JP3310274B2 - Gas concentration detector and gas concentration sensor used for it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas concentration detecting device using a gas concentration sensor for detecting the concentration of a characteristic component in exhaust gas discharged from an automobile engine, for example.

[0002]

2. Description of the Related Art Air pollution caused by, for example, exhaust gas from a vehicle engine has caused serious problems in modern society, and regulations for purification of pollutants in exhaust gas have become stricter year by year. Therefore, studies are being made to reduce the pollutants in exhaust gas by using combustion control and catalytic converters for gasoline or diesel engines. In the United States, OBD-II (On Boa
The rd Diagnostic -II) regulation requires a function to determine whether a catalytic converter for exhaust gas purification is appropriate.

On the other hand, the upstream and downstream sides of the catalyst are
Although a so-called 2O2 sensor monitor system has been introduced in which two O2 sensors are provided and the detection results of the two O2 sensors are taken, this method is not a direct method for detecting pollutants. Therefore, it has been difficult to accurately detect and determine whether or not the pollutant is actually reduced from the components in the exhaust gas.

If the combustion control monitor, the catalyst monitor, and the like can be performed by directly detecting the NOx (nitrogen oxide) concentration in the exhaust gas, the reduction of pollutants in the exhaust gas becomes more accurate and effective. . That is, if the fuel injection, the EGR rate, and the like can be feedback-controlled based on the knowledge of the NOx concentration in the exhaust gas, it is possible to reduce the pollution components discharged from the engine. Further, by providing the NOx sensor for detecting the NOx concentration downstream of the catalytic converter for purifying the exhaust gas, it is possible to easily determine the deterioration of the catalyst carried by the converter.

[0005] From such a background, there is a demand for a technique of providing a NOx sensor capable of accurately detecting the NOx concentration in exhaust gas and mounting the NOx sensor in a vehicle engine.

If the oxygen (O2) concentration in the exhaust gas can be detected simultaneously with the detection of the NOx concentration, the effect can also be exerted on the air-fuel ratio feedback control system. That is, in the air-fuel ratio control of the vehicle engine in recent years,
For example, there is a demand for increasing control accuracy and a demand for lean burn, and in response to these demands, a sensor for detecting the air-fuel ratio (oxygen concentration in exhaust gas) of the air-fuel mixture taken into the engine in a wide range and linearly. A device is also desired.

As a prior art, there has been proposed a NOx sensor of a type in which the concentration of oxygen contained in exhaust gas (gas to be detected) is reduced in advance, and then the NOx concentration is detected from the exhaust gas (Japanese Patent Laid-Open No. Hei 8-271476). Official Gazette, Automobile Engineering Society Academic Lecture Preprints 9711997-5, etc.). For example, the sensor includes a pump cell for detecting the oxygen concentration, a sensor cell for detecting the NOx concentration, and a diffusion unit adjacent to each of the cells. Then, oxygen in the chamber isolated from the exhaust gas atmosphere via the diffusion unit is exhausted by the pump cell, and the remaining NOx is decomposed and exhausted by the sensor cell, and the decomposition current value is used as the NOx concentration output.

[0008]

However, the above N
In the case of the Ox sensor, there is a problem that even if the NOx concentration is constant, if the oxygen concentration in the exhaust gas changes, the NOx output (sensor cell current) changes accordingly. This problem cannot be compensated for by controlling the oxygen concentration in the chamber to be constant. It is being studied to eliminate the NOx concentration detection error by correcting the NOx concentration output with the oxygen concentration output, but a specific method has not yet been established.

On the other hand, another problem with the NOx sensor is as follows.
There is a problem that an offset current flows in accordance with the amount of oxygen remaining near the sensor cell, and the NOx concentration output fluctuates due to the offset current. That is, when the concentration of oxygen contained in the exhaust gas is discharged by the pump cell, the oxygen cannot be completely discharged, so that the oxygen remains near the sensor cell. At this time, the sensor cell detects the addition current of the current flowing according to the NOx concentration and the current (offset current) flowing according to the residual oxygen amount, and outputs the NOx concentration (sensor cell current) by the offset current.
Causes an error.

If the residual oxygen amount (offset current) is constant in all the produced sensors, a fixed value of the offset current may be subtracted from the sensor cell current, and the difference may be used as the NOx concentration output. However, in actuality, the residual oxygen amount (offset current) changes due to individual differences between sensors, deterioration due to long-term use in a severe environment such as high temperature, and the like. Therefore, the sensor cell current includes an error corresponding to the change in the offset current, and it is impossible to detect the NOx concentration with high accuracy.

The present invention has been made in view of the above problems, and a first object of the present invention is to perform highly accurate gas concentration detection even when the oxygen concentration in a gas to be detected changes. It is to provide a gas concentration detecting device which can perform the above. A second object is to provide a gas concentration detection device capable of performing highly accurate gas concentration detection even when the amount of oxygen remaining near the sensor cell changes. further,
A third object is to provide a suitable gas concentration sensor in a gas concentration detection device that performs correction according to the residual oxygen amount.

[0012]

The gas concentration detecting device according to the present invention is based on the premise that a diffusion resistance portion for introducing a gas to be detected into an internal space and the expansion resistor accompanying a voltage application are provided.
Decomposes oxygen in the gas to be detected introduced through the diffuser
An oxygen pump cell for supplying a current corresponding to the oxygen concentration of the detected gas by discharge, by the oxygen pump cell
An oxygen detection cell for detecting the oxygen concentration of the gas after oxygen discharge, and an oxygen discharge cell by the oxygen pump cell with application of a voltage.
NOx, HC or CO is decomposed from the discharged gas to form oxygen ions.
A gas concentration sensor including a specific gas detection cell that supplies a current corresponding to the NOx concentration, the HC concentration, or the CO concentration by discharging the gas is applied.

In this configuration, for example, when the gas to be detected is an exhaust gas containing at least oxygen and nitrogen oxides (NOx), as described above, even if the NOx concentration in the exhaust gas is constant, the NOx concentration output (detection Current) inadvertently fluctuates. Then, the inventors of the present application investigated the cause of the above problem, and found that one of the causes was the oxygen concentration dependency of the gas concentration sensor.

[0014] In short, when the oxygen pump cell discharges oxygen, the diffusion resistance for introducing the exhaust gas becomes negative pressure by the oxygen content. Accordingly, a pressure difference between the inside and outside occurs in the diffusion resistance portion, and extra exhaust gas flows in from the outside. The amount of inflow of exhaust gas is proportional to the amount of oxygen discharged, that is, the current value flowing through the oxygen pump cell. Since the inflowing exhaust gas contains NOx, the value of the current flowing through the specific gas detection cell changes, and a detection error of the current value occurs. As described above, there is the oxygen concentration dependency that the current value (NOx concentration output) of the specific gas detection cell changes according to the oxygen concentration in the exhaust gas.

