JPH10325824A - Hydrocarbon sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hydrocarbon sensor which is correct and not deteriorated in accuracy while used, by using a perovskite oxide as an inactive electrode inactive for hydrocarbon. SOLUTION: An active electrode 418 and an electrode 419 are set at one face 128 and the other face 129 facing a sample gas chamber 100 of a solid electrolytic substrate 12, thereby forming an HC active cell 41. An inactive electrode 218 and an electrode 219 are also set to form an oxygen pump cell which supplies and discharges oxygen to the sample gas chamber 100. An active electrode 318 and an electrode 319 are set to form an HC inactive cell 31. The inactive electrodes 218, 318 are both composed of a perovskite oxide inactive in an oxidation reaction of hydrocarbon, e.g. La0.5 Sr0.5 MnO3 and the electrodes 219, 319, 419 and active electrode 418 are formed of platinum. The perovskite oxide is not deteriorated at a temperature as high as approximately 900 deg.C, and therefore electrode components hardly coagulate when a hydrocarbon sensor 1 is used. The sensor is never deteriorated in accuracy and enables correct measurements at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a hydrocarbon sensor for detecting the concentration of hydrocarbons contained in a sample gas such as exhaust gas discharged from an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, from the viewpoints of environmental protection and air quality improvement, exhaust emissions of internal combustion engines (e.g.
, CO, NOx) requirements are increasing.
In the United States, a self-diagnosis regulation (OBD-II) including a three-way catalytic converter deterioration diagnosis is supplied.

As a means for responding to such regulations, a hydrocarbon sensor for measuring the HC emission concentration is installed downstream of the three-way catalytic converter, and the most direct and sensitive measure for the deterioration of the three-way catalytic converter is set. HC having
Hydrocarbon sensors used to directly determine the increase in emissions are being developed (see FIG. 4).

In addition, HC discharged immediately after the engine is started
Is temporarily absorbed, and after the three-way catalytic converter is activated, it is disposed downstream of the HC adsorber for purifying the adsorbed HC with the three-way catalytic converter, and is used to detect a failure of the HC adsorber. Hydrocarbon sensors are being developed (see FIG. 5).

For example, Japanese Patent Application Laid-Open No. 5-322844 discloses that
There is disclosed a hydrocarbon sensor that detects HC concentration from an output difference between an electrode active for HC and an electrode inert for HC. This is because the inactive electrode consumes less oxygen than the active electrode, resulting in a difference in oxygen concentration near both electrodes. For this reason, the HC concentration can be detected by measuring the output difference such as the electromotive force between the two electrodes.

As the active electrode in the above-mentioned hydrocarbon sensor, there has been known an active electrode in which rhodium is added to platinum to improve the oxidation activity of platinum itself. On the other hand, as the above-mentioned inactive electrode, an electrode in which lead is added to platinum to reduce the oxidizing activity of platinum itself is known.

[0007]

However, the above-mentioned conventional hydrocarbon sensors have the following problems. When the above-mentioned inert electrode in which lead is added to platinum is exposed to a temperature atmosphere (700 to 900 ° C.) like exhaust gas of an internal combustion engine, platinum condenses and platinum and lead are present separately. . That is, a platinum-rich portion and a lead-rich portion are formed in the inert electrode.

In the above-mentioned platinum-rich portion, the property of being inactive against the HC oxidation reaction is lost. For this reason, the output of the inactive electrode increases, and the output difference between the active electrode and the inactive electrode decreases. Therefore, H
There is a problem that the detection accuracy of the C concentration is reduced.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a hydrocarbon sensor that accurately measures the concentration of HC in a sample gas and hardly deteriorates in use.

[0010]

According to a first aspect of the present invention, there is provided a carbonization device having an active electrode made of a material active on HC and an inert electrode made of a material inert on HC, and detecting an HC concentration in a sample gas. In the hydrogen sensor, the inert electrode is made of a perovskite-type oxide.

The above-mentioned sample gas includes exhaust gas discharged from an internal combustion engine such as a vehicle-mounted engine. The HC to be measured is, for example, C
₂ (ethane, ethylene) -C ₈ can be exemplified HC species (isooctane, xylene) or the like.

When measuring the concentration of HC in a sample gas using the active electrode and the inert electrode, the active electrode and the inert electrode are combined with a solid electrolyte substrate to form a kind of oxygen sensor cell as described later. Is preferred.

That is, in the active electrode, the oxidizable gas in the sample gas and HC are oxidized by the catalytic action of the active electrode, and oxygen is consumed accordingly. In the above inert electrode, only the other oxidizable gas in the sample gas is oxidized, and oxygen is consumed accordingly. Therefore, a difference in oxygen concentration occurs around the active electrode and the inactive electrode, and thus a difference occurs in the output of the oxygen sensor cell formed by these electrodes.
Since this difference is proportional to the HC concentration, the HC concentration can be measured. The above-mentioned other oxidizable gas means that when the sample gas is the exhaust gas of an internal combustion engine,
For example, H ₂ and CO are used.

The operation of the present invention will be described below. In the hydrocarbon sensor of the present invention, the inert electrode is made of a perovskite oxide. The perovskite oxide is a substance that does not deteriorate even at a high temperature of 900 ° C. For this reason, when the hydrocarbon sensor is used, the aggregation of the electrode components in the inert electrode hardly occurs, the accuracy is not deteriorated due to the aggregation, and the HC concentration can always be accurately measured.

As described above, according to the present invention, it is possible to provide a hydrocarbon sensor which accurately measures the concentration of HC in a sample gas, and which hardly deteriorates in use.

Next, as in the invention of claim 2, the perovskite-type oxide is A _{1 -X} A ' _X BO ₃ (where 0 <
x <1), wherein A is at least one element selected from La, Y, and Nd, and A ′ is Sr, C
a, at least one element selected from Ba,
Is preferably at least one element selected from Mn, Co, Ni, Fe, and Cr.

The perovskite oxide having such a composition is inactive in the oxidation reaction of HC (see FIG. 8 described later), but has a very high activity in the oxidation reaction with H ₂ and CO (see FIG. 6 described later). And FIG. 7), the activity of which is almost equal to that of a noble metal such as platinum which is an excellent catalyst. Therefore, the perovskite oxide is most suitable as an inert electrode.

Among the above perovskite oxides, La _0.5 Sr _0.5 MnO ₃ or La _0.6 Sr
It is preferable to use _0.4 Mn _0.5 Co _0.45 Ni _0.05 O ₃ or the like.

Next, as in the third aspect of the present invention, a sample gas chamber formed at least in part by a solid electrolyte substrate having oxygen ion conductivity and having a restricted flow of sample gas; An HC active cell comprising an active electrode provided on one surface facing the sample gas chamber and an electrode provided on the opposite surface, and one surface of the solid electrolyte substrate facing the sample gas chamber and an opposite surface thereof An oxygen pump cell comprising electrodes provided respectively for supplying and discharging oxygen to and from the sample gas chamber;
It is preferable to have an HC inert cell including an inert electrode provided on one surface of the solid electrolyte substrate facing the sample gas chamber and an electrode provided on the opposite surface.

In the hydrocarbon sensor according to the present invention, the flow of the sample gas into the sample gas chamber is restricted.
Therefore, the state of the sample gas chamber can be preserved to some extent. In other words, it takes some time for the sample gas outside the sensor to diffuse into the sample gas chamber, so that it is possible to smooth the HC concentration in the sample gas over time and measure the averaged HC concentration. Becomes

As means for restricting the flow of the sample gas into the sample gas chamber, it is preferable to provide a pinhole having a small diameter and supply the sample gas from the pinhole. That is, it is preferable that the sample gas introduction path to the sample gas chamber be a pinhole. Also,
It is also possible to configure the sample gas introduction path with a porous ceramic layer.

