JP2007198893A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a detecting element from getting wet, and to enhance responsiveness about detection of a concentration of a detection objective gas, in a gas sensor for detecting the concentration of the prescribed detection objective gas in a gas mixture containing moisture. <P>SOLUTION: This gas sensor 100 includes a main tube 10, a Venturi tube 12, a gas detection chamber 20, and a pipe 14. The main tube 10 is connected in series to the Venturi tube 12, and a main flow of the gas mixture flows therethrough. The gas detection chamber 20 communicated with the main tube 10 is connected to a side face of the main tube 10. The gas detection chamber 20 is connected to a contraction portion of the Venturi tube 12 by the pipe 14. The detecting element 30 is arranged in the gas detection chamber 20 to detect the concentration of the detection objective gas. A water-repellent filter 24 is arranged in a gas introduction port 22 of the gas detection chamber 20. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas sensor, and more particularly to a gas sensor that detects a concentration of a predetermined detection target gas in a mixed gas containing moisture.

  Conventionally, a gas sensor suitable for use in a humid environment has been proposed as a gas sensor for detecting the concentration of a detection target gas. For example, Patent Document 1 below uses the heat that burns when the gas to be detected (detection target gas) contacts the catalyst, and determines the concentration of the gas to be detected from the difference in electrical resistance between the detection element and the temperature compensation element. Techniques relating to gas sensors to be detected are described. In this gas sensor, a water repellent filter is arranged at the detected gas inlet of the case (gas detection chamber) that houses the detection element and the temperature compensation element, so that water in the flow path through which the detected gas flows enters the gas detection chamber. Is prevented. As a result, it is possible to prevent the detection element from being wetted, and to prevent element destruction of the detection element and sensitivity reduction.

Special table 2003/042678

  However, in the technique described in Patent Document 1, the water repellent filter obstructs the gas flow in the gas detection chamber, the detection target gas stays in the gas detection chamber, and the circulation deteriorates. Responsiveness to concentration detection was poor.

  The present invention has been made to solve the above-described problem, and in a gas sensor for detecting the concentration of a predetermined detection target gas in a mixed gas containing moisture, the detection element is prevented from being wet and the detection target The object is to improve the responsiveness of detecting the gas concentration.

In order to solve at least a part of the above-described problems, the present invention employs the following configuration.
The gas sensor of the present invention is
A gas sensor for detecting a concentration of a predetermined detection target gas in a mixed gas containing moisture,
A main pipe for flowing the mixed gas;
A venturi pipe connected to the downstream side of the flow direction of the mixed gas in the main pipe;
A bypass pipe that branches from the main pipe and flows the mixed gas in the vicinity of the throttle portion of the venturi pipe;
A detection element disposed in the bypass pipe for detecting the concentration of the detection target gas;
In the bypass pipe, a water repellent filter provided on the upstream side of the detection element in the flow direction of the mixed gas;
It is a summary to provide.

  In the present invention, when the mixed gas flows through the main pipe and the venturi pipe, the difference between the inner diameter of the main pipe and the inner diameter of the throttle portion of the venturi pipe is greater than the flow velocity of the mixed gas in the main pipe. The flow velocity of the mixed gas in the throttle portion becomes higher, and a pressure difference is generated between the upstream side of the throttle in the Venturi tube and the throttle portion according to Bernoulli's theorem. At this time, the pressure in the throttle portion of the venturi pipe is lower than the pressure on the upstream side. For this reason, the mixed gas in the bypass pipe is drawn into the venturi pipe, and the mixed gas flows from the main pipe to the bypass pipe. Therefore, in the bypass pipe, even if a water repellent filter is provided on the upstream side of the detection element in the flow direction of the mixed gas (for example, the junction between the main pipe and the bypass pipe), the mixed gas in the bypass pipe is It is possible to quickly scavenge without staying. As a result, it is possible to improve the responsiveness for detecting the concentration of the detection target gas when the concentration of the detection target gas in the mixed gas flowing through the main pipe changes. Further, in the bypass pipe, the water repellent filter provided on the upstream side of the detection element in the mixed gas flow direction can prevent moisture from entering from the main pipe to the vicinity of the detection element in the bypass pipe. That is, the gas sensor of the present invention can prevent the detection element from being wetted, and can improve the responsiveness of detecting the concentration of the detection target gas. In the present invention, there is no need to install a pump or the like for scavenging the bypass pipe.

  In the gas sensor of the present invention, a porous metal plate may be provided together with the water repellent filter.

  By doing so, it is possible to suppress deformation and breakage of the water repellent filter due to pressure fluctuation when the mixed gas flows into the bypass pipe without significantly impairing the air permeability of the water repellent filter.

  In the gas sensor of the present invention, a heater for heating the mixed gas may be further provided in the bypass pipe upstream of the detection element in the flow direction of the mixed gas in the bypass pipe.

  By doing so, even if the moisture in the mixed gas slightly permeates the water repellent filter, the moisture can be prevented from condensing in the bypass pipe.

Hereinafter, embodiments of the present invention will be described in the following order based on examples.
A. Example:
B. Variation:

A. Example:
FIG. 1 is a cross-sectional view showing a schematic configuration of a gas sensor 100 as an embodiment of the present invention. The gas sensor 100 is a gas sensor that detects the concentration of a predetermined detection target gas in a mixed gas containing moisture. For example, in a fuel cell system including a fuel cell that generates power by an electrochemical reaction between hydrogen and oxygen, the fuel cell It is used to detect the concentration of hydrogen in the anode off-gas containing moisture discharged from the anode.

