JPH10197305A - Thermal air flowmeter and measuring element for thermal air flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal air flowmeter which is manufactured at low cost, capable of temperature correction, and superior in measurement accuracy. SOLUTION: This thermal air flowmeter comprises a measuring element 1 that a heating resistor 3, temperature compensating resistor 4, and humidity sensor 5 between the heating resistor 3 and a terminal electrode 8 are formed on a semiconductor substrate 2 via an electricity insulating film, a drive detecting circuit means 15a which supplies current to the measuring element 1 and detects air flow rate signals, a control circuit 15b which calculates the rate of flow of air from the air flow rate signals of the measuring element 1, and a memory 15c which stores the correction data of air flow rate-humidity characteristics, and corrects the rate of flow of air from the humidity and correction data detected by the control circuit 15b through the use of the humidity sensor 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal air flow meter, and more particularly to a thermal air flow meter suitable for measuring an intake air amount of an internal combustion engine and a measuring element for the thermal air flow meter.

[0002]

2. Description of the Related Art Conventionally, as an air flow meter which is provided in an electronically controlled fuel injection device of an internal combustion engine of an automobile or the like and measures an intake air amount, a thermal air flow meter has become mainstream since it can directly detect a mass air amount. I have. Among them, in particular, a thermal air flow meter and its measuring element manufactured by the semiconductor micromachining technology have been attracting attention because they can be reduced in cost and can be driven with low power.

[0003] Such a conventional thermal air flowmeter using a semiconductor substrate is disclosed, for example, in Japanese Patent Application Laid-Open No. Sho 60-1.
There is one disclosed in Japanese Patent No. 42268. Although the technology described in the above publication reduces the manufacturing cost to some extent, it does not consider humidity characteristics when measuring the amount of intake air. Japanese Patent Application Laid-Open No. 7-2 is an example of a thermal air flow meter that takes into consideration the humidity correction of the intake air flow rate.
There is an apparatus disclosed in Japanese Patent Publication No. 29776, in which a humidity sensor for detecting humidity is provided separately from a measuring element for a thermal air flow meter.

[0004]

The above prior art has the following problems. The prior art described in Japanese Patent Application Laid-Open No. 60-142268 will be described with reference to FIG. FIG.
Is a plan view of a measuring element for a conventional thermal air flow meter,
It is FIG. 2 described in the gazette. In the figure, reference numeral 1 denotes a measuring element for a thermal air flow meter, and cavities 28a, 28b, 2 formed by anisotropically etching a semiconductor substrate such as silicon.
8c, two bridges 29a and 2 made of an electrically insulating film bridging
9b, the upstream side of the air flow is the bridge 29a, and the downstream side is the bridge 29b. The heating resistors 26 are arranged with an open cavity 28c between the two bridges 29a and 29b, and these bridges 29a and 29b are connected to the temperature measuring resistors 27a and 27b on the sides of the heating resistor 26, respectively. Is arranged, and further,
A temperature compensating resistor 4a for measuring the air temperature is provided in a part of the electric insulating film on the upstream side of the cavity 28a. The cavities 28a, 28b, and 28c are formed by anisotropically etching the semiconductor substrate using the openings in the electric insulating film.
It is a continuous integral cavity under the bridges 29a and 29b of the electric insulating film.

[0005] In the air flow meter using this measuring element, the heating resistor 26 is heated and driven so that the temperature becomes higher by a certain temperature than the air temperature determined by the temperature compensating resistor 4a. The air flow rate is determined by utilizing the heat transport effect of the air, and the upstream temperature measuring resistor 27a and the downstream temperature measuring resistor 27b of the flow path are used.
It is measured from the temperature difference that occurs between

[0006] In the conventional example configured as described above, no consideration is given to the detection accuracy of the air flow rate with respect to the "change in humidity" of the intake air, and there remains a problem in the detection accuracy of the air flow rate. Further, when used under severe conditions such as automobiles, the heating resistor 26, the temperature compensating resistor 4a, and the temperature measuring resistors 27a and 27b of the measuring element for the thermal air flow meter due to the temperature rise of the internal combustion engine. However, since it is not considered that heat is conducted to the heat and adversely affects the measurement accuracy, a sufficient air flow rate-support portion temperature characteristic cannot be obtained.

FIG. 22 shows a conventional thermal air flow meter that takes into account the humidity correction of the intake air flow rate. FIG. 22 is FIG. 1 described in Japanese Patent Laid-Open No. 7-229776. In the figure, 18 is an air flow meter shown in a block configuration,
31 is a humidity detector, 30 is an air flow detector, 32
Are the air flow rate signals obtained from the air flow rate detection device 30,
Reference numeral 3 denotes an output signal after the humidity correction of the air flow rate signal based on the humidity signal detected from the humidity detector 31 separately installed. In the conventional example configured as described above, the humidity detecting device (humidity sensor) 31 for detecting the humidity is installed in the intake passage separately from the air flow detecting device 30, so that the number of parts increases and the number of assembly steps increases. And the production cost is not sufficient.

