JP2690660B2 - Thermal air flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for radio wave interference of a thermal type air flow meter which measures an air flow rate using a heating resistor.

[0002]

2. Description of the Related Art In a thermal type air flow meter for measuring the intake air amount of an internal combustion engine, it has been proposed that the body having a suction air passage be made of synthetic resin in order to reduce its weight.

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, as a measure for improving the electromagnetic interference resistance characteristic, as disclosed in Japanese Patent Laid-Open No. 64-10127, there is a method in which an electromagnetic shield tube is inserted into the body to cover the periphery of the heating resistor. Proposed.

[0005]

In this structure, the connection between the peripheral edge of one end of the electromagnetic shield tube and the metal base of the drive circuit mounted on the outer wall of the body is adhered by an adhesive or welded. However, in the case of this type of thermal air flow meter that is set in the intake body of an engine with severe vibration and thermal environment, the electrical connection is poor and workability is poor due to peeling of the adhesive, fatigue of the welded part, etc. Not good.

No specific connection between the conductive case and the ground has been mentioned, and a simple and highly reliable earth connection measure has been desired.

The present invention has been made in view of the above points, and it is possible to improve the radio wave interference resistance when a resin body is used for the purpose of weight reduction by an inexpensive and highly reliable method. is there.

[0008]

Means for Solving the Problems In order to achieve the above object, the following means for solving the problems are basically proposed.

One is a thermal air flow meter in which a heating resistor for measuring an air flow rate is arranged inside the body of the intake air passage, and a drive circuit for the heating resistor is attached to the outer wall of the body. , The heating resistor is covered with an electromagnetic shield tube having a hole through which intake air passes, and the electromagnetic shield tube is
A flange is integrally formed on one end of the body by deep drawing, and the electromagnetic shield tube is fixed inside the body with the flange fixed and interposed between the conductive base of the drive circuit and the outer wall of the body. The electromagnetic shield tube was incorporated and grounded via the flange and the base (this is the first means for solving problems).

Another is to propose an electromagnetic shield tube for covering the heating resistor, which is integrally formed with the shield case of the drive circuit by deep drawing and incorporated into the body (this is the second problem solving means). And).

[0011]

By using a metal deep-drawing shield tube, the cost of parts can be reduced, and a thin product with a thickness of about 0.3 can be manufactured, which is a solution in line with the purpose of weight reduction.

As in the first means for solving the problems, a flange is provided on the electromagnetic shield tube, and the flange is interposed between the conductive base of the heating resistor drive circuit and the outer wall of the flowmeter body. By doing so, the contact area between the electromagnetic shield tube and the conductive base can be widened by the flange, and the mechanical connection (adhesion, welding,
Reliability (eg, fixing with screws), and thus the reliability of the ground connection.

In addition to the above connection, a nut is attached to the flange of the electromagnetic shield pipe by welding or by barring, and a mounting screw portion is provided, and the nut or screw portion is used to form the base of the drive circuit. Further secure connection is possible by screwing together with.

As in the second means for solving the problems, the electromagnetic shield case of the drive circuit (the shield case is connected to the ground terminal) and the electromagnetic shield tube of the heat-generating resistor are integrally molded to further improve the efficiency. The reliability of the ground of the electromagnetic shield tube and the assemblability of the device are improved.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

1 to 4 show a first embodiment of the present invention. FIG. 1 is a radial sectional view of a thermal air flow meter according to this embodiment, and FIG. 2 is an axial sectional view thereof. 3 is an open plan view of the case of the drive circuit, and FIG. 4 is a vertical sectional view and a plan view of the electromagnetic shield tube used in this embodiment.

As shown in FIGS. 1 and 2, the thermal type air flow meter comprises a body 11 having a main air passage 10 and a bypass air passage 9, and a heating resistor arranged in the bypass air passage 9 for measuring an air flow rate. 1, a temperature compensation resistor 5, a drive circuit 7 for these resistors, a base 2 of the drive circuit, a shield case 8 and the like.

The heating resistor 1 is of a hot wire type in which a platinum wire is wound on an alumina bobbin and the surface thereof is coated with a glass material. The heating resistor 1 is welded to a support pin 4. The temperature compensating resistor (cold wire) 5 has the same structure as the heat generating resistor 1 and is welded to the support pin 4. The support pin 4 is embedded in the synthetic resin columnar holder 3 leaving the tip (the portion where the heat generating resistor 1 and the temperature compensating resistor 5 are present), and is electrically connected to the drive circuit 7 via the aluminum wire 6. There is.