The first aspect of the present invention is characterized in that first detecting means for detecting a current value flowing to the oxygen pump cell, second detecting means for detecting a current value flowing to the specific gas detecting cell, and the first detecting means. Correction means for correcting the current value detected by the second detection means based on the current value detected by the detection means while reflecting the oxygen concentration dependency.

According to the above configuration, when the current value of the specific gas detection cell is corrected based on the current value of the oxygen pump cell, the correction based on the oxygen concentration dependency is performed. The conventional problem that the detection value of the NOx concentration (the current value of the specific gas detection cell) is inadvertently changed when the concentration changes is solved. As a result, even if the oxygen concentration in the detected gas changes, highly accurate gas concentration detection can be performed.

Further, according to the present invention, a mathematical formula is attempted for correction depending on the oxygen concentration dependency, and the correction amount required for the correction corresponds to the structure and sensitivity of the gas concentration sensor. Calculation was performed.

Specifically, the current value detected by the first detecting means is Ip, and the current value detected by the first detecting means is Ip.
The current value detected by the detection means is Is, the current value of the specific gas detection cell obtained after the correction is Isf, the structural constant uniquely determined from the structure of the gas concentration sensor is Ka, and the detection sensitivity of the specific gas detection cell is determined. Assuming that the correction coefficient to be performed is Kb, the correction means corrects the current value of the specific gas detection cell by using a relation represented by an arithmetic expression of Isf = Is · Kb / (Ka · Ip + Kb).

According to this configuration, the factor of the structure of the gas concentration sensor (structural constant Ka) and the factor of the detection sensitivity of the specific gas detection cell (correction coefficient Kb) are reflected in the correction,
Correction according to the oxygen concentration dependence can be simply and accurately performed.

In the above equation, as described in claim 3, the diffusion coefficient of the diffusion resistance section, the shape and volume of the diffusion resistance section, and the positions of the electrodes provided in the oxygen pump cell and the specific gas detection cell. And the structural constant may be determined.

Here, the structural constant Ka in the above equation is used.
Will be described using a simple model shown in FIG. In FIG. 33, the diffusion resistance part 10, the space part 20, and the electrode 3
0, only the diffusion resistance portion 10 has the same cross section (cross-sectional area S) and extends in the left-right direction of the drawing (length L), and the gas component (NOx) having the concentration C flows from left to right in the drawing. And That is, NOx flows from the left surface of the diffusion resistance section 10 to the space section 20 and reaches the electrode 30. In this case, the gas passing amount F per unit time is represented by F = S (cross-sectional area) · C / L (concentration gradient) · α (diffusion coefficient). In calculating the gas passing amount F, a coefficient reflecting whether the diffusion resistance portion 10 is a porous material or a pinhole is multiplied as appropriate. Then, the structural constant Ka is determined corresponding to the gas passing amount F.

According to the second and third aspects of the present invention, even if a negative pressure is generated in the diffusion resistance part due to the oxygen exhaust in the oxygen pump cell and the exhaust gas (NOx component) flows in excessively, the above arithmetic expression is used. As a result, the excess exhaust gas inflow can be canceled, and an accurate NOx concentration output can be obtained.

According to a fourth aspect of the present invention, the relationship between the oxygen concentration in the gas to be detected and the correction data required corresponding to the oxygen concentration in the gas to be detected is stored in advance to reflect the oxygen concentration dependency. Corrects the current value of the specific gas detection cell according to the stored correction data on the oxygen concentration dependency.

According to the above configuration, for example, by using the correction data stored in advance as a map, the correction according to the oxygen concentration dependency can be easily performed. In this case, it is preferable to map correction data corresponding to the arithmetic expression described in claim 2.

According to a fifth aspect of the present invention, the stored correction data is corrected so that the higher the oxygen concentration in the gas to be detected, the lower the gas concentration detected by the specific gas detection cell. According to such correction, for example, even when a negative pressure is generated in the diffusion resistance portion due to a high oxygen concentration in the exhaust gas and extra exhaust gas (NOx) flows in from the outside, the correction according to the extra exhaust gas inflow amount is performed. It can be performed, and as a result, highly accurate gas concentration detection becomes possible.

On the other hand, another reason why the NOx concentration output in the exhaust gas fluctuates may be the influence of the amount of oxygen remaining near the specific gas detection cell. That is, when the amount of residual oxygen near the specific gas detection cell changes, the offset current fluctuates accordingly, and the detection accuracy of the NOx concentration decreases. In this case, the residual oxygen amount (offset current) changes due to individual differences between sensors, deterioration due to long-time use in a severe environment such as high temperature, and the NOx concentration output fluctuates carelessly.

Therefore, the invention according to claim 6 is provided with correction means for correcting the current value of the specific gas detection cell based on the amount of oxygen remaining near the specific gas detection cell.
According to the configuration of claim 6, when the residual oxygen amount in the vicinity of the specific gas detection cell changes due to individual differences of sensors, usage environment, and the like, the influence of the residual oxygen is reliably nullified. As a result, even if the amount of oxygen remaining near the specific gas detection cell (sensor cell) changes, highly accurate gas concentration detection can be performed.

In the invention according to claim 7, there is provided offset current detection means for detecting an offset current flowing through the specific gas detection cell in accordance with the amount of residual oxygen near the specific gas detection cell, and the correction means comprises: The current value of the specific gas detection cell is corrected based on the detected offset current.

In this case, the offset current is directly detected,
By correcting the current value (NOx concentration current) of the specific gas detection cell with the detected offset current, even if the amount of oxygen remaining near the specific gas detection cell (sensor cell) changes, highly accurate gas concentration detection can be performed. Can be implemented.

According to the present invention, the output characteristics of the specific gas detection cell include an offset current component and an oxygen pump.
A first region for detecting an addition current with a specific gas component after oxygen is exhausted by the accelerator, and a second region for detecting only an offset current component, wherein the offset current detection means comprises:
An offset current is detected using the second region.

According to the configuration of the eighth aspect, the offset current can be simply and accurately measured directly by using the second region of the specific gas detection cell output characteristic. Therefore, the offset current can be properly detected, and the detection accuracy of the gas concentration is improved.

According to the ninth aspect of the present invention, the output characteristics of the specific gas detection cell include an offset current component and an oxygen pump.
A first area for detecting an added current with a specific gas component after oxygen is discharged by the capsule, and a second area for detecting only an offset current component, and detecting a current value before correction in the first area; An offset current is detected in the second region, and the correction unit corrects the detected current value before correction with the offset current.

According to the configuration of the ninth aspect, the current value before correction and the offset current can be respectively detected, and the current value before correction is corrected by the offset current, so that the current value near the specific gas detection cell (sensor cell) can be detected. Even if the amount of remaining oxygen changes, highly accurate gas concentration detection can be performed.

According to the tenth aspect, a voltage is applied in the first area when detecting a current value before correction, and a voltage is applied in the second area when detecting an offset current. Thus, a voltage switching means for selectively switching the applied voltage of the specific gas detection cell is provided.

According to the configuration of the tenth aspect, by selectively switching the voltage applied to the specific gas detecting cell as described above, the offset current can be properly detected, and the accuracy of detecting the gas concentration is improved.

