JP6240468B2 - Flow detection sensor - Google Patents

Description

  The present invention relates to a flow rate detection sensor for detecting a volume flow rate of a fluid flowing through a flow path.

  As a technique for measuring the flow velocity, a flow detection sensor having a cantilever part is installed in a bypass path that bypasses the main flow path, and a piezoresistive layer is provided in the cantilever part that is elastically deformed by the differential pressure between the upstream and downstream in the flow path, One that calculates the flow velocity of the fluid in the main flow path based on the resistance change of the piezoresistive layer is known (see, for example, Patent Document 1).

JP 2012-145356 A

  If the channel cross-sectional area through which the fluid passes changes due to the elastic deformation of the cantilever, the linearity between the flow rate and the resistance change amount of the piezoresistive layer is not maintained, and the flow of the fluid is changed. Therefore, there is a problem that it may be difficult to accurately detect the flow rate.

  The problem to be solved by the present invention is to provide a flow rate detection sensor capable of improving detection accuracy.

[ 1 ] A flow rate detection sensor according to the present invention is a flow rate detection sensor for detecting a volumetric flow rate of a fluid, and is capable of being deformed according to the flow of the fluid and having a beam portion having a piezoresistance layer Instructing the canceling means, a resistance detecting means for detecting a resistance change amount of the piezoresistive layer accompanying the deformation of the beam portion, a canceling means for generating a force in a direction to cancel the deformation of the beam portion, and the canceling means A first calculating means for calculating a feedback amount based on the resistance change amount; and a second calculating means for calculating a volume flow rate of the fluid based on the feedback amount; By generating a force having a magnitude corresponding to the amount of feedback, the deformation of the beam portion is canceled out, and the differential pressure detecting element has a through hole and a piece so as to project the beam portion into the through hole. Alternatively, it includes a support body that supports both ends, and the canceling means includes a conductor provided in the beam section, and a magnetic field generation section that generates a magnetic field in a region including the conductor, The feedback amount is a value of a current flowing through the conductor, and the second calculation unit includes a correction unit that corrects the feedback amount, and the correction unit includes the first correction resistance change amount and the correction amount. a third calculating means for calculating the correction value based on the variation ratio of the second correction amount of change in resistance, a fourth calculating means for correcting calculating the feedback amount in the correction value, wherein the The first and second correction resistance change amounts are the resistance change amounts of the piezoresistive layer measured by the resistance detection means when the volume flow rate of the fluid is zero, and the second correction change amount Second time to measure resistance change , From the first time to measure the first correction resistance change amount, and wherein the Atodea Rukoto.

  According to the present invention, the flow rate is calculated based on the feedback amount while canceling the deformation of the beam portion based on the resistance change amount of the piezoresistive layer by feedback control, so the flow rate is detected with the beam portion closed. be able to. For this reason, the linearity between the flow rate and the resistance change amount of the piezoresistive layer can be maintained, and the influence of the deformation of the beam portion on the flow rate can be reduced, so that the accuracy of the flow rate detection is improved. Can be planned.

FIG. 1 is a diagram illustrating an overall configuration of a flow rate detection sensor according to a first embodiment of the present invention. FIG. 2A is a cross-sectional view of the flow rate detection sensor in the bypass path in the first embodiment of the present invention, and FIG. 2B is the flow rate in the bypass path in the first embodiment of the present invention. It is a top view of a detection sensor. FIG. 3A is a plan view of the differential pressure detecting element according to the first embodiment of the present invention, and FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. . FIG. 4A is a plan view showing a modification of the differential pressure detecting element in the first embodiment of the present invention, and FIG. 4B is along the line IVB-IVB in FIG. It is sectional drawing. FIG. 5 is a process diagram showing the method for manufacturing the differential pressure detecting element in the first embodiment of the present invention. FIG. 6A to FIG. 6H are cross-sectional views showing the steps in FIG. FIG. 7A to FIG. 7G are cross-sectional views showing the steps in FIG. FIG. 8 is a diagram for explaining feedback control in the first embodiment of the present invention. FIG. 9 is a diagram showing a configuration of a flow rate detection sensor according to a modification of the first embodiment of the present invention. FIG. 10A is a cross-sectional view of the flow rate detection sensor in the bypass path in the second embodiment of the present invention, and FIG. 10B is the flow rate in the bypass path in the second embodiment of the present invention. It is a top view of a detection sensor. FIG. 11A is a plan view of a differential pressure detection element according to the second embodiment of the present invention, and FIG. 11B is a cross-sectional view taken along line XIB-XIB in FIG. 11A. . FIG. 12 is a diagram showing the configuration of the flow rate correction unit in a modification of the second embodiment of the present invention. FIG. 13 is a flowchart illustrating flow rate correction during operation according to the modification of the second embodiment of the present invention. FIG. 14 is a view showing a flow chart of flow rate correction at the time of initial setting in a modification of the second embodiment of the present invention. FIG. 15 is a diagram showing a flow chart of flow rate correction at the time of maintenance in a modification of the second embodiment of the present invention. FIG. 16 is a diagram showing a configuration of a flow rate detection sensor according to the third embodiment of the present invention.

<First Embodiment>
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing the overall configuration of a flow rate detection sensor according to the first embodiment of the present invention, and FIGS. 2A and 2B are diagrams of the flow rate sensor in the bypass path according to the first embodiment of the present invention. 3A and 3B are a plan view and a cross-sectional view of the differential pressure detecting element according to the first embodiment of the present invention, and FIGS. 4A and 4B are FIG. 4A and FIG. It is the top view and sectional drawing which show the modification of a differential pressure | voltage detection element.

  As shown in FIG. 1, the flow rate detection sensor 10 according to the first exemplary embodiment of the present invention is a device that measures the volume flow rate of the fluid flowing through the main flow path 1. The flow rate detection sensor 10 includes a differential pressure detection element 20, a solenoid coil 30, a resistance detection unit 40, a current calculation unit 50, and a flow rate calculation unit 60. As an example of the fluid flowing in the main flow path 1, for example, a gas such as air can be exemplified, but a liquid may be used.

