JP2021081263A - Thermal flowrate sensor - Google Patents

Abstract

To provide a thermal flowrate sensor with which it is possible to reduce costs by downsizing of a sensor substrate, and which is hardly breakable upon contact with foreign matter in a fluid.SOLUTION: The thermal flowrate sensor includes a sensor substrate 2 including a frame part 4 that encloses an open hole 6 and a sensor element support part 5 that protrudes from the frame part 4 into the open hole 6 and composed of a heat conductive material attached to a second wall 15 of a passage 11 in which a fluid 12 to be measured flows. Also included is a heat insulating material 21 which is filled in the open hole 6 so that an outer surface 5a of the sensor element support part 5 that is opposite the passage 11 is exposed. Also included is a sensor element 3 composed of a temperature sensor and a heater provided to the outer surface 5a of the sensor element support part 5.SELECTED DRAWING: Figure 4

Description

The present invention relates to a thermal flow rate sensor that detects a flow rate by utilizing a temperature change of a fluid.

As a conventional thermal flow rate sensor that detects the flow rate of a fluid such as a gas or liquid, a sensor having a diaphragm structure using MEMS (Micro Electro Mechanical Systems) is known. This type of sensor has limited scope due to strength and durability issues. In particular, the application to liquids is not fully utilized due to the complexity of electrode removal and the concern about damage to the diaphragm.

Patent Document 1 discloses a structure of a conventional thermal flow rate sensor and a method of installing it in a flow path. In this type of thermal flow sensor, in general, only the detection portion is exposed in the flow path through which the measurement fluid flows, and the electrode take-out portion is often installed separately from the flow path. The detection unit and the electrode extraction portion are provided on the same sensor base material. Therefore, the sensor base material has an extension portion extending from the detection portion to the electrode extraction portion.

Japanese Patent No. 3302444

However, if the electrode take-out portion is separated from the flow path, there is a problem that the sensor base material becomes large and the cost increases because the extension portion must be provided on the sensor base material.
Further, since the detection unit is provided on a relatively thin diaphragm and is exposed in the flow path, there is also a problem that the detection unit is easily damaged by contact with foreign matter such as particles contained in the fluid.

An object of the present invention is to provide a thermal flow rate sensor which can reduce the cost by downsizing the sensor base material and is not easily damaged even if foreign matter in the fluid comes into contact with the sensor.

In order to achieve this object, the thermal flow sensor according to the present invention has a frame portion surrounding the through hole and a sensor element support portion protruding from the frame portion into the through hole, and is a fluid to be measured. A sensor base material made of a heat conductive material in which the frame portion and the sensor element support portion are attached to the wall of the flow path through which the sensor element is supported so as to be exposed in the flow path, and the flow path in the sensor element support portion. A thermal insulating material filled in the through hole so that the outer surface on the opposite side is exposed, and a sensor element including a temperature sensor and a heater provided on the outer surface of the sensor element support portion are provided. It is something that is.

In the present invention, in the thermal flow sensor, an electrode provided on an outer surface of the frame portion on the opposite side of the flow path to which the sensor element support portion is connected and the sensor element support are provided. A wiring conductor provided on the outer surface of the portion opposite to the flow path and electrically connecting the sensor element and the electrode may be provided.

In the present invention, in the thermal flow sensor, the wall of the flow path has a penetrating portion that communicates with the inside and outside of the flow path, and the sensor base material and the thermal insulating material close the penetrating portion. It may form a part of the wall.

In the present invention, in the thermal flow sensor, the sensor element support portions are provided at a plurality of positions in the frame portion in which the fluid to be measured is arranged in the flow direction, and the plurality of sensor element support portions are supported. The sensor element may be provided in each portion.

In the present invention, in the thermal flow rate sensor, the sensor element may be composed of a platinum resistor.

