JPH04291115A - Hot-wire air flowmeter - Google Patents

Abstract

PURPOSE:To block the heat conduction of an exothermic resistor so as to improve the responsiveness and accuracy of a hot-wire air flowmeter by providing a heating resistor on the exothermic resistor. CONSTITUTION:An exothermic resistor substrate 3 constituted by forming patterns of an exothermic and heating resistors 5 and 6 on one surface of a dielectric substrate 7 by vapor deposition, etc., and coating the patterns with an overcoat glass film 8 is connected to a supporting member 10 by means of a connecting member 9 and the member 10 is connected to a circuit board 12 by means of a connecting member 11. Therefore, a hot-wire air flowmeter which is excellent in responsiveness and accuracy can be formed by blocking the heat conduction from the exothermic section by heating near the connecting section on the exothermic resistor.

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 for detecting the intake air flow rate of an internal combustion engine.

0002

[Prior art] A thermal air flowmeter using a film resistor is
A large amount of heat escapes due to heat conduction from the support member at the connecting portion of the film resistor, and a response delay due to this has been a problem. As a countermeasure against this, for example,
According to No. 3, a heating means is provided on the support member of the heating resistor to block heat escape from the heating resistor. Alternatively, according to Japanese Patent Application Laid-Open No. 62-98219, a heat insulating material is provided between the heating resistor and the support member to block heat escape from the heating resistor.

0003

[Problems to be Solved by the Invention] In the above-mentioned prior art, with regard to the method of providing heating means on the support member, the distance between the heating resistor and the heating section is long, and heat escape between them is not taken into account, resulting in a delay in response. There was a problem that performance variations still cannot be resolved. Furthermore, since the heating means is installed on the support member, there is a problem in mass productivity.

On the other hand, regarding the method of inserting a heat insulating material between the heat generating resistor and the support member, there is no flexibility in the bonding method because the bonding material for the heat generating resistor and the support member is limited.
Furthermore, there was a problem in that the vibration resistance of the joint was weak.

An object of the present invention is to form a pattern of the heating means on the dielectric substrate of the heat generating resistor and to place the heat generating part and the heating means adjacent to each other, thereby improving responsiveness and precision, and further improving vibration resistance. Our objective is to provide a thermal air flowmeter that can be easily mass-produced.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a heating means is formed on a dielectric substrate of a heat generating resistor adjacent to a heat generating portion.

Furthermore, in order to improve mass productivity, the heating means is formed at the same time as the heating resistor.

Furthermore, in order to improve vibration resistance, hard brazing is used as the connection method.

Furthermore, in order to achieve the above object, a temperature sensor is provided at the starting point of the heat transfer path that allows heat to escape from the heating resistor, and the temperature of that part is detected to determine the amount of power supplied to the heating resistor. or a separate heating resistor is provided to heat the starting point of the heat transfer path.

0010

[Function] By forming the heating resistor in a separate pattern near the support member of the heating resistor, the heating resistor blocks heat conduction from the heat generating portion, so that responsiveness can be improved.

Furthermore, since the heating resistor is joined to the support member, the amount of heat escaping due to heat conduction varies depending on variations in the joining portion. Although this is caused by variations in accuracy, the heat generating resistor of the present invention has less heat conduction to the joint, so accuracy can be improved.

Furthermore, since the film pattern of the heat generating resistor and the film pattern of the heating section can be formed simultaneously, mass productivity can be improved compared to other heat generating resistor substrates having a heat insulating structure.

Furthermore, since heat insulation is possible on the heating resistor substrate, a material with high thermal conductivity can be used as the bonding material with the support member, so that the bonding portion can be made high in strength.

[0014]

[Embodiment] An embodiment of the present invention will be explained with reference to FIG. Inside the air passage B21B of the body 1, which has an air passage A21A and an air passage B21B for passing the air flow supplied to the engine of the automobile, there is a heating resistor substrate 3 for detecting the air flow rate and a sensor for detecting the air flow temperature. A temperature resistor substrate 4 is installed. Furthermore, the signals detected by the heating resistor board 3 and the temperature-sensitive resistor board 4 are input to a control module 2 fixed outside the body 1, and the structure is such that it outputs a voltage signal corresponding to the air flow rate. ing.