  1 illustrates a situation in which the fluid flows in the main channel 1 from the left side to the right side, but the flow direction of the fluid is not particularly limited to this, and the fluid flows in the main channel 1 on the right side. May flow from left to right.

  A bypass path 2 is branched from the main flow path 1, and the main flow path 1 and the bypass path 2 are connected by the upstream opening 3 and also by the downstream opening 4. As shown in FIGS. 2A and 2B, an attachment member 35 is installed in the bypass path 2, and the differential pressure detecting element 20 and the solenoid coil 30 are attached to the attachment member 35. .

  In the conventional flow rate detection sensor, the pressure difference between the openings of the bypass passage is detected by elastic deformation of the cantilever portion of the differential pressure detection element, and the flow rate is calculated based on the pressure difference. In contrast, in the first embodiment of the present invention, the solenoid coil 30 is subjected to feedback control, which will be described later, while canceling the elastic deformation of the cantilever portion 22 of the differential pressure detecting element 20 using the magnetic force of the solenoid coil 30. The volume flow rate of the fluid is calculated based on the value of the current to flow.

  As shown in FIGS. 3A and 3B, the differential pressure detecting element 20 is a MEMS (Micro Electro Mechanical Systems) element including a support 21, a cantilever portion 22, and electrodes 23 and 24. It is.

  As will be described later, the support 21 and the cantilever portion 22 are integrally formed by processing an SOI (Silicon on Insulator) wafer 80, and the support 21 includes a first silicon layer 81, a silicon oxide layer. 82 and a laminated body composed of the second silicon layer 83. A through-hole 211 that penetrates the support 21 is formed in the support 21.

On the other hand, the cantilever portion 22 includes a second silicon layer 83 and a pair of piezoresistive layers 221 and 222. The cantilever portion 22 is formed on the support 21 so as to protrude into the opening above the through hole 211. Cantilevered. In the cantilever portion 22, the second silicon layer 83 is located on the free end side, whereas the piezoresistive layers 221 and 222 are located on the fixed end side, and the outer edge of the cantilever portion 22 and the through hole 211. A gap (gap) 224 is secured between the two openings. The gap 224 has such a narrow width that almost no fluid flows in the bypass passage 2 and is not particularly limited. For example, the clearance 224 is 0.1 [μm] to 10 [μm].
It is preferable to have a width of about].

  The piezoresistive layers 221 and 222 are formed by doping the second silicon layer 83 with n-type or p-type impurities, and the resistance of the piezoresistive layers 221 and 222 with the elastic deformation of the cantilever portion 22. The value changes. For this reason, in the first embodiment of the present invention, the piezoresistive layers 221 and 222 are provided at the root portion where the strain is greatest in the cantilever portion 22, and the cantilever portion 22 is provided in the piezoresistive layers 221 and 222. And is connected to the periphery of the opening of the through hole 211.

  The piezoresistive layers 221 and 222 are electrically connected in series via connection leads 223 provided on the cantilever portion 22. Note that the entire cantilever portion 22 may be formed of a piezoresistive layer, and in this case, the connection lead 223 is unnecessary.

  Furthermore, in the first embodiment of the present invention, the magnetic body 225 is provided on the upper surface of the cantilever portion 22. The magnetic body 225 is located at the free end of the cantilever portion 22. Examples of the material constituting the magnetic body 225 include a ferromagnetic metal material such as Ni—Fe (permalloy). The magnetic body 225 may be magnetized so that the flow of the fluid in the main flow path 1 in both directions can be dealt with. Further, the installation position of the magnetic body 225 is not particularly limited as long as it is on the cantilever part 22, but it is preferable that the magnetic body 225 is closer to the free end of the cantilever part 22.

  Instead of the cantilever part 22, as shown in FIG. 4A and FIG. 4B, the beam part 22B may be supported by the support body 21 so as to protrude from the opening of the through hole 211. . In this case, the magnetic body 225 is provided at a substantially central portion of the beam portion 22B. The cantilever part 22 and the beam part 22B in the first embodiment of the present invention correspond to an example of the beam part in the present invention.

  The electrodes 23 and 24 are provided on the upper surface of the support 21. The first electrode 23 is electrically connected to the first piezoresistive layer 221 through the first lead 231. The second electrode 24 is also electrically connected to the second piezoresistive layer 222 via the second lead 241. The electrodes 23 and 24 are electrically connected to the above-described resistance detection unit 40 through a wiring or the like (not shown).

  When the connection lead 223 is made of a material having magnetism, the magnetic body 225 may be made of the same material as the connection lead 223. In this case, a conductive layer may be provided on the entire surface of the cantilever portion 22 excluding the root portion, and the connection lead 223 and the magnetic body 225 may be integrally formed.

  A method for manufacturing the differential pressure detecting element 20 having the magnetic body 225 described above will be described with reference to FIGS.

  FIG. 5 is a process diagram showing a method of manufacturing a differential pressure detecting element according to the first embodiment of the present invention, and FIGS. 6A to 7G are cross-sectional views showing steps in FIG.

  First, in step S11 of FIG. 5, an SOI wafer 80 is prepared as shown in FIG. The SOI wafer 80 includes a first silicon layer 81 (handle layer), a silicon oxide layer 82 (BOX (Buried Oxide) layer), and a second silicon layer 83 (active layer). Three layers 81 to 83 are stacked so that the silicon oxide layer 82 is sandwiched between the two silicon layers 81 and 83.

  Although not particularly limited, the thickness of the first silicon layer 81 is about 300 [μm], the thickness of the silicon oxide layer 82 is about 0.4 [μm], and the thickness of the second silicon layer 83 is about 0.2 μm. It is preferably about 3 [μm].