In the present invention, since the electrical connection with the sensor element can be made on the side opposite to the flow path, it is not necessary to provide an extension portion on the sensor base material so as to be separated from the flow path. Further, in the sensor element support portion, the direction in which heat is transferred can be limited to the direction toward the flow path and the direction away from the flow path, and the diaphragm structure becomes unnecessary for the sensor element to operate. Therefore, the thickness of the sensor element support portion can be formed to be thicker than that of the diaphragm, and the resistance to contact with foreign matter in the fluid is increased.
Therefore, according to the present invention, it is possible to reduce the cost by downsizing the sensor base material, and to provide a thermal flow rate sensor that is not easily damaged even if foreign matter in the fluid comes into contact with it.

It is a top view of the thermal flow rate sensor which concerns on this invention. FIG. 2 is a sectional view taken along line II-II in FIG. FIG. 3 is a sectional view taken along line III-III in FIG. It is sectional drawing of the thermal flow rate sensor which shows the state attached to the flow path forming member. It is a top view which shows the modification of the thermal flow rate sensor. It is a top view which shows the modification of the thermal flow rate sensor.

Hereinafter, an embodiment of the thermal flow sensor according to the present invention will be described in detail with reference to FIGS. 1 to 4.
The thermal flow rate sensor 1 shown in FIG. 1 is configured by providing a plurality of sensor elements 3 on a sensor base material 2 formed in a rectangular shape in a plan view shown in FIG. The sensor base material 2 is composed of a frame portion 4 that constitutes an outer shape, and a plurality of sensor element support portions 5 that are connected to the frame portion 4 so as to project into the frame portion 4.

The material forming the sensor base material 2 is a heat conductive material. The material forming the sensor base material 2 is preferably a material having a relatively high thermal conductivity, such as silicon. The frame portion 4 is formed by a frame-shaped plate that surrounds the through hole 6. A plurality of electrodes 7 are provided in a portion of the frame portion 4 to which the sensor element support portion 5 is connected.
Each of the plurality of sensor element support portions 5 is formed in a thin strip shape, and is connected to the frame portion 4 at one end in the longitudinal direction. The sensor element support portion 5 according to this embodiment is formed integrally with the frame portion 4 and has the same thickness as the frame portion 4, and is formed on one side of the frame portion 4 (in FIG. 1). It projects from the right side) into the through hole 6 and extends to the vicinity of the other side of the frame 4.

Further, the sensor element support portions 5 are provided at a plurality of positions in the frame portion 4 which are arranged at regular intervals in a predetermined direction. The predetermined direction is the direction in which the fluid 12 to be measured flows in the flow path 11 (see FIG. 4) described later. In FIG. 1, the direction in which the fluid 12 to be measured flows is the vertical direction of FIG. 1 as shown by an arrow F. That is, the sensor element support portions 5 are provided at a plurality of positions in the frame portion 4 in which the fluid 12 to be measured is lined up in the flow direction. In this embodiment, three sensor element support portions 5 are provided in the frame portion 4. Each sensor element support portion 5 is formed long in a direction orthogonal to the direction in which the fluid 12 flows, and is formed so that the direction in which the fluid 12 flows is the width direction.

As shown in FIG. 4, the sensor base material 2 is attached to the flow path forming member 13. The flow path forming member 13 has a flow path 11 through which the fluid 12 to be measured flows. The cross-sectional shape of the flow path 11 shown in FIG. 4 is a rectangle whose width direction (horizontal direction in FIG. 4) is longer than the height direction (vertical direction in FIG. 4) when viewed from the direction in which the fluid 12 flows. The flow path forming member 13 according to this embodiment includes first and second walls 14 and 15 extending in the width direction of the flow path 11, and third and fourth walls 16 extending in the height direction of the flow path 11. Has 17. Of these first to fourth walls 14 to 17, the second wall 15 extending in the width direction of the flow path 11 is formed with a penetrating portion 18 communicating with the inside and outside of the flow path 11.

The sensor base material 2 is inserted into the through portion 18 of the second wall 15, and is inserted into the flow path side end of the through portion 18 so that the frame portion 4 and the sensor element support portion 5 are exposed in the flow path 11. It is glued with an adhesive (not shown).
The through hole 6 of the sensor base material 2 is filled with the heat insulating material 21. As the heat insulating material 21, for example, a plastic material having high heat insulating properties can be used. As shown in FIG. 4, the heat insulating material 21 according to this embodiment has outer surfaces 4a, 5a, 21a of the frame portion 4, the sensor element support portion 5, and the thermal insulating material 21 on the opposite side of the flow path 11 described above. Is filled in the through hole 6 so as to be exposed.

