JPH07190824A - Thermal flowmeter - Google Patents

Abstract

PURPOSE:To provide a thermal flowmeter which is hard to generate a gap between a base plate and a shield case and has improved durability and measuring accuracy. CONSTITUTION:A coupling state of a conductive cap 31, a base plate 14 and a shield case 20 is improved in this thermal flowmeter. The conductive cap 31 is provided with an engaging part 31a at an end part on the side of an air path. The conductive cap 31 is engaged with the base plate 14 by the engaging part 31a. An end part on the other side is coupled with the shield case by electric resistance welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow meter for detecting a gas flow rate in a gas passage by means of 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 flowmeters are provided in a gas passage such as an intake passage of an internal combustion engine in order to detect the flow rate of the flowing gas. As an example of such a flow meter, as disclosed in Japanese Patent Publication No. 1-45009, a thermal type flow meter using a heating resistor element for flow rate detection such as a hot wire or a hot film is known. .

FIG. 2 shows a typical example of the structure of a conventional thermal type flow meter. In the figure, an electrically insulating holder 12 made of resin
Is attached through the wall portion 6a of the gas passage 6, and the post 10 is attached through this holder 12. The end of the post 10 in the gas passage 6 is
The holder 12 is provided so as to be projected more than an end portion in the gas passage, and the inside end portion of the gas passage of the holder 12 has a heating resistor element 2 and a heat-sensitive resistor element for detecting a flow rate of a hot wire, a hot film, or the like. 4 is welded and fixed. Therefore, by mounting the holder 12 at a predetermined position such as in the bypass passage 8 of the gas passage 6, the heat generating resistor element 2 and the heat sensitive resistor element 4 supported by the post 10 are arranged at the predetermined position in the gas passage 6. Will be done.

On the other hand, the outer end of the gas passage of the holder 12 is inserted into the base plate 14, and the outer end of the gas passage of the post 10 penetrating the holder 12 is connected by a wire bonding wire 18 to both of the resistor elements. It is electrically connected to the control circuit 16 for controlling the circuits 2 and 4. The control circuit 16 is housed in a shield case 20 for protecting the control circuit 16 from electromagnetic noise, and the shield case 20 is mounted on the holder 12 and the base plate 14. The post 10 and the control circuit 16 are electrically connected to each other through a window provided in the shield case 20.

In the gas flow rate detection using the thermal type flow meter thus arranged and arranged, the temperature difference between the heat generating resistor element 2 and the heat sensitive resistor element 4 is caused by the action of the control circuit 16 by the gas passage 6. It is controlled to be constant regardless of the gas flow rate inside. That is, in the control circuit 16, the feedback circuit operates in response to the heat radiated by the gas flow rate to drive the power transistor, and the amount of electricity supplied to the heating resistor element 2 is controlled. In this case, when the gas flow rate is high, a high current is passed through the heating resistor element 2, and when the gas flow rate is low, a low current is passed, and the gas flow rate is calculated from the monotonically increasing function.

The shield case 20 is provided to protect the control circuit 16 from electromagnetic noise, but the shield case 20 is the base plate 1.
4 and the gas passage wall 6a must be grounded. The reason for this is that the shield case 20 is charged by electromagnetic waves and the like in a state where it is not grounded, and the shield effect is lost. Therefore,
In order to electrically connect the shield case 20 and the base plate 14, as shown in FIG.
It has been practiced to embed 0 in the base plate 14 and perform electric resistance welding between the cap 30 and the shield case 20.

[0007]

However, in such a conventional thermal type flow meter, when an external force is applied to the thermal type flow meter in the direction of arrow A as shown in FIG. 4, the shield case 20 and the cap 30 are exposed. And move, shield case 2
0 or a gap is generated between the base plate 14 or the cap 30 is removed from the base plate 14 to reduce the durability of the thermal type flow meter, and the shield effect is lost, which adversely affects the measurement accuracy of the thermal type flow meter. There was a challenge to exert.

Further, in the detection of the gas flow rate by the thermal type flow meter, the power transistor or the like generates heat for controlling the energization amount of the heating resistor element as described above, but the base plate 14 radiates this heat. It also has a function. However, the heat generation function is hindered by the above-described voids, and this heat is generated by the holder 12 and the post 1.
It is transmitted to the resistance elements 2 and 4 via 0, and there is a problem that the measurement accuracy of the thermal type flow meter is deteriorated. The present invention has been made in view of the above problems of the conventional technology, and the purpose thereof is to make it difficult to form a gap between the base plate and the shield case, and to improve the durability and the measurement accuracy. To provide a flow meter.