  Examples of a method for forming such an SOI wafer 80 include a method in which another silicon substrate is bonded to a silicon substrate on which an oxide film is formed, a SIMOX (Separation by Implanted Oxygen) method, a smart cut method, and the like. it can.

  Next, in step S <b> 12 of FIG. 5, piezoresistive layers 221 and 222 are formed on the second silicon layer 83 of the SOI wafer 80.

  Specifically, first, as shown in FIG. 6B, a first resist layer 91 is formed on the second silicon layer 83 of the SOI wafer 80. The first resist layer 91 has an opening corresponding to the shape of the piezoresistive layers 221 and 222.

  6C, the n-type or p-type impurity is doped into the second silicon layer 83 through the opening of the first resist layer 91, so that the piezoresistive layers 221 and 222 are formed. After that, the first resist layer 91 is removed. Examples of a technique for doping the second silicon layer 83 with an impurity include a thermal diffusion method (Thermal Diffusion) and an ion implantation method (Ion Implantation).

  Although not particularly shown, the entire second silicon layer 83 may be doped without forming the first resist layer 91. In this case, as described above, the connection lead 223 can be omitted.

  Next, in step S13 of FIG. 5, a magnetic body 225 is formed on the SOI wafer 80 on which the piezoresistive layers 221 and 222 are formed.

  Specifically, first, as shown in FIG. 6D, the magnetic layer 84 is formed on the entire upper surface of the SOI wafer 80. As a material constituting the magnetic layer 84, a ferromagnetic metal material such as Ni-Fe (permalloy) can be exemplified. Examples of the method for forming the magnetic layer 84 include methods such as sputtering, vacuum deposition, and plating.

  Next, as shown in FIG. 6E, a second resist layer 92 is formed on the magnetic layer 84. The second resist layer 92 has a shape corresponding to the magnetic body 225 described above. Next, as shown in FIG. 6 (f), the magnetic body 225 is formed by selectively removing the magnetic layer 84 by wet etching or dry etching, and then the second resist layer 92 is formed on the magnetic body 225. Remove.

  Next, in step S14 of FIG. 5, as shown in FIG. 6G, a conductive layer 85 is formed on the entire upper surface of the SOI wafer 80 on which the piezoresistive layers 221 and 222 and the magnetic body 225 are formed. Examples of the material constituting the conductive layer 85 include metal materials such as copper, aluminum, and gold. Examples of the method for forming the conductive layer 85 include methods such as sputtering, vacuum deposition, and plating.

  Note that a base layer may be formed on the entire upper surface of the SOI wafer 80 before the magnetic layer 84 and the conductive layer 85 are formed. Thereby, the adhesion of the conductive layer 85 to the second silicon layer 83 can be improved, and the metal material constituting the conductive layer 85 can be prevented from diffusing into the second silicon layer 83. Examples of the material constituting such an underlayer include chromium, nickel, titanium, titanium-tungsten, and the like.

  Next, in step S15 of FIG. 5, the second silicon layer 83 is patterned.

  Specifically, first, as shown in FIG. 6H, a third resist layer 93 is formed on the conductive layer 85. The third resist layer 93 has an opening corresponding to the shape of the gap 224 of the differential pressure detecting element 20.

  Next, as shown in FIG. 7A, the conductive layer 85 is selectively removed by wet etching or dry etching through the opening of the third resist layer 93, and then the third resist layer 93 is made conductive. Remove from above layer 85.

Next, as shown in FIG. 7B, by using the conductive layer 85 patterned as described above as a mask, the second silicon layer 83 is etched to define a gap that defines the outer edge of the cantilever portion 22. 224 is formed. At this time, the silicon oxide layer 82 functions as an etching stopper. As a specific etching method for the second silicon layer 83, for example, dry etching such as DRIE (Deep Reactive Ion Etching) can be exemplified.

  Next, in step S <b> 16 of FIG. 5, the electrodes 23 and 24 and the leads 223, 231, and 241 are formed by patterning the conductive layer 85.

Specifically, first, as shown in FIG. 7C, a fourth resist layer 94 is formed on the conductive layer 85. The fourth resist layer 94 is composed of electrodes 23 and 24 and leads 223, 231 and 2.
41. Next, as illustrated in FIG. 7D, the conductive layer 85 on which the fourth resist layer 94 is formed is etched, and then the fourth resist layer 94 is removed from above the conductive layer 85. Note that a portion of the conductive layer 85 covering the magnetic body 225 may be left on the magnetic body 225 without being etched.

  Next, in step S <b> 17 of FIG. 5, a fifth resist layer 95 is formed on the lower surface of the SOI wafer 80 as shown in FIG. The fifth resist layer 95 has an opening corresponding to the shape of the through hole 211 described above.

  Next, as shown in FIG. 7F, the first silicon layer 81 is etched from below. At this time, the silicon oxide layer 82 functions as an etching stopper. As a specific etching method for the first silicon layer 81, for example, dry etching such as DRIE can be exemplified.

  Next, in step S18 of FIG. 5, as shown in FIG. 7G, the silicon oxide layer 82 is etched from below to form the support 21 having the through holes 211. As a specific etching method for the silicon oxide layer 82, for example, wet etching using hydrofluoric acid (HF) can be exemplified.

  By executing Steps S11 to S18 described above, a large number of differential pressure detecting elements 20 are collectively formed on one SOI wafer 80. Therefore, in step S19 in FIG. 5, the individual differential pressure detection elements 20 are completed by dividing the multiple differential pressure detection elements 20 into pieces by dicing.

  In addition, the manufacturing method of the differential pressure | voltage detection element 20 is not limited to what is shown in FIG. For example, the magnetic body 225 may be formed after the electrodes 23 and 24 are formed (after step S16 in FIG. 5).

  The differential pressure detecting element 20 manufactured as described above is installed in the bypass path 2 together with the solenoid coil 30 via the mounting member 35 as shown in FIGS. 1, 2 (a) and 2 (b). ing. The mounting member 35 includes a plate portion 351, a flange portion 353, and a support protrusion 354, as shown in FIG.

