Fluid resistance element, fluid control device, and method for manufacturing a fluid resistance element

Abstract

To allow a fluid resistance element to be fixed to a channel while enjoying the benefits offered by the ceramic fluid resistance element.SOLUTION: A fluid resistance element includes a ceramic channel formation member 10 having one or more resistance channels 10a, and a metal coating member 20 covering an outer peripheral surface 11 of the ceramic channel formation member 10, and is configured to provide a swollen part 26 that swells toward the outer peripheral surface 11 of the ceramic channel formation member 10 on an inner peripheral surface 25 of the coating member 20.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a fluid resistance element, a fluid control device including the fluid resistance element, and a method for manufacturing a fluid resistance element.

Background Art

[0002] As a conventional fluid resistance element, as disclosed in Patent Document 1, there is one in which a plurality of extremely thin resistance channels are formed in a columnar ceramic.

[0003] Such ceramic fluid resistance elements have physical properties that conventional metal ones do not, such as a coefficient of thermal expansion close to zero, high hardness, and excellent heat resistance and corrosion resistance, and enable accurate measurement of flow rate particularly during small flow rate control.

[0004] However, due to the physical property of ceramic that it hardly deforms, there is a problem that it is difficult to fix a ceramic fluid resistance element to a flow path. Although Patent Document 1 discloses aspects such as interference fitting or clearance fitting of a columnar ceramic to a cylindrical metal, all of these fixing methods are technically difficult, and there are many problems for practical application.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0006] Accordingly, the present invention has been made to solve all of the above problems at once, and its main object is to enable the fluid resistance element to be fixed to a flow path while enjoying the advantages of a ceramic fluid resistance element.

Means for Solving the Problem

[0007] In other words, the fluid resistance element according to the present invention comprises a ceramic channel forming member having one or more resistance channels, and a metal covering member covering the outer circumferential surface of the channel forming member, characterized in that a bulge portion is provided on the inner circumferential surface of the covering member that bulges toward the outer circumferential surface of the channel forming member.

[0008] With a fluid resistance element configured in this way, since the flow channel forming member is made of ceramic, it is possible to enjoy the advantages unique to ceramics, such as a near-zero coefficient of thermal expansion, high hardness, and excellent heat resistance and corrosion resistance. Furthermore, by forming the bulge on the inner circumferential surface of the covering member by applying force to the metal covering member from the radially outer side and crimping it, the flow path forming member can be fixed to the covering member, and by fixing this metal covering member to another pipe member, for example by welding, the fluid resistance element can be fixed to a desired location in the flow path.

[0009] It is preferable that the bulging portion is formed along the circumferential direction of the inner surface of the covering member. With this configuration, the flow path forming member can be more securely fixed to the covering member.

[0010] It is preferable that the outer circumferential surface of the covering member is provided with a recess that is recessed radially inward toward the outer circumferential surface of the flow channel forming member. In this way, by providing a recess on the outer circumferential surface of the covering member, the aforementioned bulge can be formed on the inner circumferential surface of the covering member, and the flow path forming member can be fixed to the covering member.

[0011] Preferably, the covering member is cylindrical and has a housing space for housing the flow path forming member, and the predetermined region along the axial direction that forms the housing space is thinner than other regions along the axial direction. With this configuration, the designated area forming the containment space is thinner than the other areas, making it easy to see at a glance where the flow path forming member is located. Furthermore, making it thinner makes it easier to crimp this designated area, thus improving work efficiency.

[0012] Preferably, the covering member is provided downstream of the flow path forming member and has a downstream flow path to which the fluid that has passed through the resistance flow path is guided, and the downstream flow path has a small-diameter portion in which the flow path diameter is smaller than the outer diameter of the flow path forming member. In this configuration, the channel-forming member inserted into the covering member will be obstructed by the smaller diameter portion, thus preventing the channel-forming member from coming loose downstream.

[0013] It is preferable that the downstream channel is provided downstream of the small-diameter section and has an enlarged diameter section in which the channel diameter widens from the upstream side to the downstream side. With this design, the pressure of the fluid that has passed through the resistance channel can be made uniform in the enlarged section before being guided downstream, allowing for more accurate measurement of the flow rate.

