JP2000009509A - Flow sensor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and easily take a measurement in a low flow-rate range. SOLUTION: In the flow sensor element equipped with at least one substrate 1 and a thin-film heating element 3 formed on the substrate 1 while thermally insulated from the substrate 1 and extended at right angles to the flow direction of fluid, the width (a) of the heating element 3 in the flow direction of the fluid is so set that there is no effect of the conduction of heat in the heating element 3 due to the flow of the fluid. Consequently, when the heating body 3 is heated, the conduction of the heat in the heating element 3 is suppressed to make it easy to conduct the heat of the heating element 3 to the fluid. Consequently, the disorder of the linearity of the relation between the flow velocity of the fluid and output variation corresponding to the temperature variation of the heating element is improved to accurately and easily take a measurement in the low flow rate range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor element used for a measuring device for measuring the flow velocity and flow rate of a fluid such as gas, or for controlling the amount of air taken into an automobile engine.

[0002]

2. Description of the Related Art As described in Japanese Patent Application Laid-Open Nos. Hei 2-1932019, Hei 4-72523, Hei 4-93768, and the like, a flow sensor element of this type is provided on the surface of a substrate. From the upstream side to the downstream side along the flow of the fluid, the first temperature measuring low antibody, the heating element, and the second temperature measuring low antibody are arranged, the heating element is heated, and the There is a configuration in which the flow velocity or flow rate of a fluid is determined based on the difference between the outputs of the first and second low-temperature measuring antibodies that change.

In such a configuration, Japanese Patent Application Laid-Open No. 4-72
In the invention described in JP-A-523-523, the heating element is constituted by a first heating element and a second heating element which are electrically independent. Further, the invention described in Japanese Patent Application Laid-Open No. 4-93768 specifies the arrangement of the first and second low temperature measuring antibodies.

[0004] As another structure different from the above structure, two heating elements are arranged in the direction of the flow of the fluid, these heating elements are heated, and the voltage difference between the heating elements that changes with the flow of the fluid causes the fluid to flow. There is a flow sensor element for obtaining the flow velocity and flow rate of the flow sensor.

Further, there is a flow sensor element in which one heating element is provided in the flow of the fluid, and the flow rate and the flow rate of the fluid are obtained by the output corresponding to the temperature change of the heating element which changes with the flow of the fluid. .

Here, a flow sensor element 10 shown in FIG.
0 will be described. In this example, a heating element 1 is
In this example, a low-temperature measuring antibody 103 located on the upstream side and a low-temperature measuring antibody 104 located on the downstream side are provided. These heating elements 102 and the temperature-measuring low antibodies 103 and 104 are formed on the surface of the substrate 101 by a thin film technique,
By forming the moat 105 on the substrate 101 by anisotropic etching, it is thermally insulated from the substrate 101.

[0007] Such a flow sensor element 100 is used by being arranged in a flow of a fluid. And the heating element 1
02 and heated to the temperature of th, the temperature measurement low antibody 10
3 rises to the temperature of t1, and the temperature measurement low antibody 104 rises to the temperature of t2. When the fluid flows in this state, the heating element 102 and the temperature-measuring low antibodies 103 and 104 lose heat to the fluid. At this time, the amount of heat deprived by the fluid is proportional to the flow velocity of the fluid. Therefore, the flow velocity and flow rate of the fluid are obtained by measuring the deprived heat quantity.

The actual measurement can be performed by measuring any of the following values.

(1) Temperature change ΔT1 of the first temperature-measuring low antibody 103 (2) Temperature change ΔT2 of the second temperature-measuring low antibody 104 (3) Constant temperature th of the heating element 102 when driven at a constant temperature (4) Change in temperature th of heating element 102 when driving element 102 is driven with fixed driving energy ΔTh (5) Temperature change ΔT1, Δ of temperature measuring low antibodies 103 and 104
Difference in T2 In the above measurement, the temperature changes ΔT1 and ΔT2 of the low temperature measuring antibodies 103 and 104 are Pt
It can be determined by using a material having a predetermined temperature coefficient of resistance, such as, and measuring the change in resistance. Further, in order to drive the heating element 102 at a constant temperature, there is a method of driving the heating element 102 using a heating element 102 formed of a material such as pt having a predetermined resistance temperature coefficient so that the resistance value is constant. is there.

The measurement methods (1) to (5) are selected depending on how the flow sensor element in which the temperature-measuring low antibody and the heating element are arranged is used.