  The plate portion 351 has a disk shape having an outer shape larger than the inner diameter of the bypass passage 2, and an opening 352 is formed in the central portion thereof. The differential pressure detection element 20 is fixed to the opening 352, and the differential pressure detection element 20 is configured such that the cantilever portion 22 is orthogonal to the fluid flow direction and the through hole 211 is along the fluid flow direction. It is arranged in the bypass 2.

  The flange portion 353 has a cylindrical shape having an outer diameter slightly smaller than the inner diameter of the bypass path 2, and is erected in the vicinity of the outer periphery of the plate portion 351. The flange member 353 is in close contact with the inner surface of the bypass passage 2 and the outer peripheral portion of the plate portion 351 enters the wall surface of the bypass passage 2, so that the attachment member 35 is fixed to the bypass passage 2.

  On the other hand, the support protrusion 354 is erected on the plate portion 351 so as to surround the opening 352 of the plate portion 351. The support protrusion 354 has an annular shape, and the solenoid coil 30 is formed by winding the conductive wire 31 around the outer peripheral surface of the support protrusion 354. A magnetic body 225 is positioned on the central axis 32 (see FIG. 3B) of the solenoid coil 30.

  Although not particularly illustrated, support protrusions 354 may be provided on both surfaces of the plate portion 351, and the solenoid coils 30 may be disposed on both sides of the differential pressure detecting element 20. Thereby, it is possible to cope with the flow of the fluid in the main flow path 1 in both directions.

  As shown in FIG. 1, when a fluid is flowing in the main flow path 1, pressure loss occurs due to friction with the wall surface and the pressure becomes lower toward the downstream side. The pressure in the downstream opening 4 is lower than On the other hand, as described above, the gap 224 of the differential pressure detecting element 20 is narrow to such an extent that fluid hardly flows. For this reason, the pressure of the upstream opening 3 is applied to the upstream side of the cantilever part 22, while the pressure of the downstream opening 4 is applied to the downstream side of the cantilever part 22. Then, the cantilever portion 22 of the differential pressure detecting element 20 is elastically deformed by the pressure difference between the openings 3 and 4, and the piezoresistive layers 221 and 222 are distorted.

  The resistance detector 40 detects the resistance value of the piezoresistive layers 221 and 222 accompanying the elastic deformation of the cantilever part 22 via the electrodes 23 and 24, and calculates the resistance change amount dR [Ω] from the resistance value. .

  On the other hand, the solenoid coil 30 can form a magnetic field in a region including the cantilever portion 22 by energization. The magnetic body 225 provided in the cantilever portion 22 is attracted toward a region having a high magnetic flux density (that is, the central axis of the solenoid coil 30) by the magnetic gradient of the magnetic field formed by the solenoid coil 30. Note that the magnetic body 225 and the solenoid coil 30 in the first embodiment of the present invention correspond to an example of the canceling unit in the present invention.

The current calculation unit 50 calculates the current value Ifb [A] of the solenoid coil 30 according to the following equation (1). However, Ifb_old [A] is the value of the feedback current flowing when dR [Ω] is measured, and k is a proportional constant. Other relational expressions include the following expressions (2) to (4). “flow” is a volume flow rate [m ³ / s] of the fluid, “Fflow” is a force [N] applied to the cantilever portion 22 by the differential pressure of the fluid, and “Ffb” is a force [N] applied to the cantilever portion 22 by the magnetic force of the solenoid coil 30. M and n are proportional constants.

Ifb = Ifb_old + k × dR (1)
Fflow = m × flow (2)
Ffb = Fflow (3)
Ifb = n × Ffb (4)

  The above equation (1) is based on a general feedback control method. In addition, the above equation (2) is based on the fact that the force applied to the cantilever is proportional to the flow rate, and the equation (3) is based on the balance when dR [Ω] becomes 0, (4 ) Is based on the fact that the magnitude of the magnetic gradient at the same position is proportional to the magnitude of the current flowing through the solenoid coil 30.

  The current calculation unit 50 calculates the current value Ifb according to the above equations (2) to (4). When k is negative, the current value Ifb increases when the resistance change amount dR [Ω] is a negative value. On the other hand, when the resistance change amount dR [Ω] is a positive value, the current value Ifb decreases. However, k is not limited to negative and is determined so that the resistance change amount dR [Ω] converges to zero.

  By causing the current Ifb calculated by the above equation (1) to flow through the solenoid coil 30, as shown in FIG. 8, a force Ffb having a magnitude commensurate with the force Fflow caused by the differential pressure of the fluid is generated. The cantilever portion 22 is applied to the cantilever portion 22 by the magnetic force of 30, and the deformation of the cantilever portion 22 is canceled and the amount of deformation becomes zero. FIG. 8 is a diagram for explaining feedback control in the first embodiment of the present invention. The current value Ifb in the first embodiment of the present invention corresponds to an example of the feedback amount in the present invention.

  On the other hand, the flow rate calculation unit 60 calculates the volume flow rate flow of the fluid according to the following equation (5) based on the current value Ifb [A] calculated by the current calculation unit 50.

  flow = Ifb / (m × n) (5)

  The resistance detection unit 40, current calculation unit 50, and flow rate calculation unit 60 described above are configured by, for example, a computer or an analog circuit. The current calculation unit 50 in the first embodiment of the present invention corresponds to an example of the first calculation unit in the present invention, and the flow rate calculation unit 60 in the first embodiment of the present invention is the second calculation unit in the present invention. It corresponds to an example.

  As described above, in the first embodiment of the present invention, the current value Ifb used in the feedback control while canceling the deformation of the cantilever portion 22 based on the resistance change amount dR of the piezoresistive layers 221 and 222 by the feedback control. Is used to calculate the flow rate. For this reason, since the volume flow rate flow of the fluid can be detected in a state where the cantilever portion 22 is closed, the accuracy of the flow rate detection is improved.

