JPH11326273A - Detecting apparatus for oxygen concentration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a detecting apparatus which prevents the aggravation of its detecting accuracy caused when an unburned component in a gas to be measured is stuck to an electrode for oxygen-concentration measurement. SOLUTION: A detection part 550 in an NOx sensor 500 is provided with a pump cell 582, for measurement, which is composed of a first solid electrolyte layer 552 as well as a detecting electrode 580 and a reference electrode 581 which are installed on its surface and its rear surface. When an electronic control unit(ECU) judges that an unburned component which is stuck to the detecting electrode 580 reaches a prescribed amount, a voltage for electrode treatment is applied across both electrodes 580, 581. Thereby, oxygen inside a reference-gas introduction space 580 is pumped to the detecting electrode 580 from the reference electrode 580. The unburned component which is stuck to the detecting electrode 580 is reacted with the pumped oxygen, and it is burned and removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration detecting device for detecting the concentration of oxygen contained in a gas to be measured, and more particularly to a pumping action by a pair of electrodes provided on a solid electrolyte body. The present invention relates to an oxygen concentration detection device that detects the concentration of oxygen contained in a gas to be measured or the concentration of oxygen contained in a constituent component (for example, nitrogen oxide or the like) in the gas to be measured.

[0002]

2. Description of the Related Art Conventionally, as a technique relating to such an oxygen concentration detecting apparatus, for example, a "nitrogen oxide sensor" described in Japanese Patent Application Laid-Open No. 9-288084 can be mentioned.

This nitrogen oxide sensor is made of zirconia (Z
a first chamber into which a gas to be measured is introduced, which is made of a solid electrolyte material through which oxygen ions such as rO2) can pass.
A second chamber communicated with the first chamber via the diffusion-controlling portion and a reference gas introduction space into which the atmosphere is introduced are formed.

[0004] In a partition part that partitions the first chamber from the outside,
A main pump cell for pumping, that is, pumping, oxygen ions in the first chamber to the outside is provided, and the gas to be measured introduced into the first chamber has an extremely high oxygen partial pressure due to the pumping of the main pump cell. It is controlled to a low predetermined pressure. The gas to be measured whose oxygen partial pressure has been controlled in this way is further introduced into the second chamber via the diffusion-controlling section.

[0005] A measurement pump cell for pumping oxygen ions in the second chamber into the reference gas introduction space is provided in a partition part that divides the second chamber and the reference gas introduction space. The measurement pump cell includes a detection electrode provided on the inner surface of the second chamber and a reference electrode provided on the inner surface of the reference gas introduction space. The detection electrode also functions as a catalyst for reducing nitrogen oxides (hereinafter abbreviated as "NOx") contained in the gas to be measured, and is formed of, for example, rhodium (Rh).

In the nitrogen oxide sensor having the above configuration, NOx in the gas to be measured introduced into the second chamber is reduced and decomposed by the detection electrode, so that the NOx is reduced.
Is produced in an amount corresponding to the concentration of When a predetermined voltage is applied between the detection electrode and the reference electrode, the generated oxygen (oxygen ions) is pumped from the detection electrode to the reference electrode, and a pump current flows between these two electrodes. And so on. Therefore, by measuring the magnitude of the pump current, the concentration of oxygen present in the second chamber is detected, and the concentration of NOx contained in the gas to be measured can be indirectly detected from the oxygen concentration. .

[0007]

By the way, in addition to the above-mentioned NOx, the exhaust gas discharged from an internal combustion engine such as a vehicle or marine engine usually has extremely high reactivity with oxygen such as hydrocarbon (HC). (Hereinafter, referred to as “unburned component”). Therefore, when the nitrogen oxide sensor is used in an atmosphere of an exhaust gas containing such unburned components, the unburned components adhere to the detection electrode, and the attached unburned components detect NOx in the exhaust gas or detect NOx in the exhaust gas. In some cases, the electrode reacts with oxygen generated by the NOx reducing action. As a result, when a large amount of unburned components may adhere to the detection electrode due to long-term use, the emission gas NO
x The correlation between the concentration and the pump current
There was a possibility that the detection accuracy of the x concentration was deteriorated.

Further, such a deterioration in detection accuracy is not limited to the nitrogen oxide sensor as described above, and may occur in an oxygen sensor for detecting the concentration of oxygen itself contained in exhaust gas, for example. . That is, even in such an oxygen sensor, if a large amount of unburned components adheres to the detection electrode, oxygen that should be pumped between the electrodes reacts with the unburned component adhered to the detection electrode, and the pump This is because the current value may be reduced from the original value.

The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent deterioration of detection accuracy caused by unburned components in a gas to be measured adhering to an electrode for measuring oxygen concentration. It is an object of the present invention to provide an oxygen concentration detecting device capable of performing the above.

[0010]

According to a first aspect of the present invention, a first electrode and a second electrode are provided on a solid electrolyte body, and the first electrode and the second electrode are in contact with the first electrode. A voltage is applied between the electrodes to move oxygen in the gas to be measured from the first electrode to the second electrode via the solid electrolyte member, and the current flowing between the electrodes due to the movement of oxygen is reduced. In the oxygen concentration detecting device for detecting the concentration of oxygen in the gas to be measured based on the first electrode and the first electrode, oxygen is transferred to the first electrode via the solid electrolyte body. A third electrode to which a voltage is applied is provided.

According to a second aspect of the present invention, in the oxygen concentration detecting device according to the first aspect, the third electrode is provided on the solid electrolyte body as the same electrode as the second electrode. And

Further, according to a third aspect of the present invention, in the oxygen concentration detecting device according to the first aspect, the third electrode is provided on the solid electrolyte body as a separate electrode from the second electrode. It is assumed.

According to the first to third aspects of the present invention, an electrode processing voltage is applied between the first electrode and the third electrode, so that the third electrode is connected to the third electrode via the solid electrolyte. Oxygen moves to the first electrode. Then, the unburned components adhering to the first electrode react with the transferred oxygen to be burned and removed.

According to a fourth aspect of the present invention, in the oxygen concentration detecting device according to any one of the first to third aspects, the solid electrolyte body has an air introduction space into which air is introduced, and the third electrode is It is arranged on the solid electrolyte body so as to be in contact with the atmosphere in the atmosphere introduction space.

According to this structure, in addition to the effect of the invention described in any one of the first to third aspects, a larger amount of oxygen moves from the third electrode to the first electrode. According to a fifth aspect of the present invention, the first electrode is formed of a reduction catalyst material that functions as a reduction catalyst for nitrogen oxides contained in the gas to be measured, and the nitrogen oxide is formed based on the reducing action of the first electrode. When the oxygen decomposed from the gas moves from the first electrode to the second electrode via the solid electrolyte body, the concentration of oxygen in the gas to be measured is detected based on the value of the current flowing between the electrodes. ing.

According to the above configuration, in addition to the operation of the invention described in any one of the first to fourth aspects, the exhaust gas is contained in the exhaust gas based on the value of the current flowing between the first electrode and the third electrode. The concentration of nitrogen oxides is detected.

Further, according to the invention described in claim 6,
When the reduction catalyst material is configured to include a predetermined amount of the oxidation catalyst material, in addition to the effect of the invention described in claim 5, the oxidation catalyst material contained in the reduction catalyst material allows the unburned component and oxygen to be separated. The oxidation reaction is accelerated.
Here, as a specific embodiment of the invention described in claim 6, as in the invention described in claim 7, a configuration in which the reduction catalyst material is rhodium and the oxidation catalyst material is platinum is preferable.

Further, according to the invention described in claim 8,
By setting the weight ratio of platinum to rhodium to 1 to 5%, the reduction of the reduction effect of rhodium is suppressed as much as possible, and the effect of promoting the oxidation of unburned components by platinum is ensured.

According to a ninth aspect of the present invention, in the oxygen concentration detecting apparatus according to the first to eighth aspects, the first electrode and the third electrode are connected only when a predetermined voltage application condition is satisfied.
Voltage applying means for applying an electrode processing voltage between the electrodes.

According to such a configuration, by appropriately setting the voltage application condition, the unburned components adhering to the first electrode can be removed at an appropriate timing. By the way, if there is a gas to be measured containing a large amount of unburned components near the first electrode, the oxygen that has moved to the first electrode reacts with the unburned components adhering to the first electrode. Without performing the measurement, there is a concern that the gas may react with the unburned components in the gas to be measured.

Therefore, as in the invention according to claim 10, the voltage application means sets the voltage application condition such that the concentration of the unburned component in the gas to be measured is equal to or lower than a predetermined value. According to such a configuration, of the oxygen moving to the first electrode side, the amount of oxygen reacting with the unburned component in the gas to be measured is reduced.

