Fluid resistance element, fluid control device and manufacturing method for 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 the fluid resistance element. [Background technology]

[0002] As shown in Patent Document 1, a conventional fluid resistance element has a cylindrical ceramic body having a plurality of very thin resistance flow paths formed therein.

[0003] Compared to conventional metallic fluid resistance elements, these ceramic fluid resistance elements have physical properties such as a coefficient of thermal expansion close to zero, high hardness, and excellent heat and corrosion resistance, making it possible to measure flow rates with high accuracy, especially when controlling small flow rates.

[0004] However, due to the physical property of ceramics being almost undeformable, it is difficult to fix a ceramic fluid resistance element to a flow path. Although Patent Document 1 lists a method of fitting a cylindrical ceramic to a cylindrical metal by means of an interference fit or a clearance fit, all of these fixing methods are technically difficult and have many problems to be solved in practice. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. WO2021 / 095492 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve all of the above problems at once, and its main objective is to make it possible to fix a ceramic fluid resistance element to a flow path while still enjoying the benefits of the fluid resistance element. [Means for solving the problem]

[0007] In other words, the fluid resistance element of the present invention comprises a ceramic flow path forming member having one or more resistance flow paths, and a metallic covering member covering the outer peripheral surface of the flow path forming member, and is characterized in that the inner peripheral surface of the covering member is provided with a bulge portion that bulges toward the outer peripheral surface of the flow path forming member.

[0008] In a fluid resistance element configured in this manner, since the flow path forming member is made of ceramic, it is possible to enjoy the advantages unique to ceramics, such as a thermal expansion coefficient close to zero, high hardness, and excellent heat resistance and corrosion resistance. Furthermore, by forming a bulge portion on the inner surface of the covering member by applying force from the radial outside to crimp the metallic covering member, it is possible to fix the flow path forming member to the covering member, and by fixing this metallic covering member to another pipe member, for example, by welding, the fluid resistance element can be fixed at the desired location in the flow path.

[0009] It is preferable that the bulge is formed along the circumferential direction of the inner circumferential surface of the covering member. According to this configuration, the flow passage forming member can be fixed to the covering member more reliably.

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

[0011] It is preferable that the covering member is cylindrical and has a storage space for accommodating the flow path forming member, and that a specific region along the axial direction that forms the storage space is thinner than other regions along the axial direction. With this configuration, the specified area forming the storage space is made thinner than the other areas, so that it is possible to see at a glance where the flow path forming member is stored, and by making the specified area thinner, it is easier to crimp this specified area, thereby improving workability.

[0012] It is preferable that the covering member is provided downstream of the flow path forming member and has a downstream flow path to which fluid that has passed through the resistance flow path is guided, and the downstream flow path has a small diameter portion whose flow path diameter is smaller than the outer diameter of the flow path forming member. In this case, the flow passage forming member inserted into the covering member is caught in the small diameter portion, so that it is possible to prevent the flow passage forming member from coming off downstream.

[0013] It is preferable that the downstream flow passage has an expanding diameter portion provided downstream of the small diameter portion, the diameter of the flow passage expanding from the upstream side to the downstream side. In this case, the pressure of the fluid that has passed through the resistance flow path can be made uniform in the expanded diameter section before being guided downstream, making it possible to measure the flow rate with greater accuracy.

[0014] It is preferable that the covering member is provided upstream of the flow passage forming member and has a reduced diameter portion in which the flow passage diameter is reduced from the upstream side to the downstream side. In this case, the reduced diameter portion functions as a guide when inserting the flow passage forming member, thereby improving workability.

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

[0016] In addition, the fluid control device of the present invention is characterized in that it comprises the above-mentioned fluid resistance element provided in a flow path through which a fluid flows, an upstream pressure sensor and a downstream pressure sensor provided upstream and downstream 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 in that it comprises the above-mentioned fluid resistance element provided in a flow path through which a fluid flows, a sensor flow path connecting the upstream and downstream sides of the flow path, an upstream electrical resistance element and a downstream electrical resistance element provided in the sensor flow path, and a flow control valve provided in the flow path. A differential pressure type fluid control device or a thermal type fluid control device configured in this manner includes the above-mentioned fluid resistance element, and therefore can achieve the same effects as the fluid resistance element according to the present invention.

[0017] As a more specific embodiment, a plurality of the fluid resistance elements may be provided in series or in parallel in the flow path.

[0018] It is preferable that the plurality of fluid resistance elements have resistance values ​​different from one another. In this case, a variety of resistance values ​​can be obtained by using a plurality of fluid resistance elements.

