JP2003294691A - Gas sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To a gas sensor element in which a rich shift hardly occurs. <P>SOLUTION: The gas sensor element 1 comprises a solid electrolyte body 11, an electrode 121 on the side of a gas to be measured and a reference electrode 122 both provided for the solid electrolyte body 11, a chamber 140 facing the electrode 121 on the side of the gas to be measured, a guiding-out hole 150 for connecting the chamber 140 to external atmosphere of the gas sensor element 1, and a diffused resistor layer 16 made of a porous material which covers an opening part 151 of the guiding-out hole 150 on the side of the external atmosphere. The diffused resistor layer 16 is directly exposed to the external atmosphere. The gas sensor element 1 is constituted in such a way that its external surface has no members provided with diffused resistors except the diffused resistor layer 16. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a gas sensor element that can be used for combustion control of an internal combustion engine for a vehicle.

[0002]

2. Description of the Related Art A gas sensor having a built-in A / F sensor element is provided in an exhaust system of a vehicle engine, an air-fuel ratio is measured from the oxygen concentration in the exhaust gas, etc., and combustion control of the engine can be performed using this. is there. When a three-way catalyst is used to purify the exhaust gas of a vehicle, it is important that the air-fuel ratio has a specific value in the combustion chamber of the vehicle engine in order to purify the exhaust gas efficiently. Therefore, by accurately measuring the air-fuel ratio with the A / F sensor element, highly accurate combustion control can be realized, and the exhaust gas purification efficiency by the three-way catalyst can be improved (this is the exhaust gas control feedback). It is the principle of the system).

[0003]

By the way, the inventors have found a phenomenon that an output of the A / F sensor element, which has been left for a long time, undergoes a rich shift within about 10 seconds after reaching the activation temperature. It was The activation temperature is the A / F
This is the temperature at which the sensor element can detect A / F.

This rich shift becomes a problem when the above A / F sensor element is used in an exhaust gas control feedback system mounted on a vehicle. That is, when the output rich shift occurs in the air-fuel ratio control immediately after the engine is started, the combustion of the engine is made extremely unstable. In the worst case, control the air-fuel ratio of the engine to the extremely lean side,
There is also a risk of misfire (engine stop).

The rich shift is considered to occur and disappear by the following process. That is, the rich shift occurs after the A / F sensor element is left in a high humidity atmosphere for a long time. When the A / F sensor element is left in a high-humidity atmosphere, water enters the element and is adsorbed. In particular, in the case of the elements having the configurations as described in Comparative Examples 1 and 2 described later, a large amount is adsorbed between the diffusion resistance layer and the exhaust gas side electrode and in the vicinity of the electrode.

The water is desorbed and vaporized when the A / F sensor element reaches the activation temperature. The vaporized water, that is, water vapor, tries to escape to the outside of the device through the porous diffusion layer and the like while expanding in volume, but it takes a certain amount of time to pass through the porous diffusion layer. Therefore, the water vapor pressure rises inside the element (particularly in the vicinity of the measured gas side electrode), and the oxygen partial pressure relatively decreases. This causes a rich shift in the output of the A / F sensor element (A portion shown in FIG. 2).

However, the water vapor gradually escapes to the outside through the porous diffusion layer, and at the same time, the exhaust gas around the element is taken into the inside. As a result, the rich shift subsides over time and a normal output is obtained. Thus, it is considered that the rapid volume expansion of water vapor due to desorption of water → vaporization causes a large rich shift of about 1 to 2 A / F. Of course, if the atmosphere outside the element is dry, this kind of problem does not occur, but the exhaust pipe of the parked vehicle is in a high humidity atmosphere due to the moisture contained in the exhaust gas, and in an environment that increases the probability of rich shift occurrence. is there.

Incidentally, such a problem is the same in various gas sensor elements (oxygen sensor element, NOx sensor element, etc.) used for combustion control of an internal combustion engine for vehicles and an exhaust gas control feedback system other than the A / F sensor element. Is a problem that arises.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a gas sensor element in which a rich shift is unlikely to occur.

[0010]

According to a first aspect of the present invention, there is provided a solid electrolyte body, a measurement gas side electrode and a reference electrode provided on the solid electrolyte body, and a chamber facing the measurement gas side electrode. The gas sensor element is characterized in that it has a lead-out hole which connects the chamber to the atmosphere outside the gas sensor element and has a lead-out hole which is directly connected to the atmosphere outside the chamber (claim 1).

