JPH11148910A - Method and apparatus for detecting concentration of discharged gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a zero point calibration of particularly an NOx gas sensor, by providing a means for calibrating an output zero point of a gas sensor indicating a concentration of zero of a predetermined component by a detected output of an atmospheric ambience. SOLUTION: A detecting means of an NOx sensor controller detects a second oxygen pump current IP2 of an NOx sensor, and an operation part outputs the current to a memory. An engine control unit sets an NOx concentration in a discharged gas to be zero or the same level as the atmosphere, e.g. a driving condition of the NOx concentration of zero and an oxygen concentration of 20.9%. An offset correction means has inputs of a signal indicating the driving condition and IP1, IP2 signals of IP1, IP2 detection means corresponding to the driving condition, outputs a predetermined offset signal and stores an IP2 detected on the occasion of the driving condition into the memory with relating the IP2 to the oxygen concentration of 20.9%. The stored value becomes a fresh offset value corresponding to the oxygen concentration 20.9% after a detection output of the NOx sensor is calibrated. The operation part operates based on the offset value and calibrates each offset value corresponding to each oxygen concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas concentration detection method and apparatus for measuring the concentration of harmful gas components contained in gas discharged from an internal combustion engine, and more particularly to a method and apparatus for calibrating the zero point of the output of a NOx gas sensor. About.

[0002]

2. Description of the Related Art With the tightening of exhaust gas regulations, there is a strong demand for a sensor capable of directly measuring the concentrations of CO, HC and NOx, which are harmful gas components in exhaust gas. Therefore, development of a gas sensor of an oxide semiconductor type or a limiting current type using an oxygen ion conductor such as ZrO ₂ has been advanced. An oxide semiconductor type gas sensor is a sensor that utilizes the fact that a change in electric resistance of an oxide semiconductor is proportional to an amount of a predetermined gas component adsorbed on the oxide semiconductor.
On the other hand, as a limiting current type gas sensor (NOx sensor), for example, an electrode having NOx dissociation catalytic ability is arranged on an oxygen ion conductor to form an oxygen ion pump cell, and the oxygen ion pump cell faces a space facing the oxygen ion pump cell. A sensor that diffuses a gas having a controlled oxygen concentration, decomposes NOx in the space, pumps out dissociated oxygen ions using the oxygen ion pump cell, and obtains a NOx gas concentration from a current flowing through the oxygen ion pump cell. Proposed.

[0003]

However, gas sensors of the oxide semiconductor type have a problem in reproducibility. on the other hand,
The limit current type sensor has no problem in reproducibility and repeatability, but has a problem that a current to be detected in principle (a current flowing in the oxygen ion pump cell) is as small as several microamps. In addition, a harmful gas component (for example, N
Since the decomposition of Ox) is controlled or suppressed, the catalyst activity changes over a long period of use, and the zero point (the detection output of the gas sensor indicating that the concentration of the predetermined component is substantially zero) shifts. I have For this reason,
Both types of gas sensors vary greatly in use environment like sensors installed in internal combustion engines, particularly in exhaust gas systems of vehicles, and have not been used as sensors used for a long time.

In view of the above circumstances, an object of the present invention is to provide an exhaust gas concentration detection method and apparatus using a gas sensor capable of performing highly accurate gas concentration measurement over a long period of time, and in particular, a detection output of a NOx gas sensor. And a device for calibrating the zero point of the above.

[0005]

In order to solve the above-mentioned problems, a first means of the present invention provides a method for indicating that the concentration of a predetermined component is zero based on a detection output of a gas sensor in an air atmosphere. It is characterized by comprising means or steps for calibrating the zero point of the detection output of the gas sensor, and means or steps for detecting the concentration of the predetermined component based on the calibrated detection output. A second means of the present invention is a means or a step for cutting the fuel supply to the internal combustion engine, and the concentration of the predetermined component in the gas introduced into the gas sensor by the cut is substantially zero or substantially equal to the atmosphere. Means or a step of calibrating a zero point of the detection output of the gas sensor indicating that the concentration of the predetermined component is zero, based on the detection output of the gas sensor when Means for detecting the concentration of the predetermined component based on the information.

The third means is a means or a step for reducing a predetermined component in the exhaust gas by enriching the air-fuel ratio of the internal combustion engine, and the reduction reduces the concentration of the predetermined component to substantially zero or substantially to the atmosphere. A means or a step of calibrating a zero point of the detection output of the gas sensor indicating that the concentration of the predetermined component is zero, based on the detection output of the gas sensor at the same level, and the calibrated detection output Means or a step of detecting the concentration of the predetermined component based on
It is characterized by having. The fourth means is a means or a step of operating the internal combustion engine under conditions where the concentration of a predetermined component in the gas discharged from the internal combustion engine can be estimated or known, and based on a detection output of a gas sensor under the operating conditions. A means or a step of calibrating the detection output of the gas sensor; and a means or a step of detecting the concentration of the predetermined component based on the calibrated detection output.