The structure of the heating resistor substrate 3 is shown in FIGS. 2A and 2B. Width 1.0mm, length 10mm, thickness 0.
A heating resistor 5 is formed on one side of a 25 mm dielectric substrate 7 made of alumina by vapor deposition. Furthermore, an overcoat glass 8 is coated on the top of the heat generating resistor 5 to protect the heat generating resistor 5, thereby forming a heat generating resistor substrate 3. The heating resistor substrate 3 is connected to a support member 10 made of glass by a connection member (A) 9 made of hard brazing or low melting point glass, and the support member 10 is connected to a connection member (B) 11 made of epoxy adhesive or the like. This structure is connected to the circuit board 12 by. The heating resistor 6 of the present invention has a dielectric substrate 7 near the connecting portion between the heating resistor substrate 3 and the support member 10.
The heating resistor 5 is formed on the same surface by vapor deposition or the like. Further, the electrode portions of the heating resistor 5 and the heating resistor 6 and the conductive pattern 14 of the circuit board 12 are electrically connected by a flexible wire 13 to constitute a control circuit. By adding the heating resistor 6, there is an effect of suppressing the heat escaping from the heating resistor 5 to the circuit board 12 through the support member 10, and since the heat transfer between the heating resistor 5 and the air flow is reliably performed, the response is improved. This has the effect of providing a thermal air flowmeter with good performance and accuracy.

FIGS. 4, 5, 6 and 7 show other embodiments of the present invention. FIG. 4 shows the heating resistor substrate 3 described in the embodiments of FIGS. 2 and 3 connected to supporting members 10 at both ends. Further, the same number of heating resistors 6 as the number of connections are provided near the connection portions with each support member 10. With this structure, the same effects as those shown in FIGS. 2 and 3 can be obtained, and the vibration resistance is further improved.

5 to 7 show that, in contrast to the embodiments shown in FIGS. 2 and 3, the thermal resistor 6 is formed on one surface other than the surface on which the heating resistor 5 is formed, and heat is generated by the through-hole electrode 15. A connection portion is provided on the surface on which the resistor 5 is formed. This embodiment ensures a degree of freedom in the formation surface of the heat generating resistor 5, and has the effect that a more accurate pattern of the heat generating resistor 5 can be formed.

FIG. 8 shows an example in which the heating resistor substrate 3 is fixed at both ends in contrast to the embodiments shown in FIGS. 5 to 7, and the same effects as in FIGS. 5 to 7 are obtained.

FIG. 9 shows a heating control circuit for the heating resistor 6. As shown in FIG. The heating resistor 6 is electrically connected to the output stage of the constant voltage circuit 16 and is always heated with a constant voltage.

10, FIG. 11, and FIG. 12 show the embodiments shown in FIGS. 2 and 3 in which a heating temperature detection resistor 17 is provided in parallel with the heating resistor 6. In FIGS. Figure 10 is cantilever fixed, Figure 1
1 is fixed at both ends. FIG. 12 shows the control circuit. The heat generating resistor 6 and the heating temperature detecting resistor 17 constitute a bridge circuit, and the heat generating resistor 6 is heated to a constant temperature via an operational amplifier 18 and a power transistor 19. This structure allows highly accurate heating control.

In FIG. 13, in order to always control the heating temperature of the heating resistor 6 with a constant temperature difference with respect to the temperature of the heating resistor 5, a comparator is used to compare the heating current of the heating resistor 5 and the heating current of the heating resistor 6. 20 is a control circuit for constantly comparing the heating current of the heating resistor 6 and a power transistor 19 for controlling the heating current of the heating resistor 6. By adopting this embodiment,
This has the effect of improving responsiveness when airflow suddenly changes.

FIG. 14 shows the temperature distribution of the heating resistor substrate 3 when the heating resistor 6 according to the present invention is employed. The heating temperature of the heating resistor 5 is a maximum of 250° C. and decreases as it approaches the support member 10. The temperature of 10 parts of the support member is about 150°C. from this result,
The heating temperature of the heating resistor 6 is desirably 150° C. or higher, and by setting the temperature to this temperature, the heating resistor 5 is heated to the support member 10.
This has the effect of providing a thermal air flow meter with good responsiveness and accuracy.

[0023]

According to the present invention, by heating the vicinity of the support member of the heat generating resistor to around 150°C, it is possible to prevent heat from escaping from the heat generating resistor to the support member. Since heat is reliably transferred to the air flow, it is possible to provide a thermal air flowmeter with good responsiveness and accuracy.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the thermal air flow meter of the present invention.

FIG. 2 is a front view of the heating resistor substrate of the present invention.

FIG. 3 is a cross-sectional view of the heating resistor substrate of the present invention.

FIG. 4 shows an embodiment of the heating resistor substrate of the present invention.

FIG. 5 is a front view of the heating resistor substrate of the present invention.

FIG. 6 is a cross-sectional view of FIG. 5;

FIG. 7 is a cross-sectional view of FIG. 6;

FIG. 8 shows an embodiment of the heating resistor substrate of the present invention.