Accordingly, an object of the present invention is to provide a thermal air flow meter and a thermal air flow meter which solve the problems of the prior art and which are low in cost and excellent in air flow-humidity characteristics and air flow-support temperature characteristics in flow measurement. It is to provide a measuring element for a flow meter.

[0009]

A thermal air flow meter which achieves the above object has a thermal air flow meter having a humidity sensor formed on the same substrate on which a heating resistor and the like for measuring the air flow rate are formed. A measuring element for the meter, a drive detecting circuit for supplying a current to the measuring element and detecting an air flow signal, a control circuit for calculating an air flow rate from the air flow signal, and an air flow rate
A memory for storing correction data of humidity characteristics,
The control circuit corrects the air flow rate from the humidity detected using the humidity sensor and the correction data.

Another feature is that a humidity sensor formed on the same substrate on which a heating resistor or the like for measuring an air flow rate is formed, and a heat transfer device which is transferred when the substrate is mounted on another component. A measuring element for a thermal air flow meter having a temperature sensor for detecting a representative temperature representing the influence on the heating resistor and the like, a drive detection circuit for supplying a current to the measuring element and detecting an air flow signal, A control circuit that calculates an air flow rate from the air flow rate signal; and a memory that stores correction data of an air flow rate-humidity characteristic and an air flow rate-supporting part temperature characteristic, wherein the control circuit obtains from the humidity sensor. The air flow rate is corrected based on the obtained humidity, the temperature of the supporting portion obtained from the temperature sensor, and the correction data.

[0011] The characteristic of the measuring element for the thermal air flow meter that achieves the above object is that the heating element for measuring the air flow rate is formed on the same substrate on which the heating element touches. A humidity sensor is formed at a position outside the streamline region.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing a measuring element 1 for a thermal air flow meter according to a first embodiment of the present invention,
FIG. 2 is a cross-sectional view taken along the line AA ′ of the measuring element 1 of FIG. 1, and FIG.
FIG. 2 is a sectional view showing the humidity sensor according to the first embodiment of the present invention, and is a sectional view taken along the line BB ′ of FIG. 1. 1, 2, and 3, a measuring element 1 includes a semiconductor substrate 2 made of silicon or the like having a cavity 6 formed from the lower surface of the semiconductor substrate 2 by anisotropic etching to a boundary surface of an electric insulating film 7a, and an electric insulating film. 7a, a heating resistor 3 formed on 7a, a temperature compensating resistor 4 for measuring the air temperature and forming a bridge circuit with the heating resistor 3, and connecting an air flow signal of the measuring element 1 to an external circuit. , A humidity sensor 5 formed between the heating resistor 3 and the terminal electrode 8 to measure humidity, and an electric insulating film 7b for protecting each resistor. You.

The humidity sensor 5 has a structure in which comb-shaped electrodes 10a and 10b facing each other are covered with a film 11 of a polyimide-based organic material whose dielectric constant changes due to moisture absorption.
The humidity is detected from a change in capacitance between the electrodes 10a and 10b. Here, the requirements that the humidity sensor 5 should have will be described. If the humidity (relative humidity) depends on the temperature, and if the humidity is detected from the air (air flow 9) heated by the heating resistor, the desired value is obtained. Will measure different humidity. Therefore, it is necessary to detect the humidity from the air (air flow 9) at a position outside the streamline region of the air (air flow 9) touched by the heating resistor for measuring the air flow rate.
That is, the characteristic of the measuring element for the thermal air flow meter according to the present invention is that the heating resistor for measuring the air flow rate is on the same substrate on which the heating resistor is out of a streamline area of the air touched by the heating resistor. It can be said that the position is where a humidity sensor is formed.

On the other hand, a heating current is applied to the heating resistor 3 so that the temperature of the heating resistor 3 becomes higher than the temperature of the temperature compensating resistor 4 disposed at the end of the flow path of the air flow 9 by a certain temperature. The air flow rate is measured from a heating current value flowing through the heating resistor 3 based on a heat transfer effect by forced cooling of the heating resistor 3 by the air flow 9. The cavity 6 and the electric insulating film 7 near the heating resistor 3 are formed to ensure thermal insulation from the heating resistor 3 to the substrate 2 and to secure measurement accuracy. Further, a temperature compensating resistor 4 forming a bridge circuit with the heating resistor 3
As shown in FIG. 1, is positioned at the tip of the substrate 2 and protrudes into the flow path of the air flow 9, and is heated by the heating resistor 3 in either the forward flow or the backward flow. It is arranged so as not to be affected by the flow of air, which enables accurate measurement of the air flow. The temperature compensating resistor 4 can also be used for measuring the air temperature (that is, the intake air temperature) as described later.