According to the eleventh aspect of the present invention, there is provided an electromotive force detecting means for detecting an electromotive force of the specific gas detecting cell, and the correcting means is adapted to detect the specific gas in accordance with the detected electromotive force of the specific gas detecting cell. Correct the current value of the sensing cell.

For example, when the amount of residual oxygen in a specific gas detection cell is large, an excess of oxygen is caused, so that the electromotive force of the specific gas detection cell decreases. That is, the electromotive force of the specific gas detection cell changes as a reflection of the residual oxygen amount. Therefore, by correcting the current value of the specific gas detection cell according to the electromotive force of the specific gas detection cell as described above, even if the amount of oxygen remaining near the specific gas detection cell (sensor cell) changes, highly accurate gas Concentration detection can be performed.

In the twelfth aspect of the present invention, the electromotive force detection means includes a switch for opening an electric path for applying a voltage to the specific gas detection cell, and applies a voltage to the specific gas detection cell by the switch. Measuring means for measuring an electromotive force generated in the specific gas detection cell when the electric path is opened. According to this configuration, the electromotive force of the specific gas detection cell can be accurately and easily measured.

Further, in the invention according to claim 13, the first detecting means for detecting a current value flowing to the oxygen pump cell, the second detecting means for detecting a current value flowing to the specific gas detecting cell, and the first detecting means Based on the current value detected by the means, the first correction for correcting the current value detected by the second detection means while reflecting the oxygen concentration dependency, and based on the amount of oxygen remaining near the specific gas detection cell, Correction means for performing the second correction for correcting the current value of the specific gas detection cell.

According to the configuration of the thirteenth aspect, the first correction for eliminating the influence of the oxygen concentration dependency and the second correction for eliminating the influence of the residual oxygen amount can be realized by the same apparatus. Therefore, even if the oxygen concentration in the gas to be detected changes or the amount of oxygen remaining near the specific gas detection cell (sensor cell) changes, highly accurate gas concentration detection can be performed.

Here, in many cases, the first correction is required at any time according to, for example, a change in the oxygen concentration in the exhaust gas, whereas the second correction is required when an individual difference of the sensor or a change with time occurs. Become. Therefore, in the apparatus that performs both the first and second corrections as described above, the execution frequency of each correction is appropriately changed as set forth in claims 14 and 15 below.

In the invention according to claim 14, the correction means judges whether the first correction and the second correction are necessary, and selectively executes each correction according to the judgment result. For example, the second
The correction is performed only when it is necessary to eliminate the variation due to the individual difference of the sensor or the change with time.

According to a fifteenth aspect of the present invention, the correction means calculates the first and second correction amounts, respectively,
The frequency of calculating the correction amount of the second correction is lower than the frequency of calculating the correction amount of the first correction. For example, while the first correction (calculation of the correction amount) is performed in a period of several msec, the second correction (calculation of the correction amount) is performed in a period of several seconds.

According to the fourteenth and fifteenth aspects, it is possible to carry out a correction according to necessity, and it is possible to realize a more appropriate gas concentration detecting device. In this case, for example, when a microcomputer is used, the calculation load can be reduced.

As a gas concentration sensor applied to the gas concentration detecting device, there is the following configuration of claims 16 and 17. 17. The gas concentration sensor according to claim 16, wherein the output characteristics of the specific gas detection cell include an offset current component and an oxygen pump.
A first area for detecting an added current with a specific gas component after oxygen is exhausted by the cell and a second area for detecting only an offset current component are provided.

In the gas concentration sensor according to the seventeenth aspect,
Each electrode of the oxygen pump cell and the specific gas detection cell facing the diffusion resistance section is an electrode that is inactive with respect to the specific gas component after oxygen is discharged by the oxygen pump cell .

According to the gas concentration sensor of the present invention, a second region is newly provided in addition to the existing sensor having the first region so as to respond to the residual oxygen amount near the specific gas detection cell. The offset current can be directly detected. Therefore, a suitable sensor can be provided in the gas concentration detection device that performs the correction according to the residual oxygen amount.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings. The gas concentration detection device according to the present embodiment is applied to an automobile gasoline engine, and in the air-fuel ratio control system of the engine, the fuel injection amount to the engine is determined based on the detection result by the gas concentration detection device. Feedback control is performed at a desired air-fuel ratio (A / F). Particularly, in this embodiment, the oxygen (O2) concentration in the exhaust gas and the N
A so-called composite gas sensor capable of simultaneously detecting the Ox concentration is used, and gas concentration information is acquired from the sensor.

That is, in the apparatus of this embodiment, while the air-fuel ratio is feedback-controlled based on the detected oxygen concentration, the control of the NOx catalyst (eg, NOx storage reduction type catalyst) attached to the engine exhaust pipe is controlled based on the detected NOx concentration. Is performed. Briefly describing the control of the NOx catalyst, the amount of NOx discharged without being purified by the NOx catalyst is determined from the detection result of the gas concentration sensor, and when the unpurified amount of NOx increases, the NOx purification capability is restored. Is executed. In the regeneration process, a rich gas may be temporarily supplied to the NOx catalyst to remove ions adsorbed on the catalyst.

The outline of the gas concentration detecting device according to the present embodiment will be described with reference to the block diagram of FIG. The gas concentration sensor 100 has, as its main components, a pump cell 110 as a first cell for detecting oxygen concentration, and a NOx
Sensor cell 12 as second cell for detecting concentration
0.

The sensor control circuit 200 includes oxygen concentration detecting means 210 as first detecting means and NOx concentration detecting means 220 as second detecting means. The oxygen concentration detecting means 210 is connected to the pump cell electrode of the gas concentration sensor 100 and has a function of applying a voltage to the pump cell 110 and detecting a pump cell current corresponding to the oxygen concentration. The oxygen concentration detecting means 210 outputs the detected oxygen concentration as a signal SG1 to the NOx current correction circuit 300 and an external device (not shown) (for example, an engine control ECU).

The NOx concentration detecting means 220 is connected to the sensor cell electrode of the gas concentration sensor 100,
And a function of applying a voltage to the sensor 20 and detecting a sensor cell current corresponding to the NOx concentration. The NOx concentration detecting means 220 outputs the detected NOx concentration to the NOx current correction circuit 300 as a signal SG2.

NOx current correction circuit 30 as correction means
0 is the signal SG1 from the oxygen concentration detecting means 210 and NO
The signal SG2 from the x density detecting means 220 is input and N
The NOx current error due to the oxygen concentration is corrected as a reflection that the Ox concentration output has the oxygen concentration dependency. And
The correction circuit 300 outputs the corrected NOx concentration output as a signal S
G3 is output to an external device (for example, an engine control ECU).