The fifth means is a gas sensor for detecting the concentration of a predetermined component in the gas discharged from the internal combustion engine, and an operation for setting the operating condition of the internal combustion engine at which the concentration of the predetermined component can be estimated or known. A condition setting means, and a calibration means for calibrating the detection output of the gas sensor based on the detection output of the gas sensor under the operating conditions set by the operation condition setting means. Sixth means is a NOx storage type catalyst disposed in an exhaust pipe of an internal combustion engine, and the NOx storage catalyst in the exhaust pipe.
A NOx sensor attached downstream of the storage catalyst for detecting the NOx concentration in the exhaust gas, and operating condition setting means for temporarily setting the air-fuel ratio to a rich atmosphere to purify the NOx stored in the NOx storage catalyst And means for detecting a deterioration state of the NOx storage catalyst based on a change in the detection output of the NOx sensor before and after the rich atmosphere.

A seventh means is a NOx selective reduction catalyst disposed in an exhaust pipe of an internal combustion engine, and a NOx which is attached to the exhaust pipe downstream of the NOx selective reduction catalyst and detects a NOx concentration in exhaust gas. A sensor, means for adding HC to the exhaust gas of the internal combustion engine, and means for detecting a deterioration state of the NOx selective reduction catalyst based on a change in the detection output of the NOx sensor before and after the addition of HC. It is characterized by having.

A method of calibrating the detection output of a gas sensor according to the present invention is a method of calibrating a gas sensor based on the detection output of a gas sensor under the condition that the concentration of a harmful exhaust gas component can be estimated among the operating conditions of an internal combustion engine. )
It is characterized by performing. Generally, in an internal combustion engine of a vehicle having an electronically controlled fuel supply device, for example,
When the output becomes unnecessary such as at the time of deceleration, the fuel supply is cut off, so that the concentration of harmful gas components such as NOx, HC and CO in the exhaust gas becomes almost the same level as the atmosphere. On the other hand, under normal operating conditions, the concentration of harmful gas components emitted from the internal combustion engine is significantly higher than the level in the atmosphere. Therefore, by calibrating the gas sensor when the fuel cut is activated, the concentration of the harmful exhaust gas component can be accurately detected even after long-term use. Also, as described above, since the zero point (offset) of the detection output changes due to long-term use of the gas sensor, the zero point may be corrected. That is, the detection output when the fuel cut is activated may be set to a level indicating, for example, zero NOx concentration.

Further, when the offset value of the detection output of the gas sensor (the detection output when the concentration of the detected component is zero, the detection output at the zero point) has oxygen concentration dependency (when the offset value changes depending on the oxygen concentration). ), All offsets (for each oxygen concentration) may be corrected based on the detected output value at the time of the fuel cut in which the concentration of the detected component and the oxygen concentration are known. For example, the initial value (OF) of the offset corresponding to the predetermined oxygen concentration stored in the memory
1) and the difference between the detected output value (OF2) corresponding to the predetermined oxygen concentration at the time of the fuel cut, "OF1-OF2", and the offset value OF [O corresponding to each oxygen concentration stored in the memory. ₂ ] and store that value in a memory as a new offset value OF [O ₂ ]. Further, with a sensor capable of measuring the oxygen concentration, the oxygen concentration at the time of fuel cut is almost the same as that in the atmosphere, ie, the oxygen concentration 2
Since 0.9% of the gas is supplied to the sensor, the sensitivity (gain) can be calibrated. For example, by applying the detection method of the present invention to a NOx sensor described later, the sensitivity of the first oxygen pump current can be calibrated, and the oxygen concentration can be accurately measured even after endurance use.

Further, the gas sensor is a NOx sensor,
When this NOx sensor is installed downstream of the NOx storage catalyst, a spike having a rich atmosphere is provided to reduce the stored NOx. At this timing, since there is almost no NOx emission, the zero point can be calibrated in the same manner as described above. Further, in this case, by comparing the detection output of the NOx sensor before and after the spike of the rich atmosphere is applied, it is possible to detect the deterioration of the catalyst (reduction of the NOx storage amount) without having to consider the change in the offset.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described. A gas sensor to which the present invention is preferably applied is a gas sensor that can detect the concentration of harmful components in exhaust gas of an internal combustion engine, for example, flammable CO, HC, and NOx components. As the CO sensor, for example, a gas sensor using an oxide semiconductor element such as In ₂ O ₃ is applied. Also,
Each of the HC sensors includes an oxygen pump element and an oxygen concentration cell element exposed to a test gas, and flows to the oxygen pump element when an electromotive force generated in the oxygen concentration cell element reaches a predetermined value or less. A gas sensor for obtaining a combustible gas component concentration from a current value is applied. Further, a gas sensor including an oxygen pump cell, an oxygen sensor cell, and a combustible gas component concentration detecting unit made of an oxide semiconductor is applied. As the NOx sensor, a NOx sensor having two sets of diffusion resistance parts, an oxygen ion pump cell, and a gap is applied. The measurement principle of this NOx sensor is as follows.

