KR20100115098A - Gas sensor - Google Patents

Abstract

PURPOSE: A gas sensor which accurately measures nitric oxide gas of low concentration in a short time is provided to prevent the degrading of measurement precision by serially arranging a plurality of sensitive members on a gas passage. CONSTITUTION: A gas sensor comprises a sensor body, a sensitive member(104) and an electrode(105). The sensor body comprises an gas inlet(101), a gas outlet(109) and a gas passage. The sensitive member is arranged on the gas passage. The sensitive member chemically combines with a measurement target gas. The electrode measures the electrical feature of the sensitive member. The sensitive member is formed on a cross section of the gas passage.

Description

Gas sensor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to gas sensors, and more particularly to gas sensors capable of measuring low concentrations of nitric oxide gas with high precision in a short time.

In the case of a gas sensor for measuring the concentration of a specific gas contained in the vehicle exhaust gas, etc., an electric detection signal such as electric resistance, electric potential, current, etc. is generated according to the concentration of the gas to be measured, and the method of measuring the generated electric signal Mainly used.

In the case of automotive exhaust measurement, the durability of the measurement environment requires high durability and fast measurement time. In addition, in the case of nitrogen oxide (NOx) gas mainly measured in automobile exhaust gas, precise measurement is difficult due to not only a constant amount of the exhaust gas but also a small amount. Accordingly, there is a need in the art for a gas sensor having high sensitivity and high durability, high durability, and rapidity.

One object of the present invention is to provide a gas sensor and a gas concentration measuring method capable of measuring a low concentration of nitric oxide gas with high precision in a short time.

In order to achieve the above object, one embodiment of the present invention,

A sensor body having a gas inlet and a gas outlet and a gas passage therebetween, and disposed in the gas passage and chemically combining with and absorbing the gas to be measured introduced through the gas inlet, thereby absorbing electrical properties. Provided is a gas sensor comprising a sensitizer having a changing material and a pair of electrodes connected to the sensitizer for measuring electrical characteristics of the sensitizer.

In one embodiment of the present invention, the sensitizer may be formed in one cross section of the gas passage.

In one embodiment of the present invention, a plurality of the sensitizer is provided, it may be spaced apart from each other on the path of the measurement target gas.

In this case, it is preferable that the said plurality of sensitive bodies are arranged in series with each other.

In one embodiment of the present invention, the sensitizer may be a phase is converted by absorbing the gas to be measured.

In an embodiment of the present disclosure, the electrical characteristic of the measurement target gas that is changed by absorbing the measurement target gas may be at least one of an electric capacity and an electric resistance.

In one embodiment of the present invention, further comprising a flow rate control unit and a damping unit formed on the path of the gas to be measured between the gas inlet and the sensitive body, the cross-sectional area of the flow control unit than the cross-sectional area of the gas inlet and the damping unit Can be small.

In this case, the cross-sectional area of the sensitive body is preferably smaller than the cross-sectional area of the damping portion.

In one embodiment of the present invention, the gas outlet may have the smallest cross-sectional area of the gas passage.

In one embodiment of the present invention, in addition to the gas inlet and the gas outlet may be provided with no other path through which gas can be introduced.

In one embodiment of the present invention, the measurement target gas may be nitrogen oxide gas.

In this case, the gas accumulator may include a first material for converting nitrogen monoxide into nitrogen dioxide and a second material for chemically bonding with nitrogen dioxide and then releasing the bound nitrogen dioxide at a predetermined temperature or more.

In addition, the first material may be one selected from the group consisting of Pt, Au, and alloys thereof.

In addition, the second material may be one selected from the group consisting of barium oxide, potassium oxide, and oxide of perovskite structure.

The sensitizer may further include a body portion having the first and second materials formed on a surface thereof and having a structure in which a plurality of protrusions are formed on the surface.

The sensitizer may further include a body portion having the first and second materials formed on a surface thereof and a porous ceramic material.

In one embodiment of the present invention, the sensitizer may release the absorbed measurement target gas in a reducing atmosphere after absorbing the measurement target gas.

In this case, the reducing atmosphere can be obtained by fuel injection or hydrogen gas of an automobile.

In addition, the reducing gas may further include a reducing gas inlet to form a reducing atmosphere.

In one embodiment of the present invention, the sensor body may be made of alumina.

