JPH11108887A - Measuring apparatus for concentration of nitrogen oxide and control method for measuring apparatus for concentration of nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring apparatus by which the concentration of nitrogen oxides can be measured precisely even when an oxygen partial pressure in a gas, to be measured, is changed by a method wherein a means which finds the concentration of the nitrogen oxides is provided with a means by which the detection output of the concentration of the nitrogen oxides is corrected on the basis of the output of an oxygen-partial-pressure detecting cell. SOLUTION: The output of an oxygen-partial-pressure detecting cell 7 is input to a Vs constant control part 41, a voltage which is applied to a first oxygen ion pump cell 6 is controlled, and the electromotive force of the oxygen-partial-pressure detecting cell 7 is made constant. A first oxygen ion pump current and a second oxygen ion pump current are input to a controller 40, an oxygen concentration is found by an oxygen-concentration computing part 40a on the basis of the first oxygen ion pump current so as to be output, and an oxygen- concentration correction signal is output. Then, the oxygen concentration in the detection output of the concentration of nitrogen oxides is corrected by an NOx concentration computing part 40b on the basis of the second oxygen ion pump current and on the basis of the change amount of the detection output of the oxygen concentration. As a result, the influence of a change in the oxygen concentration is excluded, and the concentration of the nitrogen oxides can be detected precisely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitrogen oxide concentration measuring apparatus used for detecting exhaust gas components of a combustor, an automobile, a ship, an airplane, or other moving or industrial internal combustion engines, and a combustion gas component of a boiler or the like. More particularly, the present invention relates to a control method of a nitrogen oxide concentration measuring instrument for measuring a nitrogen oxide concentration in an atmosphere in which the oxygen concentration in a gas to be measured changes suddenly, and an apparatus therefor.

[0002]

2. Description of the Related Art In recent years, with the tightening of exhaust gas regulations, studies have been made to directly measure NOx in exhaust gas from engines and the like to control engines and catalysts. For example, oxygen in the gas to be measured introduced into the first measurement chamber is converted into Z
A first oxygen ion pump cell made of an oxygen ion conductor such as rO ₂ pumps out NOx so as not to decompose and introduces a gas having a reduced oxygen concentration into the second measurement chamber.
With a second oxygen ion pump cell made of an oxygen ion conductor such as ZrO ₂ , NOx is decomposed by further pumping oxygen from the gas introduced into the second measurement chamber, and the NOx concentration is converted to the second oxygen ion pump cell. The NOx gas sensor (nitrogen oxide concentration measuring device) that detects the flowing current
Since the NOx gas concentration can be measured relatively without being affected by interfering gases such as C and CO, researches have been widely conducted in recent years. Generally, in such nitrogen oxide sensors, Z
A pair of electrodes are arranged on both surfaces of an oxygen ion conductor such as rO ₂ , and one of the electrodes is an atmosphere of the first measurement chamber,
The other electrode is exposed to a reference oxygen atmosphere, and the voltage applied to the first oxygen ion pump cell is changed based on the output of the oxygen partial pressure detection cell for measuring the oxygen concentration in the first measurement chamber. , The oxygen concentration in the first measurement chamber is controlled to be constant.

[0003]

However, according to the findings of the present inventors, when the oxygen concentration in the gas to be measured greatly changes, a delay occurs in the voltage control for the first oxygen ion pump cell described above. It has been found that it is difficult to measure an accurate nitrogen oxide concentration measurement using the nitrogen oxide sensor. In particular, in gasoline lean-burn engines and diesel engines, which have been increasing in recent years, the oxygen concentration in exhaust gas greatly changes depending on operating conditions. I. It has been found that it is difficult to accurately measure the NOx concentration in the exhaust gas using only the method of changing and controlling the pumping capacity of the first oxygen ion pump cell even when using D control or the like.

In view of the above circumstances, an object of the present invention is to provide a nitrogen oxide concentration measuring apparatus and a nitrogen oxide concentration measuring apparatus capable of accurately measuring a nitrogen oxide concentration even when the oxygen partial pressure in a gas to be measured changes. An object of the present invention is to provide a method for controlling a concentration measuring instrument.

[0005]

According to a first aspect of the present invention, there is provided a first measuring chamber into which a gas to be measured is introduced via a first diffusion resistor, and sufficient oxygen supplied to outside or inside the first measuring chamber. A first oxygen ion pump cell that pumps or pumps gas into the first measuring chamber, a second measuring chamber into which gas is introduced from the first measuring chamber via a second diffusion resistor, and an inside and an outside of the second measuring chamber. A voltage is applied to the pair of electrodes to decompose the nitrogen oxides in the second measurement chamber and pump out the dissociated oxygen. Second oxygen ion pump current ”)
An oxygen ion pump cell; and means for obtaining a nitrogen oxide concentration based on the second oxygen ion pump current when the oxygen partial pressure in the gas to be measured changes.