Hereinafter, the configuration of the gas concentration detecting device will be described in detail. First, the configuration of the gas concentration sensor 100 will be described with reference to FIG. The gas concentration sensor 100 has a two-cell structure, and is configured as a so-called composite gas sensor capable of detecting the oxygen concentration simultaneously with the detection of the NOx concentration. The gas concentration sensor 100 includes a pump cell 110, a sensor cell 1
20, a porous diffusion layer 101 as a diffusion resistance portion, an air duct 102, and a heater 103 are required, and these members are laminated. The sensor 100 is attached to the engine exhaust pipe at the right end of the figure, and the upper and lower surfaces and the left surface are exposed to exhaust gas.

More specifically, the pump cell 110 is provided between the porous diffusion layer 101 and the exhaust gas space. A pump first electrode 111 is provided on the exhaust gas side (upper side in the figure) of the pump cell 110, and is located on the porous diffusion layer 101 side (lower side in the figure).
Is provided with a pump second electrode 112. The sensor cell 120 is provided between the porous diffusion layer 101 and the air duct 102. Porous diffusion layer 1 of sensor cell 120
A sensor first electrode 121 is provided on the 01 side (upper side in the figure), and a sensor second electrode 122 is provided on the atmosphere duct 102 side (lower side in the figure). Exhaust gas is introduced into the porous diffusion layer 101 from the left side of the figure and flows to the right side of the figure.

The pump cell 110 and the sensor cell 120 have a solid electrolyte formed by lamination, and these solid electrolytes are converted to ZrO 2, HfO 2, ThO 2, Bi 2 O 3, etc.
It is composed of an oxygen ion conductive oxide fired body in which aO, MgO, Y2 O3, Yb2 O3, etc. are dissolved as a stabilizer. Further, the porous diffusion layer 101 is made of a heat-resistant inorganic substance such as alumina, magnesia, quartzite, spinel, and mullite.

The first pump on the exhaust gas side of the pump cell 110
The electrode 111 and the sensor first and second electrodes 121 and 122 of the sensor cell 120 are made of a noble metal having high catalytic activity such as platinum Pt. On the other hand, the pump second electrode 112 on the porous diffusion layer 101 side of the pump cell 110 is made of a noble metal such as Au-Pt which is inert to the NOx gas (it is difficult to decompose the NOx gas).

The heater 103 is embedded in the insulating layer 104,
An air duct 102 is formed between the insulating layer 104 and the sensor cell 120. Atmosphere is introduced into the air duct 102 constituting the reference gas chamber from the outside, and the air is used as a reference gas serving as a reference for the oxygen concentration. Insulation layer 1
04 is made of alumina or the like, and the heater 103 is made of cermet of platinum and alumina. Heater 103
Generates thermal energy by external power supply in order to activate the entire sensor (including electrodes) including the pump cell 110 and the sensor cell 120.

The operation of the gas concentration sensor 100 having the above configuration will be described with reference to FIG. As shown in FIG. 4A, an exhaust gas component is introduced into the porous diffusion layer 101 from the left side of the figure, and when the exhaust gas passes near the pump cell, a decomposition reaction is caused by applying a voltage to the pump cell 110. Occur. The exhaust gas contains oxygen (O2), nitrogen oxides (NOx), carbon dioxide (CO2), and water (H2 O).
And other gas components.

As described above, the pump second of the pump cell 110
The electrode 112 is formed of a NOx inert electrode (an electrode that hardly decomposes NOx gas). Therefore, as shown in FIG. 4B, only oxygen (O2) in the exhaust gas is decomposed in the pump cell 110 and discharged from the pump first electrode 111 into the exhaust gas. At this time, the current flowing through the pump cell 110 is detected as the concentration of oxygen contained in the exhaust gas.

The oxygen (O 2) in the exhaust gas is not completely decomposed in the pump cell 110, and a part of the oxygen (O 2) flows to the vicinity of the sensor cell as it is. Then, as shown in FIG. 4C, by applying a voltage to the sensor cell 120, residual oxygen (O2) and NOx are decomposed. That is, the residual oxygen (O2) and NOx are decomposed at the sensor first electrode 121 of the sensor cell 120, respectively, and are sent from the sensor second electrode 122 through the sensor cell 120 to the atmosphere duct 1
02 is released into the atmosphere. At this time, the sensor cell 12
The current flowing to zero is detected as the concentration of NOx contained in the exhaust gas. The decomposition current due to residual oxygen (O2) becomes an offset current.

Next, the characteristics of the pump cell 110 for detecting the oxygen concentration and the characteristics of the sensor cell 120 for detecting the NOx concentration will be described with reference to FIGS. First, pump cell characteristics will be described with reference to FIG.

As shown in the VI characteristic diagram of FIG. 5, the pump cell has a limiting current characteristic with respect to the oxygen concentration. In the figure, the limit current detection area is composed of a linear portion parallel to the V axis, and the area shifts toward the positive voltage side as the oxygen concentration increases.

Here, if the applied voltage is fixed to a constant value when the oxygen concentration changes, the above-mentioned limit current detection range (V
It is not possible to perform accurate oxygen concentration detection using a straight line parallel to the axis). This also means that a sufficient amount of oxygen cannot be exhausted by the pump cell 110, the residual oxygen in the sensor cell 120 increases, and a large error occurs in the current for detecting the NOx concentration. Therefore, control is performed to apply a voltage equivalent to the angle of the DC resistance component (inclined portion that increases with an increase in applied voltage) of the pump cell, that is, a voltage as shown by the applied voltage line LX1 in FIG. , A desired sensor current (limit current) can always be detected.

Incidentally, since the pump second electrode 112 (the electrode on the side of the porous diffusion layer 101) of the pump cell 110 is a NOx inactive electrode, NOx gas is hardly decomposed in the pump cell 110. As shown, when the voltage exceeds a certain level, NOx is decomposed, and a pump cell current corresponding to the NOx concentration flows in addition to the pump cell current corresponding to the oxygen concentration (broken line in FIG. 5). Therefore, the applied voltage line LX1 is designed so as not to decompose NOx gas.

Next, sensor cell characteristics will be described with reference to FIG. As shown in the VI characteristic diagram of FIG. 6, the sensor cell has a limit current characteristic with respect to the NOx concentration. In the figure, in the portion A1, a current corresponding to the offset (offset current) flows due to residual oxygen flowing into the sensor cell 120 through the porous diffusion layer 101, and in the portion A2, a decomposition current of NOx flows (in the figure, 1000 ppm is shown). In addition, a portion where the current larger than “A1 + A2”, that is, the current at the right end of the drawing increases (NOx concentration is 1000
At pm, the decomposition current of H2 O flows in A3).
At this time, the limit current corresponding to the NOx concentration in the exhaust gas is detected as a current value of “A1 + A2”. The limit current detection area that defines the NOx decomposition current is composed of a linear portion parallel to the V axis, and the area shifts slightly to the positive voltage side as the NOx concentration increases. When detecting the NOx concentration, by controlling the applied voltage along the applied voltage line LX2 in FIG. 6, a desired sensor current (limit current) can always be detected regardless of the NOx concentration in the exhaust gas.