Further, when the gas to be measured is the exhaust gas of the combustion equipment, the voltage applying means is provided when the supply of the combustion fuel to the combustion equipment is stopped. 13. The configuration according to claim 12, wherein it is determined that the concentration of the unburned component is equal to or lower than a predetermined value, and when the gas to be measured is exhaust gas from a combustion device capable of performing lean combustion. As in the invention described above, the voltage applying means determines that the concentration of the unburned component is equal to or lower than a predetermined value when the combustion state in the combustion equipment is the lean combustion state. It is reliably determined that the concentration of the unburned component in the exhaust gas is equal to or lower than a predetermined value, and the process of removing the unburned component attached to the first electrode is performed based on the determination. It is assumed that the combustion equipment includes an internal combustion engine such as a gasoline engine and a diesel engine.

According to a thirteenth aspect of the present invention, in the oxygen concentration detecting device according to the ninth aspect, the amount of unburned components adhering to the first electrode is determined by measuring a contact time between the gas to be measured and the first electrode. The voltage application means is configured to make the estimated amount of adhesion of the unburned component equal to or more than a predetermined amount as the voltage application condition.

According to the above configuration, when the unburned component adhering to the first electrode is less than the predetermined amount and the influence on the detection accuracy is small, the process of removing the unburned component is not executed.

According to a fourteenth aspect of the present invention, in the oxygen concentration detecting device according to the thirteenth aspect, the voltage applying means determines that the amount of unburned component adhering estimated by the estimating means is equal to or greater than a predetermined amount. The voltage application condition is such that the concentration of the fuel component is equal to or lower than a predetermined value.

According to the above construction, in addition to the function of the invention described in claim 13, the amount of oxygen that reacts with the unburned components in the gas to be measured among the oxygen moving to the first electrode side is reduced. I will be.

According to a fifteenth aspect of the present invention, in the oxygen concentration detecting device according to the thirteenth or fourteenth aspect,
The gas to be measured is the exhaust gas of the combustion equipment, and the estimating means estimates the amount of the unburned component adhered to the first electrode based on at least one of the operation time and the number of starts of the combustion equipment.

The amount of unburned components adhering to the first electrode increases as the electrode is in contact with the exhaust gas of the combustion equipment, in other words, as the operating time of the combustion equipment increases. Also, generally, when starting the combustion equipment, the combustion state becomes unstable and the unburned components in the exhaust gas tend to increase,
Further, when the supply amount of the combustion fuel is increased in order to improve the startability, this tendency becomes remarkable. For this reason,
The amount of unburned components adhering to the first electrode increases as the number of starts of the combustion equipment increases, in other words, as the time of contact with the exhaust gas containing a large amount of unburned components increases.

According to the above construction, in addition to the function of the invention described in the thirteenth or fourteenth aspect, at least the operating time and the number of starts of the combustion equipment having a high correlation with the amount of the unburned component adhered to the first electrode. Based on one of them, the amount of the unburned component adhered to the first electrode can be easily and accurately estimated.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Hereinafter, an oxygen concentration detecting apparatus according to the present invention will be described using a nitrogen oxide (hereinafter referred to as "NOx").
) Will be described as a first embodiment embodied as a NOx concentration detecting device for detecting the concentration of the NOx.

FIG. 1 shows a vehicle gasoline engine (hereinafter referred to as a gasoline engine).
FIG. 2 is a schematic configuration diagram illustrating an engine 10, an exhaust gas recirculation device 19 and a NOx concentration detection device provided in the engine 10.

The engine 10 has a plurality of combustion chambers (not shown).
Cylinder Block 10a Having Cylinder and Cylinder Head 1
0b, and an intake passage 11 and an exhaust passage 12 connected to each combustion chamber. The intake passage 11 has the same passage 11
A throttle valve 16 for adjusting the amount of intake air passing through the inside is provided. The cylinder head 10b is provided with an injector 23 to which fuel is supplied through the delivery pipe 15. A catalytic converter 17 for purifying exhaust gas passing through the exhaust passage 12 is provided in a downstream portion of the exhaust passage 12.

In the engine 10, when high-pressure fuel is injected from the injector 23 into the combustion chamber, the injected fuel is mixed with the intake air introduced into the combustion chamber through the intake passage 11 to form an air-fuel mixture. Further, the air-fuel mixture is burned in a combustion chamber by being ignited by a spark plug (not shown).

Here, in the engine 10 of the present embodiment, the combustion system in the combustion chamber includes a normal combustion system in which the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio and combustion, and a stoichiometric air-fuel ratio. It is possible to switch between a lean combustion system in which combustion is performed by setting a lean air-fuel ratio larger than the fuel ratio. Such switching of the combustion method is performed based on the engine operating state of the engine 10.

The air-fuel mixture burned in the combustion chamber is introduced into the exhaust passage 12 as exhaust gas, and when passing through the catalytic converter 17, after each of the CO, NOx and HC components is purified, Released into the atmosphere.

The exhaust gas usually contains fuel such as hydrocarbon (HC) in addition to carbon dioxide (CO 2), carbon monoxide (CO), oxygen (O 2), nitrogen oxide (NOx). Contains unburned components. Further, the concentration of the unburned components in the exhaust gas greatly differs depending on the combustion method. That is, when the lean combustion method is selected as the combustion method in the combustion chamber, the intake air amount is excessive with respect to the injected fuel, and therefore, compared to the case where the normal combustion method is selected as the combustion method. Then, the concentration of the unburned component decreases.

Next, an exhaust gas recirculation device (hereinafter referred to as "EG
R (referred to as EGR (Exaust Gas Recircuration) device) 19 will be described. This EGR device 19
As is well known, a part of the exhaust gas passing through the exhaust passage 12 is recirculated to the intake passage 11 to lower the combustion temperature in a combustion chamber (not shown) to reduce the NOx contained in the exhaust gas. This is for reducing the amount (NOx concentration).

The EGR device 1 will be described in more detail.
9 is an EGR passage 2 that connects the exhaust passage 12 and a portion of the intake passage 11 downstream of the throttle valve 16.
0, a control valve 21 provided in the middle of the EGR passage 20;
Various sensors for detecting the engine operating state, and an electronic control unit (hereinafter, referred to as “ECU”) 3 that controls the opening of the control valve 21 based on detection signals from the various sensors.
0.

The control valve 21 controls the amount of exhaust gas (EGR gas) recirculated through the EGR passage 20 (EGR gas).
) Is adjusted in accordance with the degree of opening, and includes an actuator for adjusting the degree of opening, such as a stepping motor.

The various sensors include, for example, a rotational speed sensor 22 and an accelerator sensor 24. The rotation speed sensor 22 is provided near a crankshaft (not shown) of the engine 10 and outputs a detection signal corresponding to the rotation speed of the crankshaft, that is, the engine speed NE.
Output to On the other hand, the accelerator sensor 24 is provided near the accelerator pedal 18 operated by the driver,
A detection signal corresponding to the depression amount of the pedal 18, that is, the accelerator opening ACCP is output to the ECU 30.

As shown in FIG. 1, the ECU 30 stores a central processing unit (CPU) 31 for executing arithmetic processing, various control programs, control function data, and the like. A memory 32 to be stored, an input circuit 33 to which detection signals from various sensors are input, and a drive circuit 34 for driving the injector 23, the control valve 21, and the like are provided.

In the EGR device 19 configured as described above, the ECU 30 calculates the target EGR rate (the ratio of the EGR amount to the intake air amount) based on the engine speed NE and the accelerator opening ACCP, and also sets the NOx. The actual EGR rate is estimated based on the NOx concentration of the exhaust gas detected by the concentration detecting device. And the ECU 30
Adjusts the EGR rate to a value suitable for the operating state by feedback-controlling the opening of the control valve 21 so that the two become equal. The procedure for detecting the NOx concentration by the NOx concentration detecting device will be described later.

The ECU 30 is provided with the above EGR
Rate control, throttle valve 16 opening control,
Fuel injection control, ignition timing control, and the like are executed, and the start and stop of these various controls are performed based on an off / off operation of an ignition switch 28 operated by a driver.

That is, as shown in FIG. 1, an ignition switch 28 is connected to the ECU 30, and an ignition signal IGSWT is input from the switch 28 through an input circuit 33. And the ECU 30
Means that the ignition switch 28 is operated from the off position to the on position, so that the ignition signal IGS
The various controls described above are started when the WT switches from “OFF” to “ON”. On the other hand, when the ignition switch 28 is operated from the ON position to the OFF position to switch the ignition signal IGSWT from “ON” to “OFF”, the ECU 30 stops the fuel injection and the ignition of the air-fuel mixture to stop the engine 10. The operation is stopped, and the failure diagnosis result and the control learning value are stored in the memory 32.
Stops various controls after writing to.

