JPH07306072A - Heat-generating resistance body for apparatus for measuring flow rate of air - Google Patents

Abstract

PURPOSE:To improve a measuring accuracy for a flow rate of air in a range of high flow rates in an apparatus measuring an air flow rate. CONSTITUTION:A cross section of a supporting body 2 holding a resistance body 1 of a heat-generating resistance body 5 is made elliptic or streamline, thereby improving an accuracy of an apparatus for measuring an air flow rate. The effect is noticed particularly in a range of high flow rates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating resistor for an air flow measuring device for measuring the amount of air taken into an internal combustion engine of an automobile.

[0002]

2. Description of the Related Art At present, as an exothermic resistor for an air flow measuring device, there is an example described in Japanese Patent Application Laid-Open No. 56-108907.
In this known example, the support for holding the heating resistor is a cylindrical pipe made of alumina. In addition, a plate-shaped heating resistor has been made public. The heating resistors of these known examples are installed in an air passage, and have a structure that detects the air flow rate by heat transfer when the air flow contacts the heating resistor.

However, when measuring a large amount of air flow in the known heating resistor, Karman vortices are apt to occur behind the heating resistor and the temperature sensitive resistor due to the large fluid resistance in the shape of a circle or plate. It becomes a state. When the Karman vortex occurs, a problem that the accuracy of measuring the air flow rate deteriorates occurs.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to meet the high precision required for an air flow rate measuring device.

[0005]

In order to achieve the above object, the support made of an insulating material for holding a resistor is made to have an elliptical or streamline cross-sectional shape.

[0006]

[Operation] When an obstacle is installed in the air passage, Karman vortices are generated behind the obstacle, causing fluid resistance and blocking the air passage. Therefore, an apparent pressure loss occurs in the air passage. The air velocity in the air passage becomes slower. Due to this apparent pressure loss, an air flow measurement error occurs. In the case of an air flow rate measuring device, the obstacles installed in the air passage are a heating resistor and a temperature sensitive resistor, and when a Karman vortex is generated, heat transfer to the air is affected by the Karman vortex, which is normal. May cause heat transfer in different states, resulting in errors.

If the heating resistor installed in the air passage has a shape and structure that suppresses the generation of Karman vortices as much as possible, the accuracy of the air flow rate measurement can be kept stable from low flow rate to high flow rate. Particularly, in order to suppress the generation of Karman vortices, it is effective to devise the cross-sectional shape of the heating resistor.
Formula (1) is a general formula that represents the fluid resistance of an obstacle installed in the air flow.

[0008]

[Equation 1]

D: Fluid resistance u: Flow velocity in passage C _D : Resistance coefficient A: Cross-sectional area of support ρ: Density of air From equation (1), the fluid resistance in the air passage is affected by the square of the air flow velocity. , It is proportional to the resistance coefficient, and it can be seen that the influence of fluid resistance increases as the flow rate increases. It has been known in the equation (1) that the resistance coefficient of the obstacle itself, which is installed in the air flow, differs depending on the sectional shape of the heating resistor. Since this resistance coefficient is proportional to the projected area of the obstacle against the air flow, it is effective to use a shape with a small projected area such as a circle, an ellipse rather than a plate, or a streamline. When the heating resistor has a circular cross section, the resistance coefficient is 0.68 to 1.2, whereas when the elliptical shape has a resistance coefficient of about 0.6.
Is 6. Further, when the cross-sectional shape is streamlined, the resistance coefficient ≦ 0.1 is possible, though it depends on the shape. Therefore, the resistance coefficient can be reduced by making the cross-sectional shape of the heating resistor elliptical or streamlined, and the effect of further reducing the fluid resistance can be expected to suppress the generation of Karman vortices, particularly in the high flow rate region. This has the effect of improving the accuracy of air flow measurement.

[0010]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a heat-generating resistor and a temperature-sensitive resistor which have reduced fluid resistance according to the present invention. 2, FIG. 3, FIG. 4, and FIG. 5 are embodiments of the heat-generating resistor and the temperature-sensitive resistor that reduce the fluid resistance of the present invention. FIG. 6 shows the effect of the present invention on the air flow rate measuring device. FIG. 7 is a sectional structural view of the air flow rate measuring device.