[0014] Preferably, the covering member is provided upstream of the flow path forming member and has a reduced diameter portion where the flow path diameter decreases from the upstream side to the downstream side. With this design, the reduced diameter section functions as a guide when inserting the flow path forming member, thus improving work efficiency.

[0015] In order to fix the fluid resistance element at a desired location in the flow path, it is preferable that both axial ends of the covering member are welded to another pipe member.

[0016] Furthermore, the fluid control device according to the present invention is characterized by comprising the above-mentioned fluid resistance element provided in a fluid flow path, an upstream pressure sensor and a downstream pressure sensor provided on the upstream and downstream sides of the fluid resistance element in the flow path, and a flow control valve provided in the flow path. Furthermore, another fluid control device according to the present invention is characterized by comprising: the above-described fluid resistance element provided in a flow path through which a fluid flows; a sensor flow path connecting an upstream side and a downstream side in the flow path; an upstream-side electrical resistance element and a downstream-side electrical resistance element provided in the sensor flow path; and a flow rate adjustment valve provided in the flow path. A differential pressure-type fluid control device or a thermal-type fluid control device configured as described above includes the above-described fluid resistance element, and thus can achieve the same operational effects as those of the fluid resistance element according to the present invention.

[0017] As a more specific embodiment, there may be mentioned an aspect in which a plurality of said fluid resistance elements are provided in series or in parallel in said flow path.

[0018] It is preferable that the plurality of fluid resistance elements have resistance values different from each other. With this configuration, various resistance values can be obtained by using the plurality of fluid resistance elements.

[0019] Further, a method for manufacturing a fluid resistance element according to the present invention is characterized by comprising the steps of: covering an outer peripheral surface of a ceramic flow path forming member having one or more resistance flow paths with a metal covering member; and fixing the flow path forming member to the covering member by caulking the covering member while applying a force to the covering member from a radially outer side. With such a manufacturing method, the same operational effects as those of the above-described fluid resistance element can be obtained, and the fluid resistance element can be fixed to a desired position in the flow path while enjoying the advantages provided by the ceramic fluid resistance element. Effects of the Invention

[0020] According to the present invention configured as described above, the fluid resistance element can be fixed to a desired position in the flow path while enjoying various advantages provided by the flow path forming member being made of ceramic. Brief Description of the Drawings

[0021] [Figure 1]1 is a fluid circuit diagram of a fluid control device according to an embodiment of the present invention. [Figure 2] A cross-sectional view showing a part of the internal structure of the fluid control device of the same embodiment. [Figure 3] A schematic diagram showing the configuration of the fluid resistance element of the same embodiment. [Figure 4] A schematic diagram showing the configuration of the fluid resistance element of the same embodiment. [Figure 5] A schematic diagram for explaining caulking of the same embodiment. [Figure 6] A schematic diagram showing the arrangement of fluid resistance elements in another embodiment. [Figure 7] A schematic diagram showing the arrangement of fluid resistance elements in another embodiment. [Figure 8] A schematic diagram showing the configuration of a holding block in another embodiment. [Figure 9] A fluid circuit diagram of a fluid control device in another embodiment. MODE FOR CARRYING OUT THE INVENTION

[0022] Hereinafter, an embodiment of a fluid resistance element according to the present invention will be described with reference to the drawings.

[0023] The fluid resistance element of the present embodiment is one of the constituent elements of a fluid control device that controls the mass flow rate of, for example, a material gas used in semiconductor manufacturing.

[0024] Specifically, as shown in the fluid circuit diagram of FIG. 1 and a part of the internal structure of FIG. 2, this fluid control device 100 includes an internal flow path L through which a fluid to be controlled flows, a flow rate regulating valve V provided on the internal flow path L, a flow rate measurement mechanism X provided downstream of the flow rate regulating valve V for measuring the flow rate of the fluid flowing through the internal flow path L, and a control circuit C1 that controls the flow rate regulating valve V so that the flow rate measured by the flow rate measurement mechanism X reaches a predetermined target flow rate.