By filling the through hole 6 with the heat insulating material 21 in this way, the through hole 6 of the sensor base material 2 is closed by the heat insulating material 21, and a plate having no holes is formed. The sensor base material 2 constituting this plate is fixed to the flow path forming member 13 so that the penetrating portion 18 of the flow path forming member 13 is closed.
The surfaces 4b, 5b, 21b exposed in the flow path 11 of the frame portion 4, the sensor element support portion 5, and the heat insulating material 21 are on the same plane as the inner wall surface 15a of the second wall 15 of the flow path forming member 13. It is positioned in. By fixing the sensor base material 2 to the second wall 15 in this way, the sensor base material 2 and the heat insulating material 21 close the penetrating portion 18 to form a part of the second wall 15. become.

Although not shown in detail, the sensor element 3 is composed of a temperature sensor and a heater, and is provided on each of the three sensor element support portions 5 on the above-mentioned outer surface 5a. The sensor element 3 according to this embodiment is formed of a platinum resistor as a material. The material of the sensor element 3 is not limited to the platinum resistor, and can be changed as appropriate. As the temperature sensor, for example, a thermopile using Al and Poly-Si may be used. The heater can be replaced with a general metal material.

The sensor element 3 is electrically connected to the electrode 7 of the frame portion 4 via a wiring conductor 22 (see FIG. 1) provided on the outer surface 5a of the sensor element support portion 5. As shown in FIG. 4, the electrode 7 is connected to the signal extraction board 24 via the lead wire 23, and further, the flow rate measurement (not shown) via a cable (not shown) connected to the signal extraction board 24. It is connected to the electric circuit for. The signal extraction board 24 is provided on the outer surface of the flow path forming member 13. The electric circuit for measuring the flow rate measures the flow rate of the fluid 12 based on a conventionally well-known measuring method. In the thermal flow sensor 1 according to this embodiment, the sensor element 3 located at the center of the three sensor elements 3 functions as a heater, and the sensor elements 3 located on both sides, that is, the upstream side and the downstream side, respectively. It functions as a temperature sensor. The electric circuit for measuring the flow rate according to this embodiment calculates the flow rate by measuring the heat distribution of the heater according to the flow velocity of the measuring fluid.

In the thermal flow rate sensor 1 configured in this way, when the sensor element 3 is energized to generate heat, the heat is transferred from the outer surface 5a side of the sensor element support portion 5 to the surface 5b on the flow path 11 side. .. This heat is blocked by the heat insulating material 21 and is not transferred to other adjacent sensor element support portions 5. Therefore, the direction in which heat is transferred can be limited to the thickness direction of the sensor element support portion 5 (the direction toward the flow path 11 and the direction away from the flow path 11), and the heat capacity of the portion where the sensor element 3 is provided is reduced. .. As a result, the diaphragm structure used in the conventional thermal flow rate sensor becomes unnecessary, and the sensor element support portion 5 can be formed thicker than the diaphragm. The sensor element support portion 5 formed so thick has increased resistance to contact with foreign matter in the fluid 12.

Further, in the thermal flow rate sensor 1 according to this embodiment, since the sensor element 3 is provided on the side opposite to the flow path 11 with the sensor element support portion 5 interposed therebetween, the electrical connection with the sensor element 3 is established. This can be done on the opposite side of the flow path 11. Therefore, the extension portion provided on the sensor base material of the conventional thermal flow sensor so as to be separated from the flow path is unnecessary for the sensor base material 2 according to this embodiment. As a result, the sensor base material 2 could be made smaller than the conventional one.
Therefore, according to this embodiment, it is possible to reduce the cost by downsizing the sensor base material 2, and it is possible to provide a thermal flow rate sensor that is not easily damaged even if foreign matter in the fluid 12 comes into contact with it. ..