Next, the configuration of the NOx concentration detecting device will be described. This NOx concentration detecting device is capable of detecting NO
x NOx sensor 500 for detecting x concentration
The ECU 30 is connected to the x sensor 500, receives the detection signal, and controls the operation of the NOx sensor 500. NOx sensor 5
00 is an EGR in the exhaust passage 12 so that a tip side portion thereof comes into contact with exhaust gas passing through the exhaust passage 12.
It is attached to a portion on the downstream side of the connection portion of the passage 20.

Hereinafter, the configuration of the NOx sensor 500 will be described. FIG. 2 is a cross-sectional view of a front end portion of the NOx sensor 500 that contacts exhaust gas. FIG. 3 is a sectional view taken along line 3-3 in FIG. 2, and FIG.
FIG. 4 is a sectional view taken along line 4-4 of FIG.

As shown in these figures, the NOx sensor 5
Reference numeral 00 is a rectangular plate as a whole, and includes a heater section 510 and a detection section 550 stacked on the heater section 510.

The heater section 510 is for heating the detecting section 550 to a predetermined temperature. This heater section 51
0 denotes a first substrate layer 511, a second substrate layer 512 laminated on the upper surface of the first substrate layer 511, a heating element 513 interposed between the two substrate layers 511 and 512, and a heating element 513. 513 is constituted by an insulating layer 514 covering the same. Each of the substrate layers 511 and 512 is formed of a solid electrolyte material having oxygen ion conductivity such as zirconia (ZrO2), and the heating element 513 is formed of a conductive material such as platinum (Pt). ing. The insulating layer 514 is formed of an insulating ceramic material such as alumina (Al2 O3).

On the other hand, the detecting section 550 includes a first spacer layer 551, a first solid electrolyte layer 552, a second spacer layer 553, and a second solid electrolyte layer 554 on the upper surface of the second substrate layer 512. It is configured by being sequentially laminated. Each of these layers 551 to 554 is a heater section 5
It is formed of the same solid electrolyte material as the ten substrate layers 511 and 512.

As shown in FIG. 3, the second spacer layer 55
3 includes a first rectangular hole 553a and a second rectangular hole 553.
b, a first communicating portion 553c for communicating the first rectangular hole 553a with the outside, and a second communicating portion 553d for communicating both rectangular holes 553a and 553b are formed. The first spacer layer 551 has a rectangular recess 551a.
Are formed.

A reference gas introduction space 560 is provided between the second substrate layer 512 and the first solid electrolyte layer 552. The reference gas introduction space 560 is defined by the upper surface of the second substrate layer 512, the inner wall surface of the concave portion 551a, and the lower surface of the first solid electrolyte layer 552, and has a base end portion (the right side in FIG. 2). By opening the (portion), an atmosphere with a known oxygen partial pressure is introduced as a reference gas into the portion.

A first chamber 561 and a second chamber 56 are provided between the first solid electrolyte layer 552 and the second solid electrolyte layer 554.
2, the first diffusion control hole 563, and the second diffusion control hole 5
64 are provided.

The first diffusion-controlling hole 563 communicates the outside where the exhaust gas is present with the first chamber 561 so that the exhaust gas is introduced into the first chamber 561 under a predetermined diffusion resistance. And is defined by the upper surface of the first solid electrolyte layer 552, the inner wall surface of the first communication portion 553c, and the lower surface of the second solid electrolyte layer 554.

The first chamber 561 has a first diffusion-controlling hole 563.
To adjust the partial pressure of oxygen of the exhaust gas introduced through the first solid electrolyte layer 552, the upper surface of the first solid electrolyte layer 552, the inner wall surface of the first rectangular hole 553a, and the second solid electrolyte layer 554. It is defined by the lower surface.

The second diffusion-controlling hole 564 communicates the exhaust gas in the first chamber 561 with the second chamber 5 under a predetermined diffusion resistance by communicating the first chamber 561 and the second chamber 562.
62, the upper surface of the first solid electrolyte layer 552, the inner wall surface of the second communication portion 553d, and the second
Are defined by the lower surface of the solid electrolyte layer 554.

The second chamber 562 is for detecting the NOx concentration of the exhaust gas introduced from the first chamber 561, and is provided on the upper surface of the first solid electrolyte layer 552, the second rectangular hole 5
The inner wall surface of the second solid electrolyte layer 554 is defined by the lower surface of the second solid electrolyte layer 554.

A portion of the lower surface of the second solid electrolyte layer 554 located inside the first chamber 561 is formed in a rectangular plate shape from a porous cermet material made of a metal such as Pt and a ceramic such as ZrO 2. Inner pump electrode 57
0 is provided. In addition, the second solid electrolyte layer 554
A portion corresponding to the inner pump electrode 570 on the upper surface of the outer pump electrode 571 formed in a rectangular plate shape by the same porous cermet material as the inner pump electrode 570 is provided.
Is provided.

The inner pump electrode 570 and the outer pump electrode 571 and the second solid electrolyte layer 554
A main pump cell 572 for moving (pumping) oxygen between the first chamber 561 and the outside is constituted by the portion sandwiched between 70 and 571.

In the main pump cell 572, when a control voltage (pump voltage) Vp1 is applied between the inner pump electrode 570 and the outer pump electrode 571, an amount of oxygen corresponding to the magnitude of the control voltage Vp1 is discharged. It is pumped from the first chamber 561 to the outside or from the outside to the first chamber 561 via the second solid electrolyte layer 554. Therefore, by controlling the control voltage Vp1, the oxygen partial pressure (oxygen concentration) in the first chamber 561 can be adjusted to a desired value.

A detection electrode 580 is provided on a portion of the upper surface of the first solid electrolyte layer 552 located inside the second chamber 562. On the other hand, at a portion corresponding to the detection electrode 580 on the lower surface of the first solid electrolyte layer 552, a reference electrode 581 that is in contact with the atmosphere in the reference gas introduction space 560 is provided.

The detection electrode 580 functions not only as a pumping electrode together with the reference electrode 581 but also as a NOx reduction catalyst, and is provided with rhodium (Rh).
It is formed in a rectangular plate shape by a porous cermet material composed of a metal to which Pt is uniformly added at a weight ratio of 1 to 5% and a ceramic such as ZrO2. on the other hand,
Like the pump electrodes 570 and 571, the reference electrode 581 is formed in a rectangular plate shape using a porous cermet material made of a metal such as Pt and a ceramic such as ZrO2.

In the first solid electrolyte layer 552, both electrodes 580, 581
Constitutes a measurement pump cell 582 for pumping oxygen between the second chamber 562 and the reference gas introduction space 560.

As described above, the exhaust gas whose oxygen partial pressure has been adjusted to a predetermined pressure in the first chamber 561 is introduced into the second chamber 562 through the second diffusion-controlling hole 564, and comes into contact with the detection electrode 580. The exhaust gas is used as the detection electrode 5
By being decomposed into nitrogen (N2) and O2 by the reducing action of 80, the oxygen partial pressure near the detection electrode 580 becomes a pressure value corresponding to the NOx concentration contained in the exhaust gas.

Further, in the measurement pump cell 582,
When a constant detection voltage (pump voltage) Vp2 is applied between the detection electrode 580 and the reference electrode 581, the detection electrode 5
O2 near 80 becomes oxygen ions (O2-) and is pumped from the detection electrode 580 to the reference electrode 581. As a result, NOx is present between the detection electrode 580 and the reference electrode 581.
Pump current Ip2 corresponding to the concentration of O2 generated by the reductive decomposition of Therefore, the NOx concentration can be detected based on the value of the pump current Ip2.

In this case, since the oxygen ions near the detection electrode 580 are pumped to the reference electrode 581, the detection voltage Vp2 is set such that the detection electrode 580 is a negative electrode and the reference electrode 58
1 is applied between both electrodes 580 and 581 with the positive electrode as the positive electrode.

Further, the inner pump electrode 570 and the reference electrode 581, and the respective layers of the second solid electrolyte layer 554, the second spacer layer 553, and the first solid electrolyte layer 552,
A control oxygen partial pressure detection cell 590 for detecting the oxygen partial pressure in the first chamber 561 is configured.

In the control oxygen partial pressure detection cell 590,
When the exhaust gas of the first chamber 561 contacts the inner pump electrode 570 and the atmosphere of the reference gas introduction space 560 contacts the reference electrode 581, the electromotive force V1 based on the oxygen partial pressure difference between the exhaust gas and the atmosphere. Are both electrodes 570,
Occurs during 581. Therefore, the oxygen partial pressure in the first chamber 561 can be detected based on the magnitude of the electromotive force V1.