FIG. 2 shows the electrical configuration of the sensor control circuit 200 shown in FIG. In the configuration of FIG.
A lean gas is introduced into the porous diffusion layer 101 of the gas concentration sensor 100, and a pump cell 110 is introduced from the diffusion layer 101 side.
Pump cell 110 based on the time when excess oxygen is exhausted through the pump (based on the direction of the pump cell current Ip at that time).
Are defined. That is, the terminal connected to the pump first electrode 111 is defined as a positive terminal, and the terminal connected to the pump second electrode 112 is defined as a negative terminal. Similarly, on the sensor cell 120 side, based on when exhaust gas containing NOx, that is, lean gas is introduced into the porous diffusion layer 101 (based on the direction of the sensor cell current Is at that time), the sensor second electrode 122 The connected terminal is defined as a positive terminal, and the terminal connected to the sensor first electrode 121 is defined as a negative terminal.

In the sensor control circuit 200, the voltage of the reference voltage circuit 231 is applied to the common negative terminal of the pump cell 110 and the sensor cell 120 via the amplifier circuit 232. That is, the voltage Va is generated by the reference voltage circuit 231, and the voltage Va is input to the non-inverting input terminal of the amplifier circuit 232. The output terminal of the amplifier circuit 232 is connected to the inverting input terminal of the amplifier circuit 232, and the voltage Va of the reference voltage circuit 231 is applied as a voltage follower to the pump second electrode 112 (the negative terminal of the pump cell 110).
And the sensor first electrode 121 (the negative terminal of the sensor cell 120). Thereby, each cell 110, 12
The negative terminal of 0 becomes a reference voltage Va floating above the GND voltage (0 V voltage).

The oxygen concentration detecting means 210 is provided with a pump voltage command circuit 211 for controlling the voltage applied to the pump cell 110. The pump voltage command circuit 211 outputs a command voltage Vb corresponding to the pump cell current Ip using the applied voltage line LX1 in FIG.

The command voltage Vb from the pump voltage command circuit 211 is input to a non-inverting input terminal of an amplifier circuit 212 for applying a voltage to the pump cell 110 and supplying a current corresponding to the oxygen concentration. The output terminal of the amplifier circuit 212 is connected to one end of a current detection resistor 213 for detecting the pump cell current Ip, and the other end of the current detection resistor 213 is connected to the pump first electrode 111 (the positive terminal of the pump cell). Also connected to the inverting input terminal of the amplifier circuit 212. Thereby, the voltage of the pump first electrode 111 is controlled to be always the same as the command voltage Vb of the pump voltage command circuit 211.

The output voltage of the amplifier circuit 212 is output from the terminal Vd, and the voltage of the pump first electrode 111 is output from the terminal Vb. The voltages at the terminals Vb and Vd are taken into the pump voltage command circuit 211 and are taken into the NOx current correction circuit 300 as the signal SG1 in FIG.

In such a case, the pump cell applied voltage Vp and the pump cell current Ip are calculated by the following equations. Vp = Vb−Va Ip = (Vd−Vb) / R1 where R1 is the resistance value of the current detection resistor 213.

The NOx concentration detecting means 220 is provided with a sensor voltage command circuit 221 for controlling the voltage applied to the sensor cell 120. Sensor voltage command circuit 22
1 outputs a command voltage Vc corresponding to the sensor cell current Is using the applied voltage line LX2 in FIG.

The command voltage Vc from the sensor voltage command circuit 221 is input to a non-inverting input terminal of an amplifier circuit 222 for applying a voltage to the sensor cell 120 and supplying a current corresponding to the NOx concentration. An output terminal of the amplifier circuit 222 is connected to a current detection resistor 223 for detecting the sensor cell current Is.
The other end of the current detection resistor 223 is connected to the sensor second electrode 122 (the positive terminal of the sensor cell) and to the inverting input terminal of the amplifier circuit 222. Thus, the voltage of the sensor second electrode 122 is controlled to be always the same as the command voltage Vc of the sensor voltage command circuit 221.

The output voltage of the amplifier circuit 222 is output from the terminal Ve, and the voltage of the sensor second electrode 122 is output from the terminal Vc. The voltages at the terminals Vc and Ve are taken into the sensor voltage command circuit 221 and also taken into the NOx current correction circuit 300 as the signal SG2 in FIG.

In such a case, the sensor cell applied voltage Vs and the sensor cell current Is are calculated by the following equations. Vs = Vc−Va Is = (Ve−Vc) / R2 where R2 is the resistance value of the current detection resistor 223.

The pump voltage command circuit 211 and the sensor voltage command circuit 221 are constituted by one microcomputer, and more specifically, the CPU and the A as shown in FIG.
/ D and D / A converters. That is, in the microcomputers constituting the instruction circuits 211 and 221, the voltages of the terminals Vd, Vb, Ve and Vc in FIG. 2 are input to the A / D converters (A / D1 to A / D4). Is done. In addition, each D / A converter (D / A1,
D / A2) outputs a pump cell command voltage Vb and a sensor cell command voltage Vc, respectively.

The applied voltage control performed by the CPU in the command circuits 211 and 221 will be described with reference to the flowchart of FIG. The routine in FIG. 9 is an applied voltage control subroutine executed in the middle of a main routine (not shown).

In FIG. 9, first, in steps 101 and 10
2, the terminal voltage V of the current detection resistor 213 in FIG.
d and Vb are read by A / D1 and A / D2 in FIG. 7, respectively. Next, in steps 103 and 104, both terminal voltages Ve and Vc of the current detection resistor 223 in FIG.
Each is read by D3 and A / D4.

In step 105, the pump cell current Ip is calculated (Ip = (Vd−Vb) / R1). In the subsequent step 106, the pump cell current Ip is calculated using the applied voltage line LX1 shown in FIG. Pump cell 1
A target applied voltage to 10 is calculated (map calculation). Further, in step 107, the obtained target applied voltage is output as the command voltage Vb via the D / A1.

Next, at step 108, the sensor cell current Is is calculated (Is = (Ve−Vc) / R2). At the next step 109, the calculated sensor cell current Is is calculated using the applied voltage line LX2 shown in FIG. Is calculated (map calculation). Further, at step 110, the obtained target applied voltage is output as the command voltage Vc via the D / A2, and then the present routine is terminated.

The NOx current correction circuit 300 comprises a microcomputer having a CPU and A / D and D / A converters as shown in FIG.
/ D11 to A / D14) have the respective terminals Vd,
The voltages Vb, Ve, and Vc are respectively input. The CPU
The pump cell current Ip and the sensor cell current Is are calculated based on the voltages of the terminals Vd, Vb, Ve, and Vc, the sensor cell current Is is corrected using the pump cell current Ip, and the corrected sensor cell current Isf after the correction is calculated. The signal SG3 is output via a D / A converter or using serial communication. Actually, pump (sensor) voltage command circuits 211 and 221 shown in FIG.
The NOx current correction circuit 300 shown in FIG.