  The first embodiment of the invention described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Accordingly, each element disclosed in the first embodiment of the present invention is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  For example, in the above-described embodiment, the deformation of the cantilever part 22 is canceled by using the magnetic force generated between the magnetic body 225 of the cantilever part 22 and the solenoid coil 30, but the present invention is not particularly limited thereto. A configuration as shown in FIG.

  FIG. 9 is a diagram showing a configuration of a flow rate detection sensor according to another embodiment of the present invention. As shown in the figure, in this embodiment, a conductive layer 226 is formed on the upper surface of the cantilever part 22, and electrodes 33 and 34 are arranged above and below the cantilever part 22. Then, a voltage is applied between the conductive layer 226 and one of the electrodes 33 and 34 to draw the cantilever part 22 toward the electrodes 33 and 34, thereby canceling the deformation of the cantilever part 22. In this example, the voltage value applied between the conductive layer 226 and one of the electrodes 33 and 34 corresponds to an example of the feedback amount in the present invention.

  In the example shown in FIG. 9, the conductive layer 226 is provided only on the upper surface of the cantilever part 22. However, the present invention is not particularly limited thereto, and a conductive layer may be provided on the lower surface of the cantilever part 22. Further, although the conductive layer 226 and the connection lead 223 are provided separately, the present invention is not particularly limited to this, and the conductive layer 226 and the connection lead 223 may be integrally formed.

<Second Embodiment>
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

  The flow rate detection sensor can be shown in FIG. 1 having substantially the same configuration as that of the first embodiment. However, this flow rate detection sensor is not provided with the solenoid coil 30 and includes a magnetic field generator 1030 on the mounting member 1035 (FIGS. 10A and 10B). As an example of the magnetic field generation unit 1030, for example, an electromagnet may be used, but using a permanent magnet is more preferable because power consumption is reduced.

  In the conventional flow rate detection sensor, the pressure difference between the openings of the bypass passage is detected by elastic deformation of the cantilever portion of the differential pressure detection element, and the flow rate is calculated based on the pressure difference. On the other hand, in the second embodiment of the present invention, as shown in FIGS. 10A and 10B, the differential pressure detecting element 1020 is utilized by using the magnetic force of the magnetic field generating unit 1030 by feedback control to be described later. The volume flow rate of the fluid is calculated based on the value of the current flowing through the conductor 1225 provided in the cantilever portion 1022 while canceling the elastic deformation of the cantilever portion 1022 (FIG. 11A).

  Furthermore, in the second embodiment of the present invention, a conductor 1225 is provided on the upper surface of the cantilever portion 1022 as shown in FIG. In addition to the illustration, the conductor 1225 may be provided on the lower surface of the cantilever portion 1022. The conductor 1225 is located at the free end of the cantilever portion 1022. As a material constituting the conductor 1225, for example, a metal material such as gold can be exemplified. By using gold having a small resistance value, there is an advantage that it can be driven with low power and low heat generation. This conductor 1225 may be deposited on a cantilever, or a semiconductor may be doped with an impurity at a high concentration, whereby the flow of fluid in the main flow path 1001 can be dealt with in both directions. The installation position of the conductor 1225 is not particularly limited as long as it is on the cantilever portion 1022, but is preferably close to the free end of the cantilever portion 1022.

  Although not shown, instead of the cantilever portion 1022, the beam portion is projected so as to protrude into the opening of the through hole 1211 in the same manner as the configuration shown in FIGS. 4A and 4B of the first embodiment. The support may be supported at both ends. In this case, a conductor is provided at a substantially central portion of the beam portion.

  As shown in FIG. 11A, the first electrode 1023 and the second electrode 1024 are provided on the upper surface of the support body 1021. The first electrode 1023 is electrically connected to the first piezoresistive layer 1221 through the first lead 1231. The second electrode 1024 is also electrically connected to the second piezoresistive layer 1222 through the second lead 1241. The first piezoresistive layer 1221 and the second piezoresistive layer 1222 are connected by a connection lead 1223. In addition, the first electrode 1023 and the second electrode 1024 are electrically connected to the above-described resistance detection unit 1040 via a wiring or the like not particularly shown.

  As shown in FIG. 11A, the third electrode 2023 and the fourth electrode 2024 are provided on the upper surface of the support body 1021. The third electrode 2023 is electrically connected to the conductor 1225 through the third lead 2231 and the first conductor connecting portion 2221. The fourth electrode 2024 is electrically connected to the conductor 1225 through the fourth lead 2241 and the second conductor connecting portion 2222. The third electrode 2023 and the fourth electrode 2024 are electrically connected to the current calculation unit 1050 via a wiring or the like (not shown).

  The manufacturing method of the differential pressure detecting element in the second embodiment of the present invention will be omitted because it will be described by replacing the magnetic body 225 with the conductor 1225.

  As shown in FIGS. 10A and 10B, the magnetic field generator 1030 is provided in the plate part 1351 so as to surround the opening 1352 of the plate part 1351. The magnetic field generator 1030 has a semi-annular shape, and the conductor 1225 is located on the central axis 1032 as shown in FIG.

  As in FIG. 1 shown in the first embodiment, the configuration of the resistance detection unit 1040, the current calculation unit 1050, and the flow rate calculation unit 1060 in the second embodiment is the same as that of the resistance detection unit 40 in the first embodiment. The configuration is the same as that of the unit 50 and the flow rate calculation unit 60. The resistance detection unit 1040 detects the resistance value of the piezoresistive layers 1221 and 1222 accompanying the elastic deformation of the cantilever unit 1022 via the electrodes 1023 and 1024, and calculates a resistance change amount dR2 [Ω].