The second invention has a solid electrolyte body, a gas to be measured side electrode and a reference electrode provided on the solid electrolyte body, and a chamber facing the electrode to be measured gas side, There is a lead-out hole that connects the chamber and the external atmosphere of the gas sensor element, and a diffusion resistance layer made of a porous material is provided so as to cover the opening of the lead-out hole on the side of the external atmosphere. According to another aspect of the gas sensor element, the gas sensor element is configured so that it is exposed to the outside atmosphere, and the outer surface of the member is free from any other member having a diffusion resistance.

The operational effects of the first and second inventions will be described. The gas sensor element according to the above invention has a lead-out hole connecting the chamber facing the measured gas side electrode and the external atmosphere. The gas sensor element is exposed to a high humidity atmosphere for a long time and reaches the activation temperature with a large amount of water entering inside,
When the water content becomes water vapor, the water vapor is rapidly released to the outside atmosphere through the outlet. Therefore, a rich shift due to a decrease in oxygen partial pressure in the chamber is less likely to occur.

As described above, according to the present invention, it is possible to provide a gas sensor element in which a rich shift is unlikely to occur.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A gas sensor element according to the present invention comprises an oxygen ion conductive solid electrolyte provided with a gas side electrode to be measured and a reference electrode, and an oxygen ion current flowing through an electrochemical cell constituted by these electrodes. Based on the above, the predetermined gas concentration is measured. In addition to an oxygen sensor element that measures the oxygen concentration in the gas to be measured, there is also a gas sensor element that is configured to decompose a specific gas to generate oxygen ions and measure the concentration of the specific gas based on the oxygen ions. . Examples of the specific gas include NOx, CO, and HC. Further, there is a gas sensor element that is installed in the exhaust system of an internal combustion engine, measures the oxygen concentration in the exhaust gas, and measures the air-fuel ratio (A / F) in the combustion chamber of the internal combustion engine based on the measured value.

The chamber is a place where the gas to be measured enters through the diffusion resistance layer and the outlet. The gas sensor element according to the present invention performs measurement based on an oxygen ion current generated from a gas concentration difference between the chamber and the reference gas facing the reference electrode. Further, the introduction hole may be constituted by a pinhole provided on the introduction hole forming plate covering the chamber.

Further, in the gas sensor element according to the first aspect of the invention, the chamber may be directly connected to the outside of the element through the lead-out hole. In this case, the gas under measurement enters the chamber through the outlet.

Further, in the second invention, by providing the diffusion resistance layer, it is possible to prevent the output fluctuation depending on the temperature of the gas to be measured and obtain a more accurate sensor output. Further, after the diffusion resistance layer is provided, the diffusion resistance layer can be trimmed by cutting or the like to finely adjust the sensor output. This configuration is convenient because there is no need to provide an external adjustment circuit.

Further, the diffusion layer according to the second aspect of the present invention is configured such that the diffusion resistance layer is directly exposed to the external atmosphere, and there is no member having another diffusion resistance on the outer surface thereof. As a result, the release of water vapor is not hindered in the part other than the diffusion resistance layer. Further, when moisture (water vapor) goes to the outside of the element, it receives a certain amount of diffusion resistance at the time of passing through the diffusion resistance layer, but the presence of the lead-out hole suppresses an increase in the partial pressure of water vapor in the chamber. Therefore, rich shift can be suppressed.

Further, it is preferable that a plurality of the lead-out holes are provided (claim 3). The paths through which water (water vapor) escapes are the lead-out holes and the diffusion resistance layer. Here, if the opening area of the lead-out holes is constant (the limiting current value is set to a predetermined value, the opening area of the lead-out holes is set to a predetermined value), it does not depend on the number of lead-out holes. By providing a plurality of holes, it is possible to disperse the amount of water (water vapor) that escapes from one hole and accelerate the escape time. Therefore, rich shift is less likely to occur.