The present invention has been invented for the purpose of improving the accuracy of measuring an air flow rate of an air flow rate measuring device. An example will be described with reference to FIG. The heat-generating resistor and the temperature-sensitive resistor used in the air flow rate measuring device are formed by spirally winding a resistor 1 made of a conductive metal around a support 2 made of an insulator. The support 2 is characterized in that its cross-sectional shape is elliptical, and is a strip provided with holes in the horizontal direction. Leads 3 made of a conductive metal are bonded and fixed to both ends of this hole with an adhesive 4 or the like. The resistor 1 is welded to both ends of the lead 3 to become the heat generating resistor 5 or the temperature sensitive resistor 6 having a predetermined resistance value. Further, the surface of the resistor 1 is coated with glass or the like 7 to protect the resistor 1.
It is a structure that has been applied.

The heating resistor 5 in which the resistor 1 is wound around the support 2 having an elliptical cross section has a smaller projected area with respect to the air flow than when the support 2 has a circular cross section. Therefore, the resistance coefficient to the air flow is reduced. The fluid resistance is proportional to the square of the flow velocity of the air passing through the air passage, and is proportional to the resistance coefficient, so that the accuracy of the air flow rate measurement is improved particularly in a high flow rate range as compared with the case where the support 2 has a circular cross section. effective.

FIG. 2 shows an embodiment of the present invention shown in FIG. The cross-sectional shape of the support 2 that supports the resistor 1 is characterized by a streamlined wing shape. In the case of a streamlined cross section, the projected area of the support for the air flow is much smaller than that of a circular or elliptical cross section, so that the resistance coefficient can be further reduced. Therefore, the effect of suppressing the generation of Karman vortices generated behind the heating resistor installed in the air passage improves the air flow rate measurement accuracy in the high flow rate range, and is effective in improving the accuracy of the air flow rate measurement device. is there.

FIG. 3 is also an embodiment of the present invention shown in FIG. The resistor 1 is a conductive metal thin film 8 formed on the support 2 by sputtering or vapor deposition. The thin film 8 is trimmed by a method such as a laser so as to have a predetermined resistance value, thereby forming the heating resistor 5. This heating resistor 5 is the support 2
When fixing the leads 3 to the holes provided in the horizontal direction, it is necessary to fix the support 2 and the leads 3 with a conductive adhesive 9 for electrical connection. Also, to protect the thin film 8,
The surface of the thin film 8 is coated with a coating 7 such as glass.

FIG. 4 shows another embodiment of the present invention shown in FIG. A thin film 8 is formed on the surface of the support 2, and the thin film 8 is trimmed to have a predetermined resistance value. In the heating resistor 5, the cross section of the support 2 is streamlined, and similar to the present invention of FIG. This has the effect of improving the accuracy of air flow rate measurement in the high flow rate range.

FIG. 5 is another embodiment of the invention presented in FIG. Two heating resistors 5 having a structure in which a thin film 8 is formed on the surface of a support body 2 having a streamline cross section are prepared, and the leads 3 are placed between the two heating resistors in a state of facing each other.
By fixing with a conductive adhesive 9 with the interposition of, the streamlined supports 2 facing each other are fixed to form the heating resistor 5.

In the case of the heating resistor 5 having a structure in which the streamlined supports 2 face each other, the heating portion area of the heating resistor 5 installed in the air passage, that is, the heat transfer portion area to the air is doubled. Therefore, the Reynolds number is high and it is in a turbulent state, and the air flow in a high flow area where the air flow measurement accuracy is poor due to the generation of Karman vortex, and the air flow in the transition area where noise is large due to the boundary between laminar flow and turbulent Since it can be captured in a wide area, the averaging accuracy of the air flow rate is high, and the measurement accuracy of the air flow rate is improved.

FIG. 6 is an embodiment showing the effect when the heating resistor 5 of the present invention is used in an air flow measuring device. Comparing the heating resistor 5 having a circular cross section with the heating resistor 5 having an elliptical cross section, there is no change in the variation in the air flow rate measurement error in the region where the air flow rate is low.
The variation in the air flow rate measurement error in the high flow rate region is apparently small when the heating resistor 5 having an oval cross section is used, and it can be seen that it is effective in reducing the air flow rate measurement error.