  On the other hand, the magnetic field generator 1030 can form a magnetic field in a region including the cantilever part 1022. The conductor 1225 provided in the cantilever portion 1022 is attracted toward a region having a high magnetic flux density (that is, the central axis of the magnetic field generating portion 1030) by the magnetic gradient of the magnetic field formed by the magnetic field generating portion 1030. The conductor 1225 and the magnetic field generator 1030 in the second embodiment of the present invention correspond to an example of the canceling unit in the present invention.

  The resistance detection unit 1040, current calculation unit 1050, and flow rate calculation unit 1060 described above are configured by, for example, a computer or an analog circuit. The current calculation unit 1050 in the second embodiment of the present invention corresponds to an example of a first calculation unit in the present invention, and the flow rate calculation unit 1060 corresponds to an example of a second calculation unit in the present invention.

  FIG. 12 shows the configuration of the flow rate correction unit 2001 in a modification of the second embodiment of the present invention.

  The flow rate correction unit 2001 includes a correction value calculation unit 2002 that calculates a correction value based on the first correction resistance change amount dR2a and the second correction resistance change amount dR2b, and a correction that corrects the flow rate based on the correction value. A flow rate calculation unit 2003 is provided.

  When a permanent magnet is used as the magnetic field generator 1030, it is conceivable that the magnetic force of the permanent magnet is weakened due to deterioration over time. When the magnetic force is weakened, the magnetic field generated in the region including the conductor is changed, and the feedback amount instructed to the canceling unit is changed, so that an error may occur in the calculation result of the flow rate calculation unit 1060.

  In order to suppress a flow rate calculation error due to weakening of the magnetic force of the permanent magnet, the flow rate correction unit 2001 is used to correct the flow rate. Thereby, even if a change occurs in the strength of the magnetic field generated in the region including the conductor by the magnetic field generation unit 1030, the optimum flow rate can be calculated.

  Furthermore, the flow rate correction unit 2001 includes a first storage unit 2004 that writes and stores the first correction resistance change amount dR2a. The flow rate correction unit 2001 includes a second storage unit 2005 that writes and stores the second correction resistance change amount dR2b. The first correction resistance change amount dR2a may be, for example, a measurement value at the time of shipment of the flow sensor, or may be a measurement value at the initial stage of operation such as at the time of installation. On the other hand, the second correction resistance change amount dR2b is preferably the latest measured value after operation. In this case, the second time when the second correction resistance change amount is measured is later than the first time when the first correction resistance change amount is measured.

  The flow rate correction unit 2001 according to the second embodiment of the present invention corresponds to an example of a correction unit according to the present invention. In addition, the correction value calculation unit 2002 in the second embodiment of the present invention corresponds to an example of a third calculation unit in the present invention, and the correction flow rate calculation unit 2003 corresponds to an example of a fourth calculation unit in the present invention. .

  The correction value calculation unit 2002 includes the first correction resistance change amount dR2a that is written and stored in the first storage unit 2004 in advance, and the second correction that is written and stored in the second storage unit 2005 in advance. The variation ratio of the resistance change amount dR2b is calculated as the correction value a. In this case, the corrected flow rate calculation unit 2003 corrects the flow rate based on the calculated correction value a.

  Alternatively, the correction value a calculated by the correction value calculation unit 2002 may be written and stored in the second storage unit 2005 instead of the second correction resistance change amount dR2b.

  When the correction value a calculated by the correction value calculation unit 2002 is written and stored in the second storage unit 2005 in advance, the correction flow rate calculation unit 2003 stores the correction value a stored in the second storage unit 2005. Read and correct the flow rate based on the correction value a.

  In the modification of the second embodiment of the present invention, the first storage unit 2004 corresponds to an example of the first storage unit in the present invention, and the second storage unit 2005 is the second storage unit in the present invention. It corresponds to an example.

  FIG. 13 shows a flowchart during operation as a modification of the second embodiment of the present invention.

  First, the resistance change amount dR2 is detected by the resistance detector 1040 (S1).

  Next, the current calculation unit 1050 calculates a feedback amount based on the detected resistance change amount dR2, and sets a current to flow through the conductor 1225 based on the feedback amount (S2).

  Subsequently, the flow rate calculation unit 1060 calculates the flow rate based on the feedback amount (S3). The current calculation unit 1050 may be provided as the current output unit.

  Further, the correction value calculation unit 2002 includes a first correction resistance change amount dR2a written in advance in the first storage unit 2004 and a second correction resistance change amount written in advance in the second storage unit 2005. A correction value a is calculated based on dR2b (S4). The correction value a can be, for example, a variation ratio between the first correction resistance change amount dR2a and the second correction resistance change amount dR2b. The second time when the second correction resistance change amount dR2b is measured is later than the first time when the first correction resistance change amount dR2a is measured. Further, it is preferable that the data written to the second storage unit 2005 is updated as appropriate.

  Finally, the corrected flow rate calculation unit 2003 corrects the flow rate based on the correction value a (S5).

  FIG. 14 shows a flowchart at the time of initial setting as a modification of the second embodiment of the present invention. At the initial setting, it is preferable that there is no flow rate. The initial setting time is, for example, the shipment time or the installation time of the flow sensor. The state where there is no flow rate is a state where the cantilever portion 1022 is not deformed and the feedback current is zero.

  First, a correction value calculation current is passed through the conductor 1225 (S11). A current calculation unit 1050 may be provided as a correction value calculation current output unit (not shown). The correction value calculation current may be a necessary and sufficient minute current capable of measuring the resistance change amount dR2.

  Next, the resistance detection unit 1040 detects the resistance change amount dR2 (S12).

  Finally, the resistance change amount dR2 is written and stored in the first storage unit 2004 as the first correction resistance change amount dR2a (S13).

  FIG. 15 shows a flowchart at the time of maintenance as a modification of the second embodiment of the present invention. When performing maintenance, it is preferable that there is no flow rate. The state where there is no flow rate is a state where the cantilever portion 1022 is not deformed and the feedback current is zero.