[0019] In addition, a manufacturing method for a fluid resistance element according to the present invention is a method 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 metallic covering member, and fixing the flow path forming member to the covering member by applying a force to the covering member from the radial outside to crimp it. This manufacturing method can achieve the same effects as the fluid resistance element described above, and can fix the fluid resistance element to the desired location in the flow path while enjoying the benefits of a ceramic fluid resistance element. Effect of the Invention

[0020] According to the present invention configured in this manner, it is possible to obtain various advantages resulting from the flow path forming member being made of ceramic, and at the same time, it is possible to fix the fluid resistance element at a desired location in the flow path. [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. [Diagram 2] FIG. 2 is a cross-sectional view showing a part of the internal structure of the fluid control device according to the embodiment. [Diagram 3] FIG. 2 is a schematic diagram showing the configuration of the fluid resistance element of the embodiment. [Figure 4] FIG. 2 is a schematic diagram showing the configuration of the fluid resistance element of the embodiment. [Diagram 5] FIG. 4 is a schematic diagram for explaining the crimping process according to the embodiment; [Figure 6] FIG. 11 is a schematic diagram showing an arrangement of fluid resistance elements in another embodiment. [Figure 7] FIG. 11 is a schematic diagram showing an arrangement of fluid resistance elements in another embodiment. [Figure 8] FIG. 13 is a schematic diagram showing a configuration of a holding block according to another embodiment. [Figure 9] FIG. 11 is a fluid circuit diagram of a fluid control device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 this embodiment is one of the components of a fluid control device that controls the mass flow rate of a material gas or the like used in semiconductor manufacturing, for example.

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

[0025] The flow measurement mechanism X is of a differential pressure type, and as shown in FIG. 1, includes an upstream pressure sensor Pa provided upstream of the internal flow path L, a downstream pressure sensor Pb provided downstream of the upstream pressure sensor Pa, a fluid resistance element R provided 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 calculation circuit C2 that calculates the flow rate of the fluid flowing through the internal flow path L based on the pressure measurement values ​​by 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, and specifically includes a ceramic flow path forming member 10 having a flow path 10a that provides resistance (hereinafter also referred to as the resistance flow path 10a), and a metallic covering member 20 that covers the outer peripheral surface 11 of this flow path forming member 10.

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

[0029] The resistance flow paths 10a penetrate the flow path forming member 10 in the axial direction, and are linear with a circular cross section, and examples of such paths include those formed on the tube axis of the flow path forming member 10, and a plurality of resistance flow paths regularly arranged around the tube axis. Here, the resistance flow paths 10a have a diameter dimension (inner diameter) of less than 1 mm and about several tens of μm (e.g., 30 μm), and a length dimension (dimension along the axial direction) of about several mm to several tens of mm (e.g., 7 mm), the same as the flow path forming member 10, but these dimensions may 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 resistance flow paths 10a, is equal to or greater than 200, and more preferably equal to or greater than 300. The resistance value of the fluid resistance element R is determined based on the aspect ratio and the number of resistance flow paths 10a.

[0031] The covering member 20 is made of a metal, such as stainless steel or a nickel-based alloy, that is at least lower in hardness than ceramics.

[0032] As shown in FIGS. 3 and 4, the covering member 20 is cylindrical and covers the entire outer circumferential surface 11 of the flow passage forming member 10, in other words, houses the flow passage forming member 10 therein.

[0033] More specifically, as shown in FIG. 4, the covering member 20 has an accommodation space 21 that accommodates the flow path forming member 10, an upstream flow path 22 upstream of the accommodation space 21, and a downstream flow path 23 downstream of the accommodation 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 that is slightly larger than the outer diameter of the flow path forming member 10 .

[0035] In this embodiment, the accommodating space 21 accommodates the flow path forming member 10 from the center to the downstream end 10b, and the upstream end 10c of the flow path forming member 10 protrudes from the accommodating space 21 to the upstream side.

[0036] However, the flow path forming member 10 may be accommodated in the accommodation space 21 from the center to the upstream end 10c, with the downstream end 10b of the flow path forming member 10 protruding downstream from the accommodation space 21, or only the center of the flow path forming member 10 may be accommodated in the accommodation space 21, with the upstream end 10c and downstream end 10b of the flow path forming member 10 protruding from the accommodation space 21. Furthermore, the accommodation space 21 may be a space that accommodates the entire flow path forming member 10.

