JP2007101561A - Flow rate detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow rate detector which can detect higher flow rate by heightening thermal bond between heating element and thermal resistive element with no difficulty in mass production. <P>SOLUTION: The flow rate detector contains upstream temperature sensor 3U and downstream temperature sensor 3D allocated on both ends of a heater 2 with their comb teeth-shaped irregular direction to be approximately in parallel with a flow direction A of the detected fluid. In this case, heat from the heater 2 first heats crank-shaped connection J of these temperature sensors 3U, 3D formed as comb teeth, and then the heat is transferred through linear section S along the crank shape in the direction approximately in parallel with flow direction of the detected fluid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flow rate detector that detects the flow rate of a fluid to be detected (for example, air).

  Conventionally, as this type of flow rate detector, a diaphragm type flow rate detector comprising two sensors and a heater element has been used. FIG. 7 shows a schematic cross-sectional structure of a conventional diaphragm type flow velocity detector. FIG. 6 is a plan view of the diaphragm portion. 6 and 7, 1 is a silicon chip (base), 1-1 is a diaphragm portion formed in a thin shape by providing a space 1-2 on the upper surface of the base 1, and 2 is on the diaphragm portion 1-1. The metal thin film heating element (heater), 3U (3U0) and 3D (3D0) formed on the metal thin film thermal resistor (temperature sensor) formed on both sides of the heater 2 and 4 are slits penetrating the diaphragm. is there.

  The heater 2 and the temperature sensors 3U0 and 3D0 are covered with a thin insulating layer 5 made of, for example, silicon nitride. The heater 2 and the temperature sensors 3U0 and 3D0 have a comb-teeth shape in which a plurality of crank shapes are connected, and the concave-convex direction of the comb-teeth shape is arranged substantially orthogonal to the flow direction A of the fluid to be detected.

  The principle of the flow velocity measurement method using this flow velocity detector will be described. The heater 2 is driven so as to be a certain temperature higher than the ambient temperature, and the temperature sensors 3U0 and 3D0 are driven with a constant current or a constant voltage. In this driven state, when the flow velocity of the fluid to be detected is zero, the temperatures of the temperature sensors 3U0 and 3D0 are the same, and there is no difference in the resistance values of the temperature sensors 3U0 and 3D0. When there is a flow of the fluid to be detected, the temperature sensor (upstream temperature sensor) 3U0 located upstream is cooled because heat is carried away by the flow of the fluid to be detected toward the heater 2. On the other hand, the temperature sensor (downstream temperature sensor) 3D0 located downstream is heated by the flow of the detected fluid heated by the heater 2. Due to the occurrence of the temperature difference between the upstream side and the downstream side, a difference occurs in the resistance value between the upstream temperature sensor 3U0 and the downstream temperature sensor 3D0. By detecting this difference in resistance value as a difference in voltage value, the flow velocity detector obtains the flow velocity of the fluid to be detected.

  In this conventional flow velocity detector, for example, when the flow velocity of the fluid to be detected is 20 m / s or more, the temperature of the temperature sensors 3U0 and 3D0 is saturated, and the flow velocity cannot be detected. FIG. 5 shows the relationship between the flow velocity and the sensor output. A characteristic I shown in the figure is a flow velocity-sensor output characteristic of a conventional flow velocity detector, and the sensor output is saturated from around 20 m / s, and a high flow velocity cannot be detected. This is due to the low thermal coupling between the heater 2 and the temperature sensors 3U0 and 3D0.

  As a configuration for enhancing the thermal coupling between the heater 2 and the temperature sensors 3U0 and 3D0, the present applicant has proposed a flow velocity sensor as shown in Patent Document 1 and Patent Document 2 shown below. In the flow rate sensor of Patent Document 1, a heater and a temperature sensor are formed on a diaphragm so as to overlap each other, thereby increasing the thermal coupling and enabling detection of a high flow rate. In the flow rate sensor of Patent Document 2, thermal coupling is enhanced by covering the upper surfaces of the heater and the temperature sensor juxtaposed on the diaphragm with a metal layer, thereby enabling detection of a high flow rate.

Japanese Patent Publication No. 4-74672 Japanese Examined Patent Publication No. 6-68451 JP-A-61-88532

  However, in the flow rate sensors of Patent Document 1 and Patent Document 2, it is possible to detect a high flow rate by increasing the thermal coupling between the heater and the temperature sensor, but there is a problem that manufacturing is difficult and mass production is difficult. .