  First, a correction value calculation current is passed through the conductor 1225 (S21). A current calculation unit 1050 may be provided as a correction value calculation current output unit (not shown). The correction value calculation current may be a necessary and sufficient minute current capable of measuring the resistance change amount dR2.

  Next, the resistance detection unit 1040 detects the resistance change amount dR2 (S22).

  Finally, the resistance change amount dR2 is written and stored in the second storage unit 2005 as the correction resistance change amount dR2b (S23). It is preferable that the data to be written in the second storage unit 2005 is updated as appropriate.

  The data to be written in the second storage unit 2005 may be the correction value a calculated by the correction value calculation unit 2002 instead of the correction resistance change amount dR2b described above. The correction value calculation unit 2002 calculates the correction value a based on the measured correction resistance change amount dR2b and the first correction resistance change amount dR2a stored in advance in the first storage unit 2004. The correction value a can be, for example, a variation ratio between the first correction resistance change amount dR2a and the second correction resistance change amount dR2b. The second time when the second correction resistance change amount dR2b is measured is later than the first time when the first correction resistance change amount dR2a is measured. Further, it is preferable that the data written to the second storage unit 2005 is updated as appropriate. The corrected flow rate calculation unit 2003 corrects the flow rate based on the correction value a written in advance in the second storage unit 2005.

The current calculation unit 1050 calculates the current value Ifb2 [A] of the conductor 1225 according to the following equation (6). However, Ifb2_old [A] is the value of the feedback current flowing when dR2 [Ω] is measured, and k2 is a proportionality constant. Other relational expressions include the following expressions (7) to (9). flow2 is a volume flow rate [m ³ / s] of the fluid, Fflow2 is a force [N] applied to the cantilever portion 1022 due to the differential pressure of the fluid, and Ffb2 is a cantilever portion 1022 due to the magnetic force of the conductor 1225 and the magnetic field generating portion 1030. [N], and m2 and n2 are proportional constants.

Ifb2 = Ifb2_old + k2 × dR2 (6)
Fflow2 = m2 × flow2 (7)
Ffb2 = Fflow2 (8)
Ifb2 = n2 × Ffb2 (9)

  The above equation (6) is based on a general feedback control method. Further, the above expression (7) is based on the fact that the force applied to the cantilever is proportional to the flow rate, and the expression (8) is based on the balance when dR [Ω] becomes 0, (9 ) Is based on the fact that the magnitude of the magnetic gradient at the same position is proportional to the magnitude of the current flowing through the conductor 1225.

  The current calculation unit 1050 calculates the current value Ifb2 according to the above equations (6) to (9). When k2 is negative, the current value Ifb2 increases when the resistance change amount dR2 [Ω] is a negative value. On the other hand, when the resistance change amount dR2 [Ω] is a positive value, the current value Ifb2 decreases. However, k2 is not limited to negative and is determined so that the resistance change amount dR2 [Ω] converges to zero.

  FIG. 8 is a diagram for explaining the feedback control in the first embodiment of the present invention, but it can be similarly described in the second embodiment of the present invention. By causing the current Ifb2 calculated by the above equation (6) to flow through the conductor 1225, the force Ffb2 having a magnitude commensurate with the force Fflow2 due to the differential pressure of the fluid is generated between the conductor 1225 and the magnetic field generator 1030. The magnetic force is applied to the cantilever portion 1022, the deformation of the cantilever portion 1022 is canceled out, and the amount of deformation becomes zero. The current value Ifb2 in the second embodiment of the present invention corresponds to an example of the feedback amount in the present invention.

  On the other hand, the flow rate calculation unit 1060 calculates the volume flow rate flow2 of the fluid according to the following equation (10) based on the current value Ifb2 [A] calculated by the current calculation unit 1050.

  flow2 = Ifb2 / (m2 × n2) (10)

  Further, the force Ffb2 applied to the cantilever 1022 due to the magnetic field strength of the conductor 1225 and the magnetic field generator 1030 is based on the current value Ifb2 and length Lb flowing through the conductor and the magnetic field density B of the magnetic field generator 1030. It is determined by equation (11).

  Ffb2 = Ifb2 × B × Lb (11)

  A method for correcting the fluid volume flow rate flow2 will be described. The corrected volume flow rate flow2 ′ of the fluid is calculated by the equation (12) based on the volume flow rate flow2 of the fluid before correction and the correction value a. “a” is a correction value calculated by the correction value calculation unit 2002.

  flow2 ′ = a × flow2 (12)

  The resistance detection unit 1040, current calculation unit 1050, and flow rate calculation unit 1060 described above are configured by, for example, a computer or an analog circuit. The current calculation unit 1050 in the second embodiment of the present invention corresponds to an example of the first calculation unit in the present invention, and the flow rate calculation unit 1060 in the second embodiment of the present invention is the second calculation unit in the present invention. It corresponds to an example.

  As described above, in the second embodiment of the present invention, the current value Ifb2 used in the feedback control while canceling the deformation of the cantilever portion 1022 based on the resistance change amount dR2 of the piezoresistive layers 1221 and 1222 by the feedback control. Is used to calculate the flow rate. For this reason, it is possible to detect the volume flow rate flow2 of the fluid with the cantilever portion 1022 closed. Furthermore, in the modification of the second embodiment of the present invention, the correction flow rate calculation unit 2003 can correct the calculation error of the flow rate due to the change in the magnetic force of the magnetic field generation unit 1030, so the accuracy of flow rate detection is improved. To do.

  The above-described second embodiment of the invention and its modifications are described for easy understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the second embodiment of the present invention and its modifications is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

<Third Embodiment>
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

  An embodiment of the differential pressure detecting element is shown in FIG. According to FIG. 16, the force acting on the cantilever portion 1022 can be offset by the action of the current flowing through the connection lead 1223 a, the current flowing through the connection lead 1223 b, and the magnetic force of the magnetic field generation unit 1030. Hereinafter, the offset method will be described.