  As shown in the figure, the gas sensor 100 includes a main pipe 10, a venturi pipe 12, a gas detection chamber 20, and a pipe 14. The main pipe 10 and the venturi pipe 12 are connected in series, and the main flow of the mixed gas flows from the main pipe 10 to the venturi pipe 12 through these. The venturi 12 increases the flow rate by constricting the flow of fluid, and generates a lower pressure at a portion where the flow rate is high than at a portion where the flow rate is low. The inner diameter of the main pipe 10 and the inner diameter of the throttle portion of the venturi pipe 12 can be arbitrarily set.

  A gas detection chamber 20 communicating with the main pipe 10 is connected to the side surface of the main pipe 10. The gas detection chamber 20 and the throttle portion of the venturi pipe 12 are connected by a pipe 14. Therefore, the mixed gas branched from the main pipe 10 and introduced from the gas introduction port 22 of the gas detection chamber 20 passes through the gas detection chamber 20, the gas discharge port 28 of the gas detection chamber 20, and the pipe 14, and then is venturi pipe. 12 flows. The gas detection chamber 20 and the pipe 14 correspond to a bypass pipe in the present invention.

  In the gas detection chamber 20, a detection element 30 that detects the concentration of the detection target gas and a circuit board 40 that performs signal processing of signals output from the detection element 30 are arranged. Various elements such as a semiconductor element can be applied as the detection element 30. In addition, the detection element 30 is arrange | positioned in the gas detection chamber 20 in the part in which mixed gas does not stay easily. Further, the circuit board 40 may be disposed outside the gas detection chamber 20.

  A water repellent filter 24 and a porous metal plate 26 are disposed at the gas inlet 22 of the gas detection chamber 20. The water repellent filter 24 can prevent moisture in the mixed gas flowing through the main pipe 10 from entering the gas detection chamber 20. Further, the porous metal plate 26 suppresses deformation or breakage of the water repellent filter 24 due to pressure fluctuation when the mixed gas flows into the gas detection chamber 20 without greatly impairing the air permeability of the water repellent filter 24. Can do.

  According to the gas sensor 100 of the present embodiment described above, when a mixed gas flows through the main pipe 10 and the venturi pipe 12, the difference between the inner diameter of the main pipe 10 and the inner diameter of the throttle portion of the venturi pipe 12 is The flow velocity of the mixed gas in the throttle portion of the venturi pipe 12 is higher than the flow velocity of the mixed gas in the main pipe 10, and the pressure difference between the upstream side of the throttle in the venturi pipe 12 and the throttle portion is determined by Bernoulli's theorem. Arise. At this time, the pressure in the throttle portion of the venturi tube 12 is lower than the upstream pressure. For this reason, the mixed gas in the pipe 14 is drawn into the venturi pipe 12, and the mixed gas flows from the main pipe 10 to the gas detection chamber 20 and the pipe 14. Therefore, even if the water repellent filter 24 is provided at the gas inlet 22 of the gas detection chamber 20, the gas detection chamber 20 and the mixed gas in the pipe 14 can be quickly purged without staying. . As a result, it is possible to improve the responsiveness of detecting the concentration of the detection target gas when the concentration of the detection target gas in the mixed gas flowing through the main pipe 10 changes. Further, the water repellent filter 24 can prevent moisture from entering from the main pipe 10 to the vicinity of the detection element 30 in the gas detection chamber 20. That is, the gas sensor 100 according to the present embodiment can prevent the detection element 30 from being wetted, and can improve the responsiveness for detecting the concentration of the detection target gas. Further, there is no need to install a pump or the like for scavenging the gas detection chamber 20.

B. Variation:
Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and can be implemented in various modes without departing from the scope of the present invention. For example, the following modifications are possible.

B1. Modification 1:
In the above embodiment, the porous metal plate 26 is provided in the gas inlet 22 of the gas detection chamber 20 together with the water repellent filter 24. However, the porous metal plate 26 may not be provided.

B2. Modification 2:
In the gas sensor 100 of the above embodiment, a heater for heating the mixed gas may be further provided in the gas detection chamber 20. By doing so, even if moisture in the mixed gas flowing through the main pipe 10 permeates the water repellent filter 24 slightly, the moisture can be prevented from condensing in the gas detection chamber 20.

B3. Modification 3:
The gas sensor 100 of the above embodiment may further include means for controlling the restriction of the venturi pipe 12, and for example, the restriction may be controlled according to the flow rate of the mixed gas flowing through the main pipe 10. By doing so, even when the flow rate of the mixed gas flowing through the main pipe 10 is relatively small, the responsiveness with respect to the detection of the concentration of the detection target gas can be improved.

B4. Modification 4:
In the above embodiment, the gas sensor 100 is provided with the gas detection chamber 20 and the pipe 14, but may be provided with one bypass pipe in which both are integrated.

It is sectional drawing which shows schematic structure of the gas sensor 100 as one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Gas sensor 10 ... Main piping 12 ... Venturi tube 14 ... Piping 20 ... Gas detection chamber 22 ... Gas introduction port 24 ... Water-repellent filter 26 ... Porous metal plate 28 ... Gas discharge port 30 ... Detection element 40 ... Circuit board

Claims (1)

A gas sensor for detecting a concentration of a predetermined detection target gas in a mixed gas containing moisture,
A main pipe for flowing the mixed gas;
A venturi pipe connected to the downstream side of the flow direction of the mixed gas in the main pipe;
A bypass pipe that branches from the main pipe and flows the mixed gas in the vicinity of the throttle portion of the venturi pipe;
A detection element disposed in the bypass pipe for detecting the concentration of the detection target gas;
In the bypass pipe, a water repellent filter provided on the upstream side of the detection element in the flow direction of the mixed gas;
A gas sensor comprising:

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