JP2886719B2 - Thermal 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 thermal flow meter for detecting the amount of gas flowing in a gas passage by using a heating resistor element for detecting a flow rate such as a hot wire or a hot film.

[0002]

2. Description of the Related Art Conventionally, various flow meters are provided in a gas passage such as an intake air passage of an internal combustion engine to detect the amount of gas flowing in the gas passage. And
As one of such flow meters, for example, Japanese Patent Publication No. 1-4
There is known a thermal type flow meter using a heating resistor element for detecting a flow rate of a hot wire, a hot film, or the like as disclosed in Japanese Patent Application Laid-Open No. 5009 or the like. By the way, a typical structure of this thermal flow meter is schematically as shown in FIG. 1, where 12 is attached to the gas passage 6 so as to penetrate through the passage wall. The post 10 is arranged so as to be an electrically insulating holder exposed in the gas passage 6 and penetrate through the holder 12 and into the gas passage 6. A heating resistor element 2 for detecting a flow rate of a hot wire, a hot film, or the like is provided in the gas passage inside the post 10.
Further, the thermal resistor element 4 is fixed by welding. Thus, by attaching the holder 12 to a predetermined position such as in the bypass passage 8 of the gas passage 6, the heating resistor element 2 and the heat-sensitive resistor element 4 are supported by the post 10, and At a predetermined position.

[0003] On the other hand, a base 1 is formed on the outside of the gas passage of the holder 12 by forming an outer flange portion thereof.
4 are integrally fixed and the heating resistor element 2 is located at a position straddling the holder 12 and the base 14.
And a control circuit 1 for controlling the operation of the thermal resistor element 4
6 is placed. The control circuit 16 is electrically connected to a portion of the post 10 outside the gas passage by a wire bonding wire 18. The control circuit 16 is usually housed in a shield case 20, and the connection between the control circuit 16 and the post 10 is made through a window provided at the bottom of the case. Thus, in the control circuit 16, the power transistor is driven via the feedback circuit so that the temperature difference between the heating resistor element 2 and the thermosensitive resistor element 4 is always kept constant irrespective of the flowing gas amount. The heating resistor element 2 is controlled to be energized.

In such a thermal type flow meter, heat is generated by a power transistor or the like in the control circuit 16, and the heat is transmitted through the holder 12 or the post 10 to generate the heat-generating resistor element 2 or the heat-sensitive resistor. There is an inherent problem that the detection accuracy of those elements is reduced by affecting the elements 4. Therefore, usually, the base 14 is formed of aluminum or the like, and is used as a heat radiating plate to release heat generated in the control circuit 16. However, in order to reduce the size of the thermal flow meter, the control circuit 1
6 is mounted not only on the base 14 but also on the holder 12, so that the heat generated in the control circuit 16 cannot be transmitted to the holder 12, and Heat may also be transmitted to the resistor element 2 and the thermosensitive resistor element 4 to lower the detection accuracy.

Conventionally, such a holder 12
A resin molded body is used, and the holder 12 is usually molded by a simultaneous molding technique in a state where the post 10 and the base 14 are arranged in a molding die.
Thus, in such an integrally molded article, there is a problem that the position of the post 10 moves and tilts due to the pressure of the resin at the time of molding. As a result, the heating resistor element 2 attached to the post 10 and There is a problem that the position of the heat-sensitive resistor element 4 in the gas passage 6 varies, which adversely affects the output characteristics. Furthermore, the resin shrinks when it solidifies,
Due to the occurrence of sink marks, such a holder 12 has a problem in that the dimensional accuracy of the sealing surface at the mounting portion with respect to the gas passage 6 is difficult to obtain, and gas leaks from the gas passage 6 or outside air enters the gas passage 6. In addition, there is a problem that the positional accuracy of the mounting position with respect to the gas passage 6 is deteriorated.

[0006]

The present invention has been made in view of the above circumstances, and a problem to be solved is that heat generated in a control circuit of a thermal flow meter is generated by a heat generating resistor element and a heat sensitive element. An object of the present invention is to prevent transmission to a resistor element so that the detection accuracy thereof is not adversely affected. Also, so that the position of the post can be held stably,
An object of the present invention is to improve the positional accuracy of a heating resistor element and a thermosensitive resistor element supported by a post. Furthermore, when a resin molded body is used as the holder, it is necessary to reduce the sink mark, improve the dimensional accuracy, and improve the sealing performance between the gas passage and the position accuracy of the mounting position of the holder with respect to the gas passage. It is in.