Further, since the HC active cell is a cell for detecting oxygen concentration, the active electrode is a platinum electrode having high catalytic activity and excellent in high-temperature durability, or 1 to 50% by weight of rhodium added to platinum. It is preferred to be composed of the above materials. In addition, palladium and ruthenium metals having high complete oxidation reaction activity, or alloys of these metal elements can be used. As the oxygen ion conductive solid electrolyte substrate, for example, yttria-stabilized zirconia (YSZ) can be used.

In the hydrocarbon sensor according to the present invention, the oxygen pump cell is operated according to the output of the HC active cell in order to maintain the oxygen concentration in the sample gas chamber at a predetermined value as described later. It is preferable to provide a mechanism such as possible feedback control.

Thus, when the oxygen concentration in the sample gas is high, oxygen is discharged from the sample gas chamber by the oxygen pump cell based on the detected value of the HC active cell, while the oxygen concentration in the sample gas is low. In this case, oxygen can be supplied to the sample gas chamber by the oxygen pump cell based on the detected value of the HC active cell. By making the oxygen concentration in the sample gas chamber almost constant as described above, the output difference between the active cell and the inactive cell can be reliably made to be in a state in which the output difference is proportional to the HC concentration. The concentration can be detected.

Here, the preferable predetermined value of the oxygen concentration in the sample gas chamber differs depending on the mechanism for detecting the oxygen concentration by the HC active cell. It is preferable to control the oxygen concentration so as to be about 0.45 V. When the oxygen concentration is detected based on the limiting current of the HC active cell, it is preferable to control the air-fuel ratio of the sample gas chamber to be about λ = 1.

The measurement of the HC concentration in the hydrocarbon sensor according to the present invention can be performed as follows. The sample gas is supplied to the sample gas chamber,
The oxygen concentration in the sample gas chamber is detected by the HC active cell. Here, when the oxygen concentration is larger than a predetermined value,
The oxygen pump cell is negatively operated to discharge oxygen from the sample gas chamber, and the oxygen concentration in the sample gas chamber is set to a predetermined value.
On the other hand, when the oxygen concentration is smaller than the predetermined value, the oxygen pump cell is operated positively to supply oxygen to the sample gas chamber and set the oxygen concentration in the sample gas chamber to the predetermined value.

At the surface of the active electrode of the HC active cell, HC is oxidized and oxygen is consumed. Further, HC oxidation does not occur on the surface of the inert electrode of the HC inert cell. Here, a reaction between HC and oxygen occurs near the HC active cell, but no reaction occurs between HC and oxygen near the HC inactive cell. Accordingly, the oxygen concentration becomes H near the HC active cell.
It becomes lower than the vicinity of the C inactive cell.

For this reason, the output values of the HC active cell and the HC inactive cell, which are cells capable of detecting the oxygen concentration, are different values, and the output difference is proportional to the HC concentration.
Thus, the HC concentration can be measured.

Next, a sample gas chamber at least partially formed by an oxygen ion-conductive first solid electrolyte substrate and having a restricted flow of the sample gas is provided. A second chamber formed at least in part by the first solid electrolyte substrate, and one surface of the first solid electrolyte substrate facing the sample gas chamber and the first solid electrolyte; It is preferable that a detection cell including an electrode provided on the opposite surface of the electrolyte substrate facing the second chamber is provided, and one of the electrodes in the detection cell is an active electrode and the other is an inactive electrode.

The measurement of the HC concentration in the hydrocarbon sensor according to the present invention can be performed as follows. On the side of the detection cell where the active electrode is located, HC is oxidized and oxygen is consumed. Further, oxygen is not consumed on the side where the inactive electrode exists because HC is not oxidized. Therefore, a difference in oxygen concentration occurs on both sides of the detection cell, and this detection cell becomes an oxygen concentration electromotive force type oxygen sensor cell. Therefore, the output of the detection cell is proportional to the HC concentration,
The measurement of the HC concentration becomes possible.

By arranging the active electrode and the inactive electrode in one cell as described above, the output difference such as electromotive force can be directly measured, and a simple configuration that does not require another circuit such as a comparator is provided. can do.

Next, as in the invention of claim 5, at least a part of the second chamber is formed by an oxygen ion conductive second solid electrolyte substrate, and the second chamber of the second solid electrolyte substrate is formed. An oxygen sensor cell for detecting the oxygen concentration in the second chamber, comprising an electrode provided on one surface facing the second chamber and an opposite surface thereof, and one surface facing the second chamber of the second solid electrolyte substrate. And an oxygen pump cell which comprises electrodes provided on the opposite surface thereof and supplies and discharges oxygen to and from the second chamber. As a result, the oxygen concentration in the second chamber can be maintained at a predetermined value, and more accurate detection of the HC concentration becomes possible.

Next, as in the invention of claim 6, a sample gas chamber at least partially formed by an oxygen ion-conductive first solid electrolyte substrate, and the flow of sample gas is restricted, A detection cell comprising two electrodes provided on one surface of the solid electrolyte substrate facing the sample gas chamber, wherein one of the electrodes in the detection cell is an active electrode and the other is an inactive electrode. preferable.

By arranging the active electrode and the inactive electrode on one surface, it is possible to directly measure an output difference such as an electromotive force, thereby providing a simple configuration that does not require other circuits such as a comparator. be able to. In addition, by arranging the active electrode and the inactive electrode on one surface, the number of laminations can be reduced, and the effect of easy production can be obtained.

Next, at least a part of the sample gas chamber is formed by an oxygen ion conductive second solid electrolyte substrate, and the sample gas chamber is formed in the sample gas chamber of the second solid electrolyte substrate. An oxygen pump cell comprising electrodes provided on one faced side and the opposite face thereof for supplying and discharging oxygen to and from the sample gas chamber, and one oxygen pump cell facing the sample gas chamber of the second solid electrolyte substrate. It is preferable to have an oxygen sensor cell comprising electrodes provided on the surface and the opposite surface thereof and detecting the oxygen concentration in the sample gas chamber.

As a result, the oxygen concentration in the sample gas chamber can be maintained at a predetermined value, and more accurate HC concentration can be detected.

Next, it is preferable that the electrode facing the sample gas chamber or the second chamber in the oxygen pump cell is an inert electrode made of a material inert to HC. On the surface of the oxygen pump cell, a phenomenon of desorption of oxygen molecules from the electrode surface and a phenomenon of adsorption of oxygen molecules to the electrode surface occur. Therefore, the activity of the oxygen molecules around the oxygen pump cell is increased, and the oxygen molecules easily react with HC.

For this reason, if the electrodes of the oxygen pump cell are made of platinum or the like, HC is oxidized on the surface of the oxygen pump cell. From the above, HC
By using an inert electrode for the oxygen pump cell, it is possible to prevent HC contained in the sample gas from being consumed on the oxygen pump cell. Therefore, H
It becomes possible to measure the C concentration accurately.

Next, it is preferable that the inactive electrode is made of a perovskite oxide. The above perovskite oxide has high conductivity, and
Since it hardly deteriorates even at a high temperature of 00 ° C., it is optimal as an electrode of the oxygen pump cell.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 A hydrocarbon sensor according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIGS. 1 and 2, the hydrocarbon sensor 1 of this embodiment has an active electrode 418 made of a material active on HC and an inert electrode 318 made of a material inert on HC. Is detected. The inert electrode 318 is made of a perovskite oxide. In this example, La _0.5 Sr _0.5 MnO ₃ is used as the oxide.