FIG. 7 illustrates the structure of an air flow rate measuring device using the heating resistor of the present invention as an embodiment. Reference numeral 5 is a heating resistor installed in the sub air passage 10. 6 is a temperature-sensitive resistor for temperature compensation, which is installed in the same sub air passage 10 as the heating resistor. Reference numeral 11 is a drive circuit for electrically processing the signal detected by the heating resistor 5. 12 is a main air passage through which most of the air flows.

The heating resistor 5 and the temperature sensitive resistor 6 are both resistors, and resistors having the same temperature coefficient of resistance are used.
Both are electrically connected to the drive circuit 11. The heat generating resistor 5 and the temperature sensitive resistor 6 of the air flow rate measuring device are held by being welded to the pins in the sub air passage 10 through which a part of the intake air passes. This pin is electrically connected to the drive circuit and serves as a terminal for electrically connecting the heating resistor 5 and the drive circuit 11. The drive circuit 11 is a body 13
It is fixed to and becomes an integral structure.

Next, the operating principle will be described. The drive circuit 11 supplies an applied current for heating the heating resistor 5 to a constant temperature. The heating temperature is corrected by the temperature sensitive resistor 6 so that the temperature difference between the heating resistor 5 and the temperature of the intake air detected by the temperature sensitive resistor 6 is always kept constant regardless of the amount of intake air. . Therefore, a high current is supplied when a high flow rate flows through the main air passage 12, and a low current is supplied when a low flow rate flows so that the temperature difference between the heating resistor 5 and the temperature sensitive resistor 6 is always kept constant. In addition, it is the principle of feedback control by the drive circuit 11, and has a structure in which the heating current is detected by a resistor and an output signal is obtained. There is a monotonically increasing function relationship between the applied current supplied to the heating resistor 5 and the intake air flow rate, which is the principle of measuring the intake air flow rate.

[0023]

According to the present invention, there is an effect that it contributes to the improvement of the air flow rate measurement accuracy of the air flow rate measurement device.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a heating resistor of the present invention.

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

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

FIG. 4 is a sectional view of a heating resistor of the present invention.

FIG. 5 is a cross-sectional view of a heating resistor of the present invention.

FIG. 6 is an effect diagram of improving the measurement accuracy of the heating resistor of the present invention.

FIG. 7 is a cross-sectional structural view of an air flow rate measuring device using the heating resistor of the present invention.

[Explanation of symbols]

1 ... Resistor, 2 ... Support, 3 ... Lead, 4 ... Adhesive, 5
… Heating resistor, 6… Temperature sensitive resistor, 7… Coating, 8
... Thin film, 9 ... Conductive adhesive, 10 ... Sub air passage, 11 ...
Drive circuit, 12 ... Main air passage, 13 ... Body.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshinori Oikawa 2477 Kashima Yatsu Kashima, Katsuta City, Ibaraki Prefecture 3 Hitachi Automotive Engineering Co., Ltd.

Claims (5)

[Claims] 1. A heat-generating resistor and a temperature-sensitive resistor used in an air flow rate measuring device, wherein a support made of an insulating material holds a resistor made of a conductive metal forming the heat-generating resistor. A heating resistor for an air flow measuring device, which has an elliptical shape. 2. A heating resistor for an air flow measuring device according to claim 1, wherein a pipe or a cylinder holding the resistor has a streamline cross-sectional shape. 3. In a heating resistor and a temperature sensitive resistor having a structure in which a thin film is formed on an insulating support by sputtering or the like and the thin film is trimmed, the cross-sectional shape of the support is oval. A heating resistor for an air flow rate measuring device, characterized in that 4. A heating resistor for an air flow measuring device according to claim 3, wherein the cross-sectional shape of the support is streamlined. 5. The streamlined support according to claim 3, wherein two streamlined supports are opposed to each other, and a lead wire made of a conductive metal interposed therebetween is fixed by a conductive adhesive or the like. A heating resistor for an air flow rate measuring device, characterized in that the body is fixed while facing each other.