FIG. 4 is a sectional view showing a thermal air flow meter according to an embodiment of the present invention. That is, it is a diagram showing an embodiment in which the measuring element 1 of FIG. 1 is mounted on a thermal air flow meter. FIG. 1 is a cross-sectional view illustrating an embodiment of a thermal air flow meter mounted in an intake passage of an internal combustion engine of an automobile or the like and measuring a flow rate of intake air (referred to as intake air). As shown in the figure, the thermal air flow meter of the present embodiment includes the measuring element 1, the support 14, and the external circuit 15. Then, the measuring element 1 is arranged in the sub-passage 13 inside the intake passage 12. The external circuit 15 is connected to the terminal electrode 8 of the measuring element 1 via the support 14.
Is electrically connected to Here, normally, the intake air flows in the direction indicated by the air flow 9, and the intake air flows in the opposite direction (reverse flow) to the air flow 9 depending on predetermined conditions of the internal combustion engine.

FIG. 5 is an enlarged view showing the measuring element portion (the measuring element 1, the support 14, etc.) of FIG. FIG. 6 is a cross-sectional view taken along the line CC ′ of FIG. As can be seen in FIGS. 5 and 6, the measuring element 1 is supported on a support 14 such that the temperature-compensating resistor 4 is directly exposed to the air flow 9. Further, an external circuit 15 formed by forming a terminal electrode 16 and a signal processing circuit on an electrically insulating substrate made of alumina or the like is similarly fixed on the support 14. The measuring element 1 and the external circuit 15
Is electrically connected between the terminal electrodes 8 and 16 by wire bonding with a gold wire 17 or the like.
7, while protecting the electrode terminals 8, 16 and the external circuit 15, and covered with a protector 14a so that the humidity sensor 5 is not directly affected by the air flow 9. And furthermore,
The protection body 14a has a ventilation hole 24 having such a small size that water vapor in the intake air reaches the humidity sensor 5 in the protection body 14a.
Is formed near the humidity sensor 5 to prevent the humidity sensor 5 from being directly exposed to the airflow 9.

That is, if the measuring element 1 is mounted in an intake passage of an internal combustion engine of an automobile or the like and measures the amount of intake air, the humidity sensor 5 is covered with a protective body having a ventilation hole from the point of dust prevention and the like. It is desirable to have. As shown in FIGS. 5 and 6, the measuring element 1 mounted in this way is substantially isolated from the air flow 9 by the support 14 at the lower surface and by the electric insulating film 7 at the upper surface, as shown in FIGS. I have. Therefore, since the cavity does not have an opening in the air flow as in the above-described conventional example, dust or the like that becomes a problem when measuring the air flow rate of an internal combustion engine such as an automobile may accumulate in the cavity or the opening. It has a configuration that allows highly reliable measurement without any problem.

Next, the operation of the embodiment of the present invention will be described with reference to FIG. 7, FIG. 8, FIG. 9, FIG. 10, and FIG. FIG. 7 is a block diagram showing a thermal air flow meter according to the present invention. FIG. 5 is a block diagram illustrating a configuration of the thermal air flow meter of FIG. 4, for example. The thermal air flow meter 18 includes the measuring element 1 shown in FIG. The external circuit 15 includes a drive detection circuit 15a for supplying a current to the measurement element 1 and detecting an air flow signal, an input circuit for inputting an air flow signal from the measurement element 1 through an A / D converter, and an air flow rate. And a control circuit 15b including a CPU unit for calculating the operation of the CPU and an output circuit unit for output.
A memory 15c in which correction data for correcting the humidity of the air flow measured by the unit and the air flow measured by the obtained humidity are stored in advance.

FIG. 8 is a diagram showing a partial electric circuit of the thermal air flow meter of FIG. Heating resistor 3 and temperature compensation resistor 4
19 shows a bridge circuit in the drive detection circuit 15a including: a differential amplifier 19; a transistor 20;
21 is a power supply, and 22a and 22b are resistors. FIG. 9 is a diagram showing an equivalent electric circuit of the humidity sensor 5 of FIG. FIG.
0 is a diagram showing the relationship between the relative humidity (H) of the intake air and the capacitance (Ch) of the humidity sensor 5. FIG. 11 shows the air flow rate of the thermal air flow meter 18 according to one embodiment of the present invention.
It is a figure showing a humidity characteristic.