Next, the structure of the hydrocarbon sensor according to this embodiment will be described. As shown in FIGS. 1 and 2, the hydrocarbon sensor 1 of the present embodiment has a sample gas chamber 100 formed at least in part by a solid electrolyte substrate 12 having oxygen ion conductivity and in which the inflow of the sample gas is restricted. . The means for restricting the inflow of the sample gas is a sample gas introduction path 121 constituted by a pinhole.

The hydrocarbon sensor 1 comprises an active electrode 418 provided on one surface 128 of the solid electrolyte substrate 12 facing the sample gas chamber 100 and an opposite electrode 12
9 and an electrode 419 provided in the HC. Also, one surface 128 of the solid electrolyte substrate 12 facing the sample gas chamber 100 and the opposite surface 12
9 is provided with an oxygen pump cell 21 composed of an inert electrode 218 and an electrode 219 provided for supplying and discharging oxygen to and from the sample gas chamber 100, respectively. An HC inert cell 3 comprising an inert electrode 318 provided on one surface 128 of the solid electrolyte substrate 12 facing the sample gas chamber 100 and an electrode 319 provided on the opposite surface 129 thereof.
Have one

As shown in FIG. 1, in the oxygen pump cell 21, the inert electrode 218 and the electrode 21
9, a circuit 215 is formed via a controller 216. The controller 216 has a power supply for applying a voltage between the inactive electrode 218 and the electrode 219 and a variable resistor for controlling the voltage.

In the HC inert cell 31,
A power supply 3 is provided between the inactive electrode 318 and the electrode 319.
A circuit 315 is formed through the circuit 24 and the ammeter A1. The ammeter A1 includes an inactive electrode 318 and an electrode 319.
To detect the limit current flowing between them.

In the HC active cell 41, a power supply 424 is provided between the active electrode 418 and the electrode 419.
A circuit 415 is formed via the ammeter A2.
The ammeter A2 detects a limit current flowing between the active electrode 418 and the electrode 419.

A feedback circuit 25 is provided between the ammeter A 2 and the controller 216, and the ammeter A 2 is provided through the feedback circuit 25.
The control of the operation of the oxygen pump cell 21 using the controller 216 based on the limit current value detected in the above is performed by modern control. In this embodiment, the oxygen pump cell 2
Although the modern control is used for the operation control 1, the normal PID control or the like can be used.

Further, the oxygen pump cell 21 has the H
The oxygen concentration in the sample gas chamber 100 is maintained at a constant value based on the signal value from the C active cell 41. The signal value is a limit current value generated when a constant voltage is applied to the HC active cell 41 through the circuit 415. This limit current value is detected by the ammeter A2.

The hydrocarbon sensor 1 has a heater provided integrally. As will be described later, the heater includes a heater substrate 141, a heater section 140 provided on the heater substrate 141 to generate heat when energized, and an alumina substrate 142 covering both. Further, between the heater and the solid electrolyte substrate 12, an oxygen pump cell 21, HC
An atmosphere chamber 103 serving as a reference gas chamber for the inert cell 31 and the HC active cell 41 is provided. The air chamber 103 is provided with a small hole 146 for supplying the air.

Further, the hydrocarbon sensor 1 will be described in detail. As shown in FIGS. 1 and 2, the hydrocarbon sensor 1
Is a laminated hydrocarbon sensor 1 constituted by sandwiching an alumina substrate 125, a solid electrolyte substrate 12, and alumina substrates 127 and 142 between an alumina substrate 135 and an alumina heater substrate 141. As shown in FIG. 1, a sample gas chamber 100 is constituted by the solid electrolyte substrate 12 and the alumina substrates 125 and 135.

Since the hydrocarbon sensor 1 of this embodiment is installed in the exhaust system of an automobile as will be described later, the sample gas introduction path 121 constituted by a pinhole is provided for protection from particulate matter in exhaust gas. An electrode protection layer made of porous ceramic can be provided so as to cover the electrode.

As shown in FIG. 2, the solid electrolyte substrate 1
2 includes an inert electrode 218, an electrode 219, and an inert electrode 31.
8, an electrode 319, an active electrode 418, and an electrode 419 are provided. Further, the solid electrolyte substrate 12 is provided with the circuit 215 shown in FIG.
Is connected to the inactive electrode 31.
A terminal 263 for connecting the circuit 315 shown in FIG. 1 to the electrode 8 and the electrode 319, and a terminal 264 for connecting the circuit 415 shown in FIG. is there.

The inert electrode 218 and the electrode 21
9 and the terminal 265, the inactive electrodes 318 and 319 and the terminal 263, and the inactive electrodes 418 and 419 and the terminal 264 are connected by a lead 259. ing.

The alumina substrate 135 is provided with terminal portions 268, 269, and 270 formed so as to be able to conduct with the terminal portions 263, 264, and 265. In addition, between the terminal parts 265 and 270, between the terminal parts 263 and 268, and between the terminal parts 264 and 269, there are through holes 271 penetrating the solid electrolyte substrate 12, alumina substrates 125 and 135. Are conducted by through holes 266 and 267 penetrating through.

Next, the alumina substrate 125 is provided with a window 126 for forming the sample gas chamber 100. Further, the alumina substrate 127 is provided with a window 123 for forming the atmosphere chamber 103 shown in FIG.

Next, as shown in FIG. 2, a heater section 140 is provided on the alumina heater substrate 141, and the alumina protective substrate 142 is provided so as to cover the heater section 140. In addition, the above alumina heater substrate 1
Small holes 146 for supplying the atmosphere to the atmosphere chamber 103 are provided in the 41 and the alumina substrate 142, respectively. The heater section 140 of the alumina heater substrate 141 is provided so as not to interfere with the small hole 146.

The alumina heater substrate 141 is provided with a terminal 144 for applying electric power to the heater 140. The terminal section 144 and the heater section 140 are connected by a lead section 149.
The conduction between the terminal portion 144 and the lead portion 149 is as follows.
Through hole 1 provided in alumina heater substrate 141
43.

The solid electrolyte substrate 12 is made of yttria-stabilized zirconia (YSZ), and has a width of 7 mm, a length of 61 mm and a thickness of 0.16 mm. The alumina substrates 125, 135, 127, and 142 and the alumina heater substrate 141 are made of alumina and have a width of 7 mm, a length of 61 mm, and a thickness of 0.16 mm. The inert electrode 218, 318 is composed of La _0.5 Sr _0.5 MnO ₃ perovskite oxide which is inert to both the oxidation reaction of HC. The electrodes 219, 319, 41
9. The active electrode 418 is made of platinum.

Next, a method of manufacturing the hydrocarbon sensor 1 according to this embodiment will be described. First, La _0.5 Sr _0.5
A perovskite powder represented by MnO ₃ was prepared by the following method. Starting materials were nitrates of lanthanum, strontium, and manganese, weighed so as to have a desired composition, and dissolved in distilled water to form an aqueous solution. Here citric acid-
Hydrate is added to form a citric acid chelate complex, which is evaporated to dryness, and then calcined at 700 ° C. in the atmosphere to obtain La.
A powder of _0.5 Sr _0.5 MnO ₃ perovskite oxide was obtained. In the following Embodiments 2 and 3, a powder of perovskite-type oxide can be produced by the same production method as in Embodiment 1 except that the type and amount of nitrate as a starting material are changed.

Next, the obtained perovskite oxide powder was pasted with terpineol and ethyl cellulose. On the other hand, platinum powder used as an electrode active in the oxidation reaction of HC was also pasted with terpineol and ethyl cellulose. These pastes are applied to the solid electrolyte substrate 1
2 green sheets and alumina substrates 125 and 12
7, 135, 142, and a green sheet for the alumina heater substrate 141 was formed by printing.

