Burner flashback detection method and burner flashback detection device

Abstract

The present application relates to the field of gas stoves, and in particular to a burner flashback detection method and a burner flashback detection device. The burner flashback detection method includes the following steps: obtaining the current flame current value of the preset flame protection hole of the burner according to a first preset time interval; determining whether the current flame current value is greater than the first preset value; if so, determining whether the current flame current value is less than the second preset value; if so, repeatedly obtaining the detection flame current value of the preset flame protection hole according to the first preset time interval; if the detection flame current value less than the second preset value is obtained for a preset number of consecutive times, cutting off the gas source of the burner. The burner flashback detection method provided in the present application can identify whether the burner has recovered from the flashback state to the normal combustion state, and will only cut off the gas source of the burner when it is determined that the flashback state has not returned to normal, which will not affect the normal use of the user and improve the user experience.

Description

Technical Field

[0001] The present application relates to the field of gas stoves, and in particular to a burner flashback detection method and a burner flashback detection device. Background Art

[0002] When users place the fire cover on the fire cover base after cleaning the stove, a large gap can easily form between the mating surfaces of the fire cover and the fire cover base, affecting the burner's gas output speed. Specifically, when the combustion speed and gas output speed are within a stable range, the burner can burn normally. If the gas output speed is lower than the combustion speed, the burning gas will ignite the gas in the cavity inside the fire cover, which is professionally known as flashback. Conversely, if the combustion speed is lower than the gas output speed, the gas pressure is too high, and the gas is pushed far out of the fire cover surface, which is professionally known as flame lift.

[0003] The creation of the gap reduces the gas outlet velocity of the burner, causing the flame to ignite the internal gas, which burns inside the fire cover, thereby causing flames to form inside the burner, increasing the temperature of the burner and destroying the original design life of the burner.

[0004] Prior art gas stoves are equipped with flashback detection devices that shut off the gas supply when flashback occurs. However, in some cases, a burner flashback only lasts a short time before returning to normal combustion. Existing flashback detection devices fail to identify these situations and simply shut off the gas supply when flashback occurs, forcing the user to reopen the burner, impacting normal use. Summary of the Invention

[0005] The purpose of the present application is to provide a burner flashback detection method and a burner flashback detection device, which can identify whether the burner has recovered from a flashback state to a normal combustion state.

[0006] The present application provides a burner flashback detection method, comprising the following steps:

[0007] According to a first preset time interval, obtaining a current flame current value of a preset flame-keeping hole of the burner;

[0008] determining whether the current flame current value is greater than a first preset value;

[0009] If so, determining whether the current flame current value is less than a second preset value;

[0010] If yes, repeatedly performing the step of obtaining the detected flame current value of the preset flame-keeping hole according to the first preset time interval;

[0011] If the detected flame current value is less than the second preset value for a consecutive preset number of times, the gas source of the burner is cut off.

[0012] In the above technical solution, further, after repeatedly obtaining the detected flame current value of the preset fire-preserving hole according to the first preset time interval, the method further includes:

[0013] When the detected flame current value obtained at any time is greater than or equal to the second preset value, the current flame current value of the preset flame preservation hole of the burner is repeatedly obtained according to the first preset time interval.

[0014] In the above technical solution, further, after determining that the current flame current value is greater than the first preset value, the method further includes:

[0015] determining in response whether a current flame current value is less than a flame current value at a previous moment;

[0016] If so, determining whether the current flame current value is less than a second preset value;

[0017] If not, repeatedly execute according to the first preset time interval to obtain the current flame current value of the preset flame-keeping hole of the burner.

[0018] In the above technical solution, further, after determining whether the current flame current value is greater than the first preset value, the method further includes:

[0019] If the current flame current value is less than or equal to the first preset value, the gas source of the burner is cut off.

[0020] In the above technical solution, further, after determining whether the current flame current value is less than the second preset value, the method further includes:

[0021] When the current flame current value is greater than or equal to the second preset value, the current flame current value of the preset flame preservation hole of the burner is repeatedly obtained according to the first preset time interval.