In a second aspect, there is provided an oxygen partial pressure detecting cell provided with an oxygen partial pressure detecting electrode for detecting the oxygen partial pressure in the first measuring chamber, and the means for obtaining the nitrogen oxide concentration comprises: Means for correcting the nitrogen oxide concentration detection output based on the output of the oxygen partial pressure detection cell. In a third aspect, the correction means controls the voltage applied to the first oxygen ion pump cell based on the output of the oxygen partial pressure detection cell, and adjusts the current flowing through the first oxygen ion pump cell (hereinafter, referred to as “ The nitrogen oxide concentration detection output is corrected based on the amount of change in the first oxygen ion pump current.

In a fourth aspect, there is provided means for controlling a voltage applied to the second oxygen ion pump cell in accordance with a change in the oxygen partial pressure in the gas to be measured. In a fifth aspect, the control means decreases the voltage applied to the second oxygen ion pump cell when the oxygen partial pressure is low, and increases the voltage when the oxygen partial pressure is high.

In a sixth aspect, a nitrogen oxide concentration measuring instrument having an oxygen partial pressure detecting cell for detecting an oxygen partial pressure in the first measuring chamber or the second measuring chamber; An output and an output of the second oxygen ion pump cell are input, and when the output of the oxygen partial pressure detection cell changes, the nitrogen oxidation of the nitrogen oxide concentration measuring device is performed based on the output of the second oxygen ion pump cell. A nitrogen oxide concentration calculating unit for correcting the substance concentration detection output.

In a seventh aspect, the oxygen partial pressure sensing cell further controls the first oxygen ion pump cell so that the output of the oxygen partial pressure sensing cell is constant, and the oxygen partial pressure sensing cell And a storage unit in which the relationship between the amount of change in the output of the second oxygen ion pump current and the offset of the second oxygen ion pump current is stored in advance. In response, predetermined data is read from the storage unit, and the offset value of the second oxygen ion pump current is varied based on the data to correct the nitrogen oxide concentration detection output.

[0010] The present invention provides, in an eighth aspect, the first aspect.
There is a first oxygen ion pump cell that pumps oxygen in the gas to be measured from the measurement chamber to the outside of the measurement chamber sufficiently so that all of the nitrogen oxides are not decomposed. 9th to 8th perspectives
The ten viewpoints are the same as the contents of the second and third viewpoints.

In order to diffuse the gas having a sufficiently low oxygen concentration into the second measurement chamber, a part (for example, 0.5% or more, preferably 1% or more) of nitrogen oxide (particularly NO) is used in the first measurement chamber. It is preferable to control the operation of the first oxygen ion pump cell to such an extent that the first oxygen ion pump cell is decomposed. In this case, the amount of nitrogen oxide decomposition in the first measurement chamber based on the current flowing through the first oxygen ion pump cell Can be compensated for.

The principle of the present invention and the underlying invention will be described with reference to FIGS. FIG. 1A is a cross-sectional view for explaining a schematic configuration of a nitrogen oxide concentration measuring instrument to which the control method of the present invention is suitably applied.
(B) corresponds to a cross section indicated by oblique lines. The measuring device shown in FIG. 1A has two sets of diffusion resistance parts, an oxygen ion pump cell, and a measurement chamber, respectively, and a pair of electrodes 6a and 6b provided with a first solid electrolyte layer interposed therebetween. The first oxygen ion pump cell 6 provided with the above, the oxygen partial pressure detection cell 7 provided with a pair of oxygen partial pressure detection electrodes 7a and 7b provided with the second solid electrolyte layer interposed therebetween, and the third solid electrolyte layer The second oxygen ion pump cell 8 having a pair of electrodes 8a and 8b provided therebetween is stacked in this order, and an insulating layer is formed between each solid electrolyte layer. A first measuring chamber 2 is defined between the first oxygen ion pump cell 6 and the oxygen partial pressure detecting cell 7 by an insulating layer and a solid electrolyte layer, and similarly, the second oxygen chamber is defined by the insulating layer and the solid electrolyte layer. The second measurement chamber 4 is defined above the ion pump cell 8. Further, a first wall having a diffusion resistance is provided on a wall surface surrounding the first measurement chamber 2.
A plurality of diffusion holes 1 are provided, and an opening of a second diffusion hole 3 is provided at the center of the cross section of the first measurement chamber 2 so as to be separated from the first diffusion hole 1. The second diffusion hole 3 penetrates through the oxygen partial pressure detection cell 7 and the solid electrolyte layer and communicates the first and second measurement chambers 2 and 4 with diffusion resistance.

Next, the principle of detecting the concentration of nitrogen oxide in the sensor as shown in FIG. 1 will be described. As shown in FIG.
The nitrogen oxide concentration can be obtained by utilizing the fact that the second oxygen ion pump current Ip2 flowing through the second oxygen ion pump cell is proportional to the amount of oxygen generated by the decomposition of nitrogen oxide in steps 201 to 205. In FIG. 1, the first and second diffusion resistances are the first diffusion holes 1,
It corresponds to the gas diffusion resistance of the second diffusion hole 3 respectively.