By using the gas sensor proposed in the present invention, it is possible to measure nitrogen oxide gas at low concentration with high accuracy. In particular, by arranging a plurality of sensitizers in series in the gas passage, it is possible to prevent the measurement accuracy from being lowered as the absorption efficiency of the sensitizer is lowered.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided to more completely describe the present invention to those skilled in the art. Accordingly, the shape and size of elements in the drawings may be exaggerated for clarity, and the elements denoted by the same reference numerals in the drawings are the same elements.

1 is a schematic cross-sectional view showing a gas sensor according to an embodiment of the present invention. FIG. 2 is a schematic plan view of the gas sensor of FIG. 1 viewed from above. FIG. Referring to FIGS. 1 and 2, the gas sensor 100 according to the present embodiment is a device capable of detecting a specific gas among the gas discharged from an automobile exhaust gas and the like, and the upper body 106 and the lower body. The gas passage is formed so as to penetrate the inside of the sensor body having the 107. A sensitizer 104 is disposed in the gas passage, so that the gas to be measured can be absorbed and the amount thereof can be measured.

A pair of electrodes 105 are connected to the sensitive body 104 to measure the electrical properties of the sensitive body 104 to calculate the amount of gas to be absorbed by the sensitive body 104. The sensor body is provided with a heating means 108 that increases the temperature by applying heat to the sensitive body 104, which is to discharge the gas to be measured absorbed in the sensitive body 104, as will be described later . In addition to nitrogen oxide gas (NO, NO ₂ ), the exhaust gas of automobiles contains various gases such as CO, CO ₂ , O ₂ , N ₂ , H ₂ , HC, and nitrogen oxide gas is mainly measured. Hereinafter, for convenience of explanation, the entire gas flowing through the gas inlet 101 is referred to as the exhaust gas, and the gas for which the concentration is to be known as the measurement target gas.

As described above, the sensor body has a structure in which a gas passage through which exhaust gas can be transferred in one direction is formed between the gas inlet 101 and the gas outlet 109, and furthermore, the gas inlet 101 and the gas outlet ( In addition to 109, it is preferable not to have any other path through which gas can be introduced. This is because, as will be described later, the gas concentration is calculated based on the inflow amount of the entire gas and the absorption amount of the measurement target gas absorbed in the sensitive body 104.

In the case of this embodiment, the cross section of the passage can be appropriately adjusted to generate a gas flow from the gas inlet 101 to the gas outlet 109. In this case, the cross section corresponds to a surface perpendicular to the direction in which gas flows in the gas passage. Since the gas flow rate changes according to the cross-sectional area of the gas passage, the cross-sectional area of the gas passage is adjusted to maximize the sensor performance according to the inflow rate and the flow rate of the exhaust gas. 1 and 2, the flow controller 102 is formed on the gas path adjacent to the gas inlet 101, and the cross-sectional area of the flow controller 102 is defined as the gas inlet ( It is smaller than the cross-sectional area of 101).

Cavity damping part 103 is formed in the gas path before exhaust gas reaches the sensitive body 104, and the cross-sectional area of the flow control part 102 is made smaller than the cross-sectional area of the damping part 103. In this case, the damping unit 103 may also be disposed in the path of the measurement target gas that has passed through the sensitive body 104. In addition, the cross-sectional area of the sensitive body 104 is formed smaller than the cross-sectional areas of the gas inlet 101 and the damping portion 103, the gas outlet 109 may have the smallest cross-sectional area of the gas passage. However, the example of the cross-sectional area described above may vary slightly according to the embodiment. Since the gas flow in one direction may be generated inside the sensor body through the adjustment of the cross-sectional area, a separate configuration, such as a gas pump, is not required to lower the gas pressure in a specific area of the passage. Therefore, the sensor body may be formed of a ceramic material such as alumina, not a solid electrolyte, and thus may be easily manufactured and may be advantageous in cost reduction. In this case, the sensor body may be obtained by laminating a plurality of ceramic sheets and firing the same, and may also fire the same as the sensitive body 104.