Next, each green sheet was laminated so as to have the structure shown in FIGS. 1 and 2 to form a laminate, and the laminate was fired at about 1400 to 1550 ° C. while applying pressure. Thus, a laminated hydrocarbon sensor 1 as shown in FIG. 1 was obtained.

Next, a method of attaching the hydrocarbon sensor 1 according to the present embodiment to an exhaust path of an automobile will be described. FIG.
As shown in the figure, the hydrocarbon sensor 1 of this embodiment is assembled to a hydrocarbon sensor assembly 94, and the hydrocarbon sensor assembly 94 is used by attaching it to an exhaust path described later. The hydrocarbon sensor assembly 94 includes:
Holder 942 holding hydrocarbon sensor 1 and holder 9
A cover 941 covers the front of the sample gas sensor 42 and protects the hydrocarbon sensor 1 from exhaust gas as a sample gas.

A plurality of leads are connected to the hydrocarbon sensor 1 for the purpose of drawing output, applying a voltage, and the like. A housing 944 for storing the leads is provided with the hydrocarbon sensor. It is provided on the assembly 94. Further, the hydrocarbon sensor assembly 94 is provided with a flange 943 for fixing the same to an exhaust path.

The cover 941 has a plurality of ventilation holes 9410 through which exhaust gas serving as a sample gas flows. Further, the above-mentioned lead wires are bundled together and pulled out from the housing 944 as a covered wire 949.

As shown in FIG. 4, the hydrocarbon sensor assembly 94 is connected to a three-way catalyst 953 in an exhaust pipe 950 which is an exhaust path of an automobile engine 951.
It is installed downstream of. Note that an air-fuel ratio sensor 952 is provided on the upstream side. In the configuration of FIG. 4, the HC concentration downstream of the three-way catalyst 953 is measured based on the signal of the hydrocarbon sensor 1 of the present embodiment, and the deterioration of the three-way catalyst 953 is detected.

Alternatively, as shown in FIG. 5, the hydrocarbon sensor assembly 94 is
Is installed in the recirculation path 955 of the HC adsorption device 954 attached to the exhaust pipe 950 that is the exhaust path of the HC. In the configuration of FIG. 5, based on the signal of the hydrocarbon sensor 1 of this example, H
The failure detection of the C adsorption device 954 and the control of the reflux flow rate are performed.

In each of FIGS. 4 and 5,
The hydrocarbon sensor assembly 94 includes a flange 94.
At 3, it is fixed to the exhaust path 950 or the recirculation path 955 by a bolt via a gasket (not shown).

Next, the oxidation activity of the La _0.5 Sr _0.5 MnO ₃ perovskite type oxide used for forming the inert electrode in the present example with respect to the reducing gas is compared with that of platinum, and the results are shown in FIGS. 8 is shown. Incidentally, the reducing gas HC, CO, consists H _2, which is generally gas contained in the exhaust gas of an automobile. The measurement of the oxidation activity was carried out by measuring CO-O ₂ -N ₂ gas (FIG. 6), H ₂ -O ₂ -N ₂
Gas (FIG. 7) and C ₃ H ₆ —O ₂ —N ₂ gas (FIG. 8) were used.

More specifically, the O ₂ gas is fixed at 0.2%,
The concentration of each reducing gas (CO, C ₃ H ₆ is N _2, HC) is made variable from 10 liters to adjust the overall flow rate N ₂ /
min. Thus, the air-fuel ratio of the gas was adjusted to 10 liter / min by adjusting the reducing gas. By adjusting the air-fuel ratio of the gas to the concentration of the reducing gas, 0.5 <λ <1.1, the output of the active electrode under each condition is plotted on the horizontal axis, and the output of the inert electrode is plotted on the vertical axis. Plot. The results are shown in FIG. 6 (CO), FIG. 7 (H ₂ ), and FIG.
(HC).

In FIGS. 6 to 8, a line having a 45-degree slope indicates that the output of a platinum electrode having a high oxidation activity with respect to a reducing gas is equal to the output of an inert electrode made of a perovskite-type oxide. It shows that the oxidizing activities of the electrodes are equivalent. If the measured value is below the 45 degree line, it indicates that the platinum electrode has higher oxidation activity than the inactive electrode.

As shown in FIGS. 6 to 8, La _0.5 Sr
The oxidation activity of the inert electrode made of _0.5 MnO ₃ is CO, H
It was found that it had the same activity as the platinum electrode for the oxidation reaction of ₂ , but was inactive for the oxidation reaction of HC. From the above, it was found that La _0.5 Sr _0.5 MnO ₃ exhibited excellent characteristics as an inert electrode.

Next, detection of the concentration of HC in the sample gas by the hydrocarbon sensor 1 of this embodiment will be described. First, as shown in FIG. 4, the exhaust gas discharged from the engine 951 passes through the three-way catalyst 953, or as shown in FIG. 5, the exhaust gas discharged from the engine 951 flows to the recirculation path 955 of the HC adsorption device. And arrives around the hydrocarbon sensor 1 as a sample gas.

At this time, the oxygen concentration in the exhaust gas discharged from the engine 951 changes variously for the purpose of optimizing the operation of the three-way catalyst 953. Then, as shown in FIG. 1, the sample gas passes through the sample gas introduction path 121 and diffuses into the sample gas chamber 100.

At this time, the oxygen concentration in the sample gas chamber 100 is monitored by the limiting current value in the HC active cell 41 to which a constant voltage (for example, 0.8 V) is applied. Note that, as shown in FIG.
When the voltage applied to 1 is changed, the current does not change within a certain voltage range. The current value at this time is the limit current value. In the figure, I0, I1, and I2 are all limit current values. Then, the magnitude of the limit current value increases as the oxygen concentration increases.

The above limit current value is determined by the HC active cell 4
The current is detected by the ammeter A2 in the circuit 415 that has conducted to 1. When the air-fuel ratio in the sample gas chamber 100 detected by the limit current value is leaner than a predetermined value (for example, λ = 1), a voltage is applied to the oxygen pump cell 21 to move the sample from the sample gas chamber 100 to the atmosphere chamber 103. Emit oxygen.

At this time, as shown in FIG. 10, the discharge amount of oxygen increases as the voltage application amount increases, and the oxygen discharge amount decreases as the voltage application amount decreases. Therefore, the applied amount of the voltage in this case is optimized from the value of the ammeter A2 by the controller 216 using modern control to optimize the amount of oxygen emission, and to reduce the air-fuel ratio in the sample gas chamber 100 to approximately λ = 1. It is fixed.

On the other hand, the air-fuel ratio in the sample gas chamber 100 detected by the limit current value becomes a predetermined value (for example, λ = 1).
In the case of a richer condition, the voltage applied to the oxygen pump cell 21 is reduced, and
Supply oxygen to zero. At this time, the supply amount of oxygen
As shown by 0, the voltage decreases as the applied voltage increases, and increases as the applied voltage decreases. Therefore, the voltage application amount in this case is optimized from the value of the ammeter A2 by the controller 216 using modern control, thereby optimizing the oxygen supply amount and reducing the air-fuel ratio in the sample gas chamber 100 to approximately λ.
= 1 is fixed.

With the above control, as shown in FIG.
The sample gas chamber 10 detected by the HC active cell 41
The oxygen concentration within 0 has a slight variation (oscillation width W1), but a value within a certain range, which is Y1 on average. The limiting current value a2 in the HC activity cell 41, HC, CO, and the reducing gas H ₂ is the oxidation reaction, oxygen is generated as a result of consumed value.

On the other hand, a constant voltage (for example, 0.8 V) is also applied to the HC inactive cell 31, and the limit current value a1 is determined by the circuit 315 which is electrically connected to the HC inactive cell 31.
It is detected by the ammeter A1 inside.