[0022] In the above technical solution, further, before obtaining the current flame current value of the preset flame-keeping hole of the burner according to the first preset time interval, the method further includes:

[0023] Obtaining the start information of the burner;

[0024] After the second preset time of obtaining the start-up information of the burner, the current flame current value of the preset flame-keeping hole of the burner is obtained according to the first preset time interval.

[0025] The present application also provides a burner flashback detection device, including a controller, a memory and a bus, wherein the memory stores machine-readable instructions executable by the controller. When the burner flashback detection device is running, the controller and the memory communicate through the bus, and the machine-readable instructions are executed by the controller to execute the steps of the burner flashback detection method described in the above scheme.

[0026] In the above technical solution, further, it also includes a combustion detection component;

[0027] The combustion detection component is used to detect the flame current value of the preset flame-keeping hole of the burner, and the combustion detection component is communicatively connected with the controller.

[0028] In the above technical solution, further, the tempering detection device also includes a heat-sensitive deformation member and a current limiting member;

[0029] The inner ring fire cover of the burner is provided with a connecting flow channel to connect the gas source of the burner with the preset fire protection hole;

[0030] The flow limiting member is installed in the communication flow channel, and the flow limiting member can move relative to the communication flow channel to reduce the flow area of ​​the communication flow channel;

[0031] The heat-induced deformation member is connected to the inner ring fire cover, and the heat-induced deformation member is deformed at a preset temperature to drive the flow limiting member to move relative to the connecting flow channel.

[0032] In the above technical solution, further, the tempering detection device further includes an elastic member;

[0033] The elastic member is installed between the flow limiting member and the inner ring fire cover, so that the flow limiting member has a movement tendency to increase the flow area of ​​the communicating flow channel.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] The burner backfire detection method provided in the present application obtains the detection flame current value of the preset fire-keeping hole by repeatedly executing multiple times according to the first preset time interval. When it is determined that the detection flame current value obtained each time is less than the second preset value, it can be identified that the burner has not recovered from the backfire state to the normal combustion state. At this time, the gas source of the burner is cut off to increase the life of the burner, which will not affect the normal use of the user and improve the user experience.

[0036] This application also provides a burner flashback detection device, comprising a controller, a memory, and a bus. The memory stores machine-readable instructions executable by the controller. When the burner flashback detection device is in operation, the controller and the memory communicate via the bus. The machine-readable instructions are executed by the controller to execute the steps of the burner flashback detection method described above. Based on the above analysis, it can be seen that the burner flashback detection device also has the aforementioned beneficial effects, which will not be further elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0038] Figure 1 A flow chart of the burner flashback detection method provided in this application;

[0039] Figure 2 A schematic diagram of a partial cross-sectional structure of a burner flashback detection device provided in this application;

[0040] Figure 3 A schematic diagram of the explosion structure of the burner flashback detection device provided in this application;

[0041] Figure 4 A schematic diagram of the structure of the inner ring fire cover provided for this application;

[0042] Figure 5 This is a schematic diagram of the structure of the current limiting nail provided in this application.

[0043] In the figure: 101-electrical control box; 102-electrode needle; 103-spring; 104-current limiting nail; 105-connecting flow channel; 106-preset fire protection hole; 107-inner ring fire cover; 108-spring; 109-screw fixing hole; 110-screw; 111-positioning column; 112-cross section; 113-small channel; 114-small flow channel; 115-connecting hole. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solution of this application in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0045] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this application and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0047] Example 1

[0048] During the use of a gas stove, in the event that the burner flashback lasts for a short time and then returns to normal combustion, the present application provides the following flashback detection method, which can identify the above situation, avoid the burner from shutting off the gas source immediately after flashback occurs, and prompt the user experience.