The NOx current correction process performed by the CPU in the NOx current correction circuit 300 will be described with reference to the flowchart of FIG. The routine in FIG. 10 is a NOx current correction subroutine that is performed in the middle of a main routine (not shown).

In FIG. 10, first, steps 201 and 201
In 02, both terminal voltages Vd and Vb of the current detection resistor 213 in FIG. 2 are read by A / D11 and A / D12 in FIG. Next, in steps 203 and 204, both terminal voltages Ve and Vc of the current detection resistor 223 in FIG.
Are read by A / D13 and A / D14, respectively.

In step 205, the pump cell current Ip is calculated (Ip = (Vd−Vb) / R1). In the following step 206, the sensor cell current Is is calculated (Is = (V
e-Vc) / R2).

Thereafter, in step 207, the sensor cell current Is is corrected using the calculated pump cell current Ip. In the correction, the corrected sensor cell current Isf is calculated using the following equation (1). That is, an arithmetic expression using a structural constant Ka uniquely determined from the sensor structure and a correction coefficient Kb determined from the detection sensitivity of the sensor cell 120 (NOx sensitivity when the oxygen concentration is 0%), Isf = Is · Kb / (Ka · Ip + Kb) (1) is used to calculate the corrected sensor cell current Isf.

Here, the structural constant Ka is the value of the porous diffusion layer 1
01, the shape and volume of the diffusion layer 101, and the electrode positions of the cells 110 and 120. In the present embodiment, for example, Ka = 1.95 × 10∧−2.

The NOx sensitivity correction coefficient Kb is, for example, the sensor cell current I when the NOx concentration is 1000 ppm.
Since s is 8.13 μA, Kb = 8.13 × 10∧−3 (A).

For example, when the pump cell current Ip is 25 mA, according to the above equation (1), Isf = Is · 8.13 × 10∧−3 / (1.95 × 10∧−2 · 25 × 10∧−3 + 8) .13 × 10∧-3) = Is · 0.943, which indicates that 6% of the error of the sensor cell current Is can be canceled.

Thereafter, in step 208, the calculated corrected sensor cell current Isf is output as a NOx concentration output (signal SG3) by a D / A converter or serial communication, and then this routine is terminated once.

Before the above correction is performed, for example, FIG.
As shown in (2), when the oxygen concentration differs, the NOx concentration output (output current) corresponding to the actual NOx concentration fluctuates. For example, oxygen concentration is 10% and 20% for 0%
Changes, the NOx concentration output (output current) increases even if the NOx concentration is constant.

On the other hand, by performing the correction as described above, as shown in FIG. 11B, the oxygen concentration becomes 0%,
Even if it changes to 10% or 20%, the NOx concentration output (output current) does not change, and an accurate NOx concentration output can be obtained. That is, the influence due to the oxygen concentration dependency shown in FIG. 11A is canceled by the correction.

According to the present embodiment described in detail above, the following effects can be obtained. (A) When the pump cell 110 discharges oxygen, the porous diffusion layer 101 has a negative pressure corresponding to the oxygen content and NO from the outside.
Exhaust gas containing x flows in excess, and the sensor cell current Is (NOx concentration output) changes according to the gas inflow. As described above, the sensor cell current Is reflects the oxygen concentration dependency based on the pump cell current Ip as described above. Is corrected, the problem that the NOx concentration output fluctuates carelessly according to the oxygen concentration in the exhaust gas is solved. As a result, highly accurate gas concentration detection can be performed regardless of changes in the oxygen concentration in the exhaust gas.

(B) Structural constant Ka uniquely determined from sensor structure and correction coefficient K determined from NOx sensitivity
The sensor cell current Is is corrected by an arithmetic expression using b, Isf = Is · Kb / (Ka · Ip + Kb). Thereby, the correction reflecting the oxygen concentration dependency can be simply and accurately performed. In this case, even if a negative pressure is generated in the porous diffusion layer 101 due to the oxygen evacuation in the pump cell 110 and the exhaust gas (NOx component) excessively flows in due to the negative pressure, the excess exhaust gas Can be canceled, and an accurate NOx concentration output can be obtained.

(C) As shown in FIG. 2, each cell 11
Since the negative terminals of 0 and 120 are configured to float from the 0V voltage, a negative current can flow in each cell. For example, in FIG. 2, by setting Va> Vc (> Ve), a negative sensor cell current flows. Accordingly, the porous diffusion layer 1 does not normally flow even with a rich gas in which a negative current hardly flows and the oxygen concentration in the porous diffusion layer 101 is out of balance.
01 can be kept constant (for example, the oxygen concentration can always be kept in a stoichiometric state). As a result, the detection range of the gas concentration is expanded by enabling the detection of the rich gas, and upon returning from the rich gas to the lean gas,
The response delay of the gas concentration output can be improved.

Next, second to sixth embodiments of the present invention will be described. However, in the configurations of the following embodiments, the same components as those of the above-described first embodiment are denoted by the same reference numerals in the drawings, and the description is simplified. The following description focuses on differences from the first embodiment.

(Second Embodiment) In this embodiment,
Correction of the NOx concentration output (sensor cell current) relating to the oxygen concentration dependency is performed by using a map calculation, and the specific contents will be described with reference to the flowchart of FIG. The flowchart of FIG. 12 is a partial modification of FIG. 10, and steps 201 to 206 in FIG. 12 show common processing.

In short, each terminal Vd, Vb, Ve, Vc
After the reading of the voltage and the calculation of the pump cell current Ip and the sensor cell current Is (after execution of steps 201 to 206), in step 301, the correction value is calculated based on the calculated pump cell current Ip using the correction map of FIG. Find ΔIs. According to FIG. 13, a correction value ΔIs is given such that the larger the oxygen concentration (pump cell current Ip), the more negative the value. Note that, in this case, it is preferable to map correction data corresponding to the arithmetic expression (Expression (1)) described in the first embodiment.

Thereafter, in step 302, the corrected sensor cell current Isf is calculated by adding the calculated sensor cell current Is and the correction value ΔIs (Isf = Is +
ΔIs). In the subsequent step 303, the calculated corrected sensor cell current Isf is set as the NOx concentration output as D /
The output is performed by the A-converter or serial communication, and then this routine ends.

Comparing before and after the correction, as in the first embodiment, the above-described correction cancels the influence of the oxygen concentration dependency. That is, before correction, FIG.
As shown in FIG. 11, the NOx concentration output (output current) fluctuated due to the difference in the oxygen concentration.
As shown in (b), even if the oxygen concentration is different, NOx
The density output (output current) does not fluctuate and an accurate N
An Ox concentration output is obtained.

As described above, according to the second embodiment, similarly to the above-described first embodiment, highly accurate gas concentration detection can be performed irrespective of a change in the oxygen concentration in the exhaust gas. . In particular, in the present embodiment, the relationship between the oxygen concentration in the exhaust gas and the correction value ΔIs is stored in advance to reflect the oxygen concentration dependence, and the sensor cell current Is is calculated according to the stored correction value ΔIs relating to the oxygen concentration dependence. Since the correction is performed, the correction according to the oxygen concentration dependency can be easily performed.

