JP2000088622A - Flow rate sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow rate sensor which enables to accurate measure the flow rate of a viscous fluid in piping under wider environmental temperature conditions by minimizing the dependence on temperature of measured values of the flow rate. SOLUTION: This flow rate sensor is provided with a fluid passage pipeline 4 and a heat transfer fin plate 14 for detecting a flow rate so arranged to be affected by heat generated while being extended into the fluid passage pipeline 4 at a flow rate detection part in a flow rate detection unit 51. The sensing of temperature is executed being affected by heat absorbed by a fluid to be detected through the fin plate 14 based on the heat generated at the flow detection part to detect the flow rate of the fluid to be detected in the fluid passage pipeline 4 based on the results of the sensing of temperature. The fluid passage pipeline 4 has a fluid inflow side part 4b and a fluid outflow side part 4c and a central part 4a positioned therebetween along the direction of passage of the fluid to be detected and the fin plate 14 is extended into the fluid passage pipeline 4 at the central part 4a. The inner diameter of the central part 4a is smaller than that of the fluid inflow side part 4b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid flow rate detection technique, and more particularly to a flow rate sensor for detecting a flow rate of a fluid flowing in a pipe. The present invention particularly aims at improving the measurement accuracy of the flow sensor.

[0002]

2. Description of the Related Art
Various types of flow sensors (or flow rate sensors) for measuring the flow rate (or flow rate) of various fluids, especially liquids, are used, but because of the ease of cost reduction, a so-called thermal type (or flow rate sensor) is used. In particular, indirect heat type) flow sensors are used.

In this indirectly heated flow sensor, a thin-film heating element and a thin-film temperature sensing element are laminated on a substrate using a thin-film technology via an insulating layer, and the substrate and the fluid in the pipe are thermally separated. Those that are arranged to be connected are used. By energizing the heating element, the temperature sensing element is heated to change the electrical characteristics of the temperature sensing element, for example, the value of electrical resistance. This change in the electric resistance value (based on the temperature rise of the temperature sensing element) changes according to the flow rate (flow velocity) of the fluid flowing in the pipe. This is because a part of the calorific value of the heating element is transmitted to the fluid via the substrate, and the amount of heat diffused into the fluid changes according to the flow rate (flow velocity) of the fluid. This is because the amount of heat supplied to the body changes and the electric resistance value of the thermosensitive body changes. The change in the electric resistance value of the temperature sensing element also differs depending on the temperature of the fluid. Therefore, a temperature sensing element for temperature compensation is incorporated in an electric circuit for measuring the change in the electric resistance value of the temperature sensing element. It has also been practiced to minimize the change in the flow measurement value due to the temperature of the fluid.

[0004] Such an indirectly heated flow sensor using a thin film element is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-146,026.
There is a description in the publication.

A conventional indirectly heated flow sensor is attached to a pipe so that a substrate of a flow detecting section or a casing thermally connected to the substrate is exposed to a fluid from a wall surface of the pipe. ing.

[0006] However, when the fluid is a viscous fluid, particularly a liquid, the flow velocity distribution in a cross section orthogonal to the flow of the fluid in the pipe becomes non-uniform (the flow velocity is large at the central portion and the outer peripheral portion in the cross section). different). In the case where the substrate or the casing portion connected to the substrate is simply exposed on the conventional pipe wall, the flow velocity distribution greatly affects the accuracy of flow measurement. This is because the flow rate detection does not consider the flow velocity of the fluid flowing in the central portion of the cross section of the pipe, but only considers the flow velocity of the fluid near the pipe wall of the pipe. As described above, the conventional flow sensor has a problem that it is difficult to accurately measure the flow rate of a viscous fluid. In addition, even if the fluid has a low viscosity at room temperature, the viscosity increases as the temperature decreases, so that the above-described problems related to the viscosity of the fluid occur.

[0007] The temperature environment in which the flow rate sensor is used is extremely wide depending on geographical conditions, indoors and outdoors, and seasonal conditions and day / night are added to the temperature environment. There is a need for a flow sensor that is large and that accurately detects the flow under such a wide range of environmental temperature conditions.

Further, as described above, a temperature compensation element for temperature compensation is incorporated in a measurement circuit to minimize a change in a flow rate measurement value due to a fluid temperature.
It is still not enough, and there is a demand for further reducing the temperature dependence of the flow measurement value to further improve the measurement accuracy.

