use, the valve opening can be automatically increased to increase the flow, which can effectively improve the power and economy of the gas equipment; when the intake pressure is too small, the flow is not enough to support engine combustion. The valve can automatically close after the gas equipment flameout, which prevents the risk of gas overflow caused by accidental flameout of the gas equipment during use. It has a flameout protection function and is highly safe. When applied to pipeline air supply, the air inlet pressure and flow rate of the air inlet nozzle 101 remain basically unchanged.

The gas fuel automatic switch, automatic pressure reduction, and automatic current limiting device in this application adopts a purely mechanical structure to automatically control the on-off and pressure reduction flow limiting of gas fuel according to the negative pressure. It has a compact structure, takes up little space, and does not need to go through a solenoid valve for safety. Safety certification; dynamically controls the output gas pressure and flow according to the pressure difference between the two ends, so that the internal combustion engine can maintain the best working condition when using different gas fuels; it also has an over-pressure shutdown function, which can automatically shut down when the pressure at the gas supply end is too high. Cut off the gas supply to avoid the risk of gas overflow and achieve zero pollution to the atmosphere with high safety.

In one embodiment, with reference to Figures 1-3, the pressure reduction and flow limiting mechanism includes: a sealing valve plate 5, a bracket 6 and an elastic member 7. A clamping platform is provided above the air inlet 101, and the elastic member 7 is placed on the clamping platform. The bracket 6 is installed above the elastic member 7, and the sealing valve plate 5 is fixedly placed above the bracket 6. Bolts 4 are installed through threads at the branch of the air inlet 101 inside the body 1, and the sealing valve plate 5 is placed below the bolt 4. Due to the opening and closing of the threaded hole on the control bolt 4, the outer contour size of the sealing valve plate 5 is smaller than the inner size of the corresponding lower cavity 103 of the installation location. The decompression and flow limiting mechanism is placed above the air inlet 101 in the cavity formed by the bolt 4 and the body 1. When the bolt 4 is screwed on the branch of the air inlet 101 inside the body 1, the sealing can be strengthened through the O-ring. The sealing valve plate 5 cooperates with the bolt 4. The sealing valve plate 5 does not independently close the lower cavity 103 of the corresponding installation place. There is a gap between the side of the sealing valve plate 5 and the corresponding lower cavity 103 of the installation place. It should also be noted that the elastic member 7 can expand and contract up and down and always has a gas channel between it and the inner wall of the body 1, and its physical and chemical properties are stable. The size and elastic coefficient of the elastic member 7 need to be designed to match the specific structure.

In one embodiment, with reference to Figure 4, in the bracket 6, the upper middle of the plate-shaped shelf 602 protrudes upward to form a shelf 603, and a clamping platform 604 for fixing the sealing valve plate 5 is provided above the shelf 603; the shelf 602 The lower middle protrudes downward to form a support leg 601 , and the support leg 601 is embedded in the elastic member 7 . The sealing valve plate 5 and the bracket 6 are fixedly installed and do not separate during the process. The legs 601 are embedded in the elastic members 7 to limit the stroke and movement direction of the bracket 6. The cross-sectional area of the frame column 603 is smaller than the cross-sectional area of the frame surface 602, which allows a gas passage between the side of the bracket 6 and the inner wall of the body 1.

In one embodiment, referring to FIG. 5 , the edge of the shelf surface 602 protrudes outward to form a ridge 605 , and the ridge 605 rests on the elastic member 7 . The raised ribs 605 form a support so that the upper end of the bracket 6 is always located above the elastic member 7 , and a gas flow channel is formed between the frame surfaces 602 on both sides of the raised ribs 605 and the inner wall of the body 1 .

In one embodiment, the elastic member 7 is a spring. The spring is elastic and not fully solid, so that there is always a gas channel between the spring and the inner wall of the body 1, which can meet the usage requirements. Spring is widely used and low cost.

In one embodiment, with reference to Figure 4, an upper aluminum sheet 301 and a lower aluminum sheet 302 for fixing the lower pressure column 303 are fixedly installed in the middle of the diaphragm 3. The upper aluminum sheet 301 and the lower aluminum sheet 302 are symmetrically located on the diaphragm 3. On the upper and lower sides, the diaphragm 3 drives the lower pressure column 303 to move up and down very smoothly, and the lower pressure column 303 does not tilt.

In one embodiment, combined with Figure 2 and Figure 6, the upper cover 2 is fixedly installed above the body 1 through screws 8, the diaphragm 3 is located between the body 1 and the upper cover 2, and the edges of the diaphragm 3 are evenly distributed with multiple The edge convex film 304 has holes on the upper cover 2. The upper cover 2 can protect the diaphragm 3 and prolong its service life. The opening on the upper cover 2 is connected to the atmosphere to facilitate the reset of the diaphragm 3; the edge convex film 304 facilitates the clamping and fixing of the edge of the diaphragm 3 by the screws 8. Between the body 1 and the upper cover 2, the sealing effect at the upper opening of the body 1 is good, and the negative pressure control opening response is more timely.

