JPH06265387A - Exothermic resistor type air flow rate measuring instrument - Google Patents

Abstract

PURPOSE:To improve the radio wave interference resistance of an exothermic resistor type air flow rate measuring instrument when the body of the instrument is constituted of a resin. CONSTITUTION:By inserting a metallic shield tube 15 into a resin body 18 and actively bringing the shield tube 15 into contact with the metallic base 2 of a drive circuit by means of a pressing means which is made of a conductive material and has a spring property, etc., radio waves arriving at an intake air flow detecting section, etc., from the outside are led to the metallic base 2. Therefore, the radio wave interference resistance of this exothermic resistor type air flow rate measuring instrument using the resin body 18 can be remarkably improved by such a simple method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating resistance type air flow rate measuring device for measuring an intake air flow rate of an internal combustion engine, and more particularly to a measure for improving a radio wave interference resistance characteristic when a body material is made of resin.

[0002]

2. Description of the Related Art In a conventional structure for improving anti-electromagnetic interference resistance, it has been found that the result of measuring the anti-electromagnetic interference resistance is that the voltage drops remarkably at the point where the interference due to radio waves is most prominent. Further, there is no description of concretely or positively dealing with the contact between the shield tube and the metal base.

[0003]

SUMMARY OF THE INVENTION The present invention aims to improve the resistance to radio interference when a resin body is used for the purpose of weight reduction.
This is done by electrically connecting the metal shield tube and the metal base, and it is possible to obtain permanently reliable radio wave resistance with a simple structure.

[0004]

In order to achieve the above object, a heating resistance type air flow measuring device is provided with the following shape.

1) A spring (conductivity) is inserted between the shield tube and the metal base to establish electrical continuity, and further, it is possible to make permanent contact with the elements required as a product.

2) Partially changing the shape of the shield tube so that two parts are extruded and then bent and formed, and the contact method between the shield tube and the metal base is made permanent by utilizing elastic deformation of the shield tube material. Contact.

[0007]

By contacting the metal shield tube with the metal base, the electric charges generated in the shield tube by the radio wave are conducted to prevent the accumulation of the electric charges, thereby preventing the malfunction of the heating resistance type air flow rate measuring device. Also, the permanent contact necessary for commercialization can be dealt with by using a spring action.

[0008]

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

1 to 9 show a typical embodiment of the present invention. Reference numeral 1 is a heating resistor in which a platinum wire is wound around an alumina bobbin and the surface is coated with a glass material. This heating resistor 1 is welded to a support pin 4 inserted in a support portion (resin molded product) 3 of a metal base 2 made of a conductive member. The temperature-sensitive resistor 5, which is a temperature-correcting resistor for detecting the intake air flow rate, has the same structure as the heating resistor 1. The support pin 4 is electrically connected to the drive circuit 7 via an aluminum wire 6. The drive circuit 7 is fixed to a shield base 8 made of a conductive member with an adhesive and covered with a shield cover 9. The shield base 8 is fixed to the metal base 2 with an adhesive and is electrically conductive. The heat generating resistance type air flow rate measuring device in which the drive circuit 7, the heat generating resistor 1 and the temperature sensitive resistor 5 are welded is installed in a bypass air passage of a body 18 formed by a bypass air passage 10 and a main air passage 11. It Further, a current for heating the heating resistor 1 to a constant temperature is supplied by the drive circuit 7. This heating temperature has a constant temperature difference between the heating resistor 1 and the air temperature regardless of the amount of intake air, and the air temperature is corrected by the temperature sensitive resistor 5. Therefore, when a high flow rate flows in the air passage, a high current is applied to the heating resistor 1.
When the flow rate is low, a low current is passed to maintain a constant temperature. There is a monotonically increasing function relationship between the current flowing through the heating resistor 1 and the air flow rate, and the air flow rate is detected by this. As described above, it is necessary to improve the resistance to radio interference because a weak current flows depending on the air flow rate. Therefore, the terminal 12 connected to the external harness and the drive circuit 7 are electrically connected by the wire 13 formed of a conductive member, and the wire 13 is further connected to the shield base 8 via the feedthrough capacitor 14. Improves resistance to radio interference.