Accordingly, an object of the present invention is to provide a flow sensor capable of accurately measuring the flow rate of a viscous fluid flowing through a pipe.

Further, an object of the present invention is to reduce the temperature dependence of the flow measurement value so that it can be used under a wide range of environmental temperature conditions.
An object of the present invention is to provide a flow sensor capable of accurately measuring the flow rate of a viscous fluid flowing in a pipe.

[0011]

According to the present invention, a flow detecting section having a heat generating function and a temperature sensing function, and a fluid flow pipe for flowing a fluid to be detected are provided. And a flow rate detecting heat transfer member arranged to be affected by heat generation in the flow rate detecting section and extend into the fluid flow conduit, and the flow rate detecting section detects the flow rate based on heat generation in the flow rate detecting section. A temperature sensing effected by the heat absorption by the fluid to be detected is performed via the heat transfer member for detection, and the flow rate at which the flow rate of the fluid to be detected in the fluid flow conduit is detected based on the result of the temperature sensing The fluid flow conduit has a fluid inflow side portion, a fluid outflow side portion, and a central portion located between the fluid inflow side portion and the fluid outflow side portion along the flow direction of the fluid to be detected. The transmission member is located at the central portion. Serial and extending into the fluid flow conduit, the inner diameter of said central portion flow sensor, characterized in that less than the inner diameter of the fluid inflow side portion, is provided.

In one embodiment of the present invention, the inner diameter of the central portion is 50 to 80% of the inner diameter of the fluid inflow side portion.

In one embodiment of the present invention, the inside diameter of the fluid outflow side portion is equal to the inside diameter of the fluid inflow side portion.

In one embodiment of the present invention, there is a boundary between the central portion and the fluid inflow-side portion, where the inner diameter of the fluid flow conduit continuously changes,
The length of the boundary portion in the flow direction of the fluid to be detected is １ ／ or less of the difference between the inner diameter of the fluid inflow side portion and the inner diameter of the central portion.

In one embodiment of the present invention, the heat transfer member for flow rate detection is disposed at a distance from the fluid inflow side end of the central portion within four times the inner diameter of the central portion.

In one aspect of the present invention, the flow rate detecting section is affected by a thin film heating element formed on the flow rate detecting heat transfer member outside the fluid flow conduit and heat generated by the thin film heating element. And a thin film temperature sensing element for flow rate detection arranged as described above.

In one embodiment of the present invention, the heat transfer member for detecting a flow rate has a flat plate shape, and is disposed in the fluid flow passage along the fluid flow direction.

In one embodiment of the present invention, a fluid temperature detecting section for performing temperature compensation at the time of the flow rate detection is included, and the fluid temperature detecting section and the fluid temperature detecting section are extended into the fluid flow pipe. The arranged temperature detecting heat transfer member is thermally connected.

In one embodiment of the present invention, the heat transfer member for temperature detection is located on the fluid outflow side from the heat transfer member for flow rate detection at a central portion of the fluid flow conduit.

In one embodiment of the present invention, the heat transfer member for detecting temperature is formed in a flat plate shape and is arranged in the fluid flow passage along the fluid flow direction.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 are cross-sectional views showing an embodiment of a flow sensor according to the present invention. FIG. 1 shows a cross section along a fluid flow pipe through which a fluid to be detected flows, and FIG. 2 shows a cross section orthogonal to the pipeline.

In these figures, reference numeral 2 denotes a casing main body, and a fluid circulation pipe 4 for circulating the fluid to be detected is formed through the casing main body. The pipe 4 extends to both ends of the casing body 2. Pipe line 4
Consists of a central portion 4a located at the center along the flow direction of the fluid to be detected, and a fluid inflow side portion 4b and a fluid outflow side portion 4c located on both sides thereof. At both ends of the casing body 2, connecting portions (for example, a quick coupling structure not shown in detail) 6a and 6b for connecting to an external pipe are formed. The casing body 2 is made of synthetic resin, for example, vinyl chloride resin, glass fiber reinforced polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), or the like having high chemical resistance and oil resistance. The casing body 2 includes
An element housing portion 5 is formed above the conduit 4, and a casing lid 8 is fixed to the element housing portion 5 by screws or fitting. The casing lid 8 and the casing main body 2 constitute a casing.