Next, the procedure for detecting the NOx concentration by the NOx concentration detecting device will be described. Before starting the detection of the NOx concentration, the ECU 30 controls the energization of the heating element 513 of the heater section 510 through the drive circuit 34 to cause the heating element 513 to generate heat.
50 is heated to a predetermined temperature (for example, 400 to 900 ° C.). As a result, each layer 551 to 554 of the detection unit 550
Becomes a state where oxygen ions can move, that is, an activated state.

Next, the ECU 30 applies the control voltage Vp1 between the inner pump electrode 570 and the outer pump electrode 571 of the main pump cell 572 through the drive circuit 34, and detects the magnitude of the control voltage Vp1 to detect the control oxygen partial pressure. Control is performed based on the electromotive force V1 of the cell 590. More specifically, the memory 32 of the ECU 30 stores a very low oxygen partial pressure in the first chamber 561 at a predetermined value (for example, 1 ×
The value of the electromotive force V <b> 1 at the time when the voltage is 10 ^ −8 to 1.7 × 10 ^ −4 atm) is stored.
The magnitude of the control voltage Vp1 is feedback-controlled so that 1 becomes equal to this value. As a result, the first room 561
The partial pressure of oxygen in the exhaust gas at
The exhaust gas introduced into the second chamber 562 through the second diffusion-controlling hole 564 contains almost no oxygen as a single molecule.

Further, the ECU 30 applies the detection voltage Vp2 between the detection electrode 580 and the reference electrode 581 of the measurement pump cell 582 through the drive circuit 34, and also supplies the pump current Ip2 flowing between these electrodes 580 and 581.
Is read through the input circuit 33. As described above, since the pump current Ip2 changes according to the concentration of O2 generated by the reductive decomposition of NOx,
The CU 30 can detect the NOx concentration based on the magnitude of the pump current Ip2.

By the way, the NOx sensor 50 of this embodiment
Since 0 is attached to the exhaust passage 12 of the engine 10, the engine 10 is always exposed to exhaust gas containing unburned components such as HC during operation of the engine 10. For this reason,
If the total time of contact with the exhaust gas increases, a large amount of unburned components may adhere to the detection electrode 580 of the NOx sensor 500.

When a large amount of unburned components adheres to the detection electrode 580, as shown in FIG. 5, the unburned components (shown as HC in FIG. 5) and NOx in the second chamber 562 (one in FIG. 5). By reacting with nitrogen oxide (NO), water vapor (H20), CO2, and N2, which are extremely low in reactivity as compared with NOx, are generated. As a result, since H2 O and CO2 are hardly reduced by the detection electrode 580, the pump current Ip2 decreases, and the correlation between the pump current Ip2 and the NOx concentration decreases. Accuracy will be degraded.

Therefore, in the NOx concentration detecting apparatus of the present embodiment, a process for removing such unburned components (hereinafter, referred to as a process).
"The unburned component removal process" is executed. Hereinafter, a processing procedure regarding the “unburned component removal processing” will be described.

First, prior to performing the "unburned component removing process", the ECU 30 temporarily stops the detection of the NOx concentration. That is, the ECU 30 applies the control voltage Vp1 to the main pump cell 572, and the measurement pump cell 582
, The detection of the electromotive force V1 in the control oxygen partial pressure detection cell 590, and the detection of the pump current Ip2 in the measurement pump cell 582 are all stopped.

Next, the ECU 30 determines between the electrodes 580 and 581 of the measurement pump cell 582 through the drive circuit 34 a predetermined magnitude (for example, 0.5 to 1) whose polarity is inverted with respect to the detection voltage Vp2. .0 V) is continuously applied. In this case, the electrode processing voltage V
r is applied between the two electrodes 580 and 581 using the detection electrode 580 as a positive electrode and the reference electrode 581 as a negative electrode. Then, as described above, the electrode processing voltage V is applied between the two electrodes 580 and 581.
As a result of the application of r, O2 contained in the air in the reference gas introduction space 560 becomes oxygen ions and becomes a reference electrode 581.
, And is pumped to the detection electrode 580. For this reason, as shown in FIG. 6, the unburned components (HC) adhering to the detection electrode 580 react (oxidize) with O2 pumped by the detection electrode 580 and burn, and H2O and CO2
(Gas) and is removed from the detection electrode 580.

Therefore, according to the present embodiment, the above-described “unburned component removal processing” is periodically executed, so that the unburned components in the exhaust gas adhere to the detection electrode 580. Deterioration of detection accuracy can be prevented.

In the present embodiment, the detection electrode 580 is formed of a porous cermet material containing Pt, but this Pt has a function as an oxidation catalyst for increasing the oxidation reaction rate. Therefore, the detection electrode 580
The oxidation reaction between O2 and the unburned components pumped by the Pt is promoted by the catalytic action of Pt. As a result, the unburned components can be quickly and reliably removed without increasing the power consumption required for the “unburned component removal process”.

When the content of Pt in the detection electrode 580 is large, it is effective in promoting the oxidation reaction as described above, but since the reduction action of Rh is inhibited by Pt, the NOx sensor 500 The S / N ratio (Signal-to-Noise ratio) may be reduced.
On the other hand, when the content of Pt in the detection electrode 580 is small, such a decrease in the S / N ratio is suppressed, but the unburned components may not be sufficiently removed. Therefore, while maintaining the original function of the NOx sensor 500,
In order to reliably remove unburned components, it is important to appropriately set the content of Pt in the detection electrode 580, particularly the weight ratio of Pt to Rh as a reduction catalyst.

In this regard, in the present embodiment, the Rh of the Pt is
Is set to 1 to 5%.
Therefore, the reduction of the reduction effect of Rh is suppressed as much as possible, and the effect of promoting the oxidation of the unburned components by Pt can be reliably achieved. As a result, according to the present embodiment,
The unburned components can be reliably removed while suppressing the decrease in the S / N ratio caused by the decrease in the reducing action.

Further, unlike the configuration of the present embodiment, the second
Another electrode is provided on the upper surface of the solid electrolyte layer 554 in contact with the exhaust gas, and an electrode processing voltage Vr is applied between this electrode and the detection electrode 580, so that O2 in the exhaust gas is
Can be pumped toward the detection electrode 580 to burn unburned components on the electrode 580. However, in such a configuration, the O
2 is smaller than that in the atmosphere, and in order to pump a large amount of O2 to the detection electrode 580 in a short time, the electrode processing voltage Vr must be set relatively high.
This leads to an increase in power consumption required for the “unburned component removal processing”.

On the other hand, in the present embodiment, by applying the electrode processing voltage Vr between the reference electrode 581 and the detection electrode 580 which are in contact with the atmosphere, O2 contained in the atmosphere is pumped to the detection electrode 580 side. Thus, unburned components can be quickly and reliably removed while minimizing such power consumption.

Next, a control procedure for executing the “unburned component removal processing” at an appropriate timing will be described. First, a procedure for determining the execution timing of the “unburned component removal processing” will be described.

FIG. 7 is a flowchart showing each processing of a "removal processing timing determination routine" executed by the ECU 30 as an interrupt processing at predetermined time intervals. When the process proceeds to this routine, the ECU 30 proceeds to step 100
The elapsed time CTIM stored in the memory 32
E and the number of starts CSTAT are read.

Here, the elapsed time CTIME corresponds to the total operating time of the engine 10 after the "unburned component removal process" is completed, and when the "unburned component removal process" is not executed. Incremented by "1",
This is a counter value that is reset to “0” when a predetermined period of time has elapsed after the “unburned component removal process” ends.

The number of starts CSTAT indicates the number of starts of the engine 10 after the "unburned component removing process" is completed, and is set to "1" every time the engine 10 is started.
This is a counter value that is incremented by one, and is reset to “0” when a predetermined time has elapsed after the “unburned component removal process” ends. The values of the elapsed time CTIME and the number of times of start CSTAT are stored in the memory 32 of the ECU 30 even after the operation of the engine 10 is stopped by turning off the ignition switch 28.

Next, the ECU 30 determines whether or not the ignition signal IGSWT has been switched from "OFF" to "ON" in step 102, that is, whether or not the current control cycle is when the engine 10 is started. If it is determined that the engine is at the start, the ECU 30 determines in step 103 that the number of starts CSTAT is “1”.
Only increment. After executing the process of step 103, or when it is determined in step 102 that the engine is not at the start, the ECU 30 executes the process in step 1
Move to 04.

In step 104, the ECU 30
The number of starts CSTAT is compared with a judgment value JCSTAT. Here, the number of starts CSTAT is equal to the judgment value JCSTAT.
If it is determined that the value is less than the predetermined value, the ECU 30 shifts the processing to step 106. Then, in step 106, the ECU 30 compares the elapsed time CTIME with the determination value JCTIME.

Here, the respective judgment values JCSTAT, JC
TIME is used to determine whether the amount of unburned components adhered to the detection electrode 580 of the measurement pump cell 582 has reached a predetermined amount or more. This is a value obtained by an experiment in consideration of gas component characteristics and the like, and is stored in the memory 32 in advance.