(1) The exhaust gas flows into the first gap through the first diffusion resistance portion having the diffusion resistance. (2) The first oxygen ion pump cell removes oxygen in the first void from all N
Ox is pumped out to such an extent that it does not decompose (the oxygen partial pressure in the first gap is controlled by a signal output from the oxygen partial pressure detection electrode). (3) The gas in the first gap (the gas whose oxygen concentration is controlled) flows into the second gap through the second diffusion resistor. (4) NOx in the second gap is decomposed into N ₂ gas and O ₂ gas by pumping out oxygen further by the second oxygen ion pump cell. (5) At this time, the second oxygen pump current Ip2 flowing through the second oxygen ion pump cell and NO
Since there is a linear relationship between the x gas concentrations, the NOx gas concentration can be detected by detecting Ip2. (6)
Further, the oxygen concentration in the exhaust gas can be measured from the first oxygen pump current Ip1 flowing through the first oxygen ion pump cell when the first oxygen ion pump cell pumps out the oxygen in the first gap. Using the measured value of the concentration, the NOx decomposition rate in the first void portion can be obtained, and further, the NOx gas concentration can be corrected.

Next, a preferred method of using the NOx sensor in an exhaust gas purification system for a gasoline engine or a diesel engine will be described. Referring to FIG. 7A, in an exhaust gas purification system of a gasoline engine (particularly, a lean burn engine), an oxygen sensor, a NOx storage type three-way catalyst, and an oxygen sensor are provided in an exhaust pipe from a gasoline engine to a downstream side. (The above-described NOx sensor that also functions as an oxygen sensor) is sequentially attached.
The oxygen sensor is a sensor for controlling the engine air-fuel ratio, and based on the detection output, fuel supplied to the engine,
Air and the like are controlled. On the other hand, the NOx sensor serving also as an oxygen sensor disposed downstream of the NOx storage three-way catalyst has N
This is a sensor for detecting the Ox concentration and determining the operating state of the three-way catalyst and its deterioration. For example, an engine or the like is controlled based on the detection output so that the three-way catalyst operates optimally. This NOx storage type three-way catalyst is obtained by adding a NOx storage effect to the three-way catalyst, and the excess air ratio λ
= 1 (stoichiometric point) operates as a normal three-way catalyst,
In the lean state, NOx is temporarily stored, and by periodically adding a rich spike, the temporarily stored NOx is purified. Generally, the material of the NOx storage three-way catalyst is
Pt is obtained by adding Ba or the like having a NOx storage effect to Pt.

Further, the degree of deterioration of the NOx storage type catalyst can be detected using the NOx sensor disposed downstream of the NOx storage type catalyst. That is, in order to reduce NOx stored in the NOx storage type catalyst, a spike in a rich atmosphere (preferably, the air-fuel ratio
１４14.5) before and after this spike
The detection output of the sensor changes. If not deteriorated, the output of the NOx sensor when returning to the lean state after the spike is lower than before the spike. On the other hand, if it has deteriorated, N
Ox is not purified and the output of the NOx sensor remains high. Therefore, the deterioration of the catalyst can be determined from the change in the output of the NOx sensor before and after the rich spike. Further, when the spike is put, almost no NOx is generated.
Calibration of the zero point of the Ox sensor is also possible.

Referring to FIG. 7 (b), in the exhaust gas purifying system for a diesel engine, light oil for injecting light oil as an HC source into the exhaust gas from the diesel engine to the exhaust pipe into the exhaust pipe is provided. Injection valve, HC sensor (not shown), NOx selective reduction catalyst, NO described in detail above
The x sensors are mounted in order. The NOx selective reduction catalyst uses NO added by light oil injection as a reducing agent to reduce NO
By decomposing x into nitrogen, CO ₂ , and H ₂ O, it acts to purify x. The HC sensor is disposed on the upstream side of the NOx selective reduction catalyst and performs a function of monitoring the HC concentration in the exhaust gas after light oil injection in order to feedback-control the amount of light oil to be injected into the exhaust gas. is there. Further, the deterioration of the NOx selective reduction catalyst can be detected from the output change of the NOx sensor before and after the addition of HC. That is, according to the catalyst having the NOx purifying ability, the concentration of NOx downstream of the catalyst is reduced by adding HC,
While the output of the sensor decreases, according to the catalyst whose purification ability has deteriorated, the NOx concentration does not decrease even if HC is added, so that the output of the NOx sensor does not decrease.