In the present embodiment, two element unit holding portions 50 and 60 are formed adjacent to the pipe 4 inside the element accommodating section 5 of the casing main body 2 (ie, on the pipe 4 side). Each of these element unit holding portions 50 and 60 has a two-stage cylindrical inner surface centered on the radial direction of the pipeline 4. The first element unit holding unit 50 allows the flow rate detection unit 5
1 is held, and the fluid temperature detection unit 61 is held by the second element unit holding portion 60.

FIG. 3 is a sectional view of the flow rate detection unit 51. As shown in FIG.
Reference numeral 1 denotes a flow rate detecting unit 12, a fin plate 14 as a heat transfer member joined to the flow rate detecting unit 12 by a bonding material 16 having good thermal conductivity, an electrode terminal 52, and an electrode of the flow rate detecting unit 12. It has a bonding wire 28 electrically connected to the corresponding electrode terminal 52 and a base 53 made of synthetic resin. The base portion 53 has high chemical resistance and oil resistance, and is made of, for example, PPS or PBT. The base portion 53 has a two-stage cylindrical outer peripheral surface corresponding to the inner peripheral surface of the element unit holding portion 50. From the base portion 53, the fin plate 14
Are extended to the pipe 4 side, and a part of the electrode terminal 52 is extended to the side (outside) opposite to the pipe 4. That is, the flow rate detector 12, the bonding material 16, a part of the fin plate 14, a part of the electrode terminal 52, and the bonding wire 28 are sealed by the base 53.

As shown in FIG. 4, the flow rate detector 12 includes an insulating layer 12-2 on the upper surface (first surface) of the substrate 12-1.
Is formed thereon, and a thin film heating element 12-3 is formed thereon, and a pair of electrode layers 12-4, 12 for the thin film heating element is further formed thereon.
-5, an insulating layer 12-6 is formed thereon, a thin film temperature sensing element 12-7 for flow rate detection is formed thereon, and an insulating layer 12-8 is formed thereon. Consists of As the substrate 12-1, for example, a substrate made of silicon or alumina having a thickness of about 0.5 mm and a size of about 2 to 3 mm square can be used (when an insulating substrate such as alumina is used, the insulating layer 12- 2 can be omitted), the thin-film heating element 12-3 can be made of a cermet having a thickness of about 1 μm and patterned into a desired shape, and the electrode layers 12-4 and 12-5 have a thickness of about 1 μm. A layer made of nickel of about 0.5 μm or a layer of gold having a thickness of about 0.1 μm can be used, and the insulating layers 12-2, 12-6, and 12-8 have a thickness of about 1 μm. can be used made of SiO _2, the temperature coefficient such as platinum or nickel which is patterned into a desired shape for example meandering film thickness of about 0.5~1μm is a thin film temperature sensitive body 12-7 It can be used stable metal resistive film listening (or may be used made of NTC thermistor of manganese oxide based). As described above, since the thin-film heating element 12-3 and the thin-film thermosensitive element 12-7 are disposed very close to each other with the thin-film insulating layer 12-6 interposed therebetween, the thin-film thermosensitive element 12-7 is thin-film. Heating element 12-
3 will be immediately affected.

As shown in FIG. 3, the flow rate detector 1
2, a flat fin plate 14 as a heat transfer member is provided on one surface of the substrate 2, ie, the second surface of the substrate 12-1.
It is joined by. The fin plate 14 may be a flat plate made of, for example, copper, duralumin, or a copper-tungsten alloy, and the joining material 16 may be, for example, a silver paste.

As shown in FIGS. 1 and 2, a seal for the pipe 4 is provided between the outer peripheral surface of (the base 53 of) the flow rate detecting unit 51 and the inner peripheral surface of the element unit holding portion 50. An O-ring 54 as a member is interposed.

The fin plate 14 has an upper portion joined to the flow rate detector 12 and a lower portion attached to the central portion 4 of the pipe 4.
a. The fin plate 14 extends across the line 4 from the top to the bottom through the center in the cross section at the line center section 4a having a substantially circular cross section. However, the pipe 4 does not necessarily have to have a circular cross section, and may have an appropriate cross section. In the pipe 4, the width (dimension in the pipe direction) of the fin plate 14 is sufficiently larger than the thickness of the fin plate 14. For this reason, the fin plate 14 can satisfactorily transfer heat between the flow rate detector 12 and the fluid without significantly affecting the flow of the fluid in the pipeline center portion 4a.

