JPH06235650A - Heat resistance type air flow rate measuring device - Google Patents

Abstract

PURPOSE:To improve the electric wave interference resistance characteristics and thermal shock durability of an electrical heating resistance type air flow rate measuring device adopting resin body. CONSTITUTION:An electromagnetic shield pipe 15 consisting of alumina or brass is inserted (one-piece molding) into a resin body 11 and external electric wave arriving at an intake air flow rate detection part, etc., is mode to escape to the ground, thus drastically improving the electric wave resistance characteristics and thermal shock durability of an electical heating resistance type air flow rate measuring device adopting the resin body 11 by 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 suitable for preventing radio wave interference.

[0002]

2. Description of the Related Art In an exothermic resistance type air flow rate measuring device for measuring an intake air amount of an internal combustion engine, it has been proposed to form a body with a synthetic resin in order to reduce the weight of a body having the intake air passage. There is.

By the way, when the above-mentioned body is made of resin, it is necessary to take measures against electromagnetic interference in order to prevent noise from entering from the outside. Therefore, conventionally, an electromagnetic shield tube is inserted into the body to cover the periphery of the heating resistor.

[0004]

However, the above-mentioned conventional technique has a problem that a crack is generated in a part of the resin due to a difference in linear expansion coefficient between the resin and the electromagnetic shield tube.

An object of the present invention is to provide a heating resistance type air flow rate measuring device capable of improving the resistance to radio interference and the durability against thermal shock.

[0006]

The above object is to provide a heating resistor for measuring an air flow rate inside a body of an intake air passage made of resin, and to drive the heating resistor on an outer wall of the body. A circuit is attached, and the heating resistor is covered with an electromagnetic shield tube with a hole through which the intake air passes. This electromagnetic shield tube is a deep-drawing tube body with a flange integrally formed on one end periphery, and this flange is the drive The electromagnetic shield tube is incorporated inside the body in a fixed and intervening manner between the conductive base of the circuit and the outer wall of the body, and the electromagnetic shield tube is grounded through the flange and the base. In the resistance type air flow measuring device, it is achieved by setting the material of the electromagnetic shield tube to have a coefficient of linear expansion within 0.5 to 1.5 times that of resin and Young's modulus within 10 times. .

[0007]

By using, for example, aluminum or brass plate as the material of the electromagnetic shield tube, it is possible to prevent cracking of the resin portion due to the thermal shock test. In the case of aluminum, the specific gravity is also light and the weight can be reduced.

[0008]

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

1 to 6 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. A base 2 in which the heating resistor 1 is made of a conductive material.
It is welded to the support pin 4 inserted in the support portion (resin molded product) 3. The temperature sensing resistor 5, which is a temperature compensating resistor for detecting the intake air flow rate, has the same structure as the heat generating resistor 1. The support pin 4 is connected to the drive circuit 7 via the aluminum wire 6.
Is electrically connected to. The drive circuit 7 is fixed to a shield base 8 formed of a conductive member with an adhesive and covered with a shield cover 20. The shield base 8 is fixed to the base 2 with an adhesive and is electrically connected. The heat generation 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 11 formed by a bypass air passage 9 and a main air passage 10. It Further, an electric current for heating the heating resistor 1 to a constant temperature is passed 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 passed through the heating resistor 1, and when a low current flows, 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 and the drive circuit 7 connected to the external harness
The spaces are electrically connected by a wire 13 formed of a conductive member, and the wire 13 is connected to the shield base 8 via the feedthrough capacitor 14 to improve the electromagnetic interference resistance.

Now, the body 11 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. In this embodiment, the electromagnetic shield tube 15 is added. The electromagnetic shield tube 15 is shown in FIG.
As shown in FIG. 6, it is made of thin metal (SUS), has a cylindrical portion 15-a and a mounting flange portion 15-b, and is integrated by deep drawing. The mounting flange portion is electrically connected to the base 2 made of a conductive member by a mounting bolt 16 and is connected to the ground. The mounting flange portion 15-b has a burring portion 15-c, and the nut 17 is press-fitted into this portion. Therefore, it suffices to set the shield tube 15 in the mold at the time of molding, which is effective in reducing the number of steps. FIG. 6 is a detailed sectional view of the press-fitting portion. FIG. 7 shows the resistance to radio interference when a resin body is adopted, and can be greatly improved by providing a shield tube as shown in the figure. When a high temperature and low temperature thermal shock test was carried out in such a structure, a crack was generated in the resin body. The cause is due to the difference in linear expansion coefficient between the resin and the electromagnetic shield tube, and it was solved by changing the material from SUS to aluminum or brass plate. Generally, resin (P.B.
T) has a linear expansion coefficient of 20 to 90 × 10 = ⁻⁶ cm / cm · ° C.,
Young's modulus is 200 to 1000 kgf / mm ² , and SU
Due to the thermal and mechanical properties of S, aluminum and brass, there is no problem if the coefficient of linear expansion of the shield tube is about 18 × 10 ^-6 cm / cm · ° C or higher and the Young's modulus is about 10000 kgf / mm ² or less. I understand.

[0011]

According to the present invention, it is possible to secure measures against radio wave interference and durability against thermal shock by an inexpensive method.

[Brief description of drawings]

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

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

FIG. 3 is a plan view of FIG.

FIG. 4 is a plan view of a shield tube showing an embodiment of the present invention.

5 is a cross-sectional view of FIG.

FIG. 6 is a detailed view of the nut press-fitting portion of FIG.

FIG. 7 is a radio wave interference resistance characteristic diagram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating resistor, 2 ... Base, 5 ... Temperature sensitive resistor, 7 ... Drive circuit, 9 ... Bypass air passage, 10 ... Main air passage, 11 ... Body, 15 ... Electromagnetic shield tube.

Claims (3)

[Claims] 1. A heating resistor for measuring an air flow rate is arranged inside a body of an intake air passage made of resin, and a drive circuit for the heating resistor is attached to an outer wall of the body. The body is covered with an electromagnetic shield tube having a hole through which intake air passes, and the electromagnetic shield tube is a tube body formed by deep drawing, and a flange is integrally formed on one end periphery, and the flange is formed on the conductive base of the drive circuit and the body. In a heating resistance type air flow rate measuring device in which the electromagnetic shield tube is incorporated inside the body in a form fixed and interposed between the outer wall and the electromagnetic shield tube is grounded via the flange and the base, A heating resistance type air flow rate measuring device, wherein the material of the electromagnetic shield tube has a coefficient of linear expansion within 0.5 to 1.5 times that of resin and a Young's modulus within 10 times. 2. The heating resistance type air flow measuring device according to claim 1, wherein the material of the electromagnetic shield tube is:
An exothermic resistance type air flow rate measuring device having a linear expansion coefficient of 18 × 10 ⁻⁶ cm / cm · ° C. or more and a Young's modulus of 10,000 kgf / mm ² or less. 3. A heating resistance type air flow rate measuring device according to claim 1, wherein aluminum or brass is used as a material of the electromagnetic shield tube.