[0037] The upstream flow passage 22 communicates the upstream opening 20a of the covering member 20 with the accommodation space 21, and the flow passage forming member 10 is inserted into the accommodation space 21 via this upstream flow passage 22.

[0038] The upstream flow passage 22 has a flow passage diameter larger than the inner diameter of the accommodation space 21, and here has a flow passage length longer than the length of the accommodation space 21 along the axial direction.

[0039] In this embodiment, the upstream flow passage 22 has a reduced diameter section 221 whose flow passage diameter decreases from the upstream side toward the downstream side, and the downstream end of this reduced diameter section 221 opens into the accommodation 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 increases in diameter from the upstream side toward the accommodation space 21.

[0040] The downstream flow passage 23 communicates the downstream opening 20b of the covering member 20 with the accommodation space 21, and the fluid that has passed through the resistance flow passage 10a of the flow passage forming member 10 is guided thereto.

[0041] The downstream flow passage 23 has a small diameter portion 231 whose upstream end opens into the accommodation space 21 , and the small diameter portion 231 has a flow passage diameter smaller than the outer diameter of the flow passage 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 passage forming member 10 accommodated in the accommodation space 21 comes into contact.

[0043] The flow path forming member 10 contacts the contact surface 24, so that the flow path forming member 10 can be prevented from slipping out of the accommodation space 21 into the downstream side flow path 23.

[0044] Furthermore, the downstream flow passage 23 in this embodiment has an expanded diameter section 232 that is provided downstream of the small diameter section 231 and whose flow passage diameter expands from the upstream side to the downstream side. That is, of the inner circumferential surface 25 of the covering member 20, the portion that forms the expanded diameter section 232 has a tapered shape that gradually expands in diameter from the small diameter section 231 toward the downstream side.

[0045] In this embodiment, the flow path length of the upstream flow path 22 and the flow path length of the downstream flow path 23 are equal to each other, and the external shape of the covering member 20 in this embodiment is symmetrical with respect to the center of the axial direction as the axis of symmetry. However, the flow path length of the upstream flow path 22 and the flow path length of the downstream flow path 23 are not limited to this and may be changed as appropriate, and the external shape of the covering member 20 may also be changed as appropriate, for example, to an asymmetric shape.

[0046] By crimping the covering member 20, a bulging portion 26 that bulges toward the outer circumferential surface 11 of the flow path forming member 10 is provided on an inner circumferential surface 25 of the covering member 20, and a recessed portion 28 that is recessed radially inward toward the outer circumferential surface 11 of the flow path forming member 10 is provided on an outer circumferential surface 27 of the covering member 20. Note that crimping refers to applying a force to the covering member 20 in the radial direction to deform it, as shown in Fig. 5.

[0047] 3 and 4, in the covering member 20 of this embodiment, a predetermined region X along the axial direction that forms the above-mentioned accommodation space 21 is thinner than other regions along the axial direction. This makes it possible to grasp where in the axial direction the accommodation space 21 is formed, in other words, where the flow path forming member 10 is accommodated.

[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 over the entire circumference in the circumferential direction.

[0049] In this configuration, in the present embodiment, the entire circumference of the covering member 20 is crimped in the circumferential direction, whereby a bulge 26 is formed around the entire circumferential direction of the inner surface 25 of the covering member 20, and a recess 28 is formed around the entire circumferential direction of the outer surface 27 of the covering member 20.

[0050] More specifically, the entire circumference of the thin-walled specified region X described above is crimped, whereby a bulge 26 is formed on the inner surface forming the storage space 21, and a recess 28 is formed in the specified region X described above. The bulging portion 26 is in close contact with the outer circumferential surface 11 of the flow passage forming member 10 and holds the flow passage forming member 10 by tightening it from the radially outer side.

[0051] That is, the fluid resistance element R of this embodiment is manufactured by covering the outer peripheral surface 11 of a ceramic flow path forming member 10 having a resistance flow path 10a with a metallic covering member 20, and fixing the flow path forming member 10 to the covering member 20 by applying a force from the radial outside to crimp the covering member 20.

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

[0053] More specifically, both axial ends 20x of the covering member 20 are welded points to be welded to other pipe members Z1, Z2. By welding the other pipe members Z1, Z2 to each of these weld 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 the other pipe member Z2, thereby forming an internal flow path L.