FIG. 8 is a diagram showing a NOx according to an embodiment of the present invention.
It is a figure for explaining a control composition of an exhaust gas concentration detection system using a sensor. Referring to FIG. 8, the detection system includes an internal combustion engine, a catalyst installed in an exhaust system, a NOx sensor installed downstream of the catalyst, an engine control unit (ECU), and a NOx sensor controller. Be composed. The engine control unit sets the operating conditions (such as air-fuel ratio) of the internal combustion engine,
Determine catalyst degradation. The NOx sensor controller
Means for controlling the NOx sensor; means for detecting and outputting the first and second oxygen pump currents Ip1 and Ip2 flowing through the NOx sensor; a memory for storing a map showing the relationship between the oxygen concentration and the Ip2 offset value; (Eg Ip
1) reading an offset of Ip2 from the memory, executing a predetermined operation based on the offset and Ip2, and outputting the operation result to the memory; and operating conditions from the engine control unit. Is input, the output signals of the Ip1 and Ip2 detecting means are input, an offset correction signal is output to the memory, and a new offset value is stored in the memory based on the signal output from the arithmetic unit to the memory. Offset correction means.

The operation of this system will be described. The detection means of the NOx sensor controller detects the second oxygen pump current Ip2 of the NOx sensor and outputs it to the calculation unit, which outputs this to the memory. Here, the engine control unit sets an operating condition for setting the NOx concentration in the exhaust gas to substantially zero or substantially the same level as the atmosphere. As an example, this operating condition is set at the time of fuel cut, that is, the NOx concentration is zero and the oxygen concentration is 20.9%. A signal indicating the condition output from the engine control unit to the offset correction means and Ip1 and Ip1
Ip1, corresponding to the condition output from the p2 detection means,
When the Ip2 signal is input, the offset correction means outputs a predetermined offset correction signal to the memory, and stores the Ip2 detected under the above condition in the memory in association with the oxygen concentration of 20.9%. The stored value is the oxygen concentration 2
The corrected offset value of the NOx sensor detection output corresponding to 0.9% is obtained. Further, the arithmetic unit reads out each offset value corresponding to each oxygen concentration stored in the memory, reads out each value, Ip2 under the above condition, and the oxygen concentration 20.9 stored in the memory.
A predetermined calculation is performed based on the offset value corresponding to%. Each offset value corresponding to each oxygen concentration is calibrated based on the calculation result and stored in the memory. It is preferable that the calibration of the detection output of the gas sensor is periodically performed during the operation of the internal combustion engine. It is also possible to perform it at idling.

[0019]

An embodiment of the present invention will be described below with reference to the drawings. As the gas sensor, a NOx sensor having the structure shown in FIG. 1 was used. The NOx sensor of FIG.
A first oxygen ion pump cell 6 having a pair of electrodes 6a and 6b provided with a -1 sandwiched therebetween, and a pair of oxygen partial pressure detecting electrodes 7a and 7b provided with a solid electrolyte layer 5-2 provided therebetween. An oxygen concentration measurement cell 7, a solid electrolyte layer 5-3, and a second oxygen ion pump cell 8 having a pair of electrodes 8a and 8b provided on the surface of the solid electrolyte layer 5-4 are stacked in this order. Insulating layers 11-1, 11-2, and 11-3 are formed between the solid electrolyte layers 5-1, 5-2, 5-3, and 5-4, respectively. Between the first oxygen ion pump cell 6 and the oxygen concentration measurement cell 7, insulating layers 11-1 on the left and right sides in the figure are provided.
And the first and second solid electrolyte layers 5-1 and 5-2.
A measurement chamber (void) 2 is defined, and the insulating layer 11-3 is similarly formed.
A second measurement chamber (gap) 4 is defined above the second oxygen ion pump cell 8 by the solid electrolyte layers 5-3 and 5-4. Further, first diffusion holes (diffusion resistance portions) 1 having diffusion resistance are provided on both sides (front and back in FIG. 1) of the first measurement chamber 2 in the sensor short direction, respectively. On the other hand, an opening of the second diffusion hole (diffusion resistance portion) 3 is provided separately from the first diffusion hole 1. Second diffusion hole 3
Penetrates through the oxygen concentration measuring cell 7 and the solid electrolyte layer 5-3 to communicate the first and second measuring chambers 2 and 4 with diffusion resistance.