[0011]

FIG. 6 (a) shows the result of measurement of the flow rate of the fluid by the measurement methods (1) to (4) described above. According to this result, it can be seen that the measurement of the low flow rate region cannot be performed because the output of the heating element (including the temperature measurement low antibody) does not change with the flow rate change in the low flow rate range. This is due to the fact that the heat generated by the heating element is not easily transmitted through the inside of the heating element and is not easily transmitted to the fluid to be measured, so that the output of the heating element does not change with high sensitivity according to the flow velocity of the flowing fluid. it is conceivable that.

Next, FIG. 6B shows the result measured by the measuring method of (5). According to this result, the linearity in the high flow velocity region is broken. For this reason, it is necessary to use another complicated measurement method such as approximation by a higher-order curve or measurement by dividing the flow rate range.

An object of the present invention is to provide a flow sensor element capable of improving linearity collapse in a low flow rate region by the measurement method of (3) or (4).

[0014]

According to the first aspect of the present invention,
A flow sensor element comprising at least a substrate and a thin-film heating element that is thermally insulated from the substrate and extends in a direction perpendicular to the direction of flow of the fluid and is formed on the substrate. The width of the heating element in the direction is set to a width that is not affected by heat transfer in the heating element due to the flow of fluid.

Therefore, when the heating element is heated, it is possible to suppress the transmission of heat inside the heating element and to easily transfer the heat of the heating element to the fluid. This makes it possible to improve the linearity of the relationship between the flow velocity of the fluid and the output change corresponding to the temperature change of the heating element.

According to a second aspect of the present invention, in the first aspect of the invention, a plurality of the heating elements are arranged in parallel in a direction orthogonal to a flow direction of the fluid, and a plurality of the heating elements are arranged in the flow direction of the fluid. The intervals between the bodies are set so as not to be affected by heat transfer between the heating elements due to the flow of the fluid.

Therefore, when the heating element is heated, the transmission of heat inside the heating element and the transmission of heat between adjacent heating elements along the flow direction of the fluid are suppressed, and the heat of the heating element is reduced. Can be easily transmitted to the fluid. This makes it possible to improve the linearity of the relationship between the flow velocity of the fluid and the output change corresponding to the temperature change of the heating element.

According to a third aspect of the present invention, in the first aspect of the invention, a plurality of the heating elements are provided in parallel at a plurality of locations along the flow of the fluid so as to extend in a direction perpendicular to the direction of the flow. These heating elements are electrically connected in series with each other, and the interval between the plurality of heating elements in the fluid flow direction is an interval that is not affected by heat transfer between the heating elements due to the fluid flow. Is set to

Therefore, when the heating element is heated, transmission of heat inside the heating element and between adjacent heating elements along the flow direction of the fluid are suppressed, and the heat of the heating element is suppressed. Can be easily transmitted to the fluid. This makes it possible to improve the linearity of the relationship between the flow velocity of the fluid and the output change corresponding to the temperature change of the heating element. Further, since the plurality of heating elements are connected in series, the resistance value can be increased.

According to a fourth aspect of the present invention, in the third aspect of the present invention, a connecting line for connecting a plurality of the heating elements in series is formed of the same material as a material of the heating element. The width is set wider than the width of the heating element in the flow direction of the fluid.

Therefore, it is possible to reduce the energy consumption in the portion of the connection line other than the measurement portion for sensing the temperature of the fluid.

[0022]

FIG. 1 shows a first embodiment of the present invention.
A description will be given based on FIG. FIG. 1A is a plan view showing a heating element on a substrate, and FIG. 1B is a vertical side view of the substrate. In FIG. 1B, reference numeral 1 denotes a substrate formed of a silicon wafer. An insulating film 2 is formed on the surface of the substrate 1, and a heating element 3 formed of Pt (platinum) thereon.
And bonding pads 4 (see FIG. 1A) continuous to both ends of the heating element 3. The heating element 3 and the bonding pad 4 are formed by forming a thin film of Pt on the insulating film 2.
Is formed with a desired pattern by etching after forming the entire surface of the substrate. The moat 5 is formed on the substrate 1 by anisotropic etching from the side of the insulating film 2 while leaving the bridging portion 5 at the portion where the heating element 3 is arranged, so that the heating element 3 is thermally insulated from the substrate 1. Have been.