First, the air flow rate is measured as follows.
In the bridge circuit shown in FIG. 8, the temperature (resistance value) of the heating resistor 3 located at the center of the measuring element 1 is a certain value higher than the temperature (resistance value) of the temperature compensation resistor 4 corresponding to the air temperature.
(E.g., 150 ° C.)
Is set. When the temperature of the heating resistor 3 is lower than the set value, a difference occurs between the potentials A and B at the middle point of the bridge circuit, and the output C of the differential amplifier 19 turns on the transistor 20 to turn on the heating resistor 3. Heating current flows. Heating resistor 3
When the temperature reaches the set value, the transistor C is turned off by the output C of the differential amplifier 19, and the heating current is cut off.
In this way, the feedback control is performed so that the temperature of the heating resistor 3 becomes constant at the set value, and the heating current that increases with an increase in the air flow rate is used as a flow signal at the potential of the point A of the bridge circuit as a flow signal. Output to

On the other hand, as shown in FIG. 9, the humidity between the electrodes 10a and 10b of the humidity sensor 5 of the measuring element 1 is determined by measuring the capacitance (Ch) of an organic material such as polyimide formed between the electrodes. This is performed by utilizing the fact that the film 11 absorbs water vapor to increase the dielectric constant, and the capacitance (Ch) changes with respect to the relative humidity (H) as shown in FIG. In the drive detection circuit 15a, a signal corresponding to the capacitance (Ch) of the humidity sensor 5 is detected from the terminal electrodes 8c and 8d of the humidity sensor 5, and the relative humidity (H) shown in FIG. Capacity (Ch)
Is stored in advance, the humidity is obtained from the signal of the capacitance (Ch) by the control circuit 15b using the correlation data.

The humidity correction executed from the measured air flow rate and humidity is performed as follows. FIG. 11 shows the air flow rate.
It shows humidity characteristics. In the figure, the horizontal axis is the air flow rate
(Q), and the vertical axis indicates the measurement error (ΔQ / Q) of the air flow rate of the humidity parameter when the humidity (H) is based on 50%. As shown in the figure, when the humidity correction of the prior art is not performed, a negative error occurs in the entire flow rate range when the humidity (H) is 10% dry air, and the humidity (H) is 90%. It turns out that there is a positive error at the time. This is because the thermal conductivity of moist air containing water vapor increases in proportion to the ratio of water vapor.

In the present invention, the humidity (H) can be measured from the humidity sensor 5 as described above, and the correction data generated from the air flow rate-humidity characteristics shown in FIG. And the humidity (H) to correct the air flow rate (Q), that is, by performing arithmetic processing in the CPU unit of the control circuit 15b, the humidity can be corrected. When the humidity correction of the present invention is applied, as shown by the arrow in FIG. 11, it is possible to make the flow rate error almost zero (to match the standard of 50% humidity).

By storing in advance the characteristic air flow-humidity characteristic of each thermal air flow meter in the memory 15c, it is possible to improve the performance variation of each thermal air flow meter. . Further, there is a method of storing the air flow rate (Q), the humidity (H), and the correction value as a map, or a method of storing as an approximate error function. Furthermore, it is understood that the humidity correction of the air flow rate includes the humidity correction of the air flow rate signal.

Incidentally, the humidity sensor 5 is not limited to the configuration shown in FIGS. In the humidity sensor 5 described above, the method of detecting the capacitance (Ch) between the opposing electrodes 10a and 10b is used. However, the change in the resistance value or the impedance as the resistor (the organic material film 1) is used.
It is also possible to use a method in which the humidity is detected from the phenomenon that the resistance value or the impedance decreases when moisture is absorbed by 1).

Here, examples of other humidity sensors according to the present invention will be described. FIG. 12 is a sectional view showing a humidity sensor of a second embodiment according to the present invention, and FIG. 13 is a sectional view showing a humidity sensor of a third embodiment according to the present invention.
As another humidity sensor, as shown in FIG. 12, an electrode 10c, a film 11 made of polyimide or the like and an electrode 10d are laminated on a semiconductor substrate 2, an electric insulating film 7a, and the electrodes 10c and 10d.
It is possible to detect humidity from the capacitance between d.
At this time, it is effective to form small holes or slits in the upper electrode 10d so that the vapor of the intake air reaches the polyimide-based film 11 effectively.

Further, as shown in FIG. 13, it is also possible to measure the humidity by utilizing the characteristic that the film 11 of polyimide or the like expands in volume due to moisture absorption. In FIG. 13, a cavity 6b is formed in a semiconductor substrate 2 and an electric insulating film 7a is formed on the film 11a.
Is detected as a humidity signal from a change in resistance of the piezoresistors 23a and 23b formed near the cavity 6 due to expansion and contraction due to humidity.

Further, a humidity sensor shown in FIGS. 14 and 15 is also possible. FIG. 14 is an enlarged view showing a measuring element unit according to another embodiment of the present invention. FIG. 9 is a plan view of the mounting of the measuring element 1 when the humidity sensor 5 is of another type. Also,
FIG. 15 is a sectional view showing a humidity sensor according to a fourth embodiment of the present invention, and is a sectional view taken along the line DD 'of FIG. Here, the humidity sensor 5 includes a pair of heating resistors 10 e and 1 formed on the electric insulating film 7 on the cavity 6 b formed on the semiconductor substrate 2.
0f.