An element unit holding section 60 is disposed in the casing main body 2 at a position separated from the element unit holding section 50 along the pipeline 4. The fluid temperature detection unit 61 is held by the element unit holding section 60.

The fluid temperature detecting unit 61 is basically different from the flow rate detecting unit 51 in that a fluid temperature detecting unit is used instead of the flow rate detecting unit 12. That is, the fluid temperature detection unit 61 corresponds to the fin plate 14 ′ as a heat transfer member joined to the fluid temperature detection unit by a bonding material having good heat conductivity, the electrode terminal 62, and the electrode of the fluid temperature detection unit. And a bonding wire electrically connected to the electrode terminal 62 to be formed, and a base made of synthetic resin. From the base portion, a part of the fin plate 14 ′ extends to the side of the conduit 4, and a part of the electrode terminal 62 extends to the side (outside) opposite to the conduit 4.

The temperature detecting section is formed in a chip shape in which a similar thin-film thermosensitive element (a thin-film thermosensitive element for fluid temperature compensation) is formed on the same substrate as the flow rate detecting section 12. That is, the temperature detecting section can be configured in the same manner as in FIG. 4 except that the thin film heating element 12-3, the pair of electrode layers 12-4 and 12-5, and the insulating layer 12-6 are removed. Further, the fin plate 14 ′ is joined to the temperature detecting section by a joining material in the same manner as the flow rate detecting section 12.

As shown in FIG. 1, between the outer peripheral surface of the fluid temperature detecting unit 61 and the inner peripheral surface of the element unit holding portion 60, an O-
A ring 64 is interposed.

The fluid temperature detecting unit 61 is provided with a flow rate detecting unit 51 with respect to the fluid flowing direction in the pipe center 4a.
It is preferable to arrange it on the downstream side.

A holding plate 32 for the flow rate detecting unit 51 and the fluid temperature detecting unit 61 is disposed in the element housing portion 5 of the casing body 2, and the wiring board 26 is fixedly disposed thereon. I have. Some of the electrodes of the wiring board 26 are electrically connected to the electrode terminals 52 of the flow rate detection unit 51 by wire bonding or the like (not shown). 62 are electrically connected by wire bonding or the like (not shown). Some of the other electrodes of the wiring board 26 are connected to external leads 30, which extend outside the casing. The external lead wire 30 is previously arranged integrally at a predetermined position of the casing main body 2, and when the wiring board 26 is attached to the casing main body 2,
Electrical connection with the electrode 6 can be made.

FIG. 5 is a circuit diagram of the flow sensor of the present embodiment. The power supply is, for example, + 15V (± 10%)
And is supplied to the constant voltage circuit 102. The constant voltage circuit 102 has an output of 0.1 W at +6 V (± 3%), for example, and the output is supplied to a bridge circuit 104. The bridge circuit 104 includes a thin film temperature sensing element for flow rate detection 104-1 (12-7), a thin film temperature sensing element for temperature compensation 104-2, and variable resistors 104-3 and 104-4.

The voltages at points a and b of the bridge circuit 104 are input to the differential amplifier circuit 106. The differential amplifier circuit 106
Is made variable by a variable resistor 106a. The output of the differential amplification circuit 106 is input to the integration circuit 108. The variable amplification factor differential amplifier circuit 106 and the integration circuit 108 function as responsiveness setting means as described later.

On the other hand, the power supply is connected to the collector of the NPN transistor 110, and the emitter of the transistor 110 is connected to the heating element 112. The output of the integration circuit 108 is input to the base of the transistor 110. That is, the power supply is through the transistor 110 and the thin film heating element 112 (the above-described 12
-3), and the voltage applied to the heating element 112 is controlled by the voltage division of the transistor 110. The voltage division of the transistor 110 is controlled by the output current of the integration circuit 108 input to the base via the resistor, and the transistor 110 functions as a variable resistor, and controls the heat generation of the heating element 112. Functions as a means.

That is, in the flow rate detecting section 12, the thin film heating element 1-3 is affected by the heat absorption of the fluid to be detected through the fin plate 14 based on the heat generated by the thin film heating element 12-3.
The temperature sensing according to 2-7 is executed. As a result of the temperature sensing, a difference between the voltages Va and Vb at points a and b of the bridge circuit 104 shown in FIG. 5 is obtained.