Actually, in an atmosphere having a low oxygen concentration lower than a predetermined level, oxygen cannot be completely pumped out in the first measurement chamber due to restrictions such as (excessive) decomposition of nitrogen oxides. Therefore, the oxygen pumped out of the second measurement chamber by the second oxygen ion pump cell and the oxygen generated by the decomposition of the nitrogen oxides in the second measurement chamber and the oxygen pumped out of the first measurement chamber and diffused into the second measurement chamber. Both oxygen. That is, since the current flowing through the second oxygen ion pump cell is affected by both the remaining oxygen concentration and the nitrogen oxide concentration in the second measurement chamber, accurate measurement of the nitrogen oxide concentration is required. It is necessary to eliminate the influence of residual oxygen.

Therefore, according to the invention on which the present invention is based, the influence of oxygen is eliminated as follows. That is,
The gas to be measured (gases of various oxygen concentrations) with the nitrogen oxide concentration set to zero and the oxygen concentration changed is introduced into the measuring instrument, and the amount of current flowing through the second oxygen ion pump cell (hereinafter, this current amount is referred to as "offset"). "). A gas to be measured having a standard nitrogen oxide concentration is charged into the measuring instrument, and the amount of current flowing through the second oxygen ion pump cell is measured. From these measured values, the “gain” of the amount of change of the second oxygen ion pump current is determined. The gain is represented by the following equation.

"Gain" = (standard nitrogen oxide concentration) /
(Generated current-offset)

The offset value and the gain value calculated in this way are stored in a storage means such as a memory, and at the time of measurement, these offset and gain and the amount of current flowing through the second oxygen pump cell are stored in a microcomputer or the like. The input is used to calculate the nitrogen oxide concentration.

However, when the oxygen concentration in the gas to be measured changes, the P.O. I. Even if the first oxygen ion pump cell is used to pump oxygen so as to have a constant oxygen concentration in the first measurement chamber using a control method such as D, control delay occurs, and the first measurement chamber remains constant. Because it does not become oxygen concentration,
If the oxygen concentration in the first measurement chamber is too low and NO is decomposed in the first measurement chamber and the output decreases or the oxygen concentration increases when measuring NO in the second measurement chamber,
Since the excess oxygen that should be pumped out in the first measurement chamber is also measured, it was found that there was a problem that the output was high and the NO amount could not be measured accurately.

The present inventors have conducted intensive research to solve the above-mentioned problems, and have completed the present invention. Hereinafter, the device according to the present invention and the device according to a comparative example (the invention on which the present invention is based) will be described in comparison. First, an apparatus according to a comparative example will be described with reference to FIGS. The configuration of the element portion shown in FIG. 3 is the same as that shown in FIG. In FIG. 3, a reference electrode 7b of the oxygen partial pressure detection cell 7 is electrically connected to one input terminal of the differential amplifier 30, and an output voltage of the oxygen partial pressure detection cell 7 is input thereto. Is connected to a reference power supply. An output terminal of the differential amplifier 30 is electrically connected to an input terminal of the controller 31. The controller 31 performs proportional, integral, and derivative control based on the difference between the electromotive force of the oxygen partial pressure detection cell 7 and the voltage of the reference power supply, so that the electromotive force of the oxygen partial pressure detection cell 7 becomes equal to the voltage of the reference power supply. Thus, the voltage applied between the pair of electrodes 6a and 6b of the first oxygen ion pump cell 6 is controlled.

The device according to the comparative example shown in FIG. 4 includes a Vs constant control unit 41 corresponding to the differential amplifier 30 and the controller 31 shown in FIG. 3, and further includes a first and a second oxygen ion pump current. , Respectively, and a controller 40 that outputs an oxygen concentration value and a NOx concentration value. Vs
The constant control unit 41 receives the output of the oxygen partial pressure detection cell 7 as input, controls the voltage applied to the first oxygen ion pump cell 6, and makes the electromotive force of the oxygen partial pressure detection cell 7 constant. The controller 40 then controls the first oxygen ion pump cell 6
The first oxygen ion pump current flowing through the second oxygen ion pump cell 8 and the second oxygen ion pump current flowing through the second oxygen ion pump cell 8 are input, and the oxygen concentration calculator 40a calculates and outputs the oxygen concentration based on the first oxygen ion pump current. At the same time, an oxygen concentration correction signal is output. The NOx concentration calculating section 40b of the controller 40 receives the oxygen concentration correction signal and the second oxygen ion pump current as inputs, and outputs a nitrogen oxide concentration value whose oxygen concentration has been corrected based on these. That is, the system shown in FIG. 4 assumes a steady state in which the oxygen partial pressure (concentration) is constant, and performs the oxygen concentration correction (the correction amount is constant) in the nitrogen oxide concentration detection based on the first oxygen ion pump current. Have been done.