Further, the gas sensor element may be of a two-cell type (claim 4). Since the rich chute occurs regardless of the structure of the gas sensor element, the configuration according to the present invention can effectively prevent the rich chute even in the case of a 2-cell type element. As the two-cell type element, for example, one having an electrode for a pump cell for adjusting the oxygen concentration in the chamber layer as shown in FIG. 4 described later, a monitor sensor for monitoring the oxygen concentration in the chamber, etc. Examples include those equipped with electrodes.

Next, the diffusion resistance ratio between the lead-out hole and the diffusion resistance layer is preferably 0.05 to 0.4 (claim 5). When the diffusion resistance of the lead-out hole is D1 and the diffusion resistance of the diffusion resistance layer is D2, the diffusion resistance ratio is {D2 / (D
1 + D2)}, and this value is 0.05 to 0.4. When the above two diffusion resistances are sufficiently larger than the diffusion resistance formed in the chamber, D1 and D2 can be expressed as follows. Lean side Is = (D1 + D2) ln {(1-P _O2 ) / P} Rich side Is = (D1 + D2) ln {(1-P _M ) / P} P _O2 is oxygen partial pressure, P _M is unburned gas Partial pressure, where unburned gas is H ₂ , C _n H, CO, etc. )

By keeping the diffusion resistance ratio within the above range, the following is obtained. That is, there is a relationship as shown in FIG. 6 between the diffusion resistance ratio and the rich shift amount. According to this, when the diffusion resistance ratio is 0.4 or less, the rich shift amount is at a level where there is no practical problem. However, when the value exceeds 0.4, the rich shift amount sharply increases. It is considered that this is because the amount of water adsorbed to the diffusion resistance layer increased by thickening the diffusion resistance layer in order to increase the diffusion resistance ratio, leading to an increase in the amount of rich shift. As described above, by setting the diffusion resistance ratio to 0.4 or less, it is possible to obtain the effect of suppressing the rich shift to a level at which there is no problem in practical use.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) As shown in FIG. 1, a gas sensor element 1 of the present embodiment has a solid electrolyte body 11, a pair of measured gas side electrodes 121 and a reference electrode 122 provided on the solid electrolyte body 11, The gas sensor element 1 includes a chamber 140 facing the measured gas side electrode 121.
Has a lead-out hole 150 that connects with the external atmosphere. And
The diffusion resistance layer 16 made of a porous material is provided so as to cover the opening 151 on the external atmosphere side of the lead-out hole 150, and the diffusion resistance layer 16 is directly exposed to the external atmosphere, and the diffusion resistance layer 16 is further exposed to the external surface. It is configured so that there is no member having a diffusion resistance.

The details will be described below. The gas sensor element 1 of this example is used by being built in a gas sensor and attached to an exhaust system of an automobile engine, and is used as a part of an exhaust gas control feedback system. From the oxygen concentration in the exhaust gas to the A / F of the automobile engine combustion chamber. Is an element configured to detect the.

As shown in FIG. 1, the gas sensor element 1 of this example is a plate-shaped solid electrolyte body 11 made of zirconia having oxygen ion conductivity, and the measured gas side provided on both sides of the solid electrolyte body 11. The electrode 121 to be measured includes a reference electrode 122. The gas-to-be-measured side electrode 121 faces a chamber 150 which is a space defined by the solid electrolyte body 11, the spacer 14 and the lead-out hole forming plate 15, and the reference electrode 122 is a solid electrolyte body. The reference gas chamber 130, which is a space partitioned by 11 and the spacer 13, is faced.

The spacer 13 is provided with a heater substrate 19 provided with a heating element 190 which generates heat when energized. The heating element 190 is energized when the gas sensor element 1 of this example is used, and the gas sensor element 1 is brought to an activation temperature.

The diffusion resistance layer 16 made of porous ceramic is laminated on the lead-out hole forming plate 15 having the lead-out holes 150.
The diffusion resistance layer 16 allows the opening 15 of the lead-out hole 15 to be formed.
The entire surface of the lead-out hole forming plate 15 including 1 is covered. Further, the diffusion resistance layer 16 is directly exposed to the outside of the element, and there is nothing that impedes the flow of gas on the surface thereof.