[0009]

As a result of intensive studies to solve the above-mentioned problems, the present inventor found that the above-mentioned problems can be solved by forming a conductive cap into a specific shape, and completed the present invention. I arrived. Therefore, the thermal type flow meter of the present invention includes a holder mounted through the wall portion of the gas passage, a post penetrating the holder and protruding from the inner end portion of the gas passage of the holder, A heat-generating resistor element and a heat-sensitive resistor element attached to the inner end of the gas passage of the post, a control circuit connected to the outer end of the gas passage of the post to control both of the resistor elements, and this control circuit. In a thermal type flow meter, which is sandwiched between a shield case for accommodating a gas and an outer wall of the gas passage, and has a base plate into which an outer end of the gas passage of the holder is inserted; A conductive cap for electrically connecting the side wall of the gas passage and the outer wall of the gas passage via the base plate, and a locking portion is provided at the end of the cap on the gas passage side. And butterflies.

[0010]

In the present invention, the shield case and the base plate are connected to each other by using the conductive cap having the engaging portion at the end on the gas passage side. Therefore, even if an external force such as vibration is applied, a gap is unlikely to be formed between the base plate and the shield case. Therefore, electromagnetic wave noise from the outside is favorably shielded, the heat dissipation function of the base plate is not hindered, and the measurement accuracy and durability of the thermal type flow meter can be improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings, but the present invention is not limited thereto.
FIG. 1 is a partial cross-sectional view showing a part of the thermal type flow meter of the present invention, and shows a part similar to FIGS. 3 and 4.
In the figure, the conductive cap 31 has a locking portion 31a at its gas passage side end. The engaging portion 31a engages with the base plate 14, and the opposite end is connected to the shield case 20 by electric resistance welding.

Shield case 20 and base plate 14
And are connected via the conductive cap 31,
Very few gaps are created between them due to vibration. Therefore, the shield case 20 has the base plate 14
Is excellently grounded via the base plate 14 to perform an excellent shielding function, and the heat of the shield case 20 due to a power transistor (not shown) or the like is radiated well via the base plate 14. Further, as for the thermal type flow meter itself, the mechanical strength is improved by adopting the above-described connection mode.

The shape of the locking portion 31a is not limited, and a flange shape or the like can be exemplified, but a plurality of locking pieces may be provided in the radial direction. Further, as the material of the conductive cap 31, a material having conductivity is sufficient, but a material made of brass can be preferably used.

[0014]

As described above, according to the present invention,
Since the conductive cap has a specific shape, it is difficult to create a gap between the base plate and the shield case.
It is possible to provide a thermal flow meter with improved durability and measurement accuracy.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing a part of a thermal type flow meter of the present invention.

FIG. 2 is a cross-sectional view showing an example of a conventional thermal type flow meter.

FIG. 3 is a partially enlarged sectional view of FIG.

FIG. 4 is an explanatory cross-sectional view showing how the shield case and the cap are displaced by an external force.

[Explanation of symbols]

2,4 resistor element, 6 gas passage, 6a gas passage wall portion, 8 bypass passage, 10 post, 12 holder,
14 base plate, 16 control circuit, 18 wire bonding wire, 20 shield case, 30, 31 conductive cap, 31a locking part

Claims (2)

[Claims] 1. A holder mounted so as to penetrate through a wall portion of a gas passage, a post penetrating through the holder and protruding from an inner end portion of the gas passage of the holder, and an inner end portion of the gas passage of the post. A heat-generating resistor element and a heat-sensitive resistor element attached to the section, a control circuit connected to the gas passage outer end of the post and controlling both of the resistor elements, and a shield case that accommodates the control circuit. In a thermal type flow meter, which is sandwiched by the outer wall of the gas passage, and has a base plate into which the outer end of the gas passage of the holder is inserted, and a gas passage side wall portion of the shield case embedded in the base plate. A thermal flow comprising a conductive cap electrically connecting the outer wall of the gas passage via the base plate, and a locking portion at an end of the cap on the gas passage side. Total. 2. The thermal type flow meter according to claim 1, wherein the engaging portion of the cap has a flange shape.