[0049] See also Figure 1 As shown, the burner flashback detection method provided by the present application includes the following steps:

[0050] According to a first preset time interval, obtaining a current flame current value of a preset flame retaining hole 106 of the burner;

[0051] Determining whether the current flame current value is greater than a first preset value;

[0052] If so, determining whether the current flame current value is less than a second preset value;

[0053] If yes, repeat the process according to the first preset time interval to obtain the detected flame current value of the preset flame protection hole 106;

[0054] If the detected flame current value is less than the second preset value for a consecutive preset number of times, the gas source of the burner is cut off.

[0055] In this embodiment, the present application can determine whether a flashback condition has occurred based on the combustion condition of the flame at the flame-keeping hole of the burner detected by the electrode needle 102. Specifically, when the burner is in normal combustion conditions, the current flame current value of the preset flame-keeping hole 106 is between 5mA and 10mA. When a flashback condition occurs in the burner, the flame at the preset flame-keeping hole 106 decreases to reduce the current flame current value to below 5mA. When the burner is in an extinguished state, indicating that the preset flame-keeping hole 106 is almost flameless, the detected front flame current value is between 0 and 1.5mA.

[0056] This application obtains the current flame current value at a first preset time interval, enabling real-time monitoring of the burner while reducing detection frequency and energy consumption. Specifically, the current flame current value can be checked every 5 seconds. When the electrode needle 102 detects flame current at the preset flame retaining hole 106, it indicates that the burner is burning. The application then further determines whether the current flame current value is within the current range corresponding to a flashback condition. When the current flame current value decreases to 5mA, flashback has occurred.

[0057] For some burners, the static pressure in the burner cavity is relatively large, and the fluid flows smoothly. Although backfire occurs, the fuel gas mixture will push the combustion gas in the internal cavity outward under the injection power of the nozzle after a period of time, thereby restoring normal combustion conditions (that is, the flame burns normally on the surface of the inner ring fire cover 107, and there is no abnormal burning flame inside the burner).

[0058] After detecting the occurrence of backfire during the routine detection process, this application performs multiple consecutive detections of the flame current value of the preset flame-keeping hole 106 at intervals of 5 seconds to identify whether the combustion gas has recovered from the backfire state to normal. Specifically, for burners that can recover from the backfire state to the normal combustion state independently, they can recover automatically within 30 seconds. This application specifically sets 6 detection times, that is, after the backfire occurs, the flame is detected 6 times for 30 seconds. If the flame current value obtained during each detection is less than 5mA, it means that the burner has not recovered to normal independently. At this time, the gas source of the burner is cut off to prevent the backfire process from lasting too long and affecting the life of the burner.

[0059] In an optional solution of this embodiment, after repeatedly obtaining the detected flame current value of the preset flame preservation hole 106 at the first preset time interval, the following steps are further included:

[0060] When any detected flame current value obtained at any time is greater than or equal to the second preset value, the current flame current value of the preset flame preservation hole 106 of the burner is repeatedly obtained according to the first preset time interval.

[0061] In this embodiment, during the set 6 detection and identification processes, when the detection flame current value detected in any detection process is greater than 5mA, it means that the burner has autonomously recovered from the backfire state to the normal combustion state. At this time, the acquisition of the detection flame current value is interrupted (for example, when the detection flame current value obtained for the second time is greater than 5mA, the subsequent 4 detection processes are not executed) without cutting off the gas source of the burner, and the routine monitoring steps of the preset fire-keeping hole 106 are performed.

[0062] In an optional solution of this embodiment, after determining that the current flame current value is greater than the first preset value, the method further includes:

[0063] Determine in response whether the current flame current value is less than the flame current value at the previous moment; if so, determine whether the current flame current value is less than a second preset value; if not, repeat the process according to the first preset time interval to obtain the current flame current value of the preset flame keeping hole 106 of the burner.

[0064] In this embodiment, after flashback occurs, the flame of the preset flame retaining hole 106 continues to decrease, and the detected flame current decreases. Before determining whether the current flame current value is within the current range corresponding to the flashback state, first determining whether the acquired current flame current value is decreasing can filter out false positives caused by non-flashback conditions and reduce the program execution burden.