When the engine 10 is started, the combustion state in the combustion chamber becomes unstable, and unburned components in the exhaust gas tend to increase. In particular, at the time of startup, the amount of fuel injected from the injector 23 is increased as compared to that after completion of startup in order to stabilize the combustion state, so that the unburned components in the exhaust gas further increase.

Therefore, as the number of times of start CSTAT increases, the exhaust gas containing a large amount of unburned components is detected by the detection electrode 580.
It can be estimated that the amount of unburned component adhering to the detection electrode 580 is increased because the time of contact with the electrode becomes longer.

Similarly, as to the elapsed time CTIME, the longer the elapsed time CTIME, the more the detection electrode 5
Since the time during which the gas 80 is in contact with the exhaust gas becomes longer, it can be estimated that the amount of unburned components attached to the detection electrode 580 is increased.

Therefore, the number of starts CSTAT and the elapsed time C
The determination values JCSTAT and JC for which the TIME has been appropriately obtained.
When it becomes CTIME or more, it can be determined that the adhesion amount of the unburned component has reached a predetermined amount. That is, in step 104, the number of starts CSTAT is determined by the judgment value JC.
If it is determined that the value is not less than STAT,
6, the ECU 30 determines whether the elapsed time CTIME is equal to or greater than the determination value JCTIME.
Assuming that the unburned component adhesion amount has reached the predetermined amount, the process proceeds to step 110.

In step 110, the ECU 30
It is determined whether or not the removal processing execution flag XHCRMV is set to “0”. This removal processing execution flag XHCR
The MV is for determining whether or not a condition for starting the “unburned component removal process” is satisfied. When it is determined that the amount of unburned component adhered to the detection electrode 580 is increased. This flag is set to "1" (when a negative determination is made in steps 104 and 106) and set to "0" when a predetermined time has elapsed after the "unburned component removal processing" has been completed.

If it is determined in step 110 that the removal processing execution flag XHCRMV is set to “0”, the ECU 30 sets this removal processing execution flag XHCRMV to “1” in step 112. On the other hand, in step 110, the removal processing execution flag XHC
If it is determined that the RMV is set to "1", E
The CU 30 once ends the processing of this routine.

On the other hand, if it is determined in step 106 that the elapsed time CTIME is less than the determination value JCTIME, the ECU 30 determines that the amount of unburned component adhering to the detection electrode 580 has not yet reached the predetermined amount.
Shifts the processing to step 108. Then, in step 108, the ECU 30 increments the elapsed time CTIME by “1”, and thereafter ends the processing of this routine once.

When the amount of unburned component adhering to the detection electrode 580 reaches a predetermined amount by the above-described processes of the “removal process timing determination routine”, the removal process execution flag XHCRMMV is set to “1”. You. On the other hand, if the amount of the unburned component has not reached the predetermined amount, the elapsed time C
TIME is incremented and the engine 1
Every time 0 is started, the number of starts CSTAT is incremented, and the respective counter values CTIME and CSTAT are stored and held in the memory 32.

Next, a control procedure for executing the “unburned component removing process” will be described. FIG. 8 is a flowchart showing each process of a “removal process routine” executed by the ECU 30 as an interrupt process at predetermined time intervals.

When the process proceeds to this routine, the ECU
30 is the delay flag XDL in step 200
It is determined whether or not Y is set to “0”. This delay flag XDLY is for determining whether or not a “detection mode transition process” described later is being executed, and is set to “1” when the “unburned component removal process” is completed. This flag is set to “0” when a predetermined time has elapsed from the end of the processing.

If it is determined in step 200 that the delay flag XDLY is set to "0",
That is, if the “detection mode transition process” has not been started, the ECU 30 determines in step 202 whether the above-described removal process execution flag XHCRMV is set to “1”. Here, if it is determined that the removal processing execution flag XHCRMV is set to “0”, the ECU 30 once ends the processing of this routine.

On the other hand, if it is determined in step 202 that the removal processing execution flag XHCRMV is set to “1”, the ECU 30 further proceeds to step 204 where the mixture supplied to the combustion chamber of the engine 10 is lean. It is determined whether or not a mixture is present. Here, ECU3
A value of 0 determines that the mixture is a lean mixture when at least one of the following conditions [1] and [2] is satisfied. [1] The lean combustion method is selected as the combustion method. [2] The fuel cut control is being executed. When the above condition [1] is satisfied, for example, it is not during the warm-up operation. There are cases where all the conditions, such as not during high-load operation such as during rapid acceleration, are satisfied. Incidentally, when one of these conditions is not satisfied, the normal combustion method is selected as the combustion method.

The condition [2] is satisfied when, for example, the engine 10 is decelerating and
There is a case where the engine speed NE is equal to or higher than a predetermined speed. If it is determined in step 204 that the air-fuel mixture is a lean air-fuel mixture, the ECU 30 determines in step 208 the removal processing time CHCRMV and the determination value JCHCRMV.
Compare with

Here, the removal processing time CHCRMV is
This is equivalent to the elapsed time from the start of the “unburned component removal process”, and is incremented by “1” during the execution of the “unburned component removal process”.
Is a counter value that is reset to “0” when a predetermined time has elapsed after the completion of the operation.

The judgment value JCHCRMV is a judgment value for judging whether unburned components adhering to the detection electrode 580 have been surely removed. This judgment value JCHC
The RMV is a value that is obtained by an experiment based on the magnitude of the electrode processing voltage Vr, the magnitude of each of the above-described determination values JCSTAT, JCTIME, and the like, and is stored in the memory 32 in advance.

For example, as the electrode processing voltage Vr is set to be relatively small, the determination value JCHCRMV is set to be large. As the electrode processing voltage Vr decreases,
This is because the amount of O2 pumped to the detection electrode 580 decreases and the removal rate of unburned components decreases, so that it is necessary to lengthen the removal processing time. Also, each judgment value J
This determination value JCHCRMV is set to be larger as CSTAT and JCTIME are set to be relatively larger.
As each of the determination values JCSTAT and JCTIME is set to be larger, the detection electrode 5 is set at the start of the “unburned component removal process”.
This is because the amount of unburned components adhering to the coating 80 increases, and it is necessary to lengthen the removal processing time.

In step 208, the removal processing time CH
When it is determined that the CRMV is equal to or less than the determination value JCHCRMV, the ECU 30 shifts the processing to step 220 and executes “unburned component removal processing”. And ECU3
0 is the removal processing time CHCR
After the MV is incremented by "1", the processing of this routine is temporarily terminated.

On the other hand, if it is determined in step 208 that the removal processing time CHCRMV is greater than the determination value JCHCRMV, that is, if the “unburned component removal processing” is continuously performed for a predetermined time, the ECU 30 executes the processing. Move to step 210. In step 210, E
The CU 30 sets the delay flag XDLY to “1”.

After executing the processing of step 210, the EC
U30 shifts the processing to step 214. In step 200 described above, the delay flag XDLY is set.
Is determined to be "0", that is, also in a case where the "detection mode transition process" has already been started by the current control cycle, the ECU 30 also proceeds to step 214.
Move to

In step 214, the ECU 30
The delay time CDLY is compared with the judgment value JCDLY. Here, the delay time CDLY is equivalent to an elapsed time from the start of the execution of the “detection mode shift processing”, and is incremented by “1” during the execution of the “detection mode shift processing”. This is a counter value that is reset to “0” when the “detection mode transition process” ends.

Further, the judgment value JCDLY is determined to be a predetermined time after the start of the “detection mode transition process”, in other words, the first chamber temporarily increased by the “unburned component removal process”. This is a value for determining whether or not the oxygen partial pressure in the 561 and the second chamber 562 has decreased to a pressure value at which the NOx concentration can be detected. This judgment value JCDLY is
In the “detection mode transition process”, the main pump cell 572
Of the voltage applied between the electrodes 570 and 571 of the measurement pump cell 582 and the electrodes 580 and 581 of the measurement pump cell 582.
Is the value stored in.

In step 214, the delay time CD
When LY is determined to be equal to or less than the determination value JCDLY,
The ECU 30 proceeds to step 230. In step 230, the ECU 30 executes a “detection mode transition process”.

That is, the ECU 30 invalidates the detection of the NOx concentration and switches the feedback control of the EGR rate executed based on the NOx concentration to the open loop control. Further, the ECU 30 determines whether each of the electrodes 5 of the measurement pump cell 582 is between the electrodes 570 and 571 of the main pump cell 572.
By applying a predetermined voltage between 80 and 581, O2 present in the first chamber 561 and the second chamber 562 is forcibly pumped to the reference gas introduction space 560 or the outside. Therefore, the oxygen partial pressure of both chambers 561 and 562, which has been temporarily increased by the "unburned component removal process", gradually decreases to a pressure value at which the NOx concentration can be detected.