However, as described above, the limit current value a1 is determined by the fact that the inert electrode 318 on the sample gas chamber 100 side of the HC inert cell 31 has a La _{0.5 value} that is inactive to the HC oxidation reaction.
Since it is composed of Sr _0.5 MnO ₃ perovskite type oxide, this is a value generated as a result of oxidizing reaction of each reducing gas such as CO and H ₂ to consume oxygen. As described above, a difference corresponding to the concentration of HC occurs between the limit current values a1 and a2, and the HC concentration in the sample gas chamber 100 can be measured from the difference.

The inert electrode 218 on the sample gas chamber 100 side of the oxygen pump cell 21 is made of a La _0.5 Sr _0.5 MnO ₃ perovskite oxide that is inert to the oxidation reaction of HC. Room 100
No extra HC is consumed inside the chamber, and accurate HC concentration measurement is possible.

Next, a performance test of the hydrocarbon sensor 1 according to this embodiment will be described. In the above performance test, H
In the sample gas in which the C concentration and the oxygen concentration were adjusted, the HC concentration was detected by the hydrocarbon sensor 1 according to the present example. In this test, propylene was used as HC, and the results are shown in FIG.

According to the figure, the hydrocarbon sensor 1 according to the present example has an oxygen concentration of 0%, 0.1%,
In the case of 0.5%, an output (limit current value difference) proportional to the HC concentration was obtained in each case. Also,
The obtained difference in the limit current value was also as high as approximately 580 to 620 μA per 1000 ppm of the HC concentration, and thus it was found that the sensor according to the present example was a highly sensitive hydrocarbon sensor.
Further, it was found that the influence of the fluctuation of the oxygen concentration in the sample gas was small, and that the sensor according to this example was a hydrocarbon sensor having high detection accuracy with respect to the HC concentration.

Next, the operation and effect of this embodiment will be described. In the hydrocarbon sensor 1 of the present embodiment, the inert electrode 318 is made of a perovskite oxide La _0.5 Sr
It is composed of _0.5 MnO ₃ . The perovskite oxide is a substance that does not deteriorate even at a high temperature of 900 ° C. For this reason, when the hydrocarbon sensor 1 is used, the aggregation of the electrode components in the inert electrode 318 hardly occurs, the accuracy is not deteriorated due to the aggregation, and the HC concentration can always be accurately measured. it can.

As described above, according to the present embodiment, it is possible to provide a hydrocarbon sensor that accurately measures the concentration of HC in a sample gas and hardly deteriorates in use.

In this example, the HC active cell 4
Although a platinum electrode is used as the first active electrode 418, a platinum-rhodium alloy having a higher HC oxidation activity may be used.

Embodiment 2 As shown in FIGS. 13 to 17, the hydrocarbon sensor according to the present embodiment has one surface of a first solid electrolyte substrate in which an active electrode and an inactive electrode face a sample gas chamber and the surface thereof. It is provided on the opposite surface, where the detection cell is formed.

As shown in FIGS. 13 and 14, a sample gas chamber 501 formed at least in part by the oxygen ion conductive first solid electrolyte substrate 13 and in which the flow of the sample gas is restricted, 501 and at least a portion thereof is connected to the first solid electrolyte substrate 13.
And a second chamber 502 formed by The second chamber 502 is formed at least in part by the second solid electrolyte substrate 12 having oxygen ion conductivity.

Electrodes provided on one surface 138 of the first solid electrolyte substrate 13 facing the sample gas chamber 501 and on the opposite surface 139 of the first solid electrolyte substrate 13 facing the second chamber 502, respectively. Detection cell 51 comprising
Having. One of the electrodes in the detection cell 51 is an active electrode 518, and the other is an inactive electrode 519.

The second solid electrolyte substrate 12 comprises one surface 128 facing the second chamber 502 and electrodes 618 and 619 provided on the opposite surface 129, respectively, and detects the oxygen concentration in the second chamber 502. Oxygen sensor cell 61
And an inert electrode 218 and an electrode 219 provided on one surface 128 of the second solid electrolyte substrate 12 facing the second chamber 502 and an opposite surface 129 thereof, respectively. An oxygen pump cell 21 for supplying and discharging.

That is, as shown in FIG. 14, the hydrocarbon sensor 1 of this embodiment does not use the HC inert cell used in the first embodiment, and as shown in FIG. The HC concentration is detected using the first solid electrolyte substrate 13 whose surface is exposed and the detection cell 51 provided here. The active electrode 518 is made of platinum which is active in the oxidation reaction of each reducing gas of HC, CO, and H ₂ , and the inactive electrode 519 is inactive in the oxidation reaction of HC.
La _0.6 The oxidation reaction of the _second reducing gas is an active perovskite-type oxide Sr _0.4 Mn _0.5 Co _0.45 Ni
_It consists of _0.05 O ₃ .

As shown in FIG. 13, in the oxygen pump cell 21, the inert electrode 218 and the electrode 2
19 and a circuit 215 via a controller 216.
Are formed. The controller 216 has a power supply for applying a voltage to the inactive electrodes 218 and 219 and a variable resistor for controlling the voltage.

In the oxygen sensor cell 61,
A voltmeter V is provided between the active electrode 618 and the electrode 619.
2, a circuit 615 is formed. The above voltmeter V
2 detects the electromotive force generated between the active electrode 618 and the electrode 619. Further, a feedback circuit 25 is provided between the voltmeter V2 and the controller 216. Through this circuit, the operation control of the oxygen pump cell 21 using the controller 216 based on the electromotive force detected by the voltmeter V2. Is performed using PID control or the like.

In the detection cell 51, a voltmeter V1 is provided between the active electrode 518 and the inactive electrode 519.
A circuit 515 is formed via the. The voltmeter V1 detects an electromotive force generated between the active electrode 518 and the inactive electrode 519.

As shown in FIGS. 14 and 13, the hydrocarbon sensor 1 includes an alumina substrate 125, a first solid electrolyte substrate 13, an alumina substrate 136, a solid electrolyte substrate 12, and an alumina substrate 135 between an alumina substrate 135 and an alumina heater substrate 141. This is a laminated hydrocarbon sensor 1 constituted by supporting alumina substrates 127 and 142.

As shown in FIG. 14, the sample gas chamber 501 includes an alumina substrate 135 and a window 126 of the alumina substrate 125. The second chamber 502 includes the window 137 of the alumina substrate 136 and the second solid electrolyte substrate 12. The above sample gas chamber 5
01 and the second chamber 502, the first solid electrolyte substrate 1
3 are connected by a window 139.

As shown in FIG. 14, the second solid electrolyte substrate 12 is provided with an inert electrode 218, an electrode 219, an inert electrode 618, and an electrode 619. In addition, the second solid electrolyte substrate 12 has a terminal 564 for connecting the circuit 215 shown in FIG. 13 to the inactive electrodes 218 and 219, and the inactive electrode 618 and the electrode 619.
However, a terminal portion 565 for connecting a circuit 615 shown in FIG. 13 is provided. The leads 558 and 559 are connected between the inactive electrodes 218 and 219 and the terminal 564 and between the inactive electrodes 618 and 619 and the terminal 565.

The first solid electrolyte substrate 13 is provided with an active electrode 518 and an inactive electrode 519. Also,
The first solid electrolyte substrate 13 has the active electrode 51 thereon.
8. A terminal portion 563 for connecting the circuit 515 shown in FIG. 13 to the inactive electrode 519 is provided.
And the active electrode 518 and the inactive electrode 519 are connected by a lead portion 561.