[0025] The flow rate measuring mechanism X is of the differential pressure type and, as shown in Figure 1, comprises an upstream pressure sensor Pa located upstream of the internal flow path L, a downstream pressure sensor Pb located downstream of the upstream pressure sensor Pa, a fluid resistance element R located between the upstream pressure sensor Pa and the downstream pressure sensor Pb in the internal flow path L to generate a pressure difference, and a flow rate calculation circuit C2 that calculates the flow rate of the fluid flowing through the internal flow path L based on the pressure measurements from the upstream pressure sensor Pa and the downstream pressure sensor Pb and the resistance value of the fluid resistance element R.

[0026] In this embodiment, the fluid resistance element R is a distinctive feature and will be described in detail below.

[0027] As shown in Figures 2 to 4, the fluid resistance element R provides resistance when a fluid flows through it. Specifically, it comprises a ceramic channel forming member 10 having a resistive channel 10a (hereinafter also referred to as the resistive channel 10a), and a metal covering member 20 that covers the outer circumferential surface 11 of the channel forming member 10.

[0028] This channel-forming member 10 is molded from a ceramic such as quartz, alumina, zirconia, or silicon nitride, and is specifically cylindrical in shape, with one to several hundred resistance channels 10a formed along the axial direction. The channel-forming member 10 here has a diameter (outer diameter) of several millimeters (e.g., 1.5 mm) and a length (dimension along the axial direction) of several millimeters to several tens of millimeters (e.g., 7 mm), but these dimensions can be changed as appropriate.

[0029] The resistance channel 10a penetrates the channel forming member 10 in the axial direction and is a straight channel with a circular cross-section. Examples include one formed on the tube axis of the channel forming member 10, or multiple resistance channels regularly arranged around the tube axis. The resistance channel 10a here has a diameter (inner diameter) of less than 1 mm and about several tens of micrometers (e.g., 30 μm), and its length (dimension along the axial direction) is the same as the channel forming member 10, about several millimeters to several tens of millimeters (e.g., 7 mm), but these dimensions can be changed as appropriate.

[0030] In this embodiment, the aspect ratio, which is the ratio of the length dimension to the diameter dimension of the resistive channel 10a, is 200 or more, and more preferably 300 or more. The resistance value of this fluid resistance element R is determined based on this aspect ratio and the number of resistive channels 10a.

[0031] The covering member 20 is made of a metal that is at least less hard than ceramic, such as stainless steel or a nickel-based alloy.

[0032] As shown in Figures 3 and 4, the covering member 20 is cylindrical in shape and covers the entire outer surface 11 of the flow path forming member 10; in other words, it houses the flow path forming member 10.

[0033] More specifically, as shown in Figure 4, the covering member 20 has a housing space 21 for housing the flow path forming member 10, an upstream flow path 22 located upstream of the housing space 21, and a downstream flow path 23 located downstream of the housing space 21.

[0034] The accommodation space 21 is a space that accommodates at least a portion of the flow path forming member 10, and has an inner diameter slightly larger than the outer diameter of the flow path forming member 10.

[0035] In this embodiment, the accommodation space 21 accommodates the flow channel forming member 10 from its central portion to its downstream end 10b, while allowing the upstream end 10c of the flow channel forming member 10 to protrude upstream from the accommodation space 21.

[0036] However, the central portion of the flow channel forming member 10 up to the upstream end 10c may be housed in the housing space 21, while the downstream end 10b of the flow channel forming member 10 may protrude downstream from the housing space 21. Alternatively, only the central portion of the flow channel forming member 10 may be housed in the housing space 21, while the upstream end 10c and the downstream end 10b of the flow channel forming member 10 may protrude from the housing space 21. Furthermore, the housing space 21 may be a space that accommodates the entire flow channel forming member 10.

[0037] The upstream channel 22 connects the upstream opening 20a of the covering member 20 to the housing space 21, and the channel forming member 10 is inserted into the housing space 21 via this upstream channel 22.