The heating resistor 10e is arranged in one open chamber of the protection body 14a in which the ventilation hole 24 is formed, and the heating resistor 10f is sealed in a state where the other closed chamber of the protection body 14a is filled with dry air. Is done. The heating resistors 10e and 10f are heated so as to have a certain temperature. The humidity of the intake air is determined by the difference in heat conductivity between the heating resistor 10e installed in the room and the heating resistor 10f installed in the atmosphere of dry air due to the difference in the heat conductivity due to water vapor. It can be detected from the difference. The temperature sensor 5 is not limited to the structure of the above embodiment, and any structure can be used as long as it can detect humidity and can be formed on the measuring element 1. There is no change.

Next, a description will be given of an embodiment capable of correcting the temperature of the support portion and / or the temperature of the intake air in addition to the correction of the humidity. FIG. 16 is a plan view showing a measuring element 1 for a thermal air flow meter according to a second embodiment of the present invention. The difference between the second embodiment shown in FIG. 16 and the first embodiment is that a temperature sensor 4b for measuring the intake air temperature of the internal combustion engine is newly formed at the tip of the measuring element 1 and the measuring element 1 (For example,
A temperature sensor 25 for measuring the temperature of the support 2a (shown in FIG. 6 described above) that is supported when the semiconductor substrate 2) is mounted on another component (for example, the support 14).
Is newly installed near the humidity sensor 5.

By newly forming the temperature sensors 4b and 25 in this way, a thermal air flow meter with high flow rate measurement accuracy can be realized. Hereinafter, the operation of the support portion temperature correction and the intake air temperature correction of the present embodiment will be described. As shown in FIG. 4, in an internal combustion engine such as an automobile, the temperature of the intake passage 12 and the support 14 increases due to the heat of the internal combustion engine, and this heat is transferred to the measuring element 1 to cause an error in the measurement of the air flow rate. In some cases, the flow-temperature characteristics may be deteriorated. FIG. 17 shows a temperature distribution state between the support 14 (including the external circuit 15) and the measuring element 1 when the temperature of the support 14 rises as described above.

FIG. 17 is a diagram showing a measuring element section of a thermal air flow meter using the measuring element of FIG. 16 and a temperature distribution on the line EE 'of the measuring element section. In FIG. 17, EE ′
The temperature distribution of the measuring element 1, the support 14 and the external circuit 15 on the line is shown, and the heat of the internal combustion engine is transferred from the support 14 via the support 2a to the terminal electrode 8 of the measuring element 1, the temperature sensor 25, It is shown that the signal propagates to the heat generating resistor 3, the temperature compensating resistor 4a, the temperature sensor 4b, etc., while being transmitted to the external circuit 15.

Therefore, unnecessary heat propagates to the heating resistor 3 and the temperature compensating resistor 4a for measuring the air flow rate,
This has an adverse effect on the air flow measurement accuracy. In addition, unnecessary heat propagation occurs similarly due to heat generation from the external circuit 15 itself, which may adversely affect measurement accuracy. This effect is taken into account in the air flow rate-support portion temperature characteristic described later. In this embodiment, as shown in FIG. 16, between the heating resistor 3 and the terminal electrode 8 or between the heating resistor 3 (Or a temperature compensating resistor 4a depending on the structure of the measuring element), a temperature sensor 25 is formed near the temperature sensor 25a.
The correction of the air flow rate is performed using the detected temperature and the air flow rate-support temperature characteristic.

In other words, the heat conduction as a portion suitable for detecting the “support portion temperature Tw (representative temperature Tw) as a representative value”, which can determine the influence of unnecessary heat propagation on the measurement of the air flow rate. Path portion (for example, the support portion 2a, which is supported when the substrate of the measuring element is attached to another component,
A temperature sensor 25 for detecting the representative temperature is formed between the support portion and the heating resistor, and the like, and the air flow rate is corrected by using the temperature detected from the temperature sensor 25 to measure the flow rate. It is intended to improve accuracy. The heating resistor and the like of the second embodiment correspond to the heating resistor 3 and / or the temperature compensation resistor 4a. Further, the heating resistor and the like of the first embodiment correspond to the heating resistor 3 and / or the temperature compensating resistor 4.

FIG. 18 is a diagram showing the correction of the temperature of the support portion and the correction of the intake air temperature according to one embodiment of the present invention. That is, FIG.
8 (a) shows the air flow rate-support part temperature characteristic, and FIG.
Shows the air flow rate-intake air temperature characteristic. FIG.
In (a), the horizontal axis represents the air flow rate (Q), and the vertical axis represents the temperature of the support.
(Tw) is the measurement error of air flow based on 25 ° C (ΔQ
/ Q). When the temperature of the supporting portion (Tw) is 80 ° C. in the case where the temperature of the supporting portion is not corrected in the related art, an error of about 10% occurs particularly in a low flow rate region. On the other hand, with the configuration according to the present invention, the temperature of the support portion (Tw) obtained from the measuring element 1 having the temperature sensor 25 formed between the heating resistor 3 and the terminal electrode 8 and the measuring element 1 (heating resistor, etc.) And the air flow rate (Q) calculated by the above-described control circuit 15b is input, and correction data based on the air flow rate-support temperature characteristic shown in FIG. Then, by performing arithmetic processing in the CPU section of the control circuit 15b, it becomes possible to correct the temperature of the support section.