In this sensor, both electrodes 8a and 8b of a porous metal (Pt, Rh alloy, etc.) are formed on the same surface of the solid electrolyte 5-4 constituting the second oxygen ion pump cell 8. Although the electrodes 8a and 8b are isolated from each other by the insulating layer 11-3, oxygen ions are conducted through the solid electrolyte layer 5-4, and the second oxygen pump current Ip2 flows. The electrode 8b is prevented from being in direct contact with the outside air of the sensor by the solid electrolyte layer 5-4, the insulating layer 11-3, and the lead portion 8d, and is also provided via the porous lead portion 8d having diffusion resistance. The oxygen pumped by the second oxygen ion pump cell 8 can be led out. Further, lead portions (lines) 8c (see FIG. 2) and 8d are electrically connected to the electrodes 8a and 8b, respectively, and the lead portion 8d electrically connected to the outer electrode 8b of the second measurement chamber 4 is porous. It is capable of diffusing oxygen ions. Therefore, NO 2 is generated by the second oxygen ion pump cell 8.
Oxygen decomposed from the x gas and pumped to the electrodes 8a to 8b is released through the lead 8d. FIG. 2 corresponds to a plan cross-sectional view indicated by an arrow A line in FIG. Referring to FIG. 2, it can be seen that the lead 8d is in contact with the outside air (in the atmosphere or in the atmosphere of the gas to be measured), and communicates the outside air with the electrode 8b via the diffusion resistance.

The measurement principle of the NOx sensor shown in FIG.
As described above in the section of the embodiment, the terminal of the controller is electrically connected to each electrode of the NOx sensor via a lead portion, and is introduced into the first measurement chamber 2 through the first diffusion hole 1. An electromotive force corresponding to the oxygen concentration in the exhaust gas thus generated is generated between the pair of electrodes 7a and 7b of the oxygen concentration measurement cell 7, and is applied to the first oxygen ion pump cell 6 so that the voltage by the electromotive force becomes constant. The applied voltage is controlled (the control by the controller may be digital control using a microcomputer or analog control). Excess oxygen is pumped from the first measurement chamber 2 by the first oxygen ion pump cell 6, and the gas to be measured whose oxygen concentration is controlled to a certain level is diffused into the second measurement chamber 4 through the second diffusion holes 3. And
When a voltage is applied to the pair of electrodes 8a and 8b of the second oxygen ion pump cell 8, the remaining oxygen is further pumped out, and NOx is reduced by the catalytic action of the Pt alloy (or Rh alloy) electrode. It is decomposed into N ₂ and O _2, the O ₂
Becomes ions and conducts through the solid electrolyte layer 5-4 of the second oxygen ion pump cell 8, whereby a pair of electrodes 8 a and 8 b of the second oxygen ion pump cell 8 provided inside and outside the second measurement chamber 4 is formed. A second oxygen pump current Ip2 flows according to the amount of NOx gas decomposed into oxygen. By measuring this Ip2, the NOx gas concentration can be measured.

According to this NOx sensor, the second measurement chamber 4
The electrode 8b opposite to the electrode 8a of the second oxygen ion pump cell 8 is installed inside the element (between the stacked solid electrolytes), so that the solid electrolyte layer 5-4, the insulating layer 1
1-3 are protection means for the electrode 8b, and the lead 8d
Is a diffusion resistance means, the electrode 8b is cut off from the atmosphere of the gas to be measured (exhaust gas) and is not directly in contact with the outside air, and the oxygen pumped around the electrode 8b is pooled. The oxygen concentration around (near) the electrode 8b is stabilized, and the electromotive force generated between the pair of electrodes 8a and 8b of the second oxygen ion pump cell 8 is stabilized.
Further, since the generated electromotive force is stabilized, the effective pump voltage (Vp2-electromotive force) of the pump voltage Vp2 applied to the second oxygen ion pump cell 8 is stabilized, and NO
The oxygen concentration dependence of x gas concentration measurement is reduced.

[Production Example] Next, a production example of the NOx sensor shown in FIG. 1 will be described. FIG. 3 is a layout diagram of the NOx sensor shown in FIG. Although the sheet and paste shown in FIG. 3 are in a green state, the same reference numerals are given to the reference numerals assigned to the NOx sensor shown in FIG. In FIG. 3, a ZrO ₂ green sheet, an electrode paste, and the like are laminated in order from the upper left to the lower left and from the upper right to the lower right, dried, and fired to produce an integrated sensor. A paste material such as an insulating coat and an electrode is laminated and formed by screen printing on a predetermined ZrO ₂ green sheet. Next, Zr
An example of manufacturing each component such as an O ₂ green sheet will be described.

[ZrO_TwoSheet (5-1 layer to 5-4 layer)
Molding]: ZrO_TwoPowder at 600 ° C for 2 hours in air furnace
And calcined. Calcined ZrO_Two30 kg powder, dispersant 1
50 g and 10 kg of organic solvent together with 60 kg of cobblestone
Put into a hammel, mix for about 50 hours, disperse,
Machine binder 4kg dissolved in organic solvent 10kg
Is added and mixed for 20 hours to obtain a viscosity of about 10 Pa · s.
Was obtained. Doctor from this slurry
ZrO with a thickness of about 0.4mm _TwoGlee
A sheet was prepared and dried at 100 ° C. × 1 hour.