[0054] 2, the covering member 20 of this embodiment is covered with a heat transfer member 30 such as aluminum having good thermal conductivity, which makes it easier to transfer the temperature of the fluid flowing through the resistance flow path 10a to the surroundings. A temperature sensor T is provided near the covering member 20 to detect the temperature of the fluid flowing through the resistance flow path 10a.

[0055] According to the fluid resistance element R of the present embodiment configured as described above, since the flow passage forming member 10 is made of ceramic, it can be processed with high dimensional accuracy, and it is possible to stably manufacture a fluid resistance element R having uniform resistance characteristics. Specifically, for example, by cutting a long (for example, 1 m) ceramic having a resistance flow passage 10a formed therein to the same length (for example, about several mm) and using each of these as the flow passage forming member 10, it is possible to manufacture a number of fluid resistance elements R having uniform resistance characteristics. On the other hand, by changing the cutting length, it is possible to easily manufacture fluid resistance elements R having various resistance characteristics, which contributes to, for example, various model designs. Moreover, since the flow passage forming member 10 is made of ceramic, it can be inserted into the internal flow passage L without crushing the resistance flow passage 10a, and further, compared to those made of metal, it has the advantages of a low thermal expansion coefficient, high corrosion resistance, and low price. Moreover, since the resistance characteristics can be changed by changing the number of resistance flow passages 10a, it can also be used, for example, for ultra-low flow rate measurement. In addition, since the resistance flow passage 10a can be processed into a circular tube shape, the flow of the fluid becomes an ideal flow, and various simulations can be simplified.

[0056] In this way, while enjoying various advantages of forming the resistance flow path 10a using ceramics, the bulge portion 26 provided on the inner surface 25 of the covering member 20 is formed by crimping the metallic covering member 20 by applying force from the radial outside, so that the flow path forming member 10 can be fixed to the covering member 20. By fixing this metallic covering member 20 to another pipe member Z1, Z2, for example, by welding or the like, the fluid resistance element R can be fixed at the desired location in the flow path.

[0057] Furthermore, since the bulge 26 is formed over the entire circumference in the circumferential direction of the inner peripheral surface 25 of the covering member 20, the flow passage forming member 10 can be reliably fixed to the covering member 20.

[0058] Furthermore, since the predetermined region X along the axial direction which forms the storage space 21 of the covering member 20 is thinner than other regions along the axial direction, it is possible to grasp at a glance where the flow path forming member 10 is stored, and by making the predetermined region X thinner, it is possible to facilitate crimping, thereby improving workability.

[0059] Furthermore, since the downstream flow path 23 has a small diameter portion 231 whose flow path diameter is smaller than the outer diameter of the flow path forming member 10, the flow path forming member 10 inserted into the covering member 20 is supported by the small diameter portion 231, thereby preventing the flow path forming member 10 from slipping out to the downstream side, etc.

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

[0061] In addition, since the upstream flow passage 22 has the reduced diameter portion 221, the reduced diameter portion 221 functions as a guide when the flow passage forming member 10 is inserted, so that the workability can be improved.

[0062] Furthermore, since the flow path forming member 10 is covered with the covering member 20 when the fluid resistance element R is being handled during manufacture or transportation, the risk of contamination or damage to the flow path forming member 10 can be reduced.

[0063] The present invention is not limited to the above-described embodiment.

[0064] For example, in the above embodiment, the bulge 26 is provided on the entire circumference of the inner circumferential surface 25 of the covering member 20, but it may be provided on a part in the circumferential direction of the inner circumferential surface 25. Specifically, the bulge 26 is preferably provided on at least half the circumference of the inner circumferential surface 25 in the circumferential direction, and more preferably provided on at least ¾ of the circumference of the inner circumferential surface 25 in the circumferential direction.

[0065] In addition, in the above embodiment, a recess 28 was provided on the outer peripheral surface 27 of the covering member 20, but the recess 28 does not have to be provided on the outer peripheral surface 27 of the covering member 20 by, for example, making the portion to be crimped thick in advance.

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

[0067] 6, the covering member 20 may be provided with spaces S on the upstream and downstream sides of the accommodation 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 the flow passage forming member 10 is inserted into the accommodation space 21, it is possible to allow the position of the flow passage forming member 10 to be shifted to the upstream side or the downstream side.

[0068] Although the fluid control device 100 includes a single fluid resistance element R in the above embodiment, it may include a plurality of fluid resistance elements R as shown in FIG.

[0069] One example of this is an embodiment in which multiple fluid resistance elements R are arranged in series as shown in Figure 7(A), or an embodiment in which multiple 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 one another, or may have the same resistance from one another.