On the other hand, according to the nitrogen oxide concentration measuring apparatus shown in FIG. 5 according to the present invention, in addition to the control configuration shown in FIG. The detected voltage is directly input to the NOx concentration calculating unit 40b. Then, the NOx concentration calculating unit 40b further calculates the nitrogen oxide concentration based on the change rate (change amount) of the oxygen concentration detection output (oxygen concentration detection voltage) in addition to the oxygen concentration correction signal and the second oxygen ion pump current. The detection oxygen concentration is corrected. According to this control device, even when the oxygen concentration in the gas to be measured fluctuates greatly (in an unsteady state of the oxygen partial pressure), the nitrogen oxide concentration detection output can be changed according to the oxygen concentration change rate (change amount). Can be corrected, and the influence of the fluctuation of the oxygen concentration is eliminated, and the accurate detection of the nitrogen oxide concentration is performed.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described. In the circuit configuration shown in FIG. 3, P.I.
I. D control is performed to control the oxygen concentration in the first measurement chamber to be constant. At this time, if the target voltage for controlling the oxygen partial pressure detection cell (setting of the electromotive force generated in the oxygen partial pressure detection cell) is changed, the second oxygen ion pump current changes. The offset of the second oxygen ion pump current is measured and input to a memory such as a controller as a map, and when the electromotive force generated in the oxygen partial pressure detection cell changes when the oxygen concentration in the gas to be measured changes suddenly, By reading the offset amount corresponding to the electromotive force from the map and increasing or decreasing the offset amount from the second oxygen ion pump current, the NOx concentration can be detected more accurately.

It is preferable to detect the oxygen partial pressure in the second measurement chamber and correct the second oxygen ion pump current. However, it is necessary to provide an electrode again, and the oxygen concentration in the already existing first measurement chamber is controlled. The correction may be performed using an oxygen partial pressure detection cell for performing the correction. Also, preferably, the reference electrode of the oxygen partial pressure detection cell is disposed in the reference oxygen chamber, and a small amount of current is caused to flow, so that the atmosphere around the reference electrode has a constant oxygen concentration, and the oxygen concentration in the measurement chamber is accurately measured. Can be detected.

[0024]

An embodiment of the present invention will be described below with reference to the drawings. The nitrogen oxide concentration measuring apparatus according to one embodiment of the present invention uses a measuring device (sensor element) having the configuration shown in FIG. 1 in the control configuration shown in FIG. This nitrogen oxide concentration measuring instrument is manufactured by stacking sheets of ZrO ₂ ceramic, an insulating layer is stacked between each sheet, and a first measuring chamber is provided between the first layer and the second layer. Between the measurement chamber and the exhaust gas (measurement atmosphere), a rate controlling layer made of a porous ceramic of Al ₂ O ₃ is provided. Further, a first oxygen ion pump cell having a porous electrode containing platinum is provided on both surfaces of the first layer, and the second layer similarly has an oxygen partial pressure detection electrode. In addition, a second measurement chamber is provided between the third layer and the fourth layer, and the second oxygen ion pump cell exists in the fourth layer. FIG. 12 shows the layout of this nitrogen oxide sensor. Hereinafter, FIG.
A production example of this nitrogen oxide sensor will be described with reference to FIG.

[Manufacturing Example] As shown in FIG. 12, a ZrO ₂ green sheet and an electrode paste are laminated in the order from the upper left to the lower left and from the upper right to the lower right to form an integrated measuring device (sensor). Is done. 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,
A production example of each component such as a ZrO ₂ green sheet will be described.

[ZrO ₂ green sheet molding] ZrO ₂ powder was calcined in an atmospheric furnace at 600 ° C. for 2 hours. 30 kg of calcined ZrO ₂ powder, 150 g of dispersant, 10 organic solvents
kg together with 60 kg of cobblestone into trommel, about 50
The mixture is dispersed for a period of time, and a solution obtained by dissolving 4 kg of an organic binder in 10 kg of an organic solvent is added thereto and mixed for 20 hours to obtain a slurry having a viscosity of about 10 Pa · s.
From this slurry, the thickness of 0.4
mm ZrO ₂ green sheet is prepared at 100 ° C.
× Dry for 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: 20 g of platinum powder, 2.8 g of ZrO ₂ powder, and an appropriate amount of an organic solvent are put in a grinder (or pot mill), mixed for 4 hours, dispersed, and then mixed with an organic binder 2.
g, dissolved in 20 g of an organic solvent, and 5 g of a viscosity modifier were further added.
・ Make about s paste.

(2) For the first oxygen ion pump electrode 6b and the oxygen partial pressure detecting electrode (oxygen concentration measuring electrode) 7a: platinum powder
19.8 g, ZrO ₂ powder 2.8 g, gold powder 0.2 g, and an appropriate amount of an organic solvent were put into 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. Then, 5 g of a viscosity modifier is further 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 into a grinder (or pot mill), mixed for 12 hours, dissolved, and 20 g of a viscosity modifier is added. Mix for 3 hours and viscosity 10
A paste of about 0 Pa · s is prepared.

(4) Pt-containing porous material (for lead wire): alumina powder 10 g, platinum powder 1.5 g, organic binder 2.5
g and an organic solvent (20 g) are placed in a grinder (or pot mill), mixed for 4 hours, further added with a viscosity modifier (10 g), and mixed for 4 hours to prepare a paste having a viscosity of about 100 Pa · s.

(5) For the first diffusion hole 1: 10 g of alumina powder having an average particle diameter 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), mixed, dispersed, and further dispersed in viscosity. Add 10g of modifier and add 4g
Mix for a time to produce a paste with a viscosity of about 400 Pa · s.