The drive circuit 7 is housed in a shield case 8 formed of a conductive member, fixed to the bottom of the case 8 with an adhesive, and the case 8 is covered with a shield cover 20.

The shield case 8 is mounted on the base 2 and fixed by an adhesive, and is electrically connected to the base 2.

The holder 3 with the heating resistor 1, the temperature compensating resistor 4, the base 2 and the shield case 8 containing the drive circuit 7 are integrally assembled and housed in the housing 18. It is modular. The module is attached to the outer wall of the body 11 by fixing the housing 18 and the base 2 with screws or the like.

In this case, the holder 3 is inserted into the hole 11a provided in the body 11 and is perpendicular to the flow path, and the heat generating resistor 1 and the temperature compensating resistor 4 are set in the bypass air passage 9.

The electromagnetic shield tube 15 is inserted and fixed to the wall surface of the hole 11a (details of this fixation will be described later), and the holder 3 is covered with the electromagnetic shield tube 15 and the hole 1a is formed.
1a will be inserted.

An example of the electromagnetic shield tube 15 is shown in FIG.
This will be described below.

The electromagnetic shield tube 15 is formed by deep-drawing a metal, and has a flange 15a integrally formed at one end periphery thereof, and an air passage having a diameter equal to that of the bypass air passage 9 is formed in the shield tube body. Holes 15b are provided, and bolt insertion holes 15c are provided at both ends of the flange 15a.

The electromagnetic shield tube 15 is inserted into the hole 11a of the resin-molded body 11, and as shown in FIG. 1, the flange 15a has the module installation portion 11 on the outer wall of the body 11.
It is fixedly arranged on the plane b. In the module installation portion 11b, a nut 21 is molded at a position corresponding to the bolt insertion hole 15c of the flange 15a, and the bolt 16 is inserted into the housing 18, the base 2, and the bolt insertion hole 15c of the flange 15.
The whole circuit module of the air flow meter is attached to the outer wall of the body 11 by screwing the nut 21 through the nut 21, and the flange 15a is fixed and interposed between the module installation portion 11b of the outer wall of the body 11 and the base 2 ( The electromagnetic shield tube 15 is inserted and fixed to the body 11 in a sandwiched form. Thereby, the base 2 and the flange 15a
Securely and firmly contact each other, and the base 2 and the electromagnetic shield tube 15 are electrically connected.

Further, the base 2 maintains electrical continuity with the shield case 8 as described above, and since the shield case 8 is grounded, the electromagnetic shield tube 15 also includes the base 2.
Will be grounded through. Reference numeral 22 shown in FIG. 3 is a ground wire of the drive circuit 22.

In such a structure, a current for heating the heating resistor 1 to a constant temperature is supplied by the drive circuit 7. This heating current is controlled by the function of the temperature compensation resistor 4 so that the difference between the temperature of the heating resistor 1 and the air temperature is kept constant regardless of the amount of intake air.

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 flow rate is passed, a low current is passed to maintain a constant temperature. There is a monotonically increasing function relationship between the electric current 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 electromagnetic interference because a weak current is passed depending on the air flow rate. Therefore, the drive circuit 7 itself is covered by the shield case 8 and the shield cover 20, and 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. The wire 13 is connected to the shield base 8 via the feedthrough capacitor 14 to improve the resistance to radio interference.

Further, since the body 11 is made of synthetic resin for the purpose of weight reduction, the heat generating resistor 1, the temperature compensating resistor 5 and the support pin 4 are easily affected by the electromagnetic waves from the outside. In the embodiment, these elements 1, 5, 4 and the like are covered by the electromagnetic shield tube 15, so that the resistance to radio interference can be improved. In addition, since it was an aluminum body in the past, the resistance to radio interference was at a level without problems.

The electromagnetic shield tube 15 in this embodiment is
By including the flange 15a, the electromagnetic shield tube 15 and the base 2 can be securely fixed to each other with the bolt 16 via the flange 15a, and the reliability of mechanical and electrical connection between the shield tube 15 and the base 2 can be enhanced. . Further, the shield tube 15 is grounded simply by tightening the shield tube 15 and the flange 15a with the bolt 16, and the earth connection can be simplified.

FIG. 5 shows the anti-jamming characteristics when a resin body is used. By providing a shield tube, the same anti-jamming characteristics as when an aluminum body is used can be obtained.

FIG. 6 (a) shows the body 11 of the second embodiment of the present invention, and FIG. 6 (b) shows the construction of a single electromagnetic shield tube 15 used in this embodiment. In the figure, the same reference numerals as those in the first embodiment are the same or common elements (note that in FIG.
The same applies to the reference numerals used in the subsequent drawings).