[0038] This upstream channel 22 has a channel diameter larger than the inner diameter of the containment space 21, and a channel length longer than the length of the containment space 21 along its axial direction.

[0039] In this embodiment, the upstream flow path 22 has a reduced diameter section 221 in which the flow path diameter decreases from the upstream side to the downstream side, and the downstream end of this reduced diameter section 221 opens into the containment space 21. In other words, the portion of the inner circumferential surface 25 of the covering member 20 that forms the reduced diameter section 221 has a tapered shape that gradually widens in diameter from the upstream side towards the containment space 21.

[0040] The downstream channel 23 connects the downstream opening 20b of the covering member 20 with the containment space 21, and guides the fluid that has passed through the resistance channel 10a of the channel forming member 10.

[0041] This downstream channel 23 has a small-diameter portion 231 whose upstream end opens into the containment space 21, and this small-diameter portion 231 has a channel diameter smaller than the outer diameter of the channel forming member 10.

[0042] With this configuration, a contact surface 24 is formed on the radially outer side of the upstream opening of the small-diameter portion 231, against which the downstream end face of the flow path forming member 10 housed in the housing space 21 abuts.

[0043] Furthermore, by having the flow channel forming member 10 interlock with this contact surface 24, it is possible to prevent the flow channel forming member 10 from passing out of the housing space 21 into the downstream flow channel 23.

[0044] Furthermore, the downstream flow path 23 in this embodiment is provided downstream of the small-diameter section 231 and has an enlarged diameter section 232 in which the flow path diameter widens from the upstream side to the downstream side. In other words, the portion of the inner circumferential surface 25 of the covering member 20 that forms the enlarged diameter section 232 has a tapered shape that gradually widens from the small-diameter section 231 toward the downstream side.

[0045] In this embodiment, the flow length of the upstream flow path 22 and the flow length of the downstream flow path 23 are equal, and the external shape of the covering member 20 in this embodiment is symmetrical with the axial center as the axis of symmetry. However, the flow lengths of the upstream flow path 22 and the downstream flow path 23 are not limited to these and may be changed as appropriate, and the external shape of the covering member 20 may also be changed as appropriate, such as to make it asymmetrical.

[0046] By crimping the covering member 20, a bulge 26 is provided on the inner circumferential surface 25 of the covering member 20 that bulges toward the outer circumferential surface 11 of the flow channel forming member 10, and a recess 28 is provided on the outer circumferential surface 27 of the covering member 20 that is recessed radially inward toward the outer circumferential surface 11 of the flow channel forming member 10. Crimping means deforming the covering member 20 by applying force from the radial direction, as shown in Figure 5.

[0047] More specifically, as shown in Figures 3 and 4, the covering member 20 of this embodiment has a predetermined region X along the axial direction that forms the aforementioned accommodating space 21, which is thinner than other regions along the axial direction. This makes it possible to determine approximately where the accommodating space 21 is formed along the axial direction, or in other words, approximately where the flow path forming member 10 is housed.

[0048] In this embodiment, the entire circumference of the predetermined region X is thin-walled; in other words, the predetermined region X is formed as a recessed portion 29 that is recessed radially inward compared to other regions, extending over its entire circumference in the circumferential direction.

[0049] In this configuration, the entire circumference of the covering member 20 in the circumferential direction is crimped, thereby forming a bulge 26 over the entire circumference of the inner circumferential surface 25 of the covering member 20, and forming a recess 28 over the entire circumference of the outer circumferential surface 27 of the covering member 20.

[0050] More specifically, the entire circumference of the predetermined thin region X described above is crimped, thereby forming a bulge 26 on the inner surface that forms the housing space 21, and a recess 28 in the predetermined region X described above. This bulging portion 26 adheres closely to the outer circumferential surface 11 of the flow path forming member 10 and holds the flow path forming member 10 by tightening it from the radially outer side.