Next, an output time chart of the gas sensor element 1 according to this example was measured. The gas sensor element 1 of this example mounted on a gas sensor is attached to the exhaust system of an actual vehicle engine. Exhaust gas is generated by starting the engine, and the element 1 reaches the activation temperature by the temperature of the exhaust gas and the heating by energizing the heating element 190 built in the gas sensor element 1. FIG. 2 shows a diagram in which the output of the gas sensor element 1 is converted to A / F from the time immediately after the engine is started until 20 seconds have elapsed. Prior to the above measurement, the humidity of the exhaust system of the engine is maintained at 95% or higher, and the gas sensor element 1 is left in this state for 24 hours.

The broken line described as Example 1 in FIG. 2 is the output of the gas sensor element 1 according to this example, which is clear from the figure, but no rich shift occurred within 20 seconds from the engine start.

Further, using the gas sensor element 9 according to Comparative Example 1 described later, the time change of the output was measured in the manner described above. The result is a broken line in agreement with the comparison (1). As is clear from the figure, a very large rich shift of part A occurred in 8 to 10 seconds.

Also, after the exhaust system of the engine in which the gas sensor element 9 according to Comparative Example 1 to be described later is installed is left in a very dry atmosphere (humidity of 20% or less) for 24 hours, the output of the engine is changed as described above. The time change was measured. The result is a broken line in agreement with comparison (2). As is clear from the figure, since the element is dry, there is almost no water inside the element, and the rich shift does not occur.

Next, the function and effect of this example will be described. The gas sensor element 1 of the present example is a measurement target gas side electrode 121.
Has a lead-out hole 150 connecting the chamber 140 facing each other and the external atmosphere. The lead-out hole 150 has a diffusion resistance layer 16 so as to cover the opening 151, the diffusion resistance layer 16 is directly exposed to the outside atmosphere, and there is no member having any other diffusion resistance on the outer surface thereof. It is in.

Therefore, when the gas sensor element 1 is exposed to a high-humidity atmosphere for a long time and reaches the activation temperature with a large amount of water entering inside, and the water becomes water vapor, the water vapor diffuses into the outlet hole 150 and diffuses. It is rapidly released to the outside atmosphere through the resistance layer 16. Also, although it receives a certain amount of diffusion resistance when passing through the diffusion resistance layer 16,
The presence of 50 suppresses an increase in the partial pressure of water vapor in the chamber 140. Therefore, in the gas sensor element 1 having the configuration according to this example, a rich shift due to a decrease in the oxygen partial pressure in the chamber 140 is less likely to occur.

Further, since the gas sensor element 1 according to the present example is provided with the diffusion resistance layer 16, it is possible to prevent the output fluctuation depending on the temperature of the gas to be measured and obtain a more accurate sensor output. Further, after the diffusion resistance layer 16 is provided, the diffusion resistance layer is trimmed by cutting or the like so that the sensor output can be finely adjusted. This configuration is convenient because there is no need to provide an external adjustment circuit.

As described above, according to the present invention, it is possible to provide a gas sensor element in which rich shift is unlikely to occur.

(Embodiment 2) As shown in FIG. 3, this embodiment is a gas sensor element 1 having no diffusion resistance layer. The gas sensor element 1 includes a solid electrolyte body 11 and the solid electrolyte body 1
1 has a measured gas side electrode 121 and a reference electrode 122. It has a chamber 140 facing the measured gas side electrode 121, connects the chamber 140 to the external atmosphere of the gas sensor element 1, and has a lead-out hole 150 that directly opens from the chamber 140 to the external atmosphere. The other detailed configuration is the same as that of the first embodiment, and the function and effect are also the same as those of the first embodiment.
Is the same as.

(Embodiment 3) This embodiment is a two-cell type gas sensor element 1 as shown in FIG. This gas sensor element 1
The configuration is the same as in Example 1, but the lead-out hole forming plate 15 is made of a solid electrolyte, and a pair of electrodes 123 and 124 are provided so as to surround the lead-out hole 150. This electrode 123,1
A pump cell for keeping the oxygen concentration in the chamber 140 constant is constituted by 24 and the lead-out hole forming plate 15. The other detailed configuration is the same as that of the first embodiment, and the operation and effect are also the same as those of the first embodiment.

(Embodiment 4) This embodiment is a gas sensor element 1 having a large number of lead-out holes 150 as shown in FIG. This gas sensor element 1 has the same structure as that of the first embodiment, but has five lead-out holes 150 along a line in the longitudinal direction of the element. The other detailed configuration is similar to that of the first embodiment.