[0070] When a plurality of fluid resistance elements R are used in this manner, the fluid control device 100 may include a holding block B that integrally holds the plurality of fluid resistance elements, as shown in FIG. This holding block B is provided with a plurality of element insertion holes h1 into which the fluid resistance elements R are inserted, and after the fluid resistance elements R are inserted into these element insertion holes h1, another pipe member (not shown) is connected to each covering member 20 by welding or the like, thereby fixing the fluid resistance elements R at desired locations in the flow path. Note that the holding block B here is also provided with a temperature sensor mounting hole h2 into which a temperature sensor (not shown) is attached.

[0071] Moreover, although the flow path forming member 10 is cylindrical in the above embodiment, if the cross section of the flow path is triangular, rectangular or polygonal, the flow path forming member 10 may be columnar having a triangular, rectangular or polygonal cross section corresponding to these shapes. In this case, the covering member 20 may also be tubular having a triangular, rectangular or polygonal cross section corresponding to the cross sectional shape of the flow path.

[0072] The fluid control device 100 may be another device unit, such as a flow meter (flow rate measuring device) without the flow rate adjustment valve V.

[0073] In the above embodiment, the fluid resistance element R constitutes a pressure-type fluid control device 100, but as shown in Fig. 9, a thermal-type fluid control device 100 may be constituted by providing a thermal-type flow sensor in the internal flow path L. Specifically, the flow measurement mechanism X in this case is composed of the fluid resistance element R provided in the internal flow path L, a sensor flow path Lb connecting the upstream side and the downstream side in the internal flow path L, an upstream electric resistance element T1 and a downstream electric resistance element T2 provided in the sensor flow path Lb, and a flow rate calculation circuit C2 that calculates the flow rate of the fluid based on the values ​​output from these electric resistance elements T1 and T2.

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

[0075] 100... Fluid control device L Internal flow path Pa: Upstream pressure sensor Pb Downstream pressure sensor R: Fluid resistance element 10 Flow path forming member 11...outer surface 10a Resistance flow path 20 Covering member 21. Storage 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...Abutment surface 25...Inner peripheral surface 26...bulge 27 ...outer surface 28 Recess 29 .... Recess 20x...Axial ends X...Predetermined area

Claims

1. A ceramic flow path forming member having one or more resistance flow paths; a metal covering member that covers an outer circumferential surface of the flow path forming member, A fluid resistance element, characterized in that an inner peripheral surface of the covering member is provided with a bulging portion that bulges toward an outer peripheral surface of the flow passage forming member.

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

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

4. The fluid resistance element described in claim 1 or 2, wherein the covering member is cylindrical and has a storage space for accommodating the flow path forming member, and a specific region along the axial direction that forms the storage 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 to which a fluid that has passed through the resistance flow path is guided, 3. The fluid resistance element according to claim 1, wherein the downstream flow passage has a small diameter portion having a flow passage diameter smaller than an outer diameter of the flow passage forming member.

6. 6. The fluid resistance element according to claim 5, wherein the downstream flow passage has a diameter expansion portion provided downstream of the small diameter portion, the diameter of the flow passage expanding from the upstream side to the downstream side.

7. 3. The fluid resistance element according to claim 1, wherein the covering member is provided upstream of the flow passage forming member and has a reduced diameter portion whose flow passage diameter decreases from the upstream side to the downstream side.

8. 3. The fluid resistance element according to claim 1, wherein both axial ends of the covering member are welded to another pipe member.

9. The fluid resistance element according to claim 1 or 2, which is provided in a flow path through which a fluid flows; an upstream pressure sensor and a downstream pressure sensor provided on the upstream side and downstream side of the fluid resistance element in the flow path; a flow rate regulating valve provided in the flow path.

10. The fluid resistance element according to claim 1 or 2, which is provided in a flow path through which a fluid flows; a sensor flow path connecting an upstream side and a downstream side of the flow path; an upstream electrical resistance element and a downstream electrical resistance element provided in the sensor flow path; a flow rate regulating valve provided in the flow path.

11. The fluid control device according to claim 9 , wherein a plurality of the fluid resistance elements are provided in series or in parallel in the flow path.

12. The fluid control device according to claim 11, wherein the plurality of fluid resistance elements have resistance values ​​different from each other.

13. covering an outer circumferential surface of a ceramic flow passage forming member having one or more resistance flow passages with a metallic covering member; and fixing the flow passage forming member to the covering member by applying a force from a radially outer side to crimp the covering member.

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