The value of (Va-Vb) changes when the temperature of the thin film temperature sensing element 104-1 changes according to the flow rate of the fluid. Variable resistors 104-3, 104-4 in advance
By appropriately setting the resistance value, the value of (Va-Vb) can be made zero in the case of a desired fluid flow rate serving as a reference. At this reference flow rate, the output of the differential amplifier circuit 106 is zero, the output of the integration circuit 108 is constant, and the resistance value of the transistor 110 is also constant. In this case, the partial pressure applied to the heating element 112 is also constant, and the flow rate output at this time indicates the reference flow rate.

When the fluid flow rate increases or decreases from the reference flow rate, the output of the differential amplifier circuit 106 varies depending on the polarity (Va-Vb) depending on the polarity (the positive / negative of the resistance-temperature characteristic of the flow rate detecting temperature sensing element 104-1). ) And the magnitude changes, and the output of the integration circuit 108 changes accordingly. The rate of change of the output of the integrating circuit 108 is determined by the variable resistor 106a of the differential amplifier 106.
Can be adjusted by setting the amplification factor. The response characteristics of the control system are set by the integrating circuit 108 and the differential amplifier circuit 106.

When the flow rate of the fluid increases, the temperature of the temperature sensing element 104-1 decreases, so that the amount of heat generated by the heating element 112 is increased (that is, the amount of current is increased).
From the integration circuit 108, a control input is made to the base of the transistor 110 so as to reduce the resistance of the transistor 110.

On the other hand, when the flow rate of the fluid decreases, the temperature of the flow rate detecting temperature sensing element 104-1 increases.
12 to reduce the amount of heat generation (that is, reduce the amount of current)
As described above, a control input for increasing the resistance of the transistor 110 is made from the integration circuit 108 to the base of the transistor 110.

As described above, the heat generation of the heating element 112 is feedback-controlled so that the temperature detected by the flow rate detecting temperature sensor 104-1 always becomes the target value regardless of the change in the fluid flow rate. (If necessary, the polarity of the output of the differential amplifier circuit 106 is appropriately inverted according to the positive / negative of the resistance-temperature characteristic of the temperature sensing element 104-1 for flow rate detection). Since the voltage applied to the heating element 112 at this time corresponds to the fluid flow rate, this is taken out as a flow rate output.

According to this, regardless of the flow rate of the fluid to be detected, the flow rate detecting temperature sensing element 10 around the heating element 112 can be used.
Since the temperature of 4-1 is maintained substantially constant, the deterioration of the flow rate sensor with time is small, and the occurrence of an ignition explosion of the flammable fluid to be detected can be prevented. The heating element 11
2 does not require a constant voltage circuit.
There is an advantage that a low-output constant voltage circuit 102 for P.4 may be used. For this reason, the calorific value of the constant voltage circuit can be reduced, and the flow rate detection accuracy can be maintained well even if the flow rate sensor is downsized.

In the present embodiment, as shown in FIG. 1, the conduit 4 has an inner diameter of the central portion 4a of D1φ, an inner diameter of the fluid inflow side portion 4b of D2φ, and a fluid outflow side portion 4c. Is D3φ, and D1φ is D2φ and D3
Smaller than any of φ. Therefore, in the flow sensor according to the present embodiment, when the fluid to be detected flows from the fluid inflow side portion 4b to the central portion 4a, the flow present at the outer peripheral portion particularly in the cross section of the pipeline is caused by the steps present at these boundaries. Is disturbed. As a result, the region where the fluid flowability is increased particularly to the outer peripheral portion of the pipeline in the central portion 4a is expanded, and the fluid to be detected in contact with the fin plate 14 is averaged in a region having a high area ratio in the cross section of the pipeline. As a result, the heat radiation through the fin plate 14 more accurately reflects the flow rate of the fluid to be detected in the pipe 4.

Further, it is preferable that D2φ = D3φ since the flow rate of the fluid to be detected on the upstream side and the downstream side of the flow rate sensor is not changed.

The inner diameter D1φ of the central portion is preferably 50 to 80% of the inner diameter D2φ of the fluid inflow side portion. This is because, as D1φ / D2φ becomes less than 50% and becomes smaller, the pressure loss at the time of fluid flow tends to be remarkably large, which tends to obstruct the fluid flow itself.
This is because the effect of improving the uniformity of the flow velocity distribution in the cross section of the pipeline due to the fluid disturbance tends to decrease as / D2φ exceeds 80%.