On the other hand, the sensitizer 104 absorbs and accumulates the gas to be measured in the exhaust gas, and includes a material whose electrical characteristics change according to the absorption. The measurement target gas may be nitrogen oxide gas (hereinafter, referred to in parallel with NOx) included in an automobile exhaust gas, and the concentration thereof is relatively low, so that the measurement result may be different from that of other gases such as NH ₃ . Affected by the quantity Therefore, when the sensitizer 104 is exposed to the outside and the nitrogen oxide gas is detected in an equilibrium state, the change in concentration can be known in real time, but the precision is greatly degraded due to the influence of the surrounding environment. In the case of this embodiment, the precision was improved by using the sensitizer 104 which can accumulate nitrogen oxide gas and detect it in a high concentration state.

To this end, a material that forms the sensitizer 104 may be a material that absorbs nitrogen oxide gas and changes electrical characteristics such as capacitance or electrical resistance, and changes in electrical characteristics may be performed through a pair of electrodes 105. I can figure it out. That is, since the electrical characteristics of the sensitizer 104 change according to the absorption amount of the nitric oxide gas, the absorption amount can be calculated through the changed electrical signal, and the concentration of the nitric oxide gas can be obtained in comparison with the inflow amount of the exhaust gas. As such, in the present embodiment, the amount of the nitrogen oxide gas absorbed by the sensitizer 104 for a predetermined time is measured, and the performance that is less sensitive to the surrounding environment is compared with the method of measuring the electrical characteristics of the sensitizer 104 in real time. Can be seen. In consideration of this, all of the introduced exhaust gas needs to be designed to pass through the sensitive body 104. Therefore, as illustrated in FIG. 1, the sensitive body 104 is preferably formed to cover the entire one end face of the gas passage.

Hereinafter, the detailed configuration of the sensitizer 104 and the principle of absorbing and releasing gas from the sensitizer 104 will be described in detail. Figure 3 schematically shows the configuration of the sensitizer that can be employed in the present invention, Figures 4 and 5 show the principle that the gas is absorbed and released in the sensitizer, respectively. First, referring to FIG. 3, the sensitizer 104 may absorb nitrogen oxide gas to be detected and release the same or another type of nitrogen oxide gas, for example, nitrogen monoxide (NO) gas. However, depending on the temperature and the atmosphere may be emitted as nitrogen dioxide (NO ₂ ) gas.

In order to perform this gas accumulation function, the sensitizer 104 chemically combines the first material 122 for converting nitrogen monoxide into nitrogen dioxide and the second material 123 that chemically combines with nitrogen dioxide and releases the combined nitrogen dioxide at a predetermined temperature or more. And the first and second materials 122 and 123 are formed on the surface of the body portion 121. The body portion 121 may be made of, for example, a ceramic such as alumina (Al ₂ O ₃ ) or a solid electrolyte such as zirconia, and the surface thereof, as shown in FIG. 3, to maximize the contact area with the gas. It can have multiple protrusions formed in it. As another example, the body 121 may be formed of a porous ceramic material.

As shown in FIG. 4, the first material 122 may be made of a noble metal material such as Pt, Au, or an alloy thereof to convert nitrogen monoxide to nitrogen dioxide. Nitrogen dioxide formed by the first material 122 is absorbed by the second material 123, and nitrogen dioxide, which was originally present without passing through the first material 122, may also be absorbed by the second material 123. The second material 123 absorbs nitrogen dioxide at a condition lower than a predetermined temperature, and may release the absorbed nitrogen oxide material in the form of nitrogen monoxide gas at a higher temperature condition as shown in FIG. 5.

Therefore, if the nature of the sensitizer 104 is used, the sensitizer 104 performs a detection function by releasing nitrogen oxide gas by adjusting the temperature of the sensitizer 104 in a state in which the absorption of the nitric oxide gas is saturated. You can do it. In other words, the nitrogen oxide gas is absorbed into the sensitizer 104 for a predetermined time to obtain a concentration thereof, and the nitrogen oxide gas absorbed in the sensitizer 104 is discharged to obtain a concentration for the next predetermined time.

In this case, the temperature at which the nitric oxide gas can be released is determined according to the characteristics of the first and second materials 122 and 123 and the characteristics of the gas to be absorbed, and is 200 to 400 ° C., which is a typical temperature around an automobile exhaust port. It can be said that the range of the degree is lower than the predetermined temperature. Higher temperature conditions can be obtained by heating the sensitizer 104 when the release of nitrogen oxide gas is required. Barium oxide may be used as the second material 123 capable of selectively absorbing or releasing nitrogen oxide gas depending on the temperature. BaO combines with NO ₂ to form BaNO ₃ having a converted phase and is a substance capable of releasing nitrogen oxide gas in the form of NO above a predetermined temperature. As a material capable of a similar function, the potassium, perovskite (Perovskite) oxide oxidation of streams, e.g., BaTiO _3, SrTiO _3, SrZrO ₂ and the like.