In the case where the temperature correction of the supporting portion of the present embodiment is applied, the flow rate error is set to almost zero as shown by the arrow in FIG. 18A (the temperature of the supporting portion is adjusted to the reference of 25 ° C.). Can be. The memory 15c stores in advance an air flow rate-support temperature characteristic unique to each thermal air flow meter, and stores the air flow rate (Q), the support temperature (Tw), and the correction value. Support temperature correction is possible from the map and from an approximate error function.

Next, the intake air temperature correction will be described. The correction of the intake air temperature of the prior art is performed by the temperature compensation resistor 4a.
In this embodiment, the intake air temperature is corrected for the bridge circuit composed of the heating resistor 3 and the heating resistor 3. Therefore, correction for temperature changes such as density, kinematic viscosity coefficient, and thermal conductivity, which are physical properties of air, is not considered, and the air flow rate-intake temperature characteristic is not sufficient. Was.

In the air flow rate-intake air temperature characteristic shown in FIG. 18B, the horizontal axis is the air flow rate (Q), and the vertical axis is the intake air temperature (Ta).
Shows the measurement error (ΔQ / Q) of the air flow rate based on 25 ° C. The solid line shows the air flow rate-intake air temperature characteristic when the intake air temperature correction of the prior art is not performed. Intake air temperature
When (Ta) is low temperature (−30 ° C.), the air flow rate becomes a minus error in a low flow rate range, and becomes a plus error in a high flow rate range. On the other hand, when the temperature is high (80 ° C.), the error tends to be opposite to the low temperature. On the other hand, by the configuration according to the present invention,
The intake air temperature (Ta) obtained from the temperature sensor 4b and the air flow rate (Q) measured by the measuring element 1 and calculated by the control circuit 15b are input and stored in the memory 15c in FIG.
The correction data based on the air flow rate-intake air temperature characteristic shown in FIG. 8 (b) is called up, and the CPU unit of the control circuit 15b performs the arithmetic processing, whereby the intake air temperature can be corrected.

When the intake air temperature correction of this embodiment is applied, as shown by the arrow in FIG. 18B, the flow rate error can be made almost zero (the intake air temperature is adjusted to the reference of 25 ° C.). In the memory 15c, a unique intake air temperature characteristic is stored in advance for each thermal air flow meter, and the measured air flow rate (Q), the intake air temperature (Ta), and the correction value are stored as a map. Also, the intake air temperature correction of the present invention can be performed by storing as an approximate error function.

In this embodiment, the intake air temperature (Ta)
Was measured using a separate and independent temperature sensor 4b.
In some cases, without the temperature sensor 4b, the intake air temperature (Ta) is calculated and measured by the CPU of the control circuit 15b by calculating the intake air temperature (Ta) from the change in the resistance value of the temperature compensation resistor 4a. It is possible to Therefore, the intake air temperature can be corrected using the intake air temperature (Ta) calculated and measured. Further, in the present embodiment, the temperature sensors 4b and 25 are configured in the form of a resistor sensor of a metal thin film of platinum or the like, which is the same as the heating resistor 3 and the temperature compensation resistor 4a. Due to the sensitivity advantage of the present invention, a configuration of a semiconductor sensor such as a thermistor, a diode or a transistor is also possible.

Next, a third embodiment of the present invention will be described. FIG. 19 is a plan view showing a measuring element 1 for a thermal air flow meter according to a third embodiment of the present invention. The difference of the third embodiment from the second embodiment shown in FIG. 16 is that the second embodiment is a direct heating type in which a heating current flowing through the heating resistor 3 is used as a flow rate signal. The third embodiment uses the same temperature difference detection type as the conventional example shown in FIG. 21 in which the flow rate and the flow direction are output from the temperature difference between the temperature measuring resistors 27a and 27b arranged upstream and downstream of the heating resistor 26. There is a point.

The configuration of the third embodiment differs from that of the second embodiment in the flow rate detection method. However, the humidity sensor 5, the temperature compensation resistor 4a, and the temperature sensors 25 and 4b are provided on the measuring element 1. It is formed in the same manner as in the embodiment, and the humidity (H), the support portion temperature (Tw), and the intake air temperature (Ta) are controlled by the control circuit 15b.
, Correction data relating to the air flow rate-humidity characteristic, the air flow rate-supporting part temperature characteristic, and the air flow rate-intake temperature characteristic relating to the measuring element 1 of the third embodiment is stored in the memory 15c in advance. This enables humidity correction, support portion temperature correction, and intake air temperature correction as in the second embodiment. The heating resistor of the third embodiment corresponds to the heating resistor 26, the temperature measuring resistors 27a and 27b, and / or the temperature compensating resistor 4a.