Now, the body 18 is made of resin for the purpose of weight reduction. Conventionally, it was an aluminum body, so its radio interference resistance was at a level without problems. However, the use of resin made it necessary to take measures. Therefore, the shield tube 15 is inserted and added. This shield tube is made of a thin metal as shown in FIGS. The mounting flange portion 15'-b is electrically connected to the metal base 2 made of a conductive member by a mounting bolt 16 and is connected to the ground. Further, the mounting flange portion 15'-b has a burring portion 15'-c, and the nut 17 is press-fitted into this portion. The shield tube 15 is a simple method in which it is simply set in the mold when molding the body 18.

FIGS. 6 and 7 show the shape of the shield pipe of the present invention. The shield pipe 15 and the base 2 are in the central portion of the flange so that the shield pipe 15 and the base 2 can be brought into contact with each other other than the flange nut mounting portion like the portion S in FIG. Is provided with a convex portion 15'-d. The purpose of this is to improve the radio wave performance by letting the electric charges generated by the radio waves in the cylindrical portion of the shield tube escape to the ground as soon as possible, and the effect is shown in FIG. The shielded pipe of the present invention has almost no change from the structure of the shielded pipe shown in FIGS. 3 to 4, and since the molding method only needs to be bent after the plastic resin is molded, the processing man-hours are almost the same and the man-hours increase. The problem is avoided. FIG. 8 is a detailed sectional view of the press-fitting portion. FIG. 9 shows the resistance to electromagnetic interference when a resin body is adopted, which can be greatly improved compared to the conventional one.

FIG. 10 shows another embodiment of the present invention, in which the shape of the resin mold portion of A is changed and the portion into which the coil spring 19 is inserted is taken as shown in the figure so as to have a spring action made of a conductive material. It has a structure in which the coil spring 19 having the above is inserted and pressed by the metal base 2 from above. In this case, the shape of the shield tube itself does not change, and the man-hour is also the coil spring 19
There is no problem of increasing man-hours because it is only inserted.

[0013]

According to the present invention, the resistance to radio interference when a resin body is adopted can be maintained at the same level as that of the intake air passage body made of aluminum.

[Brief description of drawings]

FIG. 1 is an axial cross-sectional view of a heating resistance type air flow rate measuring device showing an embodiment.

FIG. 2 is a radial cross-sectional view of FIG.

FIG. 3 is a bottom view of the shield tube showing the embodiment.

4 is a cross-sectional view of FIG.

5 is a view showing a detailed portion of a press-fitting portion of the nut of FIG.

FIG. 6 is a bottom view of the shield tube showing the embodiment of the present invention.

7 is a cross-sectional view of FIG.

FIG. 8 is a radial cross-sectional view of a heating resistance type air flow rate measuring device showing an embodiment of the present invention.

FIG. 9 is a radio wave interference resistance characteristic diagram.

FIG. 10 is a radial cross-sectional view of a heating resistance type air flow rate measuring device showing another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating resistor, 2 ... Base, 5 ... Temperature-sensitive resistance, 7 ... Drive circuit, 10 ... Bypass air passage, 11 ... Main air passage, 15 ... Shield pipe, 15'-d ... Convex part, 18 ... Body, 19 ... Coil spring.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mamoru Tsumaga 2520, Takaba, Katsuta-shi, Ibaraki Hitachi, Ltd., Automotive Equipment Division (72) Inventor Kaoru Uchiyama 2520, Takata, Katsuta-shi, Ibaraki Hitachi, Ltd. Factory Automotive Equipment Division

Claims (3)

[Claims] 1. An intake air passage body made of resin is provided with a passage for intake air to be measured, and a heating resistor is arranged in the passage, and a temperature change of the heating resistor due to contact with the intake air to be measured. A drive circuit for measuring the flow rate of the intake air to be measured from the change in resistance value due to is arranged in the outer peripheral portion of the body, and the drive circuit is incorporated in the body via a metal base, where the heating resistor is In a heating resistance type air flow rate measuring device in which a metal shield tube is integrally molded with the intake air passage body so as to cover it, a protrusion is provided near the central portion of the mounting flange of the shield tube so as to protrude from the resin body, A heating resistance type air flow rate measuring device characterized in that the contact portion is positively contacted. 2. The heating resistance type air flow rate measuring device according to claim 1, further comprising a pressing means for bringing the shield tube and the metal base into contact with each other. 3. The pressing means of the heating resistance type air flow rate measuring device according to claim 2, wherein a coil spring having a spring action made of a conductive material is inserted between the shield tube and the metal base. A heating resistance type air flow rate measuring device having a structure in which the shield tube and the metal base are electrically connected to each other.