[0007]

According to the present invention, in order to solve the above-mentioned problem, an electric insulation is provided at a predetermined position of a gas passage so as to penetrate a passage wall portion and is exposed in the gas passage. And a post arranged to penetrate into the gas passage through the holder, and a post attached to the inside of the gas passage of the post, for detecting the amount of gas flowing in the gas passage. A heating resistor element and a heat-sensitive resistor element for detecting the temperature of the flowing gas; and a heating resistor element attached to a gas passage outside portion of the holder, connected to a gas passage outside portion of the post, and the heating resistor element and A thermal flow meter configured to include a control circuit for controlling the thermal resistor element, wherein the holder has a hollow structure in a form in which at least a portion located in the gas passage is closed, One volume of the hollow portion is at least 20%
The gist of the present invention is a thermal flow meter characterized by being a hollow body as described above.

Further, in the present invention, a resin molded body is advantageously used as the holder, and the post is assembled to a through hole provided in an inner portion of the gas passage, and is integrally fixed. The Rukoto.

[0009]

In summary, in the thermal flow meter according to the present invention, the holder has a hollow structure and the hollow portion is formed so as to have a volume of at least 20% or more. The generated heat is less likely to be transmitted to the heat-generating resistor element and the thermo-sensitive resistor element via the holder. Therefore, adverse effects of heat on these resistor elements due to heat can be advantageously prevented, and the detection accuracy is improved, so that the measurement accuracy of the flowing gas amount is improved.

[0010] Further, since the holder has a substantially thin molded body due to the hollow structure, when a resin molded body is used as the holder, "shrinkage" occurs.
Is advantageously reduced. Therefore, the dimensional accuracy of the molded body is increased, the sealing performance with the gas passage is improved, the accuracy of the mounting position with respect to the gas passage is improved, and the measurement accuracy of the flowing gas amount is improved.

Then, by assembling the post after molding the holder, the movement or tilting of the position of the post, which is a problem in the simultaneous molding, can be favorably prevented. Therefore, the positions of the heating resistor element and the thermosensitive resistor element in the gas passage are stabilized,
The measurement accuracy of the flowing gas amount is improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to clarify the present invention more specifically, an example of a thermal flow meter according to the present invention will be described with reference to FIG.
This will be described in detail with reference to FIG.

First, FIG. 2 shows a thermal type flow meter having a structure according to the present invention mounted on a bypass passage 24 of an intake air passage 22 of an internal combustion engine for a vehicle. Here, reference numeral 26 denotes an electrically insulating holder, which is a resin molded body, which is attached to the air passage 22 so as to penetrate the passage wall and is exposed in the air passage 22 as an attachment portion to the air passage 22. 26 so as to penetrate into the air passage 22 through the post 28.
Are arranged. The inside of the air passage of the post 28 is composed of two pairs of lead wires.
A heating resistor element 34 and a heat-sensitive resistor element 36 are welded and fixed to the pair of lead wire portions in a bridging manner. Thus, the heating resistor element 34 and the heat-sensitive resistor element 3
6 is supported by a post 28 and is arranged at a predetermined position in the air passage 22.

The heating resistor element 34 is a flow rate detecting element for detecting the amount of flowing air in the air passage 22.
As is well known, it has a structure in which a platinum wire or a platinum thin film as a resistor is formed on the outer peripheral surface of an alumina pipe. The thermal resistor element 36 is a temperature detecting element for detecting the temperature of the flowing air for temperature compensation, and has a structure similar to that of the heat generating resistor element 34.

On the other hand, an aluminum base 38 is fixed to the outside of the air passage of the holder 26 in the form of an outer flange.
A control circuit 32 for controlling the heating resistor element 34 and the heat-sensitive resistor element 36 is placed and mounted on the upper case in a state of being housed in the shield case 40. Then, in the shield case 40, the control circuit 32
The outside of the air passage of the post 28 is connected by a wire bonding wire 30. The base 38 also serves as a heat radiating plate for releasing heat generated in the control circuit 32.

The operating principle of such a thermal type flow meter is described in detail in Japanese Patent Application Laid-Open No. Hei 2-228524 and Japanese Patent Publication No. Hei 1-45009 and is well known. That is, the temperature difference between the heating resistor element 34 and the thermosensitive resistor element 36 is independent of the amount of air flowing through the air passage 22,
In the control circuit 32, the power transistor is driven via a feedback circuit so that the heating resistor element 34 is energized so as to be always kept constant. Therefore, when the amount of flowing air is large, a high current is applied to the heating resistor element 34, and when the amount of flowing air is small, a low current is applied. It detects. Then, by such continuous energization control, heat is generated in the power transistor and the like.

By the way, in this thermal type flow meter, the holder 26 is formed as a hollow body having a hollow portion 42 having a volume of at least 20% or more of the volume unlike the conventional one. Here, since the hollow portion 42 is open at the outer end surface of the air passage of the holder 26, the holder 26 has a substantially cylindrical shape with a bottom, and the bottom portion is a closed portion. , Air passage 2
It is located within 2.