  For example, in the flow rate sensor of Patent Document 1, first, in the first step, a heater pattern is formed on the surface of the diaphragm. Then, an insulating film is formed thereon (second step), and a temperature sensor pattern is formed on the insulating film (third step). In this case, when the first step is completed, the heater pattern protrudes from the diaphragm plane from a microscopic viewpoint. In general, it is difficult to form a pattern on the uneven surface in a subsequent process, which makes mass production difficult. In the second step, it is difficult to reliably obtain electrical insulation reliability between the heater and the temperature sensor, which makes mass production difficult.

  Further, when a temperature sensor is formed on the heater as in Patent Document 1, or when the upper surface of the heater and the temperature sensor is covered with a metal layer as in Patent Document 2, the difference in thermal expansion of each film. In this state, mechanical distortion occurs. Since this mechanical strain affects the resistance value of the temperature sensor (the temperature sensor works like a strain gauge), the error of the flow velocity detection value becomes large, especially during mass production, the product characteristic variation becomes large, Make mass production difficult.

  The present invention has been made to solve such a problem, and the object of the present invention is to increase the thermal coupling between the heating element and the thermal resistor without causing difficulty in mass production, and to achieve a high flow rate. It is an object of the present invention to provide a flow rate detector capable of detecting

In order to achieve such an object, the present invention provides a base, a diaphragm portion formed in a thin shape by providing a space in a part of the base, a heating element formed in the diaphragm portion, In a flow velocity detector having a thermal resistor formed on both sides of a heating element and thermally coupled to the heating element, the shape of the thermal resistor is changed from a linear portion and a connecting portion connected orthogonally to the linear portion. The comb-shaped shape is a comb-tooth shape, and the comb-shaped unevenness direction is substantially parallel to the flow direction of the fluid to be detected, and one of the crank-shaped coupling portions positioned opposite the flow direction of the fluid to be measured. The side of the heating element is placed close to the edge of the heating element so as to enhance thermal coupling, and the heating element is arranged so as not to overlap the heating element. Comb shape with a crank shape consisting of The uneven direction of the shape is obtained by so arranging the ho Isuzu orthogonally flow direction of the detected fluid.
According to this invention, the heat from the heating element first heats the crank-shaped connecting portion of the thermosensitive resistor having a comb-teeth shape, and further, along the crank shape, the linear portion is defined as the flow direction of the fluid to be detected. It will be transmitted in a parallel direction.

  According to the present invention, since the thermal resistor is arranged with the comb-shaped unevenness direction being substantially parallel to the flow direction of the fluid to be detected, the thermal resistor is opposed to the flow direction of the fluid to be measured. The crank-shaped connecting portion of the heat-sensitive resistor, in which one side of the crank-shaped connecting portion is brought close to the edge surface of the heating element so as to enhance the thermal coupling, so that the heat from the heating element is comb-shaped. In addition, the straight portion along the crank shape is transmitted in a direction substantially parallel to the flow direction of the fluid to be detected, so that there is no difficulty in mass production. It is possible to increase the thermal coupling and detect a high flow rate.

  Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 is a perspective view showing an embodiment of a flow velocity detector according to the present invention. 2 is an enlarged cross-sectional view of the central portion of the diaphragm portion of the flow velocity detector of FIG. 1 as viewed from the lateral direction along the flow direction of the fluid to be detected. 1 and 2, the same reference numerals as those in FIGS. 6 and 7 indicate the same components, and the description thereof is omitted.

  In this embodiment, the upstream temperature sensor 3U (3U1) and the downstream temperature sensor 3D (3D1) are arranged on both sides of the heater 2, and the comb-shaped uneven directions of the temperature sensors 3U1 and 3D1 are detected. The fluid flow direction A is arranged substantially parallel to the fluid flow direction A. Each of the temperature sensors 3U1 and 3D1 has a zigzag shape in which a plurality of cranks having parallel travel and return are connected in a manner similar to the contour of a comb tooth. Hereinafter, such a shape is referred to as a comb-teeth shape.