On the other hand, the nitrogen oxide gas absorbed in the sensitive body 104 may be released by controlling the temperature conditions and forming an appropriate reducing atmosphere. 6 is a schematic cross-sectional view showing a gas sensor according to an embodiment modified from the embodiment of FIG. 1. The gas sensor 200 according to the present exemplary embodiment further includes a reducing gas inlet in the structure of FIG. 1, and the elements shown by the same numbers may be applied to the description of FIG. 1 as it is. Even if the sensitive body 104 is not heated, the nitrogen oxide absorbed by forming a reducing gas atmosphere, for example, a hydrogen gas atmosphere, may be released from the sensitive body 104, and this reducing atmosphere may be used to inject automobile fuel in addition to hydrogen gas. Can also be obtained.

Therefore, in the present embodiment, the heating means 108 may be omitted. Alternatively, the reducing gas and the heating means may be used together without being omitted. In addition, although not shown separately, it is also possible to create a reducing atmosphere by discharging oxygen to the outside, the oxygen pumping unit for this may be disposed around the sensitive body 104. Specifically, the sensor body is formed of a solid electrolyte and an appropriate voltage is applied to allow oxygen to pass through the solid electrolyte in an ionic state.

FIG. 7 is a schematic cross-sectional view showing a gas sensor according to an embodiment modified from the embodiment of FIG. 1. The gas sensor 300 according to the present embodiment has a structure in which the number of the sensing bodies 104 is increased by one more in the structure of FIG. 1, and the description of FIG. Of course, a pair of electrodes 105 may also be connected to the added sensitive body 104 to measure electrical characteristics, and the number of the sensitive bodies 104 may be three or more. In this embodiment, the sensitizers 104 are two and arranged in series spaced apart from each other. Here, the serial arrangement can be seen as a structure arranged continuously on the gas path inside the gas passage, as shown in FIG. By arranging the plurality of sensitive bodies 104 in series, measurement accuracy can be further improved, which will be described with reference to FIGS. 8 to 10.

8 to 10 are graphs showing the concentration of nitric oxide gas and the amount of nitric oxide gas absorbed by the sensitive body in a specific region inside the sensor body according to the measurement time. First, referring to FIG. 8, the nitrogen oxide gas introduced through the gas inlet has a constant concentration C until it reaches the sensitive body. In this case, the concentration of the nitric oxide gas changes depending on the state of the exhaust gas, but for convenience of explanation, it is assumed that the nitric oxide gas has a constant concentration in the double gas. Referring to Fig. 9A, the absorption reaction of nitrogen oxide gas occurs from the time t1 when the exhaust gas reaches the first sensitive body, and the absorption reaction continues until the time t2 when the absorption limit amount A is reached. This amount of absorption can be obtained indirectly by measuring the capacitance of the sensitizer and the like as described above.

9B shows the concentration of nitrogen oxide gas in the exhaust gas immediately after passing through the first sensitive body. Looking at the graph of FIG. 9B, it can be seen that some of the nitric oxide gas passes through the first sensitizer before time t2 when the absorption is saturated in the first sensitizer. This is because as the absorption reaction in the sensitizer approaches saturation, the ratio of the region where absorption is possible, that is, the region where nitrogen oxide gas has not yet been absorbed, is lowered, thereby lowering the absorption efficiency of the nitrogen oxide gas. As such, if there is nitrogen oxide gas that passes through the absorber without being absorbed, the measured value may be lower than the original concentration, and the second inductor is employed to solve this problem. Therefore, the gas concentration can be measured more accurately by collecting the measurement value regarding the capacitance etc. in each of the two sensitive bodies, and comprehensively analyzing the two measurement values obtained.