The bridging portion 5 and the heating element 3 are in the flow direction of the fluid.
The width a of the heating element 3 extends in a direction orthogonal to the direction of the arrow in FIG. 1 and is set to a width that is not affected by the movement of heat in the heating element 3 due to the flow of the fluid. ing. Specifically, a is 10 μm. The bonding pads 4 at both ends of the heating element 3 are bonding wires.
(Not shown) and connected to an external control circuit. Further, the heating element 3 and the bonding pad 4 are formed of a material having a temperature coefficient of resistance (TCR) of 1000 ppm / ° C. or more.

In such a configuration, when the heating element 3 is driven by constant energy, the temperature of the heating element 3 rises. This temperature rise value changes depending on the flow rate of the fluid to be measured. However, since the resistance of the heating element 3 changes in accordance with the change in temperature, an output (resistance value) corresponding to the temperature of the heating element 3 is measured. Thus (the measurement method (4) described above), the flow rate of the fluid can be measured.

In this case, the width a of the heating element 3 in the flow direction of the fluid is set to a width (10 μm) which is not affected by the movement of heat in the heating element 3 due to the flow of the fluid. When the heating element 3 is heated, the transmission of heat inside the heating element 3 can be suppressed, and the heat of the heating element 3 can be easily transmitted to the fluid. FIG. 2 shows the above measurement results. According to the results of FIG. 2, it is understood that the linearity of the relationship between the flow rate of the fluid and the output change due to the temperature change of the heating element 3 is improved.

Such an effect can be obtained similarly by using the heating element 3 which is bent in a zigzag manner on the bridging portion 5 as shown in FIG. FIG. 3 shows the substrate 1 (see FIG. 1B).
It is a top view which shows the upper heating element 3. FIG.

Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those in the previous embodiment are denoted by the same reference numerals and description thereof is omitted. FIG. 3 shows the substrate 1 (see FIG. 1B).
It is a top view which shows the upper heating element 3. FIG. In the present embodiment,
A plurality of bridging portions 5 crossing the moat 6 are formed, and each of these bridging portions 5 is formed with a heating element 3 extending in a direction orthogonal to the direction of fluid flow.

These heating elements 3 are electrically connected to each other in series by connection lines 7. These plural heating elements 3
Are connected in series by a connection line 7, and a bonding pad 4 continuous at both ends of the band is integrally formed of Pt. Fluid flow direction of these heating elements 3
The width a (in the direction of the arrow) is determined to be a width that is not affected by the movement of heat in the heating element 3 due to the flow of the fluid, and the interval c between the plurality of heating elements 3 in the flow direction of the fluid is The interval is set so as not to be affected by the movement of heat between the heating elements 3 due to the flow. Specifically, a is set to 10 μm as in the previous embodiment, and c is set to 300 μm.

Therefore, when the heating element 3 is heated,
The transmission of heat inside the heating element 3 on each bridge portion 5 and the transmission of heat between the adjacent heating elements 3 along the flow direction of the fluid are suppressed, and the heat of the heating element 3 is transferred to the fluid. It became possible to make it easy to convey to. Thus, it was confirmed that the linearity of the relationship between the flow rate of the fluid and the output change corresponding to the temperature change of the heating element 3 can be improved as in the measurement result described with reference to FIG. Such an effect is achieved by the plurality of heating elements 3.
Can also be obtained in a configuration in which are separately provided separately.

Further, since the plurality of heating elements 3 are connected in series and formed as one band, the overall length is increased and the resistance value can be increased. Thereby, the sensitivity can be increased when measuring the flow velocity and the flow rate of the fluid.

Further, a connecting line 7 for connecting the plurality of heating elements 3 in series is formed of the same material as the heating element 3 such as Pt, and the width b of the connection line 7 is determined by the heat generation in the flow direction of the fluid. By setting the width to be wider than the width a of the body 3, the energy consumption in the portion of the connection line 7 other than the measurement portion for sensing the temperature of the fluid can be reduced.

Further, as described above, the width a of the heating element 3 is set to a width which is not affected by the movement of heat in the heating element 3 due to the flow of the fluid, and the distance c between the adjacent heating elements 3
Is set at an interval that is not affected by heat transfer between the heating elements 3 due to the flow of the fluid, the driving energy for driving the heating element 3 at a constant temperature and maintaining the temperature of the heating element 3 constant. Even if the measurement is performed by the measurement method for measuring the fluctuation of the heat generation (the measurement method of (3) above), the relationship between the output of the heating element 3 (the fluctuation value of the driving energy) and the flow rate can be given.