(6) For carbon coating: carbon powder 4
g, 2 g of an organic binder, and 40 g of an organic solvent are put into a grinder (or pot mill), mixed and dispersed, and 5 g of a viscosity modifier is added, followed by mixing for 4 hours to prepare a paste. Note that by forming a carbon coat by printing, for example, electrical contact between the electrodes is prevented. The carbon coat is used to form a first measurement chamber and a second measurement chamber. Since carbon is burned off during firing, the carbon coat layer does not exist in the fired body.

For the second diffusion hole 3: 20 g of alumina powder having an average particle size of about 2 μm, 8 g of organic binder, 20 organic solvents
g in a grinder (or pot mill), mix for 1 hour, granulate, apply pressure of about 2t / cm ² with a die press, and press in a cylindrical shape of 1.3mm in diameter and 0.8mm in thickness. A molded body (green state) is produced. The green pressed body is inserted into predetermined portions of the second and third layers of ZrO ₂ green sheets, pressed and integrated, and then fired to form second diffusion holes in the gas sensor.

[ZrO ₂ Laminating Method] After the second and third layers are pressed, a portion (diameter: 1.3 mm) through which the second diffusion hole penetrates is punched. After the punching, a green cylindrical shaped body serving as the second diffusion hole 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,
Bake for 1 hour.

A nitrogen oxide sensor (measuring device) having the following dimensions was prepared according to the above production example, and a NOx gas concentration measurement test was performed. The nitrogen oxide sensor used for measurement has a length in the longitudinal direction of 50 mm, a width (transverse direction) of 4 mm, and a thickness (laminating direction) of 1.3 mm. The thickness of the first oxygen ion pump cell is 0.3 mm, the length of the electrodes 6a and 6b in the longitudinal direction is 7 mm, the length in the transverse direction is 2 mm, and the length of the first measurement chamber in the longitudinal direction is 7 mm. The length in the hand direction is 2mm,
Height 50 μm, length of the second measurement chamber in the longitudinal direction is 7 mm, length in the transverse direction is 2 mm, height is 50 μm, length of the first diffusion hole in the longitudinal direction is 2 mm, length in the transverse direction is 1 mm, Thickness 5
0 μm, and the size of the second diffusion hole is 1 mm in diameter.

(Measurement Example 1) First, in this control system, the potential of the second oxygen ion
A gas to be measured containing 500 ppm of NO and 7% of oxygen was charged, and the gain and offset of the second oxygen ion pump current when the set voltage of the oxygen partial pressure detection cell was changed were measured. The result is shown in FIG. Further, the set voltage of the oxygen partial pressure detection cell is kept constant, and contains 1500 ppm of NO,
A gas to be measured containing 7% of oxygen was supplied, and the gain and offset of the second oxygen ion pump current when the potential of the second oxygen ion pump cell was changed were measured. The result is shown in FIG.

As shown in FIG. 6, when the set voltage of the oxygen partial pressure detection cell is lowered, the amount of oxygen remaining in the gas diffused into the second measurement chamber increases, and the second oxygen ion pump current increases. It can be seen that when the set voltage is increased, the current decreases. On the other hand, from FIG. 7, when the set voltage of the oxygen partial pressure detection cell is kept constant and the oxygen concentration in the first measurement chamber is kept constant, when the second oxygen ion pump cell voltage is lowered, the second It can be seen that the oxygen ion pump current decreases and increases when the voltage is increased.

Therefore, by utilizing the characteristics shown in FIGS. 6 and 7, when the electromotive force generated in the oxygen partial pressure detection cell is high, the voltage of the second oxygen ion pump cell is lowered, and the electromotive force is reduced. When the voltage is low, increasing the voltage cancels out the effects of oxygen and the change in oxygen concentration in the gas to be measured, so that the NOx concentration in the gas to be measured can be accurately measured.

FIG. 8 shows the result of plotting the relationship between the potential difference between the measured potential of the electrode 7b (see FIG. 3) of the oxygen partial pressure detection cell and the reference potential (450 mv) and the second oxygen ion pump current. FIG. 8 shows that there is a substantially linear relationship between the two. Therefore, this relationship is stored in advance in a storage unit included in the controller 40 (map creation), and when the oxygen concentration in the measured gas changes suddenly and the electromotive force generated in the oxygen partial pressure detection cell changes, By reading a predetermined offset amount corresponding to the electromotive force change, and increasing or decreasing the measured second oxygen ion pump current value based on the read offset amount, based on the corrected second oxygen ion pump cell output, It can be seen that an accurate nitrogen oxide concentration is required.

(Measurement Example 2) Next, a measuring apparatus (see FIG. 5) according to an embodiment of the present invention having the above-described control configuration is applied to a 1.5-liter lean-burn engine gasoline-powered gasoline vehicle. Was measured for nitrogen oxide concentration. Further, as a comparative example, measurement was similarly performed using a control device (see FIG. 4) that did not perform correction based on the output of the oxygen partial pressure detection cell. The set voltage of the oxygen partial pressure detection cell was 450 mV. At the same time, the true value was measured by an analyzer based on the FTIR method (the output of the analyzer is indicated by FTIR in the figure).
FIG. 9 shows the measurement results of the comparative example, and FIG. 10 shows the measurement results of the example. From FIGS. 9 and 10, it can be seen that in the actual vehicle running, the oxygen concentration changes every moment, and a control delay occurs in the control for keeping the potential of the oxygen partial pressure detection cell constant. And
In FIG. 9, when the potential of the oxygen partial pressure detection cell suddenly changes, NO
The x sensor (based on the second oxygen ion pump current) outputs an abnormal value, and the NOx sensor output () is significantly different from the analyzer output (), indicating that accurate NOx concentration measurement was not performed.