Next, a fourth embodiment of the present invention will be described. FIG. 20 is a plan view showing a measuring element 1 for a thermal air flow meter according to a fourth embodiment of the present invention.
The fourth embodiment differs from the second embodiment shown in FIG. 16 in that the second embodiment is a direct heating type in which the heating resistor 3 itself heats and detects the temperature. The present embodiment is characterized in that an indirectly heated system is used in which the temperature of the heating resistor 26 is detected by a temperature measuring resistor 27 disposed near the heating resistor 26. In this type of flow rate measurement, the temperature measuring resistor 27 heated indirectly by the heating resistor 26 is set to have a certain temperature higher than the temperature of the temperature compensating resistor 4a. At this time, the heating current flowing through the heating resistor 26 is Control circuit 1
5b.

The configuration of the fourth embodiment differs from that of the second embodiment in the flow rate detection method. However, the humidity sensor 5, the temperature compensating resistor 4a, and the temperature sensors 25 and 4b are provided on the measuring element 1. It is formed in the same manner as in the embodiment, and the humidity (H), the support portion temperature (Tw), and the intake air temperature (Ta) are controlled by the control circuit 15b.
The correction data of the air flow rate-humidity characteristic, the air flow rate-support temperature characteristic, and the air flow rate-intake temperature characteristic of the measuring element 1 of the fourth embodiment is stored in the memory 15c in advance. As in the second embodiment, humidity correction, support portion temperature correction, and intake air temperature correction can be performed.
The heating resistor and the like according to the fourth embodiment include a heating resistor 26,
This corresponds to the temperature measuring resistor 27 and / or the temperature compensating resistor 4a.

The first, second, third and fourth embodiments have been described above. However, even if the air flow rate detection method is other than the above, at least the heating resistor 3 (or 26)
If the humidity sensor 5 and / or the temperature sensor 25 are formed between the heating resistor 3 and the terminal electrode 8, the humidity (H), the support portion temperature (Tw), and the intake air temperature (Ta) ) Is input to the control circuit 15b, so that the correction data relating to the air flow rate-humidity characteristic, air flow rate-support temperature characteristic, and air flow rate-intake temperature characteristic of the measuring element 1 to be used is stored in the memory 15c in advance. By doing so, humidity correction, support portion temperature correction, and intake air temperature correction can be performed in the same manner as in the present embodiment. In this embodiment, the control circuit 15b and the memory 15c are separated from each other. However, it is needless to say that the effect of the present invention is not changed even when the control circuit 15b has the memory 15c built therein.

Next, a specific example of a measuring element for a thermal air flow meter according to the present invention will be described with reference to FIGS. First, silicon dioxide, silicon nitride, or the like is formed as an electric insulating film 7a on the silicon semiconductor substrate 2 to a thickness of about 0.5 μm by a method such as thermal oxidation or CVD. Further, a heating resistor 3 and a temperature compensating resistor 4 as a heating resistor and the like are provided.
And the electrodes 10a and 10b constituting the humidity sensor 5,
After being formed on the same substrate by a method such as sputtering with platinum having a thickness of about 0.2 micron, a resist is formed in a predetermined shape by a known photolithography technique, and the platinum is patterned by a method such as ion milling. . Next, after the terminal electrode 8 is formed by gold plating or the like, a portion other than the terminal electrode 8 is used as a protective film, and the electric insulator 7b is formed in a thickness of about 0.
Formed to a thickness of 5 microns. Finally, silicon substrate 2
The cavity 6 is formed by anisotropic etching using silicon dioxide or the like as a mask material from the back surface of the substrate, and cut into chips to obtain the measuring element 1.

[0047]

According to the present invention, at least the heating resistor 3 and the temperature compensating resistor 4a are provided on the semiconductor substrate 2 with the electric insulating film 7 interposed therebetween, and the humidity sensor 5 and the temperature sensor 5 are provided between the heating resistor 3 and the terminal electrode 8. Temperature sensor 25 and measuring element 1 formed with
A drive detection circuit means 15a for supplying a current;
A control circuit 15b for calculating and processing an air flow signal of the measuring element 1 and outputting the same, and a memory 15c in which correction data corresponding to the humidity and the temperature of the supporting portion detected from the humidity sensor 5 and the temperature sensor 25 are stored in advance. As a result, air flow-humidity characteristics and air flow-
A thermal air flow meter having excellent temperature characteristics of a support and a measuring element for the thermal air flow meter are provided.