[0033]

According to the first aspect of the present invention, at least a substrate and a thin film formed on the substrate are thermally insulated from the substrate and extend in the direction perpendicular to the flow direction of the fluid. Body, the width of the heating element in the flow direction of the fluid is set to a width that is not affected by the movement of heat in the heating element due to the flow of the fluid. When heated, the transfer of heat inside the heating element can be suppressed, and the heat of the heating element can be easily transmitted to the fluid. Thus, the linearity of the relationship between the flow rate of the fluid and the output change due to the temperature change of the heating element is improved, and the measurement in the low flow rate region can be performed accurately and easily.

According to a second aspect of the present invention, in the first aspect of the invention, a plurality of the heating elements are arranged in parallel in a direction orthogonal to the flow direction of the fluid, and a plurality of the heating elements are arranged in the flow direction of the fluid. Since the intervals between the bodies are set so as not to be affected by the movement of heat between the heating elements due to the flow of the fluid, when the heating elements are heated, the transfer of heat inside the heating elements, and In addition, it is possible to suppress the transfer of heat between the heating elements adjacent to each other along the flow direction of the fluid, and to easily transfer the heat of the heating elements to the fluid. This improves the linearity of the relationship between the flow rate of the fluid and the output change corresponding to the temperature change of the heating element, and enables accurate and easy measurement in the low flow rate range.

According to a third aspect of the present invention, in the first aspect of the invention, the plurality of heating elements are provided in parallel at a plurality of locations along the flow of the fluid so as to extend in a direction orthogonal to the direction of the flow. These heating elements are electrically connected in series with each other, and the interval between the plurality of heating elements in the fluid flow direction is an interval that is not affected by heat transfer between the heating elements due to the fluid flow. Is set to When the heating element is heated, transmission of heat inside the heating element and between adjacent heating elements along the flow direction of the fluid are suppressed, and heat of the heating element is easily transmitted to the fluid. It is possible to do. This improves the linearity of the relationship between the flow rate of the fluid and the output change corresponding to the temperature change of the heating element, and enables accurate and easy measurement in the low flow rate range. Further, since the plurality of heating elements are connected in series, the resistance value can be increased, thereby increasing the measurement sensitivity.

According to a fourth aspect of the present invention, in the third aspect of the present invention, a connection line connecting a plurality of the heating elements in series is formed of the same material as a material of the heating element. Since the width is set to be wider than the width of the heating element in the flow direction of the fluid, it is possible to reduce energy consumption in a portion of the connection line other than the measurement portion for sensing the temperature of the fluid.

[Brief description of the drawings]

FIG. 1A is a plan view showing a heating element on a substrate according to a first embodiment of the present invention, and FIG. 1B is a vertical sectional side view of the substrate.

FIG. 2 is a graph showing measurement results using a flow sensor element according to the embodiment.

FIG. 3 is a plan view showing a modification of the pattern of the heating element on the substrate.

FIG. 4 is a plan view showing a heating element on a substrate according to a second embodiment of the present invention.

FIG. 5 is an explanatory view showing a conventional flow sensor element together with a measuring method.

FIG. 6 is a graph showing measurement results obtained by a conventional measurement method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 3 Heating element 7 Connection line a Width of heating element c Interval of heating element b Width of connection line

Claims (4)

[Claims] 1. A flow sensor element comprising at least a substrate, and a thin-film heating element that is thermally insulated from the substrate and extends in a direction perpendicular to the direction of fluid flow and formed on the substrate. 5. The flow sensor element according to claim 1, wherein a width of the heating element in a flow direction of the fluid is set to a width which is not affected by a movement of heat in the heating element due to a flow of the fluid. 2. A plurality of the heating elements are arranged in parallel in a direction orthogonal to a flow direction of a fluid, and an interval between the plurality of heating elements in a flow direction of the fluid is a distance between the heating elements due to a flow of the fluid. 2. The flow sensor element according to claim 1, wherein the interval is set so as not to be affected by the movement of heat in the flow sensor. 3. A plurality of heating elements are provided in parallel at a plurality of locations along the flow of the fluid so as to extend in a direction orthogonal to the direction of the flow, and these heating elements are electrically connected to each other in series. The flow sensor element according to claim 1, wherein an interval between the plurality of heating elements in a flow direction of the fluid is set so as not to be affected by heat transfer between the heating elements due to the flow of the fluid. 4. A connection line for connecting a plurality of the heating elements in series is formed of the same material as that of the heating elements.
The flow sensor element according to claim 3, wherein a width of the connection line is set to be wider than a width of the heating element in a flow direction of the fluid.