The graph of FIG. 10A shows the amount of nitrogen oxide gas absorption in the second sensitizer, and t3 represents the time point at which the absorption is saturated in the second sensitizer. The nitric oxide gas that has passed through the first sensitive body is absorbed by the second sensitive body, and in particular, the measurement accuracy can be improved by allowing the nitric oxide gas passed through before the first sensitive body is saturated. In this case, looking at the graph of FIG. 10B, since there may be nitrogen oxide gas that cannot be absorbed in the second sensitive member, the sensitive member may be further disposed to improve accuracy.

The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited only by the appended claims. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

1 is a schematic cross-sectional view showing a gas sensor according to an embodiment of the present invention. FIG. 2 is a schematic plan view of the gas sensor of FIG. 1 viewed from above. FIG.

Figure 3 schematically shows the configuration of the sensitizer that can be employed in the present invention, Figures 4 and 5 show the principle that the gas is absorbed and released in the sensitizer, respectively.

6 is a schematic cross-sectional view showing a gas sensor according to an embodiment modified from the embodiment of FIG. 1.

FIG. 7 is a schematic cross-sectional view showing a gas sensor according to an embodiment modified from the embodiment of FIG. 1.

8 to 10 are graphs showing the concentration of nitric oxide gas and the amount of nitric oxide gas absorbed by the sensitive body in a specific region inside the sensor body according to the measurement time.

<Description of the symbols for the main parts of the drawings>

101: gas inlet 102: flow control unit

103: damping unit 104: induction body

105: electrode 106: upper body

107: lower body 108: heating means

109: gas outlet 110: reducing gas inlet

121: body 122, 123: first and second materials

Claims (20)

A sensor body having a gas inlet and a gas outlet and a gas passage therebetween; A sensitizer disposed in the gas passage and chemically coupled to and absorbed by the gas to be measured introduced through the gas inlet, and having a material whose electrical characteristics change by such absorption; And A pair of electrodes connected to said sensitizer for measuring electrical characteristics of said sensitizer; Gas sensor comprising a. The method of claim 1, The gas sensor is characterized in that formed on the entire cross-section of the gas passage. The method of claim 1, A plurality of the sensitizer is provided, the gas sensor, characterized in that spaced apart from each other on the path of the measurement target gas. The method of claim 3, And said plurality of sensitive bodies are arranged in series with each other. The method of claim 1, The gas sensor is characterized in that the phase is changed by absorbing the gas to be measured. The method of claim 1, The gas sensor characterized in that the electrical characteristic of the measurement target gas that is changed by absorbing the measurement target gas is at least one of capacitance and electrical resistance. The method of claim 1, And a flow rate controller and a damping portion formed on a path of the gas to be measured between the gas inlet and the sensitive body, wherein a cross-sectional area of the flow rate controller is smaller than a cross-sectional area of the gas inlet and the damping portion. The method of claim 7, wherein The cross-sectional area of the sensitive body is smaller than the cross-sectional area of the damping portion. The method of claim 1, And said gas outlet has the smallest cross-sectional area of said gas passages. The method of claim 1, Gas sensor, characterized in that it does not have any other path through which gas can be introduced in addition to the gas inlet and the gas outlet. The method of claim 1, The gas sensor is characterized in that the nitrogen oxide gas. The method of claim 11, The gas sensor comprises a gas accumulator having a first material for converting nitrogen monoxide to nitrogen dioxide and a second material for chemically bonding to nitrogen dioxide and then releasing the combined nitrogen dioxide at a predetermined temperature or more. The method of claim 12, Wherein said first material is one selected from the group consisting of Pt, Au, and alloys thereof. The method of claim 12, And the second material is one selected from the group consisting of barium oxide, potassium oxide, and oxide of perovskite structure. The method of claim 12, The sensitizer is a gas sensor, characterized in that the first and the second material is formed on the surface, further comprising a body portion having a structure in which a plurality of protrusions formed on the surface. The method of claim 12, The sensitizer is a gas sensor, characterized in that the first and the second material is formed on the surface, further comprising a body portion made of a porous ceramic material. The method of claim 1, And the sensitizer absorbs the gas to be measured and releases the absorbed gas to be measured in a reducing atmosphere. The method of claim 17, And said reducing atmosphere is obtained by fuel injection or hydrogen gas of an automobile. The method of claim 17, A gas sensor further comprises a reducing gas inlet so as to form the sensitive body in a reducing atmosphere. The method of claim 1, The sensor body is a gas sensor, characterized in that made of alumina.

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