After executing the "processing after the detection mode", the ECU 30 increments the delay time CDLY by "1" in step 232, and ends the processing of this routine once. On the other hand, in step 214, the delay time CDLY is
If it is determined that the value is larger than LY, that is, if a predetermined time has elapsed since the “detection mode transition process” was started,
In step 216, the ECU 30 sets both the delay flag XDLY and the removal processing execution flag XHCRMV to “0”. Further, in step 218, the ECU 30 determines that the removal processing time CHCRMV, the delay time CDLY, the number of starts CSTAT, and the elapsed time C
After resetting TIME to “0”, the processing of this routine is temporarily terminated.

If it is determined in step 204 that the air-fuel mixture is not a lean air-fuel mixture, the ECU 3
If the value is 0, the processing of this routine is temporarily ended. Therefore, if the “unburned component removal process” has not been started yet in this control cycle, the start of the process is delayed until an affirmative determination is made in step 204, and the “unburned component removal process” has already been started. If the processing has been started, the processing is temporarily stopped until an affirmative determination is made in step 204.

FIGS. 9 and 10 show experimental results showing the effect of executing the “unburned component removal process” according to the above control procedure. FIG. 9 shows the time transition of the sensor output from the NOx sensor 500. FIG. 10 shows the magnitude of the sensor output with respect to the NOx (NO) concentration. In each of these drawings, a solid line indicates a sensor output of the present embodiment, and a two-dot chain line indicates a sensor output when the above-described “unburned component removal processing” is not performed as a comparative example.

Referring to these figures, in the comparative example, the unburned component adhering to the detection electrode 580 increases with the lapse of time. And the linearity between the sensor output and the NOx concentration is lost. In an atmosphere where the NOx concentration is 1000 ppm or more, even if the NOx concentration is increased, the sensor output is reduced. It turns out that it hardly changes (FIG. 10).

On the other hand, in this embodiment, the sensor output hardly changes even if the sensor use time increases,
Also, even when the sensor usage time reaches 100 hours,
It can be seen that the linearity between the sensor output and the NOx concentration is maintained.

As described above, according to the present embodiment, the “unburned component removal processing” is performed at an appropriate timing according to the above control procedure.
Is performed, it is possible to suppress a decrease in detection accuracy due to the unburned component adhering to the detection electrode 580, and to reduce NOx
The original detection ability of the concentration detection device can be maintained for a long time.

By the way, in the “unburned component removal processing”, O 2 pumped from the reference gas introduction space 560 to the detection electrode 580 side does not necessarily react with unburned components adhering to the detection electrode 580. It may also react with unburned components present in the exhaust gas of the two chambers 562. Accordingly, when the amount of O2 that reacts with the unburned components in the exhaust gas of the pumped O2 increases, the removal rate of the unburned components decreases.

In this regard, in the present embodiment, when the air-fuel mixture burned in the combustion chamber is a lean air-fuel mixture, in other words, when the concentration of the unburned component in the exhaust gas is equal to or lower than a predetermined value, “ Since the “unburned component removal process” is executed, the unburned components present in the exhaust gas of the second chamber 562 out of O2 pumped from the reference gas introduction space 560 to the detection electrode 580 side are reacted. The amount of O2 that is lost is reduced. As a result, according to the present embodiment, the unburned components adhering to the detection electrode 580 can be efficiently removed.

In this embodiment, the condition [1] is that the lean burn system is selected as the burn system.
[2] Determining whether the air-fuel mixture burned in the combustion chamber is a lean air-fuel mixture by determining whether one of the fuel cut control is being performed and whether one is satisfied Can be. Since the “unburned component removal process” is executed based on the reliable determination, the removal of unburned components can be performed more efficiently.

Further, in the present embodiment, the elapsed time CTIM
It is possible to easily and accurately estimate the amount of the unburned component adhered to the detection electrode 580 based on E and the number of starts CSTAT.

Since the elapsed time CTIME and the number of start times CSTAT have become equal to or greater than the determination values JCTIME and JCSTAT as the start condition of the “unburned component removal process”, the unburned component adhering to the detection electrode 580 is determined. When the effect on detection accuracy is less than quantitative,
The "unburned component removing process" is not executed, and therefore, the detection of the NOx concentration by the NOx concentration detecting device is not interrupted. As a result, according to the present embodiment, it is possible to minimize the deterioration of the original function of the NOx concentration detecting device due to the frequent execution of the “unburned component removing process”. .

By the way, based on the application of the electrode processing voltage Vr, O 2 in the reference gas introduction space 560 is reduced to the second chamber 562.
Is forcibly pumped to the detection electrode 58.
The oxygen partial pressure near zero is temporarily increased from the pressure value when the NOx concentration is detected. Therefore,
Under such circumstances, when the detection of the NOx concentration is executed,
There is a risk of erroneous detection of the Ox concentration.

In this regard, according to the present embodiment, by executing the “detection mode transition process” from the end of the “unburned component removal process”, the second chamber 562 passes after a predetermined time has elapsed.
Until the oxygen partial pressure in the inside decreases to a pressure value at which the NOx concentration can be detected, the detection of the NOx concentration is invalidated, and the feedback control of the EGR rate is switched to the open loop control. As a result, the erroneous detection of the NOx concentration can be prevented, and the control of the EGR rate based on the erroneously detected NOx concentration can be prevented.

In particular, in the present embodiment, the detection of the NOx concentration is invalidated, and the first chamber 561 and the second chamber 56 are used by using the main pump cell 572 and the measurement pump cell 582.
2 is pumped to the reference gas introduction space 560 and the outside, so that the oxygen partial pressure in both chambers 561 and 562 can be quickly reduced to a pressure value at which the NOx concentration can be detected. In addition, the time from completion of the "unburned component removal process" to detection of the NOx concentration can be shortened.

As described above, the NOx of this embodiment
According to the concentration detecting device, the following effects can be obtained. (1) It is possible to prevent the detection accuracy from deteriorating due to the unburned components in the exhaust gas adhering to the detection electrode 580.

(2) By the oxidation catalytic action of Pt, unburned components can be quickly and reliably removed while suppressing an increase in power consumption required for the process of removing unburned components. (3) By setting the weight ratio of Pt to Rh to 1 to 5%, the reduction of the S / N ratio of the NOx sensor 500 due to the reduction of the reducing action of Rh is suppressed, and the unburned components are reliably removed. can do.

(4) Since O2 contained in the atmosphere in the reference gas introduction space 560 is pumped into the second chamber 562, the power consumption required for the process of removing the unburned components is minimized, and the unburned components are reduced. It can be quickly and reliably removed.

(5) The unburned component removal processing can be executed at an appropriate timing, and the original detection capability of the NOx concentration detection device can be maintained for a long time. (6) Of the O2 pumped into the second chamber 562, the amount of O2 that reacts with the unburned components in the exhaust gas can be reduced as much as possible, and the unburned components can be removed efficiently.

(7) It is possible to reliably determine that the air-fuel mixture burned in the combustion chamber is a lean air-fuel mixture, and it is possible to more efficiently remove unburned components based on the determination. .

(8) Elapsed time CTIME and number of starts CS
Based on the TAT, the amount of the unburned component adhered to the detection electrode 580 can be easily and accurately estimated. (9) Deterioration of the original function of the NOx concentration detecting device due to frequent execution of the unburned component removing process can be suppressed as much as possible.

(10) It is possible to prevent erroneous detection of the NOx concentration and to prevent the EGR rate from being controlled based on the erroneously detected NOx concentration.

(11) The time from completion of the unburned component removal process to detection of the NOx concentration can be shortened. [Second Embodiment] Next, a second embodiment of the present invention will be described, focusing on the differences from the first embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the first embodiment, after the removal process execution flag XHCRMV is set to "1", the "unburned component removal process" is performed when the mixture becomes a lean mixture. In the present embodiment, the removal processing execution flag XH
After the CRMV is set to “1”, the “unburned component removal process” is executed when the operation of the engine 10 is stopped. Hereinafter, such a control procedure will be described with reference to a flowchart of FIG. 11 showing each processing of the “removal processing routine”.

When the process proceeds to this routine, the ECU
30 determines in step 300 whether the removal processing execution flag XHCRMV is set to “1”. Also in the present embodiment, the removal processing execution flag X
The operation of the HCRMV is performed in the aforementioned “removal processing timing determination routine”, and when it is determined that the amount of unburned component adhered to the detection electrode 580 has reached a predetermined amount (see steps 104 and 106 shown in FIG. 8). It is set to “1” when at least one of them is negatively determined).