On the other hand, according to FIG. 10, the measured potential of the electrode 7b (see FIG. 3) of the oxygen partial pressure detecting cell and the reference potential (450
mv), a predetermined offset amount corresponding to a potential difference (electromotive force change) is read, and correction is performed to increase or decrease the second oxygen ion pump current value measured based on the read offset amount, thereby detecting oxygen partial pressure. When the cell potential changes suddenly, the peak of the NOx sensor output becomes less than half the height of FIG. 9, and the NOx sensor output () is almost the same as the analyzer output (). Indicates that this has been done.

In the embodiment described above, the correction is performed inside the controller 40 shown in FIG. 5, but by adding a predetermined circuit to the system shown in FIG. A predetermined circuit is connected to the control circuit), another control configuration according to the present invention can be realized. FIG. 11 is a view for explaining a nitrogen oxide concentration measuring apparatus according to another embodiment of the present invention. The device shown in FIG. 11 is different from the device shown in FIG. 3 in that an amplifier 3 is provided between a reference electrode 7b of the oxygen partial pressure detecting cell 7 and an outer electrode 8b of the second oxygen ion pump cell.
This is the point where 2 is arranged. The system of FIG. 11 uses the second oxygen ion according to the potential of the oxygen partial pressure detection cell (the potential difference (electromotive force change) between the potential generated at the electrode 7b of the oxygen partial pressure detection cell (see FIG. 3) and the reference potential). By varying the applied voltage to the pump cell, the above-described software-based correction by the controller is performed by hardware. That is, the pump voltage applied to the second oxygen ion pump cell is controlled so that the pump voltage is high when the voltage of the oxygen partial pressure detection cell is high, and is low when the voltage of the oxygen partial pressure detection cell is low. When a measurement test similar to that of the above-described embodiment was performed, the system shown in FIG. 11 showed that the system shown in FIG. It was confirmed that the nitrogen oxide concentration could be measured.

[0044]

As described above, according to the present invention,
Even when the oxygen concentration in the gas to be measured changes suddenly, the nitrogen oxide concentration can be obtained more accurately. That is, even in an atmosphere in which the oxygen concentration fluctuates greatly, there is no delay in control, and an accurate nitrogen oxide concentration can be obtained in real time. By applying the control method of the present invention to a nitrogen oxide detection system of an internal combustion engine, It is possible to construct a highly responsive combustion control system according to changes in oxygen concentration and nitrogen oxide concentration. Further, the measuring device of the present invention can be configured as software or hardware.

[Brief description of the drawings]

FIG. 1 is a view for explaining a nitrogen oxide concentration measuring instrument suitably used in one embodiment of the present invention,
(A) is a cross-sectional view for explaining the structure of the measuring device (element), (b) is a diagram for explaining the position of the cross section shown in (a) with respect to the entire measuring device, and (c) is the output of the measuring device. It is a figure for explaining a characteristic.

FIG. 2 is a flowchart for explaining a nitrogen oxide concentration detecting process using the nitrogen oxide concentration measuring device shown in FIG.

FIG. 3 is a diagram for explaining a nitrogen oxide concentration measuring device according to a comparative example.

FIG. 4 is a block diagram for explaining a measuring device according to a comparative example.

FIG. 5 is a block diagram for explaining a measuring device according to one embodiment of the present invention.

FIG. 6 shows a case where the potential of the second oxygen ion pump cell is kept constant by using the measuring apparatus according to one embodiment of the present invention.
It is a figure which shows the gain and offset of the 2nd oxygen ion pump current when the gas to be measured containing pm of NO and 7% of oxygen is supplied and the set voltage of the oxygen partial pressure detection cell is changed.

FIG. 7 is a diagram illustrating a measurement apparatus according to an embodiment of the present invention, in which the set voltage of the oxygen partial pressure detection cell is kept constant at 1500 pp.
FIG. 9 is a diagram showing the gain and offset of the second oxygen ion pump current when the gas to be measured containing m NO and 7% oxygen is supplied and the potential of the second oxygen ion pump cell is changed.

FIG. 8 shows a potential difference between the first measurement chamber side electrode 7b (see FIG. 3) of the oxygen partial pressure detection cell and a reference potential and a second oxygen ion pump current using the measuring device according to one embodiment of the present invention. It is a figure showing a relation.

FIG. 9 is a diagram showing the results of measuring the exhaust gas concentration of a 1.5-liter lean-burn engine gasoline-powered vehicle using the measuring device according to the comparative example.

FIG. 10 is a diagram showing the results of measuring the exhaust gas concentration of a 1.5-liter lean-burn engine gasoline vehicle using the nitrogen oxide concentration measuring device according to one embodiment of the present invention.