[0065] In an optional solution of this embodiment, after determining whether the current flame current value is greater than the first preset value, the method further includes:

[0066] If the current flame current value is less than or equal to the first preset value, the gas source of the burner is cut off.

[0067] In this embodiment, in the conventional monitoring step, if the detected current flame current value is between 0 and 1.5 mA, it indicates that the burner is in an extinguished state, and there is no need to perform subsequent steps.

[0068] In an optional solution of this embodiment, after determining whether the current flame current value is less than the second preset value, the method further includes:

[0069] When the current flame current value is greater than or equal to the second preset value, the process is repeated according to the first preset time interval to obtain the current flame current value of the preset flame retaining hole 106 of the burner.

[0070] In this embodiment, in the routine monitoring step, if the detected current flame current value is between 5 mA and 10 mA, it indicates that the burner is burning normally, and the routine monitoring step is executed cyclically.

[0071] In an optional solution of this embodiment, before obtaining the current flame current value of the preset flame-keeping hole 106 of the burner according to the first preset time interval, the method further includes:

[0072] Get the burner opening information;

[0073] After the second preset time of obtaining the start-up information of the burner, the current flame current value of the preset flame protection hole 106 of the burner is obtained according to the first preset time interval.

[0074] In this embodiment, when the user turns on the burner, the burner may fail to ignite due to user errors (e.g., improperly pressing the start knob, resulting in ignition failure). Within 10 seconds of turning on the burner, the electrode needle 102 does not detect the flame in the preset flame retaining hole 106, preventing the program from misjudging the burner's combustion status during the burner startup process. After 10 seconds, the normal monitoring steps are resumed.

[0075] Example 2

[0076] See also Figures 2 to 5 As shown, the second embodiment of the present application provides a burner flashback detection device, including a controller, a memory and a bus (all arranged at Figure 3 The memory stores machine-readable instructions executable by the controller. When the burner flashback detection device is running, the controller and the memory communicate via a bus. When the machine-readable instructions are run by the controller, the steps of the burner flashback detection method of any of the above embodiments are executed.

[0077] See also Figure 2 and Figure 3 As shown, in an optional solution of this embodiment, the burner flashback detection device also includes a combustion detection component (specifically set as an electrode needle 102 in the figure); the combustion detection component is used to detect the flame current value of the preset fire-keeping hole 106 of the burner, and the combustion detection component is communicatively connected with the controller so that the controller can execute the steps of the burner flashback detection method according to the detected flame current value.

[0078] See also Figure 2 and Figure 3 As shown, in the optional solution of this embodiment, the flashback detection device also includes a heat-sensitive deformation member and a flow-limiting member. The inner ring fire cover 107 of the burner is provided with a connecting flow channel 105 to connect the gas source channel of the burner with the preset fire-keeping hole 106 ( Figure 2 The arrow in the figure shows the flow direction of the gas); the flow limiting member is installed in the connecting flow channel 105, and the flow limiting member can move relative to the connecting flow channel 105 to reduce the flow area of ​​the connecting flow channel 105; the heat-induced deformation member is connected to the inner ring fire cover 107, and the heat-induced deformation member is deformed at a preset temperature to drive the flow limiting member to move relative to the connecting flow channel 105.

[0079] Furthermore, the tempering detection device further comprises an elastic member ( Figure 3 The elastic member is installed between the flow limiting member and the inner ring fire cover 107 so that the flow limiting member has a movement trend of increasing the flow area of ​​the connecting flow channel 105.

[0080] In this embodiment, when the flame current value is near the threshold between the flashback current range and the normal current range, false positives can occur based solely on the flame current value. For example, when the flame current value is 5.1 mA, the burner may also be flashing. This application further incorporates a mechanical structure to detect flashback, providing a double safeguard for flashback detection.