As shown in FIG. 14, terminal portions 568 and 56 formed on the alumina substrate 135 so as to be able to conduct with the terminal portions 563, 564 and 565.
9,570 are provided. The terminal portions 563 and 5
68, between terminal portions 564 and 569, and between terminal portions 56
5 and 570, through holes 573 penetrating the first solid electrolyte substrate 13 and the second solid electrolyte substrate 12,
571, and further, alumina substrates 136, 125 and 135
Through holes 572, 566, and 567 are provided, and these through holes establish electrical continuity between the terminals. Others are the same as the first embodiment.

Next, La _0.6 Sr _0.4 Mn _0.5 Co _0.45 Ni used for forming the inactive electrode in this example.
_The oxidizing activity of the _0.05 O ₃ perovskite type oxide against reducing gas is shown in FIGS. 6 to 8 in comparison with platinum. The measuring method and the evaluation method are the same as those in the first embodiment.

[0100] As shown in the drawing, the oxidation activity of the inactive electrode made of _{La 0.6 Sr 0.4 Mn 0.5 Co 0.45} Ni 0.05 O 3 used in this embodiment is CO, platinum electrode for the oxidation of H ₂ It has an activity equivalent to that of, but was found to be inactive against the HC oxidation reaction. From the above,
It was found that La _0.6 Sr _0.4 Mn _0.5 Co _0.45 Ni _0.05 O ₃ exhibited excellent characteristics as an inert electrode.

Next, the HC by the hydrocarbon sensor 1 of this embodiment will be described.
The density detection will be described. The hydrocarbon sensor 1 of the present embodiment detects the concentration of HC in the sample gas as shown below. As shown in FIG. 13, the sample gas passes through the sample gas introduction channel 121 and is
1, and subsequently diffuse into the second chamber 502. Since the communication between the two chambers is connected by the window 139 having a sufficiently large area compared to the diffusion speed of the sample gas, the phenomenon that the diffusion state of the sample gas differs between the two chambers occurs. Absent.

At this time, the oxygen concentration in the second chamber 502 is monitored in the oxygen sensor cell 61 by an electromotive force value caused by a partial pressure difference from the oxygen concentration partial pressure in the atmospheric chamber 103. Then, the electromotive force value is detected by the voltmeter V2 in the circuit 615 electrically connected to the oxygen sensor cell 61. The oxygen sensor cell 61 has an output corresponding to the oxygen concentration in the sample gas chamber 501 as shown in FIG.

This electromotive force value is a predetermined value (for example, 0.45
V) When the output is lower, that is, when the oxygen concentration in the sample gas chamber 501 is high, a voltage is applied to the oxygen pump cell 21 to discharge oxygen from the sample gas chamber 501 to the atmosphere chamber 103. At this time, as shown in FIG. 10 of the first embodiment, the amount of discharged oxygen increases as the applied voltage increases, and decreases as the applied voltage decreases. Therefore, the voltage application amount in this case is optimized by the controller 216 using the PID control from the value of the voltmeter V2, thereby optimizing the oxygen discharge amount and keeping the output value of the oxygen sensor cell 61 constant at 0.45V. .

On the other hand, when the electromotive force value indicates an output higher than the predetermined value (0.45 V),
When the oxygen concentration in 1 is low, the voltage value applied to the oxygen pump cell 21 is reduced so that oxygen can be supplied from the atmosphere chamber 103 to the sample gas chamber 501. At this time,
As shown in FIG. 10, the amount of diffusion of oxygen decreases as the amount of applied voltage increases, and increases as the amount of applied voltage decreases.

Therefore, the voltage application amount in this case is optimized from the value of the voltmeter V2 by the controller 216 using PID control, the oxygen supply amount is optimized, and the output value of the oxygen sensor cell 61 is set to 0.45V. It is constant. By the above control, as shown in FIG. 16, although the output value of the voltmeter V2 corresponding to the oxygen concentration in the sample gas chamber 501 detected by the oxygen sensor cell 61 has a slight variation (the swing width W2), A value within a certain range is approximately Y2 on average.

As described above, under the condition that the oxygen concentration in the sample gas chamber 501 is constant, HC, CO, H ₂ is detected on the active electrode 518 of the detection cell 51 on the first solid electrolyte substrate 13. Each of the reducing gases undergoes an oxidation reaction,
Oxygen is consumed. On the other hand, on the inactive electrode 519, C
Oxidizing reactions of the reducing gases O and H ₂ consume oxygen.

As described above, comparing the amount of oxygen consumed on the active electrode 518 with the amount of oxygen consumed on the inactive electrode 519, the active electrode 518 is consumed by the oxidation reaction of HC.
As a result, a large amount of oxygen is consumed, and as a result, a concentration gradient occurs on both surfaces of the solid electrolyte substrate 13 due to a difference in oxygen partial pressure.
Therefore, according to the concentration of HC in the sample gas chamber 501,
Since an electromotive force is generated on the first solid electrolyte substrate 13, HC
The concentration can be measured accurately.

Also, in this case, the second
The inert electrode 218 on the chamber 502 side is composed of La _0.6 Sr _0.4 Mn _0.5 Co _0.45 Ni _0.05 O ₃ which is inert to the oxidation reaction of HC.
Since it is composed of a perovskite oxide, the consumption of HC in the second chamber 502 does not occur, and accurate HC concentration measurement is possible.

Next, the performance of the hydrocarbon sensor 1 according to this embodiment will be described. In the test for measuring the performance described above, the HC concentration was detected by the hydrocarbon sensor 1 according to the present example in a sample gas in which the HC concentration and the oxygen concentration were adjusted as in the first embodiment. The result is shown in FIG. According to the figure, in the hydrocarbon sensor 1 according to the present example, the oxygen concentration in the sample gas is 0%, 0.1%, 0.5%.
In each case, an output (electromotive force difference) corresponding to the HC concentration could be obtained.

The obtained electromotive force difference also shows that the HC concentration is 10%.
It was as high as approximately 480 to 500 mV per 00 ppm, and it was found that the sensor according to this example was a highly sensitive hydrocarbon sensor. Further, it was found that the influence of the fluctuation of the oxygen concentration in the sample gas was small, and that the sensor of this example was a hydrocarbon sensor having high detection accuracy with respect to the HC concentration. As described above, according to this example, it is possible to provide a hydrocarbon sensor with high sensitivity and high accuracy with respect to the HC concentration.

Further, the hydrocarbon sensor of the present embodiment does not require a power supply, so that it can have a simple circuit configuration, and since the HC concentration is detected by electromotive force, a high output can be obtained. Others have the same operation and effects as the first embodiment.

Embodiment 3 As shown in FIGS. 18 to 21, this embodiment has a first sample gas chamber and a second sample gas chamber separated by partitions.
The hydrocarbon sensor has a first sample gas chamber provided with an HC inert cell and a first oxygen pump cell, and a second sample gas chamber provided with an active cell and a second oxygen pump cell.

As shown in FIG. 18, the hydrocarbon sensor of this embodiment has two independent first sample gas chambers 101 and a second sample gas chamber 102 separated by a partition wall 109. The sample gas chambers 101 and 102 are provided with sample gas introduction paths 121 and 122, respectively.

As shown in FIG. 19, a portion of the solid electrolyte substrate 12 facing the first sample gas chamber 101 is provided with a first oxygen pump cell 21 composed of a pair of inert electrodes 218 and 219. Further, an HC inert cell 3 including a pair of inert electrodes 318 and 319 is provided.
1 is provided.

A second oxygen pump cell 22 including inert electrodes 228 and 229 is provided in a portion facing the second sample gas chamber 102. Further, an HC active cell 41 including a pair of active electrodes 418 and 419 is provided. The inert electrodes 218, 228, 318 are made of HC
L, which is a perovskite-type oxide inert to the oxidation reaction of
a _0.5 Sr _0.5 MnO ₃ . Another active electrode 418 is made of platinum.