FIG. 11 is a view for explaining a nitrogen oxide concentration measuring apparatus according to another embodiment of the present invention.

FIG. 12 is a diagram for explaining a layout of a nitrogen oxide concentration measuring device (sensor element).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st diffusion hole 2 1st measurement room 3 2nd diffusion hole 4 2nd measurement room 6 1st oxygen ion pump cell 6a, 6b electrode 7 Oxygen partial pressure detection cell 7a, 7b electrode 8 2nd oxygen ion pump cell 8a, 8b Electrode 30 Differential amplifier 31 Controller (PID controller) 32 Amplifier 40 Controller 40a Oxygen concentration calculation unit 40b NOx concentration calculation unit 41 Vs (oxygen partial pressure detection cell potential) constant control unit

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takafumi Oshima 14-18 Takatsuji-cho, Mizuho-ku, Nagoya Japan Special Ceramics Co., Ltd.

Claims (14)

[Claims] A first measurement chamber into which a gas to be measured is introduced via a first diffusion resistor; a first oxygen ion pump cell for sufficiently pumping or pumping oxygen outside or inside the first measurement chamber; A second measurement chamber into which gas is introduced from the first measurement chamber via a second diffusion resistor; and a pair of electrodes provided inside and outside the second measurement chamber, and a voltage is applied to the pair of electrodes. The second oxygen that is applied to decompose the nitrogen oxides in the second measurement chamber and pump out the dissociated oxygen causes a current (hereinafter referred to as “second oxygen ion pump current”) to flow according to the nitrogen oxide concentration. An ion pump cell; and means for obtaining a nitrogen oxide concentration based on the second oxygen ion pump current in response to a change when the oxygen partial pressure in the gas to be measured changes. Oxide concentration measurement device. 2. An oxygen partial pressure detecting cell having an oxygen partial pressure detecting electrode for detecting an oxygen partial pressure in the first measuring chamber, wherein the means for obtaining the nitrogen oxide concentration comprises: 2. The nitrogen oxide concentration measurement device according to claim 1, further comprising a correction unit that corrects a nitrogen oxide concentration detection output based on the second oxygen ion pump current based on an output of the detection cell. 3. The electric current flowing through the first oxygen ion pump cell (hereinafter referred to as “the current value”) is controlled by controlling the voltage applied to the first oxygen ion pump cell based on the output of the oxygen partial pressure detection cell. The nitrogen oxide concentration measuring device measuring device according to claim 2, wherein the nitrogen oxide concentration detection output is corrected based on a change amount of "first oxygen ion pump current". 4. A first measuring chamber into which a gas to be measured is introduced via a first diffusion resistor, and sufficiently pumping or pumping oxygen in the gas to be measured from the first measuring chamber to outside or inside the measuring chamber. A first oxygen ion pump cell, and a second oxygen ion pump cell from the first measurement chamber.
A second measurement chamber into which a gas is introduced via a diffusion resistance; and a pair of electrodes provided inside and outside the second measurement chamber, and when a voltage is applied to the pair of electrodes, the second measurement chamber A second oxygen ion pump cell in which a current (hereinafter referred to as “second oxygen ion pump current”) according to the nitrogen oxide concentration flows by decomposing nitrogen oxides therein and pumping out dissociated oxygen. A nitrogen oxide concentration measuring device; and means for controlling a voltage applied to the second oxygen ion pump cell in accordance with a change in oxygen partial pressure in the gas to be measured. measuring device. 5. The apparatus according to claim 1, wherein said control means decreases the voltage applied to said second oxygen ion pump cell when said oxygen partial pressure is low, and increases said voltage when said oxygen partial pressure is high. Item 6. The nitrogen oxide concentration measuring device according to Item 4. 6. A first measuring chamber into which a gas to be measured is introduced via a first diffusion resistor, and sufficient pumping or pumping of oxygen in the gas to be measured from the first measuring chamber to outside or inside the measuring chamber. A first oxygen ion pump cell, and a second
A second measurement chamber into which a gas is introduced via a diffusion resistance; and a pair of electrodes provided inside and outside the second measurement chamber, and when a voltage is applied to the pair of electrodes, the second measurement chamber A second oxygen ion pump cell in which a current corresponding to the nitrogen oxide concentration (hereinafter referred to as a “second oxygen ion pump current”) flows by decomposing nitrogen oxides therein and pumping out dissociated oxygen; A nitrogen oxide concentration measuring device comprising: a measuring chamber or an oxygen partial pressure detecting cell for detecting an oxygen partial pressure in the second measuring chamber; and an output of the oxygen partial pressure detecting cell and the second oxygen ion pump cell. A nitrogen oxide concentration calculation for correcting the output of the nitrogen oxide concentration measurement device based on the second oxygen ion pump current when the output of the oxygen partial pressure detection cell changes with the output as an input. And a part having Nitrogen oxide concentration measurement device for. 7. An oxygen partial pressure constant control unit for controlling the first oxygen ion pump cell so that the output of the oxygen partial pressure detection cell is constant, and a change in output of the oxygen partial pressure detection cell. A storage unit in which the relationship between the amount and the offset of the second oxygen ion pump current is stored in advance, wherein the nitrogen oxide concentration calculation unit is configured to change the output of the oxygen partial pressure detection cell according to the change amount. 