[0051] In other words, the fluid resistance element R of this embodiment is manufactured by covering the outer circumferential surface 11 of a ceramic flow path forming member 10 having a resistance flow path 10a with a metal covering member 20, and fixing the flow path forming member 10 to the covering member 20 by applying force from the radially outer side and crimping it.

[0052] In this configuration, as shown in Figure 2, the covering member 20 of this embodiment has other pipe members Z1 and Z2 connected to both axial ends 20x and is fixed to these pipe members Z1 and Z2, and together with these pipe members Z1 and Z2 it forms an internal flow path L.

[0053] More specifically, the axial ends 20x of the covering member 20 are welding points to be welded to other pipe members Z1 and Z2. By welding the other pipe members Z1 and Z2 to each of these welding points, the upstream opening 20a of the covering member 20 communicates with the downstream opening of the other pipe member Z1, and the downstream opening 20b of the covering member 20 communicates with the upstream opening of yet another pipe member Z2, thereby forming an internal flow path L.

[0054] As shown in Figure 2, the covering member 20 of this embodiment is covered with a heat transfer member 30 such as aluminum, which has good thermal conductivity, making it easier to transmit the temperature of the fluid flowing through the resistive channel 10a to the surroundings. A temperature sensor T for detecting the temperature of the fluid flowing through the resistive channel 10a is provided near the covering member 20.

[0055] With the fluid resistance element R of this embodiment configured in this way, since the flow path forming member 10 is made of ceramic, it can be processed with high dimensional accuracy, making it possible to stably manufacture fluid resistance elements R with uniform resistance characteristics. Specifically, for example, by cutting a long (e.g., 1 m) ceramic with a resistance flow path 10a formed inside into pieces of the same length (e.g., a few millimeters) and using each piece as a flow path forming member 10, multiple fluid resistance elements R with uniform resistance characteristics can be manufactured. On the other hand, by changing the length to which it is cut, fluid resistance elements R with various resistance characteristics can be easily manufactured, which is useful for various model designs, for example. Moreover, since the flow path forming member 10 is made of ceramic, it can be inserted into the internal flow path L without crushing the resistance flow path 10a, and it also has advantages such as a low coefficient of thermal expansion, high corrosion resistance, and low cost compared to metal ones. Furthermore, since the resistance characteristics can be changed by changing the number of resistance flow paths 10a, it can be used for ultra-low flow rate measurements, for example. In addition, since the resistance flow path 10a can be processed into a cylindrical shape, the fluid flow becomes an ideal flow, which simplifies various simulations.

[0056] Thus, while enjoying the various advantages of forming the resistance channel 10a using ceramic, the bulge 26 provided on the inner circumferential surface 25 of the covering member 20 is formed by applying force to the metal covering member 20 from the radially outer side and crimping it. As a result, the channel forming member 10 can be fixed to the covering member 20, and by fixing this metal covering member 20 to other pipe members Z1, Z2, for example by welding, the fluid resistance element R can be fixed to a desired location in the channel.

[0057] Furthermore, since the bulging portion 26 is formed over the entire circumference of the inner circumferential surface 25 of the covering member 20, the flow path forming member 10 can be securely fixed to the covering member 20.

[0058] Furthermore, since the predetermined region X along the axial direction that forms the housing space 21 of the covering member 20 is thinner than other regions along the axial direction, it is possible to quickly determine where the flow path forming member 10 is housed, and by making it thinner, this predetermined region X can be easily crimped, thereby improving workability.

[0059] Furthermore, since the downstream channel 23 has a small-diameter section 231 whose channel diameter is smaller than the outer diameter of the channel forming member 10, the channel forming member 10 inserted into the covering member 20 is supported by the small-diameter section 231, preventing the channel forming member 10 from coming out to the downstream side.

[0060] In addition, since the downstream flow path 23 has an enlarged diameter section 232, the pressure of the fluid that has passed through the resistance flow path 10a can be made uniform in the enlarged diameter section 232 before being guided downstream, allowing for more accurate measurement of the flow rate.

[0061] Furthermore, since the upstream channel 22 has a reduced diameter section 221, the reduced diameter section 221 functions as a guide when inserting the channel forming member 10, thereby improving work efficiency.