The correction data in FIG. 13 corrects the sensor cell current Is to the negative side as the oxygen concentration in the exhaust gas increases. For example, since the oxygen concentration in the exhaust gas is high, a negative pressure is applied to the porous diffusion layer 101. Even when extra exhaust gas (NOx) flows in from outside, correction according to the extra exhaust gas inflow can be performed, and as a result, highly accurate gas concentration detection becomes possible.

(Third Embodiment) In the first and second embodiments, the NOx current correction circuit 300 is constituted by a microcomputer, and the NOx concentration output (sensor cell current) is calculated by the microcomputer. In the present embodiment, an example of realizing a NOx current correction circuit using hardware is proposed as another configuration. Other configurations are the same as those in the first embodiment.

FIG. 14 is a circuit diagram showing an electrical configuration of the NOx current correction circuit 300. In FIG. 14, NOx
The current correction circuit 300 includes a pump cell current processing circuit 301
, A sensor cell current processing circuit 302, and a variable resistor 303 for determining a correction constant according to the pump cell current Ip.
And a resistor 304, an amplifier circuit 305 for correcting the sensor cell current Is according to the pump cell current Ip, and resistors 306 and 307 provided between the sensor cell current processing circuit 302 and the amplifier circuit 305.

The pump cell current processing circuit 301 takes in both terminal voltages Vd and Vb of the current detection resistor 213 (see FIG. 2) for detecting the pump cell current Ip, and obtains a voltage (Vd-Vb) corresponding to the pump cell current Ip. Is output. The voltage (Vd−
The resistance value of the variable resistor 303 is adjusted by Vb), and the amplification factor (correction constant) of the amplifier circuit 305 is determined by the adjusted resistance value of the variable resistor 303 and the resistance value of the resistor 304. At this time, as the pump cell current Ip is larger,
The resistance value of the variable resistor 303 is adjusted to a small value, and the amplification factor is reduced. Further, as the pump cell current Ip is smaller, the resistance value of the variable resistor 303 is adjusted to a larger value, and the amplification factor is increased.

On the other hand, the sensor cell current processing circuit 302
Current detection resistor 22 for detecting sensor cell current Is
3 (refer to FIG. 2), the two terminal voltages Ve and Vc are taken in, and the voltage (Ve-Vc) corresponding to the sensor cell current Is
Is output. The voltage (Ve−Vc) output from the current processing circuit 302 is output to the non-inverting input terminal of the amplifier circuit 305 via the voltage dividing points of the resistors 306 and 307. Then, the voltage (Ve−Vc) is amplified (corrected) according to the amplification factor of the amplifier circuit 305,
It is output as an Ox concentration output (signal SG3).

In short, the sensor cell current processing circuit 302
(Ve−Vc), ie, the sensor cell current Is, is the voltage (Vd−Vb) output from the pump cell current processing circuit 301, ie, the pump cell current I.
It will be corrected by p.

According to the above configuration, a gas concentration detecting device that corrects the NOx concentration output in accordance with the oxygen concentration dependency can be realized by hardware. Third
According to the embodiment, similarly to the above-described first and second embodiments, highly accurate gas concentration detection can be performed regardless of a change in the oxygen concentration in the exhaust gas. Further, by realizing the gas concentration detection device by hardware, a gas concentration signal that changes every moment can be continuously obtained.

(Fourth Embodiment) As described above, in the gas concentration sensor 100, oxygen in the exhaust gas is
Since the exhaust gas cannot be exhausted completely at 10, an added current of the current according to the NOx concentration and the offset current according to the residual oxygen amount is detected by the sensor cell 120. This offset current corresponds to “A1” of the sensor cell characteristic shown in FIG.
And does not occur if there is no residual oxygen, but it changes according to the individual difference and the degree of deterioration of the gas concentration sensor, which causes deterioration of NOx detection accuracy.

Specifically, as shown by the broken line in FIG.
The offset current of the Ox concentration output (output current) fluctuates according to the residual oxygen amount in the sensor cell 120, so that highly accurate NOx concentration detection cannot be performed.

Therefore, in the present embodiment, a gas concentration detecting device shown in FIG. 15 is proposed in order to suppress the deterioration of the detection accuracy of the NOx concentration output due to the offset current. FIG.
, The sensor control circuit 250 includes an oxygen concentration detecting means 210 and a NOx concentration detecting means 260. The oxygen concentration detecting means 210 has a configuration similar to that of FIG. 1, detects a current corresponding to the oxygen concentration, and outputs it as a signal SG1 to an external device (not shown).

The NOx concentration detecting means 260 detects a current corresponding to the NOx concentration and outputs it as a signal SG2 to the NOx current correction circuit 310 in the same manner as in FIG. , The sensor cell 12 according to a signal SG4 input from a NOx current correction circuit 310 described later.
The applied voltage of 0 is controlled.

NOx current correction circuit 31 as correction means
0 detects an offset current corresponding to the residual oxygen amount, corrects a NOx current error with the detected offset current, and outputs an output corresponding to the corrected NOx concentration to a signal SG.
5 is output to an external device (not shown).

In the present embodiment, the structure of the sensor cell electrode of the gas concentration sensor 100 is changed in order to directly detect the offset current corresponding to the residual oxygen amount, and the details will be described below.

In the above-described gas concentration sensor 100 shown in FIG. 3, the first pump electrode 111, the first sensor electrode 121, and the second sensor electrode 122 are made of a noble metal having a high catalytic activity such as Pt, and the second pump electrode 112 (the pump cell). Only the porous diffusion layer side electrode) is made of a noble metal such as Au-Pt which is hard to decompose the NOx gas, that is, inert to the NOx gas.

In this case, the pump cell electrode (the second pump electrode 112) having a noble metal electrode such as Au-Pt decomposes NOx gas by applying a voltage higher than a predetermined value as shown by the broken line in FIG. There are features. Therefore, in the present embodiment, a noble metal electrode such as Au-Pt, which hardly decomposes NOx gas, is used for the sensor cell electrode (sensor first electrode 121) by utilizing such electrode characteristics, and the residual oxygen current and the NOx gas current are used. We propose a sensor configuration that can distinguish between.

More specifically, the electrodes of the gas concentration sensor 100 are configured as follows. The pump first electrode 111 on the exhaust gas side of the pump cell 110 and the sensor second electrode 122 on the atmosphere side of the sensor cell 120 are made of a noble metal having high catalytic activity such as Pt, while the pump first electrode 111 on the porous diffusion layer 101 side of the pump cell 110 is formed. Two electrodes 112 and sensor cell 1
20 sensor first electrode 121 on the side of porous diffusion layer 101
Is inert to NOx gas (it is difficult to decompose NOx gas)
It is made of a noble metal such as Au-Pt.