  Accordingly, the temperature sensors 3U1 and 3D1 are arranged such that the longer parallel portion of the crank shape facing each other, that is, the extending direction of the comb teeth is parallel to the flow direction of the fluid to be detected. In addition, the crank-shaped long portions (straight portions) that are parallel to each other are substantially equal in length, and the short portions (connecting portions) that connect the long portions that are adjacent to each other at right angles to the end portions of the long portions are the same. They are arranged so as to be aligned. In other words, each of the temperature sensors 3U1 and 3D1 is arranged so that the comb direction is a pitch direction, and the pitch direction is orthogonal to the flow direction of the fluid to be detected.

  In addition, the code | symbol 6 in FIG. 1 is the ambient temperature sensor (thermal resistor) formed in the edge part of the base 1. FIG. A space 1-2 is formed below the diaphragm 1-1 in the same manner as the conventional flow velocity detector shown in FIG. Since the configurations (structure, material, manufacturing method, signal processing method) other than the pattern arrangement of the temperature sensors 3U1 and 3D1 are disclosed in Patent Document 1, Patent Document 2, Patent Document 3, and the like, the details here. Description is omitted.

  In the flow rate detector of this embodiment, the thermal conductivity of each of the temperature sensors 3U1 and 3D1 made of metal is much larger than the thermal conductivity of the diaphragm portion 1-1 made of an insulator. The temperature sensors 3U1 and 3D1 are largely governed by the pattern shape. Therefore, the heat from the heater 2 heats the crank-shaped connecting portions J (see FIG. 3) of the temperature sensors 3U1 and 3D1 each having a comb-teeth shape, and further, the linear portion S along the crank shape of the connecting portions J. Is transmitted in a direction substantially parallel to the flow direction of the fluid to be detected. For this reason, the heat from the heater 2 is efficiently transmitted to the portions of the temperature sensors 3U1 and 3D1 far from the heater 2.

  Thus, in the flow rate detector of the present embodiment, the thermal coupling between the heater 2 and each of the temperature sensors 3U1 and 3D1 is increased, and a high flow rate can be detected. Here, it is preferable that the heater 2 and the crank-shaped connecting portion J of the temperature sensors 3U1 and 3D1 are arranged as close as possible.

  As described above, according to this embodiment, the amount of heat supplied from the heater 2 to each of the temperature sensors 3U1 and 3D1 increases, and the thermal coupling between the two increases, so that the flow rate of the fluid to be detected increases. However, the temperatures of the temperature sensors 3U1 and 3D1 are not easily saturated, and a high flow rate can be detected. This is particularly effective as a countermeasure for temperature saturation of the upstream temperature sensor 3U1. Moreover, since the heat supply amount to each temperature sensor 3U1, 3D1 increases, the power consumption of the heater 2 increases by this increase.

  FIG. 5 shows the flow velocity-sensor output characteristic in this case as characteristic II. In the conventional characteristic I, the sensor output was saturated from around 20 m / s, whereas in the characteristic II according to the present embodiment, the sensor output changed according to the flow velocity even when exceeding 20 m / s. You can see how high flow rates can be detected.

  In the pattern arrangement of each of the conventional temperature sensors 3U0 and 3D0 shown in FIG. 6, the heat from the heater 2 is not from the crank-shaped connecting portions J of the temperature sensors 3U0 and 3D0 that are comb-shaped. The linear portion S on the side close to the heater 2 is transmitted in a direction substantially perpendicular to the flow direction of the fluid to be detected, and heat escapes toward the end of the diaphragm portion 1-1 and the vertical direction. Heat is not efficiently transmitted to a portion far from the heater 2 of each temperature sensor 3U0, 3D0. On the other hand, in the present embodiment, the heat from the heater 2 is efficiently transmitted to the portions of the temperature sensors 3U1 and 3D1 far from the heater 2, so the heater 2 and the temperature sensors 3U1 and 3D1 The thermal coupling becomes high, and it becomes possible to detect a high flow rate.

  FIG. 4 shows a modification of the pattern arrangement of the temperature sensor. In FIG. 4, signal deriving portions from the temperature sensors 3U (3U2) and 3D (3D2) are provided at positions farthest from the heater 2. Thus, by providing the signal deriving portions from the temperature sensors 3U2 and 3D2 at the position farthest from the heater 2, the signal deriving portions of the temperature sensors 3U2 and 3D2 are passed to the base 1 outside the diaphragm portion 1-1. The amount of heat that escapes is reduced as much as possible. Since the amount of heat transferred due to the thermal conductivity is proportional to the temperature difference, the signal deriving unit of each temperature sensor 3U2, 3D2 is connected to the heater 2 rather than connecting the high temperature part close to the heater 2 and the base 1 which is generally ambient temperature. Connecting the base 1 with a lower temperature part away from the base can reduce the temperature difference and reduce heat escape.