[Printing Paste] (1) First oxygen ion pump electrode 6a, oxygen partial pressure detection electrode (oxygen reference electrode) 7b, second oxygen ion pump electrode 8
For a and 8b: Put 20 g of Pt powder, 2.8 g of ZrO ₂ powder and an appropriate amount of organic solvent in a grinder (or pot mill),
Mix and disperse for 4 hours, add 2 g of organic binder dissolved in 20 g of organic solvent, add 5 g of viscosity modifier and mix for 4 hours to obtain a viscosity of 150 Pa · s.
A paste of the degree was prepared.

(2) For the first oxygen ion pump electrode 6b and oxygen partial pressure detection electrode (oxygen reference electrode) 7a: Pt powder 1
9.8 g, ZrO ₂ powder 2.8 g, Au powder 0.2 g, and an appropriate amount of an organic solvent were put in a grinder (or pot mill), mixed and dispersed for 4 hours, and 2 g of an organic binder was dissolved in 20 g of an organic solvent. And then add 5g of viscosity modifier
Was added and mixed for 4 hours to prepare a paste having a viscosity of about 150 Pa · s.

(3) For insulating coat and protective coat: 50 g of alumina powder and an appropriate amount of an organic solvent are put in a grinder (or pot mill), mixed and dissolved for 12 hours, and 20 g of a viscosity modifier is added. Mix for 3 hours and viscosity 1
A paste of about 00 Pa · s was prepared.

(4) For Pt-containing porous material (for lead wire):
10 g of alumina powder, 1.5 g of Pt powder, 2.5 g of organic binder, and 20 g of organic solvent are put into a grinder (or pot mill) and mixed for 4 hours. Further, 10 g of a viscosity modifier is added and mixed for 4 hours. Viscosity 100 Pa · s
The paste was adjusted to a degree.

(5) For first diffusion hole: 10 g of alumina powder having an average particle size of about 2 μm, 2 g of an organic binder, and 20 g of an organic solvent are put into a grinder (or pot mill),
Mix, disperse and add 10g of viscosity modifier,
The mixture was mixed for 4 hours to prepare a paste having a viscosity of about 400 pa · s.

(6) For carbon coating: 4 g of a carbon powder, 2 g of an organic binder, and 40 g of an organic solvent are put into a grinder (or pot mill), mixed, and dispersed.
Further, 5 g of a viscosity modifier was added and mixed for 4 hours to prepare a paste. In addition, by forming the carbon coat by printing, for example, contact between the first oxygen ion pump electrode 6b and the oxygen reference electrode 7a is prevented. Also,
The carbon coat is used for forming the first measurement chamber 2 and the second measurement chamber 4. Since carbon is burned off during firing, the carbon coat layer does not exist in the fired body.

[Pellet] (7) For second diffusion hole: 20 g of alumina powder having an average particle size of about several μm, 8 g of an organic binder, and 20 g of an organic solvent
Put into a grinder (or pot mill), mix for 1 hour, granulate, apply a pressure of about 2 t / cm ² with a mold press, and apply a 1.3 mm diameter, 0.8 mm thick cylindrical press-formed body ( (Green state). The pressed green body in the green state is inserted into predetermined portions of the second and third layers of the ZrO ₂ green sheet, pressed, integrated, and fired to form the second diffusion holes 3 in the sensor.

[ZrO ₂ laminating method]
A portion (diameter: 1.3 mm) through which the second diffusion hole 3 penetrates is punched. After the punching, a green columnar molded body serving as the second diffusion hole 3 is embedded, and 1 to 4 layers of ZrO ₂ green sheets are pressed under a pressure of 5 kg / cm ² and a pressing time of 1 minute.

[Binder Removal and Firing] The compacted body was debindered at 400 ° C. × 2 hours, and 1500 ° C.
Bake for 1 hour at ℃.

[Example of Use] The NOx sensor having the structure shown in FIG.
A time endurance test was performed. The configuration of the NOx concentration detecting device is the same as that shown in FIG. 8, and the mounting position of the NOx sensor is the same as that shown in FIG. further,
The controller that controls the NOx sensor uses the gain value ((standard NOx concentration−0) / (generated current amount−offset) of the detection output (second oxygen pump current) of the NOx sensor set using the model gas evaluation device described later. )) And the offset value are stored in the memory. In particular, offset values corresponding to respective oxygen concentrations from 0% to 20.9% (21%) are stored in a memory for the purpose of canceling the oxygen concentration dependency of the offset. A predetermined offset value is read based on the oxygen concentration obtained from the oxygen pump current, and the offset value used for calculating the NOx gas concentration is optimally set.