  The force Ff3 is determined according to the equation (13). For example, lp is the current flowing in the piezoresistive layer 1221b, Bp is the magnetic field strength in the connection lead 1223a, and Lbp is the length of the connection lead 1223a.

  Ff3 = Ip × Bp × Lbp (13)

  The cantilever portion 1022a includes a piezoresistive layer 1221a and a piezoresistive layer 1222a connected by a connection lead 1223a, and a piezoresistive layer 1221b and a piezoresistive layer 1222b connected by a connection lead 1223b.

  The cantilever portion 1022a includes a connection lead 2221a and a connection lead 2222a connected by the conductor 1225a, and also includes a connection lead 2221b and a connection lead 2222b connected by the conductor 1225b.

  The conductor 1225a is formed so as to surround the connection lead 1223a. The conductor 1225b is formed so as to surround the connection lead 1223b.

  The electrode 1023a is disposed on the upper surface of the support 1021a, and is connected to the piezoresistive layer 1221a through a connection lead 1231a. The electrode 1024a is disposed on the upper surface of the support 1021a and connected to the piezoresistive layer 1222a through the connection lead 1241a.

  The electrode 1023b is disposed on the upper surface of the support 1021a, and is connected to the piezoresistive layer 1221b through a connection lead 1231b. The electrode 1024b is disposed on the upper surface of the support 1021a and connected to the piezoresistive layer 1222b through the connection lead 1241b.

  The electrode 2023a is disposed on the upper surface of the support 1021a and connected to the connection lead 2221a through the connection lead 2231a. The electrode 2024a is disposed on the upper surface of the support 1021a and connected to the connection lead 2222a via the connection lead 2241a.

  The electrode 2023b is disposed on the upper surface of the support 1021a and is connected to the connection lead 2221b through the connection lead 2231b. The electrode 2024b is disposed on the upper surface of the support 1021a and connected to the connection lead 2222b through the connection lead 2241b.

  The electrodes 1023a, 1023b, 1024a, 1024b, 2023a, 2023b, 2024a, and 2024b in FIG. 16 are disposed on the upper surface of the support body 1021a, but may be disposed on the lower surface of the support body 1021a. Further, the electrodes 1023a, 1023b, 1024a, and 1024b are electrically connected to the resistance detection unit 1040 in FIG. In addition, the electrodes 2023a, 2023b, 2024a, and 2024b are electrically connected to the current calculation unit 1050 in FIG.

  A small force Ff3a (not shown) is exerted on the cantilever portion 1022a by the action of the current flowing through the connection lead 1223a and the magnetic field of the magnetic field generation portion 1030.

  Further, a small force Ff3b (not shown) is exerted on the cantilever portion 1022a by the action of the current flowing through the connection lead 1223b and the magnetic field of the magnetic field generation portion 1030.

  The connection lead 1223a and the connection lead 1223b are arranged so that the extension lines of the current axes of the current flowing in the connection lead 1223a and the current flowing in the connection lead 1223b coincide with each other and the currents flow in opposite directions. As a result, the generated force of the force Ff3a exerted on the connecting lead 1223a and the force Ff3b exerted on the connecting lead 1223b by the magnetic force of the magnetic field generating unit 1030 is generated in a direction that cancels each other. No effect on 1022a.

  As described above, in the third embodiment of the present invention, the volume flow rate of the fluid can be detected without being affected by the force generated in the cantilever portion 1022a, so the accuracy of flow rate detection is improved.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1,1001 ... Main flow path 2, 1002 ... Bypass path 10, 1010 ... Flow rate detection sensor 20, 1020 ... Differential pressure detection element 21, 1021 ... Support body 211, 1211 ... Through-hole 22, 1022 ... Cantilever part 221, 222, 1221 , 1221a, 1221b, 1222, 1222a, 1222b ... piezoresistive layer 225 ... magnetic material 1225 ... conductor 2221,2222 ... conductor connection 23,1023 ... first electrode 24,1024 ... second electrode 30 ... solenoid coil 33, 34, 1023a, 1023b, 1024, 1024a, 1024b, 2023, 2023a, 2023b, 2024, 2024a, 2024b ... Electrode 35, 1035 ... Mounting member 40, 1040 ... Resistance detection part 50, 1050 ... Current calculation part 60, 1060 ... Flow rate calculation unit 030 ... magnetic field generator 2004 ... first storage unit 2005: second storage unit 2221 ... first conductor connecting portion 2222 ... second conductor connecting portion

Claims (1)

A flow rate detection sensor for detecting a volume flow rate of a fluid,
A differential pressure detecting element comprising a beam part that is deformable according to the flow of the fluid and has a piezoresistive layer;
Resistance detecting means for detecting a resistance change amount of the piezoresistive layer accompanying deformation of the beam portion;
Canceling means for generating a force in a direction to cancel the deformation of the beam portion;
First calculating means for calculating a feedback amount instructing the canceling means based on the resistance change amount;
Second calculating means for calculating a volumetric flow rate of the fluid based on the feedback amount,
The canceling means cancels the deformation of the beam portion by generating a force having a magnitude corresponding to the feedback amount,
The differential pressure detection element includes a support body that has a through-hole and cantilevered or both-supports the beam portion so as to protrude into the through-hole.
The offset means is
A conductor provided in the beam portion;
A magnetic field generator for generating a magnetic field in a region including the conductor,
The feedback amount is a current value flowing through the conductor,
The second calculation means includes correction means for correcting the feedback amount based on a correction value,
The correction means includes
Third calculation means for calculating the correction value based on a variation ratio of the first correction resistance change amount and the second correction resistance change amount;
Fourth calculating means for correcting the feedback amount with the correction value;
The first and second correction resistance change amounts are resistance change amounts of the piezoresistive layer measured by the resistance detection unit when the volume flow rate of the fluid is zero.
2. The flow rate detection sensor according to claim 1, wherein the second time for measuring the second correction resistance change amount is later than the first time for measuring the first correction resistance change amount.

Images