As shown in FIGS. 3 and 4, a circular through hole 44 is formed in the bottom of the holder 26 so as to correspond to the two pairs of lead wire portions inside the air passage of the post 28. Are formed, and the lead wire portion of the post 28 is pressed into the through hole 44 to
The post 28 is integrally attached to the holder 26. The through hole 44 is formed with a diameter slightly larger than the diameter of the lead wire portion, and
In order to stably support 8, preferably, its length is
It is formed so as to have a length (L) of 3.5 times or more the diameter. 46 is the post 2 at the time of press fitting.
8 are guide protrusions for guiding the lead wire portion 8 to the through hole 44.

In the thermal type flow meter having such a structure,
Since the holder 26 has a hollow structure, the control circuit 3
The heat generated in the post 2 passes through the holder 26 and
8, and furthermore, it is difficult to transmit to the heating resistor element 34 and the heat-sensitive resistor element 36, and the adverse effect of heat is reduced, so that the detection accuracy can be advantageously improved. In addition, the holder 26 becomes a thin resin molded body due to the presence of the hollow portion 42, and “sink” at the time of molding can be advantageously reduced, so that the dimensional accuracy is increased and the sealing property with the air passage 22 is improved. In addition, the accuracy of the mounting position with respect to the air passage 22 is improved, and the accuracy of air flow measurement is improved.

Then, by assembling the post 28 after the holder 26 is formed, the movement and tilting of the position of the post 28, which are problems in the simultaneous molding, can be prevented well. Further, by forming the through hole 44 for mounting the post provided in the holder 26 so as to have a length of 3.5 times or more the diameter of the hole, the tilting of the post 28 can be advantageously prevented. . Therefore, the stabilization of the positions of the heating resistor element 34 and the thermosensitive resistor element 36 improves the air flow measurement accuracy. The base 38 may be formed simultaneously with the holder 26, but if the holder 26 is formed and then assembled by press-fitting or bonding, the work of fitting the base 38 to a molding die can be omitted, and ,
There is an advantage that conditions such as molding pressure can be easily adjusted.

While one embodiment of the present invention has been described in detail above, it goes without saying that the present invention is not limited by the description of such an embodiment. In addition, the present invention, in addition to the above embodiments, unless departing from the spirit of the present invention,
It should be understood that various changes, modifications, improvements, and the like can be made based on the knowledge of those skilled in the art.

For example, in the above embodiment, the cross-sectional shape of the post 28 and the shape of the through hole 44 provided in the holder 26 are circular. However, as shown in FIGS. It can also be square. In this case, in order to advantageously prevent the tilting of the post 28, the length (L) of the through hole 44 in the elliptical through hole 44 as shown in FIG. Is preferred. Further, in the polygonal through hole 44 as shown in FIG. 6, it is preferable that the length (L) of the through hole 44 is 3.5 times or more the length of the shortest side.

[Brief description of the drawings]

FIG. 1 is an explanatory longitudinal sectional view showing an example of a conventional thermal flow meter.

FIG. 2 is an explanatory longitudinal sectional view showing an example of a thermal flow meter having a structure according to the present invention.

FIG. 3 is an enlarged sectional view showing a section taken along line III-III of the holder of FIG. 2;

FIG. 4 is an enlarged explanatory view showing a part of the holder of FIG. 2 in an enlarged manner.

FIG. 5 is an explanatory view corresponding to FIG. 3, showing a different example of the holder.

FIG. 6 is an explanatory view corresponding to FIG. 3, showing still another example of the holder.

[Explanation of symbols]

 Reference Signs List 22 air passage 24 bypass passage 26 holder 28 post 30 wire bonding wire 32 control circuit 34 heating resistor element 36 heat-sensitive resistor element 38 base 42 hollow portion 44 through hole

Claims (2)

(57) [Claims] 1. An electrically insulating holder which is mounted at a predetermined position of a gas passage so as to penetrate a passage wall and is exposed in the gas passage, and penetrates into the gas passage through the holder. A heating resistor element for detecting the amount of flowing gas in the gas passage, and a heat-sensitive resistor for detecting the temperature of the flowing gas, which are attached to the inside of the gas passage of the post. And a control circuit attached to the outside of the gas passage of the holder, connected to the outside of the gas passage of the post, and configured to control the heating resistor element and the thermosensitive resistor element. The holder is a hollow body having a hollow structure in which at least a portion located in the gas passage is closed, and the volume of the hollow portion is at least 20% or more. Thermal flow meter according to claim Rukoto. 2. The post according to claim 1, wherein the holder is a resin molded body, and the post is assembled and integrally fixed to a through hole provided in an inner portion of the gas passage. 2. The thermal flow meter according to 1.