Two sets of the controller and the NOx sensor are prepared, and initial characteristics of the NOx sensors are measured by a model gas evaluation device. When the analyzer output indicates that the NOx concentration is zero, the second oxygen pump current Each controller was adjusted so that the detection output of the controller based on the above becomes zero. Next, these NOx sensors are set to a displacement of 30
The engine was attached to the exhaust pipe of a 00 cc gasoline engine, and a 500-hour endurance test was performed in the mode shown in FIG. 4 while controlling the NOx sensor by each controller. Degree of opening). One controller performed the method of using the gas sensor according to one embodiment of the present invention, and calibrated the offset (zero point) at the time of fuel cut in the endurance mode. The other controller did not calibrate the zero point. The calibration method by one controller is as follows.

That is, referring to FIG. 5, when one of the controllers receives a fuel cut signal output from an ECU (engine control unit) of a gasoline engine, the other controller is in proportion to the second oxygen pump current. The value of the detection output is stored as an offset value (OF2) corresponding to O ₂ = 20.9%. Next, the offset value (OF1) corresponding to O ₂ = 20.9% stored in the memory is read, and the difference between OF1 and OF2 is calculated. This “OF1-OF2” is subtracted from the offset value OF [O ₂ ] corresponding to each oxygen concentration stored in the memory, and the value (OF [O ₂ ] − (OF1-OF2)) is obtained.
The corrected offset value OF [O ₂ ] is stored in the memory.

FIG. 6 shows the results of the durability test. Referring to the results of the durability test shown in FIG. 6, according to the system according to the example in which the calibration was performed, the NOx concentration detection output of the controller hardly changed even after the 500-hour durability test. In contrast, the output of the system of the comparative example in which the calibration was not performed increased by about 400 ppm.

[0038]

According to the present invention, the gas sensor is calibrated when the concentration of the component to be detected can be estimated or known under the operating conditions of the internal combustion engine, thereby detecting the gas sensor after the durable use. The output shift is canceled, and the concentration of the detected component can be accurately detected. The gas sensor to which the present invention is applied may be an HC sensor or a CO sensor in addition to the NOx sensor, or a sensor capable of measuring the oxygen concentration, for example, the oxygen concentration is not zero when the fuel is cut, and the oxygen concentration is 20.9% Is introduced, the sensitivity of oxygen concentration can be calibrated. Also,
Since the calibration of the present invention can be performed when the fuel is cut or when the air-fuel ratio is rich, there is no need to set special operating conditions for the calibration. In particular, the present invention is applied to a NOx sensor, and enables accurate measurement of a NOx concentration on the order of ppm over a long period of time (claim 4). In particular, when a NOx sensor that detects the NOx concentration in the gas exhausted from the internal combustion engine is attached downstream of the NOx storage catalyst, there is a mode in which the air-fuel ratio is set to a rich atmosphere in order to reduce the stored NOx. By using this mode, the calibration can be executed (claim 6), and the deterioration state of the NOx storage type catalyst can be detected (claim 9).
Further, according to the tenth aspect, it is possible to detect the deterioration state of the NOx selective reduction catalyst disposed in the exhaust pipe of a system using a diesel engine that cannot make the air-fuel ratio rich.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the structure of a NOx sensor used in one embodiment of the present invention.

FIG. 2 is a diagram for explaining a plane cross section indicated by an arrow A line in FIG. 1;

FIG. 3 is a diagram for explaining a layout of the NOx sensor shown in FIG. 1;

FIG. 4 is a view for explaining a durability test mode performed using the NOx sensor shown in FIG.

FIG. 5 is a diagram for explaining a method of calibrating the detection output of the NOx sensor according to one embodiment of the present invention.

FIG. 6 is a diagram for explaining the results of the durability test, in which square plots indicate data of the example and triangular plots indicate data of the comparative example.

7A and 7B are diagrams for explaining an exhaust gas concentration detection device using a NOx sensor according to one embodiment of the present invention, and FIG. 7A is a diagram illustrating a gasoline engine (particularly, a lean gas engine); Burn engine) exhaust gas purification system,
FIG. 1B is a diagram for explaining an exhaust gas concentration detection device applied to an exhaust gas purification system for a diesel engine.

FIG. 8 is a diagram for explaining an exhaust gas concentration detection system using a NOx sensor according to one embodiment of the present invention.