In one embodiment, the body 1 is provided with more than two air outlets 102 . Usually the gas outlet 102 is connected to the carburetor, whether it is a pipeline supply or a gas tank supply, the device can also supply gas to multiple gas equipment at the same time.

Embodiment 1: Referring to Figures 1-3, a gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device includes: a body 1. The body 1 is provided with an air inlet nozzle 101 and an air outlet nozzle 102. The upper part of the body 1 has an opening and is made of elastomer. The diaphragm 3 is installed above the body 1 and seals the opening. A lower pressure column 303 is installed below the diaphragm 3. A pressure reduction and flow limiting mechanism is installed inside the body 1. The valve hole of the pressure reduction and flow limiting mechanism is located below the lower pressure column 303. A sealing valve piece 5 for closing the valve hole is installed at the valve hole. From the air inlet 101 to the lower side of the top of the decompression and flow limiting mechanism is the lower chamber 103, and from the upper side of the top of the decompression and flow limiting mechanism to the air outlet 102 is the upper chamber. 104. The gas equipment is started. The air intake of the gas equipment causes the upper chamber 104 to form a negative pressure. The negative pressure causes the diaphragm 3 to drop. The lower pressure column 303 moves downward with the diaphragm 3 and presses down the sealing valve 5 to cause the decompression and flow limiting mechanism to open. The valve hole is opened, and the upper chamber 104 and the lower chamber 103 are connected to deliver gaseous fuel.

The maximum inlet pressure of gas equipment is 3.5kPa, and the normal inlet pressure is 2kPa. Turn on the gas equipment, set the air inlet pressure to 2kPa, negative pressure appears in the upper chamber 104, the diaphragm 3 drives the downward pressure column 303 to press down the sealing valve plate 5 to open the valve hole of the pressure reduction and flow limiting mechanism, and the gaseous fuel is admitted. When the sealing valve plate 5 moves down 4.2mm, the upward resultant force generated by the negative pressure in the upper chamber 104, the positive gas fuel inlet pressure and the upward restoring force of the decompression and flow limiting mechanism is approximately equal to the downward force exerted by the diaphragm 3 on the sealing valve plate 5. The resultant force of the sealing valve plate 5, at this time, the position of the sealing valve plate 5 remains basically unchanged, maintaining the normal pressure of the inlet air at 2kPa. In this embodiment, the effective diameter of the diaphragm 3 is designed to be 100mm, the diameter of the lower pressure column 303 is 6mm, the diameter of the nozzle at the air inlet 101 is 12mm, the outer diameter of the sealing valve plate 5 is 18mm, and the inner diameter of the valve hole is 16mm. The relative size of the air pressure in the upper chamber 104 and the lower chamber 103 is used to control the opening of the valve hole of the decompression and flow limiting mechanism. As the opening decreases, the intake flow of gaseous fuel will decrease. This is an automatic flow limiting process. ; The opening becomes larger, and when the intake flow of gaseous fuel remains unchanged, P2 becomes smaller, which is an automatic decompression process.

Embodiment 2: Based on the structure of Embodiment 1, combined with Figures 4-5, the pressure reduction and flow limiting mechanism includes: sealing valve plate 5, bracket 6 and elastic member 7. The elastic member 7 is a spring, above the air inlet 101 There is a clamping table, the spring is placed on the clamping table, the bracket 6 is installed above the spring, the sealing valve plate 5 is fixedly placed above the bracket 6, and the bolt 4 is threaded on the branch of the air inlet 101 inside the body 1, O-type The ring is placed at the bolt 4 for sealing to prevent air leakage. The sealing valve plate 5 is placed below the bolt 4 to control the opening and closing of the threaded hole on the bolt 4. The outer contour size of the sealing valve plate 5 is smaller than the lower cavity 103 of the corresponding installation location. Inner dimension. In the bracket 6, the upper middle of the plate-shaped frame surface 602 protrudes upward to form a frame column 603. A clamping platform 604 for fixing the sealing valve plate 5 is provided above the frame column 603. The sealing valve plate 5 is clamped on the outside of the frame column 603. The clamping platform 604 prevents the sealing valve plate 5 from detaching from the bracket 6 during operation; the lower middle of the frame surface 602 protrudes downward to form a leg 601, and the leg 601 is embedded in the spring to limit the stroke and movement direction of the bracket 6; The cross-sectional area of the column 603 is smaller than the cross-sectional area of the frame 602, which allows a gas channel between the side of the bracket 6 and the inner wall of the body 1; the edge of the frame 602 protrudes outward to form a ridge 605, and the ridge 605 rides on the spring.

Embodiment 1 further understands: the sealing valve plate 5 moves downward by 4.2mm, that is, the spring deformation is 4.2mm, and the upward restoring force of the decompression and flow limiting mechanism is generated by the spring in the depressed state.

Embodiment 3: Based on the structure of Embodiment 1, combined with Figure 6, the upper aluminum sheet 301 and the lower aluminum sheet 302 for fixing the lower pressure column 303 are fixedly installed in the middle of the diaphragm 3. The aluminum sheet 302 is symmetrically located on the upper and lower sides of the diaphragm 3; the upper cover 2 is fixedly installed above the body 1 through screws 8, the diaphragm 3 is located between the body 1 and the upper cover 2, and the edges of the diaphragm 3 are evenly distributed There are multiple edge convex films 304 and holes on the upper cover 2 .