Here, in the present embodiment, each judgment value J
By setting the sizes of CSTAT and CTIME to be smaller than those of the first embodiment, the above-mentioned predetermined amount relating to the adhesion amount of the unburned component is set to be relatively small. Thus, each judgment value JCSTAT,
The reason why JCTIME is set is that, in the present embodiment, even if the removal processing execution flag XHCRMV is set to “1” as described above, the period until the operation of the engine 10 is stopped is “unburned component”. This is to prevent the detection of the NOx concentration from being performed while the detection accuracy is lowered during the same period since the "removal process" is not executed.

If it is determined in step 300 that the removal processing execution flag XHCRMV is set to “1”, the ECU 30 further determines in step 302 whether or not the ignition signal IGSWT is “OFF”.

When it is determined in step 302 that the ignition signal IGSWT is "OFF", in other words, the operation of the engine 10 is stopped and the EG
When it is not necessary to recirculate the exhaust gas by the R device 19, the ECU 30 shifts the processing to step 306.
In step 306, the ECU 30 compares the removal processing time CHCRMV with the determination value JCHCRMV. Then, the removal processing time CHCRMV is equal to the determination value JCH.
When it is determined that the difference is equal to or lower than the CRMV, the ECU 30
The process shifts to step 320 to execute the “unburned component removal process” as in the first embodiment. And ECU
In step 322, the removal processing time CHC
After incrementing the RMV by “1”, the processing of this routine is temporarily terminated.

On the other hand, if it is determined in step 306 that the removal processing time CHCRMV is larger than the determination value JCHCRMV, that is, if the “unburned component removal processing” is continuously performed for a predetermined time, the ECU 30 executes the processing. Move to step 308. At step 308, E
The CU 30 sets the removal processing execution flag XHCRMV to “0”.
Set to. Further, in step 218, the ECU 3
0 is the removal processing time CHCRMV, the number of starts CSTA
After resetting both T and the elapsed time CTIME to “0”, the processing of this routine is temporarily ended.

In step 300 described above,
In any case where it is determined that the removal processing execution flag XHCRMV is “0”, or that the ignition signal IGSWT is determined to be “ON” in step 302, the ECU 30 once ends the processing of this routine. I do.

By executing the “unburned component removing process” according to the control procedure as described above, the present embodiment also provides (1) to (5) and (8) of the first embodiment.
In addition to the effects described above, the following effects can be further obtained.

(12) That is, according to the present embodiment, after the operation of the engine 10 is stopped, the process of removing the unburned components is performed.
The feedback control of the R rate is not interrupted. Therefore, the EGR amount in the engine 10 can always be controlled with high accuracy, and the emission can be improved.

(13) Further, according to the present embodiment, since it is not necessary to restart the detection of the NOx concentration within a short time after the removal processing of the unburned components, erroneous detection of the NOx concentration can be prevented beforehand. Can be.

Although the embodiments embodying the present invention have been described above, each of the above embodiments can be implemented with the following configuration changes. In the first embodiment, in the “detection mode transition process”, O2 in the first chamber 561 and the second chamber 562 is pumped to the reference gas introduction space 560 or the outside by the main pump cell 572 and the measurement pump cell 582. However, for example, the following configuration can be adopted.

That is, as shown in FIG. 12, an inner auxiliary pump electrode 670 is provided on a portion of the lower surface of the second solid electrolyte layer 554 located inside the second chamber 562, and the second solid electrolyte layer 554 is provided. The outer auxiliary pump electrode 671 is provided in a portion corresponding to the inner auxiliary pump electrode 670 on the upper surface of the substrate. The inner auxiliary pump electrode 670 and the outer auxiliary pump electrode 671, and the second
The auxiliary pump cell 672 is constituted by the portion of the solid electrolyte layer 554 sandwiched between the electrodes 670 and 671. Then, in the “detection mode shift processing”, in addition to the main pump cell 572 and the measurement pump cell 582, the first chamber 561 and the second chamber 5
O2 in 62 may be pumped into reference gas introduction space 560 or outside.

According to such a configuration, the oxygen partial pressure in the first chamber 561 and the second chamber 562 can be reduced in a short time, and the detection of the NOx concentration can be performed after the “unburned component removal processing” is completed. The time until it becomes possible can be further reduced.

In the first embodiment, the “unburned component removal processing” is executed on condition that the air-fuel mixture is a lean air-fuel mixture. For example, an air flow meter (not shown) in the intake passage 11 is used. The fact that the intake air amount detected by the above is not more than a predetermined value may be further added to the execution condition. The amount of exhaust gas discharged to the exhaust passage 12 changes according to the amount of intake air, and the smaller the amount of air, the smaller the absolute amount of unburned components in the second chamber 562 tends to be. It is.

The "unburned component removing process" may be executed on condition that the recirculation of the exhaust gas by the EGR device 19 is stopped (EGR ratio = 0). In each of the above embodiments, in the “unburned component removal process”, between the respective electrodes 580 and 581 of the measurement pump cell 582,
Although the electrode processing voltage Vr was continuously applied,
The application mode of the electrode processing voltage Vr can be changed to, for example, a step shape or a pulse shape according to the concentration of the unburned component contained in the exhaust gas.

In each of the above embodiments, when the “unburned component removing process” is executed, the heating element 5
By temporarily increasing the supply power to the power supply 13, the temperature of the detection unit 550, particularly, the temperature in the vicinity of the detection electrode 580 may be further increased. According to such a configuration, the oxidation reaction between the unburned component and O2 attached to the detection electrode 580 can be further promoted, and the unburned component can be quickly and reliably removed. In particular, in the second embodiment, since the “unburned component removal processing” is performed after the operation of the engine 10 is stopped, the vicinity of the detection electrode 580 is not heated by the heat of the exhaust gas. Therefore, the above configuration is particularly effective.

In each of the above embodiments, Pt is uniformly mixed as an oxidation catalyst with the material for forming the detection electrode 580. However, any material capable of exhibiting a predetermined oxidation catalyst effect may be used.
The oxidation catalyst is not limited to Pt. Further, in addition to the configuration in which Pt is uniformly added to the material for forming the detection electrode 580 as in each of the above embodiments, for example, a part of the detection electrode 580 is formed of Pt so as to form a dot shape or a stripe shape. You may make it.

In the above embodiments, the detection voltage Vp2 is applied between the detection electrode 580 and the reference electrode 581 of the pump cell 582 for measurement, and the NOx concentration is detected based on the pump current Ip2 flowing between these electrodes 580 and 581. The detection voltage Vp is applied between the detection electrode 580 and the outer pump electrode 571 of the main pump cell 572, for example.
2, and the NOx concentration may be detected based on the pump current Ip2 flowing between the electrodes 571 and 580 at this time. Further, another electrode is provided on the upper surface of the second solid electrolyte layer 554, and a pump current Ip2 when a detection voltage Vp2 is applied between this electrode and the detection electrode 580 is provided.
In the above embodiments, the EGR rate is feedback-controlled based on the NOx concentration detected by the NOx concentration detecting device. In contrast, the NOx sensor 5
00 may be provided downstream of the catalytic converter 17 so that the deterioration of the catalytic converter 17 is determined based on the NOx concentration detected by the NOx concentration device. According to such a configuration, erroneous determination when performing the deterioration determination of the catalytic converter 17 can be prevented, and the deterioration can be reliably determined.

In each of the above embodiments, the present invention is embodied as a NOx concentration detecting device provided in the gasoline engine 10 for a vehicle. For example, an engine for stationary power, an engine for boats, and other combustion equipment As a NOx concentration detecting device for use. Further, the present invention is not limited to a gasoline engine and can be applied as a NOx concentration detecting device for a diesel engine. Further, the present invention is not limited to the NOx concentration detecting device, but may be embodied as an oxygen concentration detecting device for directly detecting the oxygen concentration in the exhaust gas.

The technical ideas that can be grasped from the above embodiments are described below together with their effects. (1) The oxygen concentration detection device according to any one of claims 1 to 15, wherein the detection of the oxygen concentration based on the current value is invalidated until a predetermined time elapses after the application of the electrode processing voltage is completed. It is characterized by further comprising means.

When an electrode processing voltage is applied between the first electrode and the second electrode and oxygen moves from the second electrode to the first electrode, the oxygen concentration in the vicinity of the first electrode is changed to the gas to be measured. It temporarily rises above the concentration of oxygen contained in it. Therefore, when the detection of the oxygen concentration is performed in such a situation, there is a possibility that the concentration of oxygen contained in the gas to be measured is erroneously detected.

In this respect, according to the above configuration, a predetermined time elapses after the application of the electrode processing voltage between the electrodes is completed, and the oxygen concentration near the first electrode returns to the original oxygen concentration again. After returning to the above, the oxygen concentration is detected. As a result, it is possible to avoid erroneous detection of the oxygen concentration due to the removal of the unburned components.