The thermal flow rate sensor 1 according to this embodiment has outer surfaces 5a and 21a on the side opposite to the flow path 11 of the frame portion 4, and has an electrode 7 at a portion to which the sensor element support portion 5 is connected. There is. Further, wiring conductors for electrically connecting the sensor element 3 and the electrode 7 are provided on the outer surfaces 5a and 21a of the sensor element support portion 5 on the opposite side of the flow path 11. The frame portion 4 can be provided with a large electrode 7 as compared with the sensor element support portion 5, and the degree of freedom in the position where the electrode 7 is provided is high. Therefore, when connecting the lead wire 23 to the electrode 7, the workability of the connection work is improved.

The second wall 15, which is one of the walls (first to fourth walls 14 to 17) forming the flow path 11 according to this embodiment, has a penetrating portion 18 communicating with the inside and outside of the flow path 11. ing. The sensor base material 2 and the heat insulating material 21 close the penetrating portion 18 to form a part of the second wall 15. Therefore, when the sensor element 3 is electrically connected to the electric circuit for flow rate measurement, wiring can be performed through the through portion 18, so that it is necessary to provide a dedicated wiring hole or recess in the flow path forming member 13. There is no.

The sensor element support portion 5 according to this embodiment is provided at a plurality of positions in the frame portion 4 arranged in the direction in which the fluid 12 to be measured flows. Each sensor element support portion 5 is provided with a sensor element 3. Therefore, in forming the thermal flow rate sensor 1 including the plurality of sensor elements 3, it is possible to reliably prevent the heat of the sensor element 3 from being transferred to the other sensor elements 3.

In the above-described embodiment, the thermal flow rate sensor using three sensor elements has been described, but the number of sensor elements can be appropriately changed as shown in FIGS. 5 and 6. In FIGS. 5 and 6, the same or equivalent members as those described with reference to FIGS. 1 to 4 are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

The thermal flow rate sensor 31 shown in FIG. 5 includes a sensor element support portion 5 and a sensor element 3 one by one. The thermal flow rate sensor 32 shown in FIG. 6 includes two sensor element support portions 5 and two sensor elements 3. Even with the thermal flow rate sensors 31 and 32 shown in FIGS. 5 and 6, the cost can be reduced by downsizing the sensor base material 2, and damage due to contact with foreign matter in the fluid 12 can be prevented. Become.

1 ... Thermal flow sensor, 2 ... Sensor base material, 3 ... Sensor element, 4 ... Frame part, 5 ... Sensor element support part, 5a, 21a ... Outer surface, 6 ... Through hole, 7 ... Electrode, 12 ... Fluid, 15 ... 2nd wall, 18 ... Penetration, 21 ... Thermal insulation, 22 ... Conductor for wiring.

Claims (5)

The frame portion surrounding the through hole and the sensor element support portion protruding from the frame portion into the through hole are provided, and the frame portion and the sensor element support portion are formed on the wall of the flow path through which the fluid to be measured flows. A sensor base material made of a heat conductive material mounted so as to be exposed in the flow path,
A heat insulating material filled in the through hole so that the outer surface of the sensor element support portion opposite to the flow path is exposed.
A thermal flow rate sensor including a temperature sensor provided on the outer surface of the sensor element support portion and a sensor element including a heater. In the thermal flow sensor according to claim 1,
further,
Electrodes provided on the outer surface of the frame portion on the opposite side of the flow path to which the sensor element support portion is connected, and
A thermal flow rate provided on the outer surface of the sensor element support portion on the side opposite to the flow path, and provided with a wiring conductor for electrically connecting the sensor element and the electrode. Sensor. In the thermal flow sensor according to claim 1 or 2.
The wall of the flow path has a penetrating portion that communicates inside and outside the flow path.
A thermal flow sensor characterized in that the sensor base material and the thermal insulating material close the penetrating portion to form a part of the wall. In the thermal flow sensor according to any one of claims 1 to 3.
The sensor element support portions are provided at a plurality of positions in the frame portion that are lined up in the direction in which the fluid to be measured flows.
A thermal flow rate sensor, wherein the sensor element is provided on each of the plurality of sensor element support portions. In the thermal flow sensor according to any one of claims 1 to 4.
The sensor element is a thermal flow sensor characterized by being composed of a platinum resistor.

Images