The difference from the first embodiment is that a nut 17 is integrated with the flange 15a of the electromagnetic shield tube 15 by welding, and this electromagnetic shield tube 15 has a resin body 11a.
It is in the point that it is integrally molded. By integrating the electromagnetic shield tube 15 with the nut 17 and the body 11, it is possible to reduce the number of steps during assembly.

FIG. 7 shows the flange 15 of the electromagnetic shield tube 15.
The screw portion 15d (the bolt 16 shown in FIG. 1 is attached to the same portion 15d) is integrally formed with a, and in this case also, the electromagnetic shield tube 15 is integrally molded with the resin body 11. It

FIG. 8 shows a fourth embodiment of the present invention. The difference between this embodiment and each of the above-described embodiments is that the electromagnetic shield is used.
The shield tube 8 and the shield tube 8 are integrally formed by deep drawing, and the electromagnetic shield tube 15 is incorporated in the body 11. In addition, the electromagnetic shield tube 15 and the holder 3 for the heating resistor are integrally formed.

According to this embodiment, by adopting the above configuration, the shield case 8 is further simplified while the assembly process is further simplified.
It is not necessary to connect the electromagnetic shield tube 15 with the electromagnetic shield tube 15, and the reliability of the electrical connection can be improved.

Incidentally, in this embodiment, it is possible to further develop it and integrally mold it with the holder 3 including the conductive base 2 and the housing portion 18.

[0040]

According to the present invention, when the resin body is used, the earth connection of the electromagnetic shield tube can be performed with a simple structure and with high reliability of mechanical and electrical connection, and the anti-electromagnetic interference characteristics can be improved. It is possible to satisfy the cost reduction.

If the present invention is applied to an aluminum body, the resistance to radio interference can be further improved.

[Brief description of the drawings]

FIG. 1 is a radial cross-sectional view of an intake air flowmeter showing a first embodiment of the present invention.

FIG. 2 is a sectional view in the axial direction of the first embodiment.

FIG. 3 is a plan view showing the opening of the first embodiment.

FIG. 4 is a vertical sectional view and a plan view of an electromagnetic shield tube used in the first embodiment.

FIG. 5 is an explanatory diagram showing the resistance to radio interference.

FIG. 6 is a partial radial cross-sectional view of a body of an air flow meter according to a second embodiment of the present invention and a vertical cross-sectional view of an electromagnetic shield tube used for the same.

FIG. 7 is a sectional view showing a part of an electromagnetic shield tube used in the third embodiment of the present invention.

FIG. 8 is a vertical sectional view showing a circuit module of a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating resistor, 2 ... Base, 3 ... Holder, 7 ... Drive circuit, 8 ... Shield case, 11 ... Body, 15 ... Shield tube, 15a ... Flange, 16 ... Bolt, 21 ... Nut

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-159020 (JP, A) JP-A-3-257328 (JP, A) JP-A 63-229327 (JP, A) JP-A 64-- 10127 (JP, A)

Claims (4)

(57) [Claims] 1. A heating resistor for measuring an air flow rate is disposed inside a body of an intake air passage, and an outer wall of the body is provided with:
In a thermal type air flow meter to which a drive circuit for the heating resistor is attached, the heating resistor 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 at one end. A flange is integrally formed on the periphery, and the electromagnetic shield tube is incorporated inside the body with the flange fixed and interposed between the conductive base of the drive circuit and the outer wall of the body. A thermal air flow meter, which is grounded via the flange and the base. 2. The flange of the electromagnetic shield tube according to claim 1, wherein a nut is provided on the flange of the electromagnetic shield tube by welding or by a barring process, and the electromagnetic shield tube with the flange is formed by resin molding. A thermal air flow meter, characterized by being integrally molded with the body. 3. A heating resistor for measuring an air flow rate is arranged inside the body of the intake air passage, and an outer wall of the body is provided with:
In a thermal type air flow meter to which a drive circuit for the heat generating resistor is attached, the heat generating resistor is covered with an electromagnetic shield tube having a hole through which intake air passes, and the electromagnetic shield tube is provided with a shield case of the drive circuit and a depth. A thermal air flow meter, which is integrally formed by drawing and incorporated in the body. 4. The body according to claim 1, wherein the body has a main air passage and a bypass air passage as an intake air passage, and the bypass air passage is covered with the electromagnetic shield pipe. A thermal air flow meter, in which a heating resistor for measuring the air flow rate is disposed.