As shown in FIG. 1, the fin plate 14 extends from the end of the central portion 4a on the side of the fluid inflow side portion 4b (ie, the boundary with the fluid inflow side portion 4b) in the direction of the conduit 4. At the position of the distance L1. This distance L1
Is preferably within four times the inner diameter D1φ of the central portion 4a, and more preferably within two times. this is,
If the distance L1 is too large, the fluid to be detected, which has been disturbed by the step at the boundary between the central portion 4a and the fluid inflow side portion 4b, tends to attenuate before the fluid reaches the fin plate 14. It is.

FIG. 6 is a graph showing the results of measuring the change in the flow rate output voltage with respect to the flow rate change at different fluid temperatures using the above-described flow rate sensor of the present embodiment. Here, kerosene was used as the fluid to be detected, D1φ was 4 mmφ, and D2φ and D3φ were 6 mm. It can be seen that there is almost no change in the flow rate output voltage due to a change in the fluid temperature. On the other hand, FIG. 7 shows that D1φ is 6 mmφ (that is, D1φ is 6 mmφ).
7 is a graph showing the result of performing similar flow measurement using the same flow sensor as that obtained in FIG. 6 except that D1φ = D2φ = D3φ). In the case of FIG. 7, a change in the flow rate output voltage due to a change in the fluid temperature is recognized.

In the above embodiment, the central portion 4a of the pipeline 4
Although an example is shown in which a distinct step is formed between the fluid passage side portion 4b and the fluid inflow side portion 4b, the present invention is not limited to such a distinct step form. There may be a boundary portion between the central portion 4a and the fluid inflow-side portion 4b where the inner diameter of the conduit 4 changes continuously.
8 and 9 are partial cross-sectional views showing a modified example having such a boundary portion. In the example of FIG. 8, the boundary portion 4d is
The cross section is chamfered in an arc shape, and the length in the pipeline direction is L2. The chamfer may be a normal one having a straight section (an angle of 45 degrees with respect to the pipe direction). In the example of FIG. 9, the boundary portion 4d is a slope having a linear cross section from the fluid inflow side portion 4b to the central portion 4a, and has a length in the pipe direction of L2. It is preferable that the length L2 of the boundary portion 4d is smaller than １ ／ of the difference between the inner diameter D2φ of the fluid inflow side portion 4b and the inner diameter D1φ of the central portion 4a. This is because as the length L2 increases, the effect of fluid disturbance due to the step at the boundary portion 4d between the central portion 4a and the fluid inflow side portion 4b tends to decrease.

In the above embodiment, the fin plates 14, 14 'traverse from the top to the bottom through the center of the cross section of the pipeline.
May extend from the upper portion of the pipe section to the vicinity of the central portion.

[0053]

As described above, according to the flow rate sensor of the present invention, since the inner diameter of the central portion of the fluid flow passage is smaller than the inner diameter of the fluid inflow side portion, the central portion and the fluid inflow side portion are reduced. The flow at the outer peripheral portion is particularly disturbed in the cross section of the pipeline by the step existing at the boundary with the flow path, and the distribution of the flow rate in the pipeline cross section can be averaged. As a result, the accuracy of the flow rate measurement performed through the heat transfer member for flow rate detection can be improved. In particular, even when the temperature of the fluid to be detected changes, the measurement accuracy does not decrease, and the flow rate can be measured under a wide range of environmental temperature conditions. Accurate flow measurement becomes possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view taken along a fluid flow conduit showing one embodiment of a flow sensor according to the present invention.

FIG. 2 is a cross-sectional view of a flow sensor according to an embodiment of the present invention, which is orthogonal to a fluid flow conduit.

FIG. 3 is a cross-sectional view of a flow detection unit of one embodiment of the flow sensor according to the present invention.

FIG. 4 is an exploded perspective view of a flow rate detector of one embodiment of the flow rate sensor according to the present invention.

FIG. 5 is a circuit configuration diagram of one embodiment of a flow sensor according to the present invention.

FIG. 6 is a graph showing a result of measuring a change in flow output voltage with respect to a change in flow at different fluid temperatures in one embodiment of the flow sensor according to the present invention.

FIG. 7 is a graph showing a result of measuring a change in flow output voltage with respect to a change in flow at different fluid temperatures in a flow sensor for comparison with the present invention.