[Brief description of the drawings]

FIG. 1 is a plan view showing a measuring element for a thermal air flow meter according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the measuring element taken along line A-A 'of FIG.

FIG. 3 is a sectional view showing a humidity sensor of a first embodiment according to the present invention.

FIG. 4 is a sectional view showing a thermal air flow meter according to an embodiment of the present invention.

FIG. 5 is an enlarged view showing the measuring element unit of FIG.

6 is a sectional view of the measuring element section taken along line C-C 'of FIG.

FIG. 7 is a block diagram showing a thermal air flow meter according to the present invention.

8 is a diagram showing a partial electric circuit of the thermal air flow meter of FIG.

FIG. 9 is a diagram showing an equivalent electric circuit of the humidity sensor of FIG. 1;

FIG. 10 is a diagram showing the relationship between the relative humidity of intake air and the capacitance of a humidity sensor.

FIG. 11 is a diagram showing an air flow rate-humidity characteristic of the thermal air flow meter according to one embodiment of the present invention.

FIG. 12 is a sectional view showing a humidity sensor according to a second embodiment of the present invention.

FIG. 13 is a sectional view showing a humidity sensor according to a third embodiment of the present invention.

FIG. 14 is an enlarged view showing a measuring element unit according to another embodiment of the present invention.

FIG. 15 is a sectional view showing a humidity sensor according to a fourth embodiment of the present invention.

FIG. 16 is a plan view showing a measuring element for a thermal air flow meter according to a second embodiment of the present invention.

FIG. 17 is a diagram showing a measuring element part of a thermal air flow meter using the measuring element of FIG. 16, and a temperature distribution on the line EE ′ of the measuring element part.

FIG. 18 is a diagram showing correction of a support portion temperature and correction of intake air temperature according to an embodiment of the present invention.

FIG. 19 is a plan view showing a measuring element for a thermal air flow meter according to a third embodiment of the present invention.

FIG. 20 is a plan view showing a measuring element for a thermal air flow meter according to a fourth embodiment of the present invention.

FIG. 21 is a plan view of a measuring element for a conventional thermal air flow meter.

FIG. 22 is a block diagram of a conventional thermal air flow meter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Measuring element, 2 ... Semiconductor substrate, 2a ... Support part, 3, 2
6, 10e, 10f: heating resistor, 4, 4a: temperature compensation resistor, 4b, 25: temperature sensor, 5: humidity sensor,
6, 6a, 6b: cavity, 7, 7a, 7b: electric insulating film,
8, 8a to 8n, 16: terminal electrode, 9: air flow, 10a
-10d: electrode, 11: membrane, 12: intake passage, 13: sub passage, 14: support, 14a: protector, 15: external circuit, 15a: drive detection circuit, 15b: control circuit, 15c
... memory, 17 ... gold wire, 18 ... thermal air flow meter, 19 ...
Differential amplifier, 20: transistor, 21: power supply, 22
a, 22b: resistance, 23a, 23b: piezo resistance, 24
... vent holes, 27, 27a, 27b ... resistance temperature detectors, 28
a, 28b, 28c ... hollow, 29a, 29b ... bridge.

Claims (5)

[Claims] 1. A measuring element for a thermal air flow meter having a humidity sensor formed on the same substrate on which a heating resistor and the like for measuring an air flow rate are formed, and a current is supplied to the measuring element to supply air to the measuring element. A drive detection circuit for detecting a flow rate signal, a control circuit for calculating an air flow rate from the air flow rate signal, and a memory storing correction data for air flow rate-humidity characteristics, wherein the control circuit includes the humidity sensor A thermal air flow meter, wherein the air flow rate is corrected from the humidity detected by using the correction data and the correction data. 2. A humidity sensor formed on the same substrate on which a heating resistor or the like for measuring an air flow rate is formed, and the heating resistor of heat transmitted when the substrate is mounted on another component. A measuring element for a thermal air flow meter having a temperature sensor for detecting a representative temperature indicating an influence on the air flow meter, a drive detection circuit for supplying a current to the measuring element and detecting an air flow signal, and the air flow signal A control circuit that calculates an air flow rate from a memory that stores correction data of air flow rate-humidity characteristics and air flow rate-support portion temperature characteristics. A thermal air flow meter, wherein the air flow rate is corrected based on the temperature of the support portion obtained from the temperature sensor and the correction data. 3. The thermal air system according to claim 1, wherein said humidity sensor is covered with a protective body having a ventilation hole for preventing direct exposure to an air flow. Flowmeter. 4. A humidity sensor is formed on the same substrate on which a heating resistor for measuring an air flow rate is formed, at a position outside a streamline region of the air touched by the heating resistor. Measuring element for thermal air flow meters. 5. A measuring element for a thermal air flow meter according to claim 4, wherein said humidity sensor is covered by a protective body having a ventilation hole.