[0062] Furthermore, during handling such as during the manufacturing or transport of the fluid resistance element R, the flow path forming member 10 is covered with the covering member 20, thus reducing the risk of contamination or damage to the flow path forming member 10.

[0063] However, the present invention is not limited to the embodiments described above.

[0064] For example, in the above embodiment, the bulge portion 26 was provided around the entire circumference of the inner circumferential surface 25 of the covering member 20, but it may also be provided on a part of the inner circumferential surface 25 in the circumferential direction. Specifically, it is preferable that the bulge portion 26 is provided around half the circumference or more of the inner circumferential surface 25, and more preferably around three-quarters of the circumference or more of the inner circumferential surface 25.

[0065] Furthermore, although a recess 28 was provided on the outer circumferential surface 27 of the covering member 20 in the above embodiment, it is not necessary to provide a recess 28 on the outer circumferential surface 27 of the covering member 20, for example, by making the crimping portion thicker in advance.

[0066] In the above embodiment, a predetermined region X along the axial direction including the housing space 21 of the covering member 20 was made thin-walled, but this thin-walled portion is not necessarily required, and the covering member 20 may, for example, have the same outer diameter from one end opening to the other end opening.

[0067] Furthermore, as shown in Figure 6, the covering member 20 may be provided with spaces S on the upstream and downstream sides of the containment space 21 into which the ends of the flow path forming member 10 can enter. These spaces S form part of the upstream flow path 22 and the downstream flow path 23. With this configuration, when inserting the flow path forming member 10 into the housing space 21, it is possible to allow the flow path forming member 10 to shift position either upstream or downstream.

[0068] In the above embodiment, the fluid control device 100 was equipped with a single fluid resistance element R, but as shown in Figure 7, it may be equipped with multiple fluid resistance elements R.

[0069] Examples of such configurations include one in which multiple fluid resistance elements R are arranged in series, as shown in Figure 7(A), and another in which two thin fluid resistance elements R are arranged in parallel, as shown in Figure 7(B). In this configuration, the multiple fluid resistance elements R may have different resistances from each other, or they may have equal resistances from each other.

[0070] When using multiple fluid resistance elements R in this manner, the fluid control device 100 may include a holding block B that integrally holds the multiple fluid resistance elements, as shown in Figure 8. This retaining block B is provided with multiple element insertion holes h1 into which fluid resistance elements R are inserted. After inserting the fluid resistance elements R into these element insertion holes h1, another pipe member (not shown) is connected to each of the covering members 20 by welding or other means, thereby fixing the fluid resistance elements R at the desired location in the flow path. The retaining block B here is also provided with a temperature sensor mounting hole h2 into which a temperature sensor (not shown) is attached.

[0071] Furthermore, although the flow path forming member 10 was cylindrical in the above embodiment, if the cross-section of the flow path is triangular, quadrilateral, or polygonal, the flow path forming member 10 may also be a columnar shape with a triangular, quadrilateral, or polygonal cross-section to correspond to these shapes. In this case, the covering member 20 may also be a cylindrical shape with a triangular, quadrilateral, or polygonal cross-section to correspond to the cross-sectional shape of the flow path.

[0072] The fluid control device 100 can be any other equipment unit, such as a flow meter (flow measuring device) without a flow control valve V.

[0073] In the above embodiment, the fluid resistance element R constituted a pressure-type fluid control device 100. However, as shown in Figure 9, a thermal-type fluid control device 100 may be configured with a thermal flow sensor in the internal flow path L. Specifically, in this case, the flow rate measuring mechanism X consists of a fluid resistance element R provided in the internal flow path L, a sensor flow path Lb connecting the upstream and downstream sides of the internal flow path L, an upstream electrical resistance element T1 and a downstream electrical resistance element T2 provided in the sensor flow path Lb, and a flow rate calculation circuit C2 that calculates the fluid flow rate based on the values ​​output from these electrical resistance elements T1 and T2.