As shown in FIG. 18, in the first oxygen pump cell 21, the circuit between the inactive electrode 218 and the electrode 219 is communicated via the controller 216.
15 are formed. In addition, the second pump cell 22
In, a circuit 214 is formed between the inactive electrode 228 and the electrode 229 via a controller 216. The circuits 214 and 215 are formed in parallel.

The controller 216 has a power supply for applying a voltage to the inactive electrodes 218, 219, 228, and 229, and a variable resistor for controlling the voltage. The inactive electrodes 218, 219, 228, and 229 are all provided to have the same area. Other configurations, circuit control methods, and the like are the same as those in the first embodiment.

As shown in FIGS. 18 and 19, the hydrocarbon sensor 1 has an alumina substrate 125 and a solid electrolyte substrate 1 between an alumina substrate 135 and an alumina heater substrate 141.
2, a laminated hydrocarbon sensor constituted by sandwiching alumina substrates 127 and 142. The first sample gas chamber 101 and the second sample gas chamber 102
Are the solid electrolyte substrate 12 and the alumina substrates 125 and 135
It is composed of

As shown in FIG. 19, the solid electrolyte substrate 12 has inactive electrodes 218, 219, 228, 229, 318, 319,
An active electrode 418 and an electrode 419 are provided.

The solid electrolyte substrate 12 is provided with a terminal portion 765 for connecting the inactive electrode 218 and the electrode 219 to a circuit 215.
A terminal portion 762 for connecting the electrode 28 and the electrode 229 to the circuit 214 is provided. The solid electrolyte substrate 12
In addition, the inactive electrode 318 and the electrode 319 are connected to the circuit 31.
5 is connected to the active electrode 41.
A terminal portion 763 for connecting the electrode 8 and the electrode 419 to the circuit 415 is provided. The terminals and the electrodes are connected by leads 258 and 259, respectively.

The alumina substrate 135 has terminal portions 767, 768, 769, 7 formed so as to be able to conduct with the terminal portions 762, 763, 764, 765.
70 is provided. In addition, each terminal section 762 to 765 and 7
67 to 770, through holes 271 penetrating the solid electrolyte substrate 12, alumina substrates 125 and 13
5 are connected to each other by through holes 266 and 267 penetrating therethrough.

The first sample gas chamber 10 is placed in the alumina substrate 125 adjacent to the solid electrolyte substrate 12.
1 and a window 1262 for forming the second sample gas chamber 102 are provided.
Other parts are the same as in the first embodiment.

The hydrocarbon sensor 1 of this embodiment detects the concentration of HC in the sample gas as described below. First, Figure 1
As shown in FIG. 8, the sample gas passes through the sample gas introduction passages 121 and 122 and the first sample gas chamber 1
01 and the second sample gas chamber 102. At this time, the oxygen concentration in the second sample gas chamber 102 is monitored by the limiting current value in the HC active cell 41 to which a constant voltage (for example, 0.8 V) is applied as shown in FIG. I have.

The limit lightning current value is detected by the ammeter A2 in the circuit 415 which is electrically connected to the HC active cell 41. Second sample gas chamber 1 detected by this limit current value
02 is leaner than a predetermined value (eg, λ = 1), the first oxygen pump cell 21 connected in parallel
And a voltage is applied to both the second oxygen pump cell 22 and
In the second sample gas chamber 102 and the first sample gas chamber 10
Oxygen is exhausted from both inside 1 to the atmosphere chamber 103.

Here, the inactive electrodes 218, 228,
Since the areas of the electrodes 219 and 229 are equal, the amount of oxygen diffusion from the first sample gas chamber 101 and the second sample gas chamber 102 is the same. At this time, as shown in FIG. 10 described above, the amount of discharged oxygen increases as the amount of applied voltage increases, and decreases as the amount of applied voltage decreases. Therefore, the applied amount of the voltage in this case is optimized by the controller 216 from the value of the ammeter A2 using modern control to optimize the oxygen discharge amount, and the inside of the first sample gas chamber 101 and the second sample gas chamber 102 is controlled. Is fixed at approximately λ = 1.

On the other hand, the air-fuel ratio in the second sample gas chamber 102 detected by the limit current value becomes a predetermined value (for example, λ
= 1), the voltage value applied to both the first oxygen pump cell 21 and the second oxygen pump cell 22 connected in parallel is reduced, and the voltage from the atmosphere chamber 103 to the first sample gas chamber 101 is reduced. The oxygen is allowed to diffuse into both inside the two sample gas chambers 102. Since the areas of the inert electrodes 218 and 228 and the electrodes 219 and 229 are equal, the amount of oxygen diffusion from the first sample gas chamber 101 and the second sample gas chamber 102 is the same.

At this time, the diffusion amount of oxygen is as shown in FIG.
As shown in the figure, it decreases as the applied voltage increases,
It increases as the amount of applied voltage decreases. Therefore, the applied amount of the voltage in this case is optimized by the controller 216 from the value of the ammeter A2 using modern control to optimize the oxygen supply amount, and the voltage in the first sample gas chamber 101 and the second sample gas chamber 102 is adjusted. Is fixed at approximately λ = 1.

With the above control, as shown in FIGS. 20 and 21, the oxygen concentration in the first sample gas chamber 101 and the oxygen concentration in the second sample gas chamber 102 slightly fluctuate (fluctuation widths W3 and W4). Although there is a certain range, the values are in a certain range, and are Y3 and Y4 on average. In addition, the swing widths W3 and W
4 and the average values Y3 and Y4 of the oxygen concentration are the same value.

The limiting current value a2 (detected by the ammeter A2) in the HC active cell 41 is HC,
This is a value generated as a result of oxidizing reaction of each reducing gas of CO and H ₂ to consume oxygen. On the other hand, a constant voltage (for example, 0.8 V) is applied to the HC inactive cell 31, and the limit current value a1 is detected by the ammeter A1 in the circuit 315 which is electrically connected to the HC inactive cell 31.

However, the limit current value a1 detected by the ammeter A1 is, as described above, the value of the HC inactive cell 31.
The inert electrode 218 on the first sample gas chamber 101 side is H
Since it is composed of a La _0.5 Sr _0.5 MnO ₃ perovskite oxide inactive to the oxidation reaction of C, CO, H
_This is the value generated as a result of the oxidation reaction of each reducing gas and the consumption of oxygen. Thus, the ammeter A1 and the ammeter A
2, the output difference is a difference in the oxidation reaction of HC, so that the HC concentration in the first sample gas chamber 101 can be measured.

In this case, the inactive electrodes 218, 318
Is composed of La _0.5 Sr _0.5 MnO ₃ , which is a perovskite oxide inactive to the oxidation reaction of HC, so that the HC is not consumed in the first sample gas chamber 101 and the HC concentration is precise. Measurement is possible.

As described above, in the hydrocarbon sensor 1 of this embodiment, the second sample gas chamber 102 for detecting the air-fuel ratio of the sample gas chamber is separated from the first sample gas chamber 101 that does not consume HC. By doing so, it is possible to more accurately detect the HC concentration. Other functions and effects are the same as those of the first embodiment.

Embodiment 4 As shown in FIG. 22, this embodiment is similar to the first solid electrolyte substrate 13 shown in FIG.
Cell 51 comprising an active electrode 518 and an inactive electrode 519 provided on one surface facing the sample gas chamber 100 of FIG.
Is a hydrocarbon sensor 1 having:

The hydrocarbon sensor 1 has a surface 12 of the second solid electrolyte substrate 12 facing the sample gas chamber 100.
8 and an oxygen pump cell 21 comprising an inactive electrode 218 and an electrode 219 provided on the opposite surface 129 thereof. The oxygen sensor cell 61 includes an inert electrode 618 and an electrode 619 provided on the surface 128 of the second solid electrolyte substrate 12 and the opposite surface 129 thereof. Other configurations are the same as those of the hydrocarbon sensor according to the second embodiment.