As described above, the sensor first electrode 121 is connected to NOx
When the electrode is changed to the inactive electrode, the sensor cell characteristics shown in FIG. 16 are obtained. According to FIG. 16, when a relatively high voltage is applied by the applied voltage line LX2, the offset current indicated by the portion A1 and the NOx decomposition current indicated by the portion A2 flow, and the current value detected as the sensor cell current Is is “ A
1 + A2 ".

Further, another applied voltage line LX3 is set on the lower voltage side than the applied voltage line LX2. When a relatively low voltage is applied by the applied voltage line LX3,
Only the offset current indicated by A1 flows and the A1 current value is detected.

In short, by controlling the sensor cell applied voltage using the applied voltage line LX2 in FIG. 16, the NOx concentration current including the offset current is detected. Further, by controlling the applied voltage of the sensor cell using the applied voltage line LX3, only the offset current is detected. Therefore, it is possible to distinguish between the offset current due to the residual oxygen and the detection current according to the NOx concentration. Note that “A1 + A
The area where the “2” current is detected corresponds to the “first area” in the claims, and the area where only the “A1” current is detected corresponds to the “second current”.

FIG. 17 shows the electrical configuration of the sensor control circuit 250 shown in FIG. The configuration of FIG. 17 is obtained by changing a part of the sensor control circuit 200 shown in FIG. 2. The difference is that the amplification circuit 222 in the NOx concentration detection means 260 has a NOx current correction circuit 31.
Signal SG4 (sensor cell command voltage Vc) from 0 is input. That is, the signal SG of the NOx current correction circuit 310
4 controls the sensor cell applied voltage.

In the configuration shown in FIG. 17, the gas concentration sensor 100 has a modified sensor cell electrode in order to distinguish between an offset current due to residual oxygen and a detection current corresponding to the NOx concentration, as described above. That is, the sensor first electrode 121 is formed of a noble metal such as Au-Pt that is inert to the NOx gas (it is difficult to decompose the NOx gas).

The NOx current correction circuit 310 is composed of a microcomputer having a CPU and A / D and D / A converters as shown in FIG. 18, and each A / D converter (A / D21, A / D22) has The voltages at the terminals Ve and Vc in FIG. 17 are respectively input. The CPU calculates the sensor cell current Is based on the voltages (signal SG2) of the terminals Ve and Vc, and sets the sensor cell command voltage Vc corresponding to the sensor cell current Is as a signal SG4 as D / D
Output from the A converter (D / A21).

The CPU corrects a NOx current error caused by residual oxygen, and outputs the corrected NOx concentration output to a signal SG5.
Is output to an external device (not shown) via a D / A converter (D / A22) or using serial communication.

The NOx current correction processing executed by the CPU in the NOx current correction circuit 310 will be described with reference to the flowcharts of FIGS. The routine of FIGS. 19 and 20 is a NOx current correction subroutine that is performed in the middle of a main routine (not shown).

First, in steps 401 and 402 in FIG. 19, both terminal voltages V of the current detection resistor 223 in FIG.
e and Vc are read by A / D21 and A / D22 in FIG. 18 respectively.
s is calculated (Is = (Ve−Vc) / R2).

In step 404, the applied voltage line (map) for setting the applied voltage to the sensor cell is switched from "LX2" to "LX3" in FIG. In step 405, a predetermined voltage value on the applied voltage line LX3 is selected, and the voltage value is applied to the sensor cell 120. That is, the sensor cell command voltage V as the signal SG4
c to the sensor control circuit 250 (NOx
Output to the density detecting means 260).

After switching the applied voltage, a predetermined time (for example,
(About 0 to 200 ms) and steps 406 and 40
7, both terminal voltages Ve and V of the current detection resistor 223 are again
c is read by A / D21 and A / D22, respectively (this value is Ve2, Vc2). In the following step 408, the sensor cell current Is2 is calculated from the detected Ve2 value and Vc2 value (Is2 = (Ve2-Vc2) /
R2).

Thereafter, in step 409 in FIG. 20, a target applied voltage to the sensor cell 120 corresponding to the calculated sensor cell current Is2 is calculated (map calculation) using the applied voltage line LX3 in FIG. Step 41
0, the obtained target applied voltage is set as a command voltage Vc (signal SG4), and the sensor control circuit 2 is connected via the D / A 21.
50 (NOx concentration detecting means 260). According to steps 409 and 410, a desired voltage for detecting the offset current Iso is applied to the sensor cell 120.

Thereafter, for a predetermined period of time (for example,
ms), and in steps 411 and 412, the terminal voltages Ve and Vc of the current detection resistor 223 are again A / D
21 and A / D 22 (this value is expressed as Ve
3, Vc3). In the following step 413, the offset current Iso is calculated from the detected Ve3 value and Vc3 value.
Is calculated (Iso = (Ve3-Vc3) / R2).

Thereafter, in step 414, the corrected sensor cell current Isf is calculated by subtracting the offset current Iso from the calculated sensor cell current Is (Isf =
Is-Iso).

In the following step 415, the calculated corrected sensor cell current Isf is output as NOx concentration output (signal S
G5) is output by a D / A converter or serial communication. Further, at step 416, the applied voltage line is returned to the original “LX2”, and then this routine is terminated.

In consideration of the fact that the fluctuation range of the offset current Iso is relatively small, the offset current Iso
May be set to a fixed value at the time of detection. In this case, the processing in steps 409 to 413 becomes unnecessary, and the sensor cell current Is calculated in step 408 is
2 is used as the offset current Iso (Is2 =
Iso).

In this embodiment, steps 404 to 413 in FIGS. 19 and 20 constitute an offset current detecting means according to the present invention.
09 and 410 constitute voltage switching means.

As described above, according to the fourth embodiment, the following characteristic effects can be obtained. (A) Since the sensor cell current Is is corrected based on the amount of oxygen remaining in the vicinity of the sensor cell 120, when the amount of oxygen remaining in the vicinity of the sensor cell changes due to individual differences between sensors, the use environment, and the like, the amount of residual oxygen The effect is reliably nullified. As a result, even if the residual oxygen amount near the sensor cell 120 changes, highly accurate gas concentration detection can be performed.

In FIG. 21, NOx concentration output (output current)
It has been described that the offset current varies according to the residual oxygen amount, and a detection error of the NOx concentration occurs.
An Ox current output (for example, a solid line output) is obtained.

(B) Since the offset current Iso is directly detected and the sensor cell current Is is corrected based on the detected offset current Iso, the influence of the residual oxygen amount can be more reliably eliminated.

(C) As a sensor cell characteristic, a first method for detecting an added current of an offset current component and a NOx gas component is used.
An area (A1 + A2 detection area in FIG. 16) and a second area (A1 detection area in FIG. 16) for detecting only the offset current component are provided. In the first area, the sensor cell current Is before correction is detected and the second area is detected. In the region, the offset current Iso is detected, and the sensor cell current Is before correction is set to the offset current Is
o. According to this configuration, by using the second region, the offset current Iso can be directly measured simply and accurately, and the detection accuracy of the gas concentration is improved.

(D) Since the sensor cell applied voltage is selectively switched between when the sensor