[0156]

According to the first to fifteenth aspects of the present invention, the electrode processing voltage is applied between the first electrode and the third electrode, so that the third electrode passes through the solid electrolyte from the third electrode. Oxygen moves to the first electrode, and unburned components adhering to the first electrode react with this oxygen and burn and are removed. As a result, even when used in an atmosphere of the gas to be measured containing a large amount of unburned components, it is possible to prevent the detection accuracy from being deteriorated due to the unburned components adhering to the first electrode.

According to the fourth aspect of the present invention,
Since a larger amount of oxygen moves from the third electrode to the first electrode, it is possible to quickly and reliably remove the unburned components while suppressing the power consumption required for the process of removing the unburned components. Can be.

According to the invention described in claims 5 to 8,
The concentration of nitrogen oxide contained in the exhaust gas can be detected based on the value of the current flowing between the first electrode and the third electrode.

In particular, according to the present invention, the oxidation reaction between the unburned component and oxygen is promoted by the oxidation catalyst material contained in the reduction catalyst material. As a result, the unburned components can be quickly and reliably removed while suppressing the power consumption required for the process of removing the unburned components.

Further, according to the eighth aspect of the present invention, the reduction of the reduction effect of rhodium is suppressed as much as possible, and the effect of promoting the oxidation of unburned components by platinum is ensured. As a result, it is possible to reliably remove unburned components while suppressing a decrease in detection accuracy (S / N ratio) due to a decrease in the reducing action.

According to the ninth to fifteenth aspects of the present invention, by appropriately setting the voltage application conditions, the unburned components adhering to the first electrode can be removed at an appropriate timing, and The original detection ability of the concentration detection device can be maintained for a long time.

In particular, according to the tenth to twelfth aspects, when the concentration of the unburned component in the gas to be measured is equal to or lower than a predetermined value, the unburned component removal processing is performed.
Of the oxygen moving to the first electrode side, the amount of oxygen that reacts with the unburned components in the gas to be measured decreases. As a result, unburned components adhering to the first electrode can be efficiently removed.

Further, according to the present invention, it is reliably determined that the concentration of the unburned component in the gas to be measured, that is, the exhaust gas, is equal to or less than a predetermined value. Since the process of removing the unburned components is performed, the unburned components can be more efficiently removed.

According to the present invention, when the unburned component attached to the first electrode is less than a predetermined amount and has little influence on the detection accuracy, the unburned component removal processing is performed. Will not be executed. As a result, it is possible to avoid a situation in which the unburned component removal processing is executed more than necessary and the detection of the oxygen concentration is frequently interrupted,
A reduction in the original function of the oxygen concentration detection device can be suppressed as much as possible.

In particular, according to the fourteenth aspect, in addition to the above effects, the unburned components adhering to the first electrode are efficiently removed while suppressing the power consumption required for the unburned component removal processing. can do.

According to the fifteenth aspect of the present invention, based on at least one of the operating time and the number of starts of the combustion equipment having a high correlation with the amount of unburned components adhered to the first electrode, The amount of the unburned component adhered to the electrode is easily and accurately estimated. As a result, the effect of suppressing the original function of the oxygen concentration detecting device as much as possible can be achieved more reliably.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a NOx concentration detection device.

FIG. 2 is a sectional view of a NOx sensor.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 in FIG. 2;

FIG. 5 shows unburned components adhering to a detection electrode and N in exhaust gas.
Explanatory drawing which shows a mode that Ox reacts.

FIG. 6 is an explanatory diagram showing how unburned components attached to the detection electrode are removed.

FIG. 7 is a flowchart illustrating a procedure for determining the timing of the unburned component removal processing.

FIG. 8 is a flowchart for explaining a procedure for removing unburned components according to the first embodiment;

FIG. 9 is a graph showing the relationship between sensor usage time and sensor output.

FIG. 10 is a graph showing the relationship between NOx concentration and sensor output.

FIG. 11 is a flowchart for explaining an unburned component removal processing procedure according to the second embodiment.

FIG. 12 is a sectional view showing an example of a configuration change of the NOx sensor.

[Explanation of symbols]

10 engine, 17 catalytic converter, 19 EGR
Apparatus, 20 EGR passage, 21 control valve, 28 ignition switch, 30 ECU, 500 NOx sensor, 510 heater section, 550 detection section, 552 first
Solid electrolyte layer, 560... Reference gas introduction space, 580.
Detection electrode, 581: Reference electrode, 582: Pump cell for measurement.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Kurachi 2-56, Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Insulator Co., Ltd. No. 56 Japanese insulator

Claims (15)

[Claims] A first electrode and a second electrode are disposed on a solid electrolyte body, and oxygen in a gas to be measured coming into contact with the first electrode is separated from the first electrode via the solid electrolyte body. A voltage is applied between the electrodes to move the gas to the second electrode, and the concentration of oxygen in the gas to be measured is detected based on a current value flowing between the electrodes due to the movement of the oxygen. The oxygen concentration detection device according to any one of claims 1 to 3, further comprising a third electrode to which an electrode processing voltage is applied between the first electrode and the first electrode to move oxygen to the first electrode via the solid electrolyte body. An oxygen concentration detection device characterized by the above-mentioned. 2. The oxygen concentration detecting apparatus according to claim 1, wherein the third electrode is disposed on the solid electrolyte body as the same electrode as the second electrode. Detection device. 3. The oxygen concentration detecting apparatus according to claim 1, wherein the third electrode is provided on the solid electrolyte body as a separate electrode from the second electrode. Concentration detection device. 4. The oxygen concentration detecting device according to claim 1, wherein the solid electrolyte body has an air introduction space into which the air is introduced, and the third electrode is provided in the air introduction space. An oxygen concentration detection device, wherein the oxygen concentration detection device is provided on the solid electrolyte body so as to come into contact with the atmosphere. 5. The oxygen concentration detection device according to claim 1, wherein the first electrode is formed of a reduction catalyst material that functions as a reduction catalyst for nitrogen oxides contained in the gas to be measured. And, when oxygen decomposed from the nitrogen oxide based on the reducing action of the first electrode moves from the first electrode to the second electrode via the solid electrolyte, between the electrodes. An oxygen concentration detecting device for detecting the concentration of oxygen in the gas to be measured based on a value of a flowing current. 6. The oxygen concentration detection device according to claim 5, wherein the reduction catalyst material includes a predetermined amount of an oxidation catalyst material. 7. The oxygen concentration detection device according to claim 6, wherein the reduction catalyst material is rhodium, and the oxidation catalyst material is platinum. 8. The oxygen concentration detecting device according to claim 7, wherein a weight ratio of the platinum to the rhodium is 1 to 5%. 9. The oxygen concentration detecting device according to claim 1, wherein the first electrode and the third electrode are disposed between the first electrode and the third electrode only when a predetermined voltage application condition is satisfied. An oxygen concentration detecting device comprising a voltage applying means for applying an electrode processing voltage. 10. The oxygen concentration detection device according to claim 9, wherein the voltage application means sets the concentration of the unburned component in the gas to be measured to a predetermined value or less as the voltage application condition. Oxygen concentration detecting device. 11. The oxygen concentration detection device according to claim 10, wherein the gas to be measured is an exhaust gas of a combustion device, and the voltage applying unit is configured to stop supplying the combustion fuel to the combustion device. An oxygen concentration detection device that determines that the concentration of the unburned component is equal to or lower than a predetermined value. 12. The oxygen concentration detecting apparatus according to claim 10, wherein the gas to be measured is an exhaust gas of a combustion device capable of performing a lean burn, and the voltage applying means determines that a combustion state of the burn device is a lean burn. An oxygen concentration detection device which determines that the concentration of the unburned component is equal to or lower than a predetermined value when the device is in a state. 13. The oxygen concentration detecting apparatus according to claim 9, wherein the amount of the unburned component adhered to the first electrode is estimated based on a contact time between the gas to be measured and the first electrode. The oxygen concentration detecting apparatus further comprising: a voltage application unit, wherein the voltage application unit sets the estimated adhesion amount of the unburned component to a predetermined amount or more as the voltage application condition. 14. The oxygen concentration detecting device according to claim 13, wherein the voltage applying unit is configured to determine that the unburned component adhesion amount estimated by the estimating unit is equal to or more than a predetermined amount and the unburned component concentration is higher than a predetermined amount. An oxygen concentration detection device, wherein the voltage application condition is not more than a predetermined value. 15. The oxygen concentration detection device according to claim 13, wherein the gas to be measured is an exhaust gas from a combustion device, and the estimating means is based on at least one of an operation time and a number of starts of the combustion device. An oxygen concentration detection device for estimating the amount of adhesion of the unburned component to the first electrode by means of the method.