The above are only preferred embodiments of the present invention and are not intended to limit the present invention in other forms. Any skilled person familiar with the art may make changes or modifications to equivalent implementations using the technical contents disclosed above. example. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims (9)

1. A gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device, including: a body (1), the body (1) is provided with an air inlet nozzle (101) and an air outlet nozzle (102), characterized in that the body (1) ) is installed with a decompression and flow-limiting mechanism inside. The lower chamber (103) is from the air inlet nozzle (101) to the lower side of the top of the decompression and flow-limiting mechanism, and the upper chamber (103) is from the upper side of the top of the decompression and flow-limiting mechanism to the air outlet (102). Cavity (104); the upper part of the main body (1) has an opening. The elastomer diaphragm (3) is installed above the main body (1) and seals the opening. A lower pressure column (303) is installed below the diaphragm (3). The pressure reduction limit The valve hole of the flow mechanism is located below the lower pressure column (303), and a sealing valve plate (5) for closing the valve hole is installed at the valve hole. 2. The gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device according to claim 1, characterized in that the pressure reducing and flow limiting mechanism includes: a sealing valve plate (5), a bracket (6) and an elastic member (7), There is a clamping table above the air inlet (101), the elastic part (7) is placed on the clamping table, the bracket (6) is installed above the elastic part (7), and the sealing valve plate (5) is fixed on the bracket (6) Above, bolts (4) are installed through threads at the branch of the air inlet (101) inside the body (1), and the sealing valve plate (5) is placed below the bolts (4) to control the threaded holes on the bolts (4). When opening and closing, the outer contour size of the sealing valve plate (5) is smaller than the inner size of the lower cavity (103) of the corresponding installation location. 3. The gas fuel automatic switch, automatic pressure reduction and automatic current limiting device according to claim 2, characterized in that in the bracket (6), the upper middle of the plate-shaped frame surface (602) protrudes upward to form a frame column (603). , there is a clamping platform (604) for fixing the sealing valve plate (5) above the frame column (603); the middle of the frame surface (602) protrudes downward to form a leg (601), and the leg (601) is embedded in the elastic in file (7). 4. The gas fuel automatic switch, automatic pressure reduction and automatic current limiting device according to claim 3, characterized in that the edge of the frame (602) protrudes outward to form a convex rib (605), and the convex rib (605) rests on the elastic Item (7) above. 5. The gas fuel automatic switch, automatic pressure reduction and automatic current limiting device according to claim 2, characterized in that the elastic member (7) is a spring. 6. The gas fuel automatic switch, automatic pressure reduction and automatic current limiting device according to claim 1, characterized in that an upper aluminum sheet (301) for fixing the lower pressure column (303) is fixedly installed in the middle of the diaphragm (3). ) and the lower aluminum sheet (302). The upper aluminum sheet (301) and the lower aluminum sheet (302) are symmetrically located on the upper and lower sides of the diaphragm (3). 7. The gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device according to any one of claims 1 to 6, characterized in that the upper cover (2) is fixedly installed above the body (1) through screws (8), and the membrane The sheet (3) is located between the body (1) and the upper cover (2). A plurality of edge convex membranes (304) are evenly distributed on the edge of the membrane sheet (3), and holes are opened in the upper cover (2). 8. The gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device according to claim 7, characterized in that the body (1) is provided with more than two gas outlets (102). 9. A gas fuel automatic switch, automatic pressure reduction and automatic current limiting method, characterized in that the gas fuel automatic switch, automatic pressure reduction and automatic current limiting device as claimed in claim 1, When the gas equipment is started, a negative pressure is formed in the upper chamber (104). The negative pressure drives the diaphragm (3) to descend. The lower pressure column (303) moves downward with the diaphragm (3) and presses down the sealing valve plate (5) to limit the pressure reduction. The valve hole of the flow mechanism is opened, and the upper chamber (104) and the lower chamber (103) are connected to transport gaseous fuel. This is an automatic opening process; When the gas equipment is working, when the inlet pressure P1 of the gas equipment is always greater than the inlet pressure P2 of the gas fuel automatic switch, automatic pressure reduction and automatic flow limiting device, the valve hole of the pressure reducing and flow limiting mechanism is always open, and the valve hole The opening changes as the difference between P1 and P2 changes. The opening of the valve hole becomes larger as ^△ P becomes larger, and becomes smaller as ^△ P becomes smaller, thereby automatically controlling the gas fuel output pressure at the air outlet (102) and Flow, the difference between P1 and P2 is P1-P2 = ^△ P, △P is a positive value, Turn off the gas equipment, the negative pressure in the upper chamber (104) is reduced to zero, and the diaphragm (3) moves upward to return to the initial position, that is, the position when not working. At this position, the valve hole is closed, and the upper chamber (104) and lower chamber (103) is not connected, this is the process of automatic shutdown.