[0074] Furthermore, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. [Explanation of Symbols]

[0075] 100... Fluid control device L ···Internal channel Pa ···Upstream pressure sensor Pb ··· Downstream pressure sensor R ··· Fluid resistance element 10 ···Flow channel forming member 11...outer surface 10a... Resistive channel 20 ···Covering material 21 ···Containment space 22...Upstream flow path 221...Reduced diameter section 23 ...downstream flow path 231...Small diameter section 232... Expanded diameter section 20a...Upstream opening 20b...Downstream opening 24...Abutting surface 25...Inner peripheral surface 26...bulge 27 ...outer surface 28 ···Recess 29 ··· recessed area 20x... Axial ends X...Predetermined area

Claims

1. Used by being inserted into a fluid passage, A ceramic channel forming member having one or more resistance channels, The system comprises a metal covering member that covers the outer circumferential surface of the flow channel forming member with a gap between them, The inner circumferential surface of the covering member is provided with a bulge that protrudes toward the outer circumferential surface of the flow channel forming member. A fluid resistance element characterized in that the bulging portion is in contact with a smooth region without irregularities on the outer surface of the flow path forming member.

2. The fluid resistance element according to claim 1, wherein the bulge is formed along the circumferential direction of the inner surface of the covering member.

3. The fluid resistance element according to claim 1 or 2, wherein the outer circumferential surface of the covering member is provided with a recess that is recessed radially inward toward the outer circumferential surface of the flow channel forming member.

4. The fluid resistance element according to claim 1 or 2, wherein the covering member is cylindrical and has a housing space for housing the flow path forming member, and a predetermined region along the axial direction that forms the housing space is thinner than other regions along the axial direction.

5. The covering member is provided downstream of the flow path forming member and has a downstream flow path through which the fluid that has passed through the resistance flow path is guided. The fluid resistance element according to claim 1 or 2, wherein the downstream flow path has a small-diameter portion in which the flow path diameter is smaller than the outer diameter of the flow path forming member.

6. The fluid resistance element according to claim 5, wherein the downstream flow path is provided downstream of the small-diameter portion and has an enlarged diameter portion in which the flow path diameter widens from the upstream side to the downstream side.

7. The fluid resistance element according to claim 1 or 2, wherein the covering member is provided upstream of the flow path forming member and has a reduced diameter portion in which the flow path diameter decreases from the upstream side to the downstream side.

8. The fluid resistance element according to claim 1 or 2, wherein both axial ends of the covering member are welding points where they are welded to another pipe member.

9. The fluid resistance element according to claim 1 or 2, wherein the bulging portion is formed by applying force from the radial direction of the covering member and deforming it.

10. A fluid resistance element according to claim 1 or 2, provided in a fluid passage, Upstream pressure sensor and downstream pressure sensor provided on the upstream and downstream sides of the fluid resistance element in the flow path, A fluid control device comprising a flow control valve provided in the aforementioned flow path.

11. A fluid resistance element according to claim 1 or 2, provided in a fluid passage, A sensor channel connecting the upstream and downstream sides of the aforementioned channel, An upstream electrical resistance element and a downstream electrical resistance element are provided in the sensor flow path, A fluid control device comprising a flow control valve provided in the aforementioned flow path.

12. The fluid control device according to claim 10, wherein a plurality of the fluid resistance elements are provided in series or in parallel in the flow path.

13. The fluid control device according to claim 12, wherein the plurality of fluid resistance elements have different resistance values.

14. A method for manufacturing a fluid resistance element used by being inserted into a fluid channel, The steps include: covering the outer circumferential surface of a ceramic channel forming member having one or more resistance channels with a metal covering member, leaving a gap between them; The method includes the step of fixing the flow path forming member to the covering member by applying force to the covering member from the radially outer side and crimping it, A method for manufacturing a fluid resistance element, characterized in that a bulge formed on the inner circumferential surface of the covering member by applying force from the radially outer side contacts a smooth region without irregularities on the outer circumferential surface of the flow channel forming member, and a gap is formed between the inner circumferential surface of the covering member and the outer circumferential surface of the flow channel forming member.

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