FIG. 8 is a partial cross-sectional view showing a modification of the embodiment of the flow sensor according to the present invention.

FIG. 9 is a partial cross-sectional view showing a modified example of one embodiment of the flow sensor according to the present invention.

[Explanation of symbols]

 Reference Signs List 2 Casing main body 4 Fluid flow conduit 4a Central part 4b Fluid inflow side part 4c Fluid outflow side part 4d Boundary part 5 Element housing part 6a, 6b Connection part 8 Casing lid part 12 Flow rate detection part 12-1 Substrate 12-2 Insulating layer 12-3 Thin film heating element 12-4, 12-5 Electrode layer 12-6 Insulating layer 12-7 Thin film temperature sensing element for flow rate detection 12-8 Insulating layer 14, 14 'Fin plate 16 Bonding material 22 Fluid temperature detection Part 26 Wiring board 28 Bonding wire 30 External lead wire 32 Holding plate 50 Element unit holding part 51 Flow rate detection unit 52 Electrode terminal 53 Base part 54 O-ring 60 Element unit holding part 61 Fluid temperature detection unit 62 Electrode terminal 63 Base part 64 O-ring 104-1 Thin film temperature sensing element for flow rate detection 104-2 Thin film temperature sensing element for temperature compensation 112 thin Membrane heating element

Continuation of the front page (72) Inventor Takayuki Takahata 1333-2, Hara-shi, Ageo-shi, Saitama F-term (reference) 2F035 EA04 EA08

Claims (10)

[Claims] 1. A flow rate detecting section having a heat generating function and a temperature sensing function, a fluid flow path for flowing a fluid to be detected, and a flow path affected by heat generated in the flow rate detecting section and located in the fluid flow path. And a heat transfer member for flow rate detection arranged so as to extend therefrom, wherein the flow rate detection section is influenced by heat absorption by the detected fluid via the heat transfer member for flow rate detection based on heat generation in the flow rate detection section. A flow sensor for detecting a flow rate of the fluid to be detected in the fluid flow conduit based on a result of the temperature sensing, wherein the fluid flow conduit extends along a flow direction of the detected fluid. A fluid inflow side portion, a fluid outflow side portion, and a central portion located therebetween, the heat transfer member for flow rate detection extending into the fluid flow conduit at the central portion; The inner diameter of the central portion is the fluid flow Flow sensor, characterized in that less than the inner diameter of the side portions. 2. The flow sensor according to claim 1, wherein an inner diameter of the central portion is 50 to 80% of an inner diameter of the fluid inflow side portion. 3. The flow sensor according to claim 1, wherein an inner diameter of the fluid outflow side portion is equal to an inner diameter of the fluid inflow side portion. 4. A boundary portion between the central portion and the fluid inflow side portion where the inner diameter of the fluid flow conduit continuously changes, and a fluid to be detected at the boundary portion is provided. The flow rate sensor according to any one of claims 1 to 3, wherein a length of the flow direction in the flow direction is equal to or less than a half of a difference between an inner diameter of the fluid inflow side portion and an inner diameter of the central portion. 5. The flow rate detecting heat transfer member is disposed at a distance from the fluid inflow side end of the central portion within four times the inner diameter of the central portion.
4. The flow sensor according to any one of 4. 6. The thin film heating element formed on the flow rate detecting heat transfer member outside the fluid flow conduit and a flow rate disposed so as to be affected by heat generated by the thin film heating element. The flow sensor according to any one of claims 1 to 5, further comprising a thin-film thermosensitive element for detection. 7. The heat transfer member for flow rate detection is formed in a flat plate shape, and is disposed in the fluid flow passage along the fluid flow direction. 7. The flow sensor according to any one of 6. 8. A fluid temperature detecting unit for compensating temperature at the time of detecting the flow rate, the fluid temperature detecting unit and a temperature detecting unit arranged to extend into the fluid flow conduit. The flow sensor according to any one of claims 1 to 7, wherein the flow sensor is thermally connected to the heat transfer member. 9. The heat transfer member for temperature detection according to claim 8, wherein the heat transfer member for temperature detection is located on the fluid outflow side with respect to the heat transfer member for flow rate detection in a central portion of the fluid flow conduit. Flow sensor. 10. The heat transfer member for temperature detection has a flat plate shape, and is disposed along the fluid flow direction in the fluid flow path.
The flow sensor according to claim 8.