FIG. 9 is a drive circuit for the heating resistor substrate of the present invention.

FIG. 10 shows an embodiment of the heating resistor substrate of the present invention.

FIG. 11 shows an embodiment of the heating resistor substrate of the present invention.

FIG. 12 shows a control circuit for the heating resistor substrate of the present invention.

FIG. 13 is a drive circuit for the heating resistor substrate of the present invention.

FIG. 14 shows the temperature distribution of the heating resistor substrate of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1...Body, 2...Control module, 3...Heating resistor board, 4...Temperature sensitive resistor board, 5...Heating resistor, 6...Heating resistor, 7...Dielectric substrate, 8...Overcoat glass, 9...
Connection member (A), 10... Support member, 11... Connection member (B
), 12... Circuit board, 13... Flexible wire, 14
... Conductor pattern, 15... Through-hole electrode, 16... Constant voltage circuit, 17... Heating temperature detection resistor, 18... Operational amplifier, 19... Power transistor, 20... Comparator, 2
1A...Air passage A, 21B...Air passage B.

Claims (14)

[Claims] 1. A body forming an air passage, a heating resistor for detecting the flow rate of air flowing inside the body, a heat-sensitive resistor for detecting the air temperature, and a detection signal from the heat-generating resistor and the heat-sensitive resistor. In a thermal air flowmeter comprising a control module that outputs a signal, the heating resistor is formed of a film resistor, and a heating resistor of a different pattern is provided near the joint of the heating resistor with the support member. A thermal air flow meter characterized by: 2. The thermal air flow meter according to claim 1, wherein the number of heating resistors is provided near the support member in a number corresponding to the number of support points of the heating resistor. 3. In claim 1 and claim 2, the heating resistor is formed on one surface of the dielectric substrate on which the heating resistor is formed, other than the surface on which the heating resistor is formed. Thermal air flow meter. 4. The thermal air flowmeter according to claim 1, wherein a constant voltage is always applied to the heating resistor by a constant voltage circuit provided in the control module, and the heating resistor is heated to a constant temperature. 5. In claim 1 and claim 2, a heating temperature detection resistor is arranged in parallel with the heating resistor in the vicinity of a joint between the heating resistor and the supporting member to detect the temperature of the heating resistor. A thermal air flow meter characterized by being equipped with. 6. The heating type air according to claim 4 and claim 5, wherein the heating temperature of the heating resistor is detected by the heat generating temperature detecting resistor and controlled to always maintain a constant temperature. Flowmeter. 7. The heating resistor according to claim 6, wherein a bridge circuit including the heating resistor and the heating temperature detection resistor is provided in the control module to control the heating resistor so that the temperature is always constant. Thermal air flow meter. 8. The thermal air flowmeter according to claim 1 and claim 4, characterized in that the difference between the heating temperature of the heating resistor and the heating temperature of the heating resistor is controlled to be always constant. . 9. In claim 8, in order to always maintain a constant heating temperature difference between the heating resistor and the heating resistor, a current value flowing through the heating resistor and a current value flowing through the heating resistor are detected; A thermal air flow meter that is characterized by controlling to a predetermined difference. 10. In claim 9, the value of the current flowing through the front heating resistor is determined by measuring the voltage between the heating resistor and a resistor connected in series, and the value of the current flowing through the heating resistor is determined by A thermal air flow meter that measures and detects the voltage across a resistor connected in series with a resistor, compares each voltage using a comparator, and controls the current value of the heating resistor using a power transistor. 11. The heating resistor according to claim 4, wherein the heating temperature of the heating resistor is controlled to 100°C to 200°C. 12. The thermal air flow meter according to claim 1, wherein the heating resistor and the support member are connected by hard brazing or glass. 13. A thermal air flow meter in which a heating resistor detects the amount of heat carried away by the airflow and detects the air flow rate from this amount of heat, wherein the heating resistor detects the amount of heat carried away by the airflow and detects the air flow rate from this amount of heat. A thermal airflow meter characterized in that a temperature sensor is installed at the starting point of a heat transfer path that allows heat to escape, and the power supplied to the heating resistor is corrected based on the output of this sensor. 14. A thermal air flow meter in which a heating resistor detects the amount of heat carried away by the air flow and detects the air flow rate from this amount of heat, wherein the heating resistor detects the amount of heat carried away by the air flow, and the amount of heat from the heating resistor does not contribute to the measurement of the air flow rate. At the starting point of the heat transfer path that allows heat to escape,
A thermal air flowmeter characterized by providing a separate heating resistor and heating it.