[0081] Specifically, when the burner flashes back, the temperature inside the burner rises, and the heat-sensitive deformation member ( Figure 2 The specific setting is that the spring piece 103 is deformed, and the deformation of the induction deformation member triggers the flow limiting member ( Figure 2 The current limiting nail 104 is specifically set to move relative to the connecting flow channel 105, and the gas flow of the connecting flow channel 105 becomes smaller, so that the flame at the preset flame protection hole 106 becomes smaller, and the flame current value detected by the electrode needle 102 is reduced, so that the occurrence of backfire can be detected, and then the subsequent 6 detection and identification steps can be performed.

[0082] More specifically, if Figures 2 to 4 As shown, the inner side of the inner ring fire cover 107 (made of copper) is provided with a screw fixing hole 109. Screw 110 passes through the hole of the spring clip 103 to fix the spring clip 103 to the inner ring fire cover 107. The spring clip 103 is provided with a curved R angle. The spring clip 103 has two states at different temperatures: one is when the burner is burning normally, the internal temperature of the burner is relatively low, and the spring clip 103 is in a naturally bent state; the other is when the burner backfires, the internal temperature of the burner rises and reaches a preset temperature, and the spring clip 103 is heated and deformed to tend to a straight surface.

[0083] The communication channel 105 includes a communication hole 115 provided on the inner side of the inner ring fire cover 107. A spring 108 and a flow-limiting nail 104 are installed in the communication hole 115. The flow-limiting nail 104 is provided with a positioning column 111 to fix the spring 108. The spring 108 abuts between the inner ring fire cover 107 and the flow-limiting nail 104, so that the flow-limiting nail 104 has a tendency to move downward, thereby preventing the head of the flow-limiting nail 104 from blocking the entrance of the communication hole 115. Figure 5As shown, the flow-limiting nail 104 has a cross-shaped cross-section 112 as shown in the figure. This structure enables it to move in the connecting hole 115 without being skewed, and four small channels 113 are formed between the flow-limiting nail 104 and the inner wall of the connecting hole 115 (the number of small channels 113 can be set from 1 to 10 according to actual conditions, and this case takes four small channels 113 as an example). The projected cross-sectional area of ​​the four small channels 113 needs to be greater than or equal to the area of ​​the gas outlet of the three preset fire-keeping holes 106 to ensure that the flow rate of the gas flow at the preset fire-keeping holes 106 is sufficient when the burner is used normally.

[0084] The movable end of the spring clip 103 presses against the surface of the current limiting pin 104 from below. When the burner flashes back, the internal temperature of the burner rises, heating the spring clip 103. The movable end of the spring clip 103 slightly deforms upward, driving the current limiting pin 104 upward. The connecting flow channel 105 also includes a small flow channel 114 formed between the head of the current limiting pin 104 and the entrance of the connecting flow channel 105. As the current limiting pin 104 continues to move upward, the flow area of ​​the small flow channel 114 continuously decreases, thereby reducing the gas output and flame of the predetermined flame retention hole 106. If the internal temperature of the burner continues to rise, the movable end of the spring 103 may directly press the current limiting pin 104. At this time, the deformation force of the spring 103 is much greater than the reverse force applied to the current limiting pin 104 by the spring 108, so that the head of the current limiting pin 104 directly blocks the entrance of the connecting flow channel 105, the intake air flow is cut off, the preset flame-keeping hole 106 cannot discharge gas for combustion, and the electrode needle 102 cannot sense the flame current, that is, the gas source of the burner is cut off.

[0085] In the case where the gas source is directly cut off after the shrapnel 103 is deformed by heat, even if the burner stops burning, since the temperature inside the burner is still relatively high, the shrapnel 103 needs to be maintained for a long time (5 to 10 minutes) before it can begin to recover, so that the airflow can circulate again, causing the burner to remain in the cut-off state for a long time. In order to avoid the above-mentioned problem that causes the user to wait for a long time before turning on the burner, the present application controls the bending degree of the shrapnel 103 through the design of the structure, so that when the shrapnel 103 produces a small deformation, it triggers the steps of the burner backfire detection method. It ensures that the shrapnel 103 will not be deformed to the point where the current limiting nail 104 blocks the entrance of the connecting hole 115, thereby ensuring that the user can turn on the burner without waiting for the shrapnel 103 to cool down when using the burner.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application. In addition, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments means that they are within the scope of the present application and form different embodiments.