Also in the hydrocarbon sensor 1 according to this embodiment, since the active electrode 518 and the inactive electrode 519 consume different amounts of oxygen, a difference in oxygen partial pressure concentration occurs on the surface of the first solid electrolyte substrate 13. . Therefore, the first solid electrolyte substrate 13 is changed according to the HC concentration in the sample gas chamber 100.
An electromotive force is generated above, and the HC concentration can be measured accurately.

[Brief description of the drawings]

FIG. 1 is a cross-sectional explanatory view of a hydrocarbon sensor according to a first embodiment.

FIG. 2 is a development explanatory view of a hydrocarbon sensor according to the first embodiment.

FIG. 3 is a partial cross-sectional explanatory view of a hydrocarbon sensor assembly according to the first embodiment.

FIG. 4 is a layout explanatory view when a hydrocarbon sensor assembly is used for detecting deterioration of a three-way catalyst installed in an exhaust system of an automobile in the first embodiment.

FIG. 5 is an explanatory view of the arrangement when the hydrocarbon sensor assembly is used for detecting a failure of the HC adsorbing device installed in the exhaust system of the vehicle in the first embodiment.

FIG. 6 is a graph showing the relationship between CO in Embodiment 1 and Embodiment 2
Diagram comparing the oxidation reaction activities of perovskite-type oxides and platinum with respect to.

FIG. 7 shows H ₂ in Embodiment Example 1 and Embodiment Example 2;
Diagram comparing the oxidation reaction activities of perovskite-type oxides and platinum with respect to.

FIG. 8 shows HC in the first embodiment and the second embodiment.
Diagram comparing the oxidation reaction activities of perovskite-type oxides and platinum with respect to.

FIG. 9 is a diagram showing a relationship between an oxygen concentration, a voltage applied to an HC active cell, and a limit current flowing therethrough in the first embodiment.

FIG. 10 is a diagram showing a relationship between an applied voltage of an oxygen pump cell and supply and discharge of oxygen to and from a sample gas chamber in the first and second embodiments.

FIG. 11 is a diagram showing a change in oxygen concentration in a sample gas chamber in the first embodiment.

FIG. 12 is a line showing a relationship between a difference in oxygen concentration in a sample gas, an HC concentration in a sample gas, and a difference between limiting current values applied to an HC inactive cell and an HC active cell in the first embodiment. FIG.

FIG. 13 is an explanatory sectional view of a hydrocarbon sensor according to the second embodiment.

FIG. 14 is a development explanatory view of a hydrocarbon sensor according to the second embodiment.

FIG. 15 is a diagram showing a relationship between an oxygen concentration and an electromotive force generated in an HC active cell according to the second embodiment.

FIG. 16 is a diagram showing a change in oxygen concentration in a sample gas chamber in a second embodiment.

FIG. 17 is a diagram showing a relationship between a difference in oxygen concentration in a sample gas, an HC concentration in the sample gas, and an electromotive force applied to a detection cell in the second embodiment.

FIG. 18 is an explanatory sectional view of a hydrocarbon sensor according to the third embodiment.

FIG. 19 is a development explanatory view of a hydrocarbon sensor according to the third embodiment.

FIG. 20 is a diagram showing a change in oxygen concentration in a first sample gas chamber in a third embodiment.

FIG. 21 is a diagram showing a change in oxygen concentration in a second sample gas chamber in a third embodiment.

FIG. 22 is an explanatory sectional view of a hydrocarbon sensor according to the fourth embodiment.

[Explanation of symbols]

 1. . . Hydrocarbon sensor, 100. . . Sample gas chamber, 12. . . 21. solid electrolyte substrate, . . Oxygen pump cell, 218, 318, 518. . . Inert electrode, 31. . . HC inert cell, 41. . . HC active cell, 418, 519. . . Active electrode, 51. . . Detection cell,

Claims (9)

[Claims] An active electrode made of a material active in HC;
A hydrocarbon sensor having an inert electrode made of a material inert to HC and detecting the concentration of HC in a sample gas, wherein the inert electrode is made of a perovskite oxide. 2. The perovskite oxide according to claim 1, wherein the perovskite oxide is represented by a general formula of A _{1 -X} A ′ _X BO ₃ (where 0 <x <1), and A is selected from La, Y and Nd. A ′ is at least one element selected from Sr, Ca, and Ba, and B is Mn, C
A hydrocarbon sensor comprising at least one element selected from the group consisting of o, Ni, Fe, and Cr. 3. The sample gas chamber according to claim 1, wherein at least a part of the sample gas chamber is formed by an oxygen ion-conductive solid electrolyte substrate, and the flow of the sample gas is restricted. An HC active cell comprising an active electrode provided on one surface facing the chamber and an electrode provided on the opposite surface, and an HC active cell provided on one surface of the solid electrolyte substrate facing the sample gas chamber and on the opposite surface thereof. An oxygen pump cell comprising an electrode and supplying and discharging oxygen to and from the sample gas chamber, and an inert electrode provided on one surface of the solid electrolyte substrate facing the sample gas chamber and provided on the opposite surface thereof And a HC inert cell comprising an electrode. 4. The sample gas chamber according to claim 1, wherein the sample gas chamber is formed at least in part by an oxygen ion-conductive first solid electrolyte substrate, and has a restricted flow of sample gas. A second chamber formed at least in part by the first solid electrolyte substrate, and one surface of the first solid electrolyte substrate facing the sample gas chamber and the first solid electrolyte substrate A hydrocarbon sensor having a detection cell comprising electrodes provided on the opposite surface facing the second chamber, wherein one of the electrodes in the detection cell is an active electrode and the other is an inactive electrode. 5. The second solid electrolyte substrate according to claim 4, wherein at least a part of the second chamber is formed of an oxygen ion conductive second solid electrolyte substrate, and the second solid electrolyte substrate faces the second chamber. An oxygen sensor cell for detecting the oxygen concentration in the second chamber, comprising an electrode provided on the surface and the opposite surface thereof, and an oxygen sensor cell for detecting the oxygen concentration in the second chamber, A hydrocarbon sensor, comprising: an electrode provided in each case; and an oxygen pump cell for supplying and discharging oxygen to and from the second chamber. 6. The sample gas chamber according to claim 1, wherein the sample gas chamber is formed at least in part by an oxygen ion conductive first solid electrolyte substrate, and the flow of the sample gas is restricted, and the first solid electrolyte substrate A detection cell consisting of two electrodes provided on one surface facing the sample gas chamber of the above, wherein one of the electrodes in the detection cell is an active electrode and the other is an inactive electrode. Hydrogen sensor. 7. The sample gas chamber according to claim 6, wherein at least a part of the sample gas chamber is formed by an oxygen ion conductive second solid electrolyte substrate, and one surface of the second solid electrolyte substrate facing the sample gas chamber. An oxygen pump cell comprising electrodes provided on the opposite surface thereof and supplying and discharging oxygen to and from the sample gas chamber, and one surface of the second solid electrolyte substrate facing the sample gas chamber and an opposite surface thereof A hydrocarbon sensor, comprising: an oxygen sensor cell for detecting an oxygen concentration in the sample gas chamber, the electrode comprising: 8. The oxygen pump cell according to claim 3, wherein the electrode facing the sample gas chamber or the second chamber in the oxygen pump cell is an inert electrode made of a material inert to HC. Hydrocarbon sensor. 9. The hydrocarbon sensor according to claim 8, wherein the inert electrode is made of a perovskite oxide.