7. The nitrogen oxide concentration detection output according to claim 6, wherein predetermined data is read from a storage unit, and the nitrogen oxide concentration detection output is corrected by changing a value of an offset of the second oxygen ion pump current based on the data. Nitrogen oxide concentration measurement device. 8. A first measuring chamber into which a gas to be measured is introduced via a first diffusion resistance, and all of the nitrogen oxides do not decompose oxygen in the gas to be measured from the first measuring chamber to the outside of the measuring chamber. A first oxygen ion pump cell for sufficiently pumping, a second measurement chamber into which gas is introduced from the first measurement chamber via a second diffusion resistor, and an inside and an outside of the second measurement chamber. A voltage corresponding to the concentration of nitrogen oxides is obtained by applying a voltage to the pair of electrodes, decomposing nitrogen oxides remaining in the second measurement chamber, and pumping out dissociated oxygen. A second oxygen ion pump cell through which a "second oxygen ion pump current" flows. When the oxygen partial pressure in the gas to be measured changes, The nitric acid based on the second oxygen ion pump current A method for controlling a nitrogen oxide concentration measuring device, comprising: correcting a nitrogen oxide concentration detecting output of the compound concentration measuring device. 9. An oxygen partial pressure detecting cell having an oxygen partial pressure detecting electrode for detecting an oxygen partial pressure in the first measuring chamber, wherein the nitrogen oxidation is performed based on an output of the oxygen partial pressure detecting cell. 9. The control method for a nitrogen oxide concentration measuring instrument according to claim 8, wherein the substance concentration detection output is corrected. 10. A current flowing through the first oxygen ion pump cell (hereinafter referred to as a "first oxygen ion pump cell") by controlling an applied voltage to the first oxygen ion pump cell based on an output of the oxygen partial pressure detection cell. 10. The control method for a nitrogen oxide concentration measuring device according to claim 9, wherein the nitrogen oxide concentration detection output is corrected based on a change amount of a pump current. 11. A first measurement chamber into which a gas to be measured is introduced via a first diffusion resistor, and all of the nitrogen oxides do not decompose oxygen in the gas to be measured from the first measurement chamber to the outside of the measurement chamber. A first oxygen ion pump cell for sufficiently pumping, a second measurement chamber into which gas is introduced from the first measurement chamber via a second diffusion resistor, and an inside and an outside of the second measurement chamber. A voltage corresponding to the concentration of nitrogen oxides is obtained by applying a voltage to the pair of electrodes, decomposing nitrogen oxides remaining in the second measurement chamber, and pumping out dissociated oxygen. A second oxygen ion pump cell through which a “second oxygen ion pump current” flows, wherein the second oxygen ion pump cell is connected to the second oxygen ion pump cell according to a change in the oxygen partial pressure in the gas to be measured. Controlling the voltage applied to the ion pump cell A method for controlling a nitrogen oxide concentration measuring device, comprising: 12. The method according to claim 1, wherein the voltage applied to the second oxygen ion pump cell is decreased when the oxygen partial pressure is low, and the voltage is increased when the oxygen partial pressure is high.
2. A control method of the nitrogen oxide concentration measuring device according to 1. 13. A first measuring chamber into which a gas to be measured is introduced via a first diffusion resistor, and all of the nitrogen oxides do not decompose oxygen in the gas to be measured from the first measuring chamber to the outside of the measuring chamber. A first oxygen ion pump cell for sufficiently pumping, a second measurement chamber into which gas is introduced from the first measurement chamber via a second diffusion resistor, and an inside and an outside of the second measurement chamber. A voltage corresponding to the concentration of nitrogen oxides is obtained by applying a voltage to the pair of electrodes, decomposing nitrogen oxides remaining in the second measurement chamber, and pumping out dissociated oxygen. And a second oxygen ion pump cell through which a “second oxygen ion pump current” flows. Further, the oxygen partial pressure in the first measurement chamber or the second measurement chamber is determined by An oxygen partial pressure detection cell to be detected, and the oxygen content The output of the detection cell and the output of the second oxygen ion pump cell are input, and when the output of the oxygen partial pressure detection cell changes, the nitrogen of the nitrogen oxide concentration measuring device based on the second oxygen ion pump current is changed. A control device for a nitrogen oxide concentration measuring device, comprising: a nitrogen oxide concentration calculating unit that corrects an oxide concentration detection output. 14. An oxygen partial pressure constant control section for controlling said first oxygen ion pump cell so that an output of said oxygen partial pressure detection cell is constant, and a change amount of an output of said oxygen partial pressure detection cell. A storage unit in which the offset relationship of the second oxygen ion pump current is stored in advance, and reads out predetermined data from the storage unit in accordance with an amount of change in the output of the oxygen partial pressure detection cell, 14. The control device for a nitrogen oxide concentration measurement device according to claim 13, wherein the nitrogen oxide concentration detection output is corrected by varying an offset value of the second oxygen ion pump current based on the following.