Claims

1. A burner flashback detection method, characterized in that: The following steps are involved: According to a first preset time interval, obtaining a current flame current value of a preset flame-keeping hole of the burner; determining whether the current flame current value is greater than a first preset value; If so, determining whether the current flame current value is less than a second preset value; If yes, repeatedly performing the step of obtaining the detected flame current value of the preset flame-keeping hole according to the first preset time interval; If the detected flame current value is less than the second preset value for a consecutive preset number of times, the gas source of the burner is cut off.

2. The burner flashback detection method according to claim 1, characterized in that: After repeatedly obtaining the detected flame current value of the preset fire-preserving hole according to the first preset time interval, the method further includes: When the detected flame current value obtained at any time is greater than or equal to the second preset value, the current flame current value of the preset flame preservation hole of the burner is repeatedly obtained according to the first preset time interval.

3. The burner flashback detection method according to claim 1, characterized in that: After determining that the current flame current value is greater than the first preset value, the method further includes: determining in response whether a current flame current value is less than a flame current value at a previous moment; If so, determining whether the current flame current value is less than a second preset value; If not, repeatedly execute according to the first preset time interval to obtain the current flame current value of the preset flame-keeping hole of the burner.

4. The burner flashback detection method according to claim 1, characterized in that: After determining whether the current flame current value is greater than a first preset value, the method further includes: If the current flame current value is less than or equal to the first preset value, the gas source of the burner is cut off.

5. The burner flashback detection method according to claim 1, characterized in that: After determining whether the current flame current value is less than a second preset value, the method further includes: When the current flame current value is greater than or equal to the second preset value, the current flame current value of the preset flame preservation hole of the burner is repeatedly obtained according to the first preset time interval.

6. The burner flashback detection method according to claim 1, characterized in that: Before obtaining the current flame current value of the preset flame-keeping hole of the burner according to the first preset time interval, the method further includes: Obtaining the start information of the burner; After the second preset time of obtaining the start-up information of the burner, the current flame current value of the preset flame-keeping hole of the burner is obtained according to the first preset time interval.

7. A burner flashback detection device, characterized in that: The burner flashback detection device includes a controller, a memory, and a bus. The memory stores machine-readable instructions executable by the controller. When the burner flashback detection device is in operation, the controller and the memory communicate with each other via the bus. When the machine-readable instructions are executed by the controller, the steps of the burner flashback detection method according to any one of claims 1 to 6 are executed.

8. The burner flashback detection device according to claim 7, characterized in that: Also includes combustion detection components; The combustion detection component is used to detect the flame current value of the preset flame-keeping hole of the burner, and the combustion detection component is communicatively connected with the controller.

9. The burner flashback detection device according to claim 8, characterized in that: The tempering detection device further includes a heat-sensing deformation member and a current limiting member; The inner ring fire cover of the burner is provided with a connecting flow channel to connect the gas source of the burner with the preset fire protection hole; The flow limiting member is installed in the communication flow channel, and the flow limiting member can move relative to the communication flow channel to reduce the flow area of ​​the communication flow channel; The heat-induced deformation member is connected to the inner ring fire cover, and the heat-induced deformation member is deformed at a preset temperature to drive the flow limiting member to move relative to the connecting flow channel.

10. The burner flashback detection device according to claim 9, characterized in that: The tempering detection device further includes an elastic member; The elastic member is installed between the flow limiting member and the inner ring fire cover, so that the flow limiting member has a movement tendency to increase the flow area of ​​the communicating flow channel.

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