In the gas sensor element 1 of this example,
The paths through which moisture (water vapor) escapes are the five outlet holes 150 and the diffusion resistance layer 16. By providing five holes, it is possible to disperse the amount of water (water vapor) that escapes from one hole and to speed up the escape time. Therefore, rich shift is less likely to occur. Other details have the same effects as those of the first embodiment.

(Comparative Example 1) As shown in FIG. 7, the gas sensor element 9 comprises, in order from the bottom, a heater substrate 190 provided with a heating element 190, a spacer 13, a solid electrolyte body 11, a spacer 14, a diffusion resistance layer 16, and This is an element in which a gas blocking layer 91 is laminated (Japanese Patent Laid-Open No. 2000-275215). The moisture (water vapor) that has entered the chamber 140 is the diffusion resistance layer 1
It goes out through 6 avoiding the gas barrier layer 91.
Since the gas blocking layer 91 is provided so as to cover the surface of the element in the stacking direction, water (water vapor) will flow out from the side surface of the element, and the path for water vapor to exit will be relatively long. . Therefore, rich shift is likely to occur.

Comparative Example 2 As shown in FIG. 8, the gas sensor element 90 is the gas sensor element 1 of the present invention shown in FIG.
A plate 92 having the same structure as that of FIG.
Is an element provided with (Japanese Utility Model Publication No. 7-23735). Since the pinhole 920 has a diffusion resistance, the moisture (water vapor) that exits from the chamber 140 here receives the diffusion resistance. That is, moisture (water vapor) goes out through the route of the lead-out hole 150, the diffusion resistance layer 16 and the pinhole 920. Therefore, even if the same lead-out hole 150 as in the present invention is provided, the rich shift cannot be prevented. This is because the pinhole 920 prevents water (water vapor) from flowing out.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between elapsed time and A / F of the gas sensor element according to the present example and the comparative example in Example 1.

FIG. 3 is an explanatory cross-sectional view of a gas sensor element having no diffusion resistance layer according to the second embodiment.

FIG. 4 is an explanatory cross-sectional view of a 2-cell type gas sensor element according to the third embodiment.

FIG. 5 is an explanatory diagram of a gas sensor element having a large number of lead-out holes according to the fourth embodiment.

FIG. 6 is a diagram showing a relationship between a diffusion resistance ratio and a rich shift amount.

FIG. 7 is an explanatory diagram of a gas sensor element in which a diffusion resistance layer and a gas blocking layer are stacked in the chamber in Comparative Example 1.

FIG. 8 is an explanatory view of a gas sensor element in which a plate having pinholes having diffusion resistance is laminated on a diffusion resistance layer in Comparative Example 2.

[Explanation of symbols]

1. ． ． Gas sensor element, 11. ． ． Solid electrolyte body, 121. ． ． Measured gas side electrode, 122. ． ． Reference electrode, 140. ． ． Chamber, 150. ． ． Outlet hole, 16. ． ． Diffusion resistance layer,

Continued front page    (72) Inventor Makoto Nakae             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO (72) Inventor Nami Fujii             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO

Claims (5)

[Claims] 1. A solid electrolyte body, a measurement gas side electrode and a reference electrode provided on the solid electrolyte body, and a chamber facing the measurement gas side electrode. The chamber and the gas sensor element are provided. A gas sensor element characterized by having a lead-out hole which is connected to an external atmosphere and which is directly connected from the chamber to the external atmosphere. 2. A solid electrolyte body, a gas to be measured side electrode and a reference electrode provided on the solid electrolyte body, and a chamber facing the gas to be measured side electrode. A diffusion resistance layer made of a porous material is provided so as to cover the opening on the external atmosphere side of the extraction hole, and the diffusion resistance layer is directly exposed to the external atmosphere. , A gas sensor element characterized in that the outer surface of the gas sensor element is configured so that there is no other member having a diffusion resistance. 3. The gas sensor element according to claim 1 or 2, further comprising a plurality of the lead-out holes. 4. The method according to claim 1, wherein
The gas sensor element is a two-cell type gas sensor element. 5. The method according to any one of claims 2 to 4,
The diffusion resistance ratio between the lead-out hole and the diffusion resistance layer is 0.
The gas sensor element is characterized in that it is 05 to 0.4.