  3 and 4, the pattern widths of the temperature sensors 3U and 3D are made narrower than the pattern width of the heater 2, but the pattern widths of the two are the same or the pattern width of the heater 2 is set to each temperature. It is good also as a structure narrower than the pattern width of the sensors 3U and 3D. In the above-described embodiment, the pattern width of the heater 2 is increased in reliability because more current flows than the temperature sensors 3U and 3D, and the pattern width of each temperature sensor 3U and 3D is as much as possible to increase sensitivity. It is narrowed to increase the resistance value. In all the embodiments described above, it is preferable that the heater 2 and the temperature sensors 3U and 3D be arranged as close as possible. Further, the heater 2 may be extended and provided so as to surround at least a part of the periphery of each temperature sensor 3U, 3D.

  In order to detect a high flow rate, it is considered better to increase the thickness of the temperature sensors 3U and 3D to increase the heat transfer efficiency and increase the heat capacity. However, increasing the thickness increases power consumption, Response speed will also be slow. On the other hand, according to the present embodiment, since the heat transfer efficiency can be increased without increasing the thickness of each temperature sensor 3U, 3D, the power consumption does not increase more than necessary, and the response speed also decreases. There is no end. Further, according to the present embodiment, only the pattern arrangement of each temperature sensor 3U, 3D or each temperature sensor 3U, 3D and heater 2 is changed, so that mass production is not difficult.

1 is a perspective view showing an embodiment of a flow rate detector according to the present invention. It is the expanded sectional view which looked at the center part of the diaphragm part of this flow velocity detector from the horizontal direction along the flow direction of the fluid to be detected. It is a top view of the diaphragm part of this flow velocity detector. It is a figure which shows the modification of the pattern arrangement | positioning of the temperature sensor on the diaphragm part of this flow velocity detector. It is a figure which compares and shows the flow velocity-sensor output characteristic of the flow velocity detector which concerns on the past and this invention. It is a top view of the diaphragm part of the conventional flow velocity detector. It is a sectional side view which shows the general | schematic cross-section of the conventional flow velocity detector.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Base, 1-1 ... Diaphragm part, 1-2 ... Space, 2 ... Heater, 3U ... Temperature sensor (Upstream temperature sensor, 3D ... Temperature sensor (Downstream temperature sensor), 4 ... Slit, 5 ... Insulation Layer 6 ... Ambient temperature sensor J ... Connecting part S ... Linear part.

Claims (4)

A base, a diaphragm formed in a thin shape with a space in a part of the base, a heating element formed in the diaphragm, and a heating element formed on both sides of the heating element and the heat In a flow rate detector with a thermal resistor to be coupled,
The thermal resistor is
It is a comb-teeth shape in which a crank shape composed of a straight portion and a connecting portion connected orthogonally to the straight portion is connected,
Make the comb-teeth shape uneven direction substantially parallel to the flow direction of the fluid to be detected,
Further, one side of the crank-shaped connecting portion that is positioned opposite to the flow direction of the fluid to be measured is brought close to the edge surface of the heating element so as to enhance thermal coupling,
Arranged not to overlap the heating element,
The heating element is
It is a comb-teeth shape connected with a crank shape composed of a linear portion and a connecting portion similar to the thermal resistor,
The comb-shaped uneven direction is arranged substantially orthogonal to the flow direction of the fluid to be detected. The flow rate detector of claim 1, wherein
The thermal resistor and the heating element are:
A flow velocity detector characterized by being arranged so that at least a part of the comb-shaped irregularities bite each other. The flow rate detector of claim 1, wherein
The flow rate detector, wherein the signal deriving unit from the thermal resistor is provided at a position farthest from the heating element. The flow rate detector of claim 1, wherein
The thermal resistor is
Each of the crank-shaped straight portions is substantially equal in length,
The flow velocity detector, wherein the crank-shaped connecting portions are arranged so as to be aligned on the same straight line.

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