[Explanation of symbols]

 1: 1st diffusion hole (diffusion resistance part) 2: 1st measurement chamber (gap part) 3: 2nd diffusion hole (diffusion resistance part) 4: 2nd measurement chamber (gap part) 5-1 ... 5- 4: solid electrolyte layer 6: first oxygen ion pump cell 6a, 6b: electrode 6c: lead portion 7: oxygen concentration measurement cell 7a, 7b: electrode 8: second oxygen ion pump cell 8a, 8b: electrode 8c, 8d: Lead portions 11-1,..., 11-3: insulating layer

Claims (10)

[Claims] An exhaust gas concentration detection method using a gas sensor for detecting a concentration of a predetermined component in gas exhausted from an internal combustion engine, wherein the method is based on a detection output of the gas sensor in an air atmosphere.
A gas sensor, comprising: calibrating a zero point of a detection output of the gas sensor indicating that the concentration of the predetermined component is zero, and detecting the concentration of the predetermined component based on the calibrated detection output. Exhaust gas concentration detection method. 2. An exhaust gas concentration detection method using a gas sensor for detecting the concentration of a predetermined component in gas exhausted from an internal combustion engine, wherein a fuel supply to the internal combustion engine is cut off and introduced into the gas sensor. Based on the detection output of the gas sensor when the concentration of the predetermined component in the gas to be performed is set to substantially zero or substantially the same level as the atmosphere, indicating that the concentration of the predetermined component is zero. An exhaust gas concentration detection method, comprising: calibrating a zero point of a detection output of a gas sensor, and detecting a concentration of the predetermined component based on the calibrated detection output. 3. An exhaust gas concentration detection method using a gas sensor for detecting a concentration of a predetermined component in a gas discharged from an internal combustion engine, wherein the predetermined component is reduced by making an air-fuel ratio of the internal combustion engine rich. The detection of the gas sensor indicating that the concentration of the predetermined component is zero based on the detection output of the gas sensor when the concentration of the predetermined component is substantially zero or substantially the same level as the atmosphere An exhaust gas concentration detection method, comprising: calibrating a zero point of an output; and detecting a concentration of the predetermined component based on the calibrated detection output. 4. The exhaust gas concentration detecting method according to claim 1, wherein said gas sensor is a NOx sensor. 5. The NOx sensor includes first and second gaps, first and second diffusion resistance parts, and first and second oxygen ion pump cells, and the gas flows through the first diffusion resistance part. Is diffused into the first void portion, and the first oxygen ion pump cell is configured to perform the first diffusion so that the oxygen concentration in the gas diffused into the first void portion via the first diffusion resistance portion becomes a predetermined concentration. Oxygen is pumped out of the gap, and the gas having the predetermined oxygen concentration is diffused from the first gap through the second diffusion resistor to the second gap, and NOx is removed in the second gap. The exhaust gas concentration according to claim 4, wherein the NOx concentration is detected based on a current flowing through the second oxygen ion pump cell by decomposing and pumping oxygen ions dissociated by the second oxygen ion pump cell. Detection method. 6. The detection of the NOx sensor when the NOx sensor is mounted downstream of the NOx storage catalyst and the air-fuel ratio is temporarily made rich to purify the NOx stored in the NOx storage catalyst. The exhaust gas concentration detection method according to claim 4, wherein the calibration of the zero point is performed based on an output. 7. An exhaust gas concentration detection method using a gas sensor for detecting a concentration of a predetermined component in gas discharged from an internal combustion engine, wherein the concentration of the predetermined component is estimated or known under a condition that the concentration of the predetermined component can be estimated or known. Operating the gas sensor, calibrating the detection output of the gas sensor based on the detection output of the gas sensor under the operating conditions, and detecting the concentration of the predetermined component based on the calibrated detection output. Gas concentration detection method. 8. A gas sensor for detecting a concentration of a predetermined component in a gas discharged from the internal combustion engine, and operating condition setting means for setting an operating condition of the internal combustion engine at which the concentration of the predetermined component can be estimated or known. A calibration means for calibrating the detection output of the gas sensor based on the detection output of the gas sensor under the operating conditions set by the operating condition setting means. 9. A NOx storage catalyst disposed in an exhaust pipe of an internal combustion engine, a NOx sensor attached to the exhaust pipe downstream of the NOx storage catalyst to detect a NOx concentration in exhaust gas, and a NOx storage device. Operating condition setting means for temporarily setting the air-fuel ratio to a rich atmosphere in order to purify NOx stored in the type catalyst, and the NO based on a change in the detection output of the NOx sensor before and after the rich atmosphere is set.
a means for detecting a deterioration state of the x-storage catalyst. 10. NOx disposed in an exhaust pipe of an internal combustion engine
A selective reduction catalyst, a NOx sensor attached to the exhaust pipe downstream of the NOx selective reduction catalyst to detect a NOx concentration in exhaust gas, a unit for adding HC to exhaust gas of the internal combustion engine, Means for detecting the state of deterioration of the NOx selective reduction catalyst based on a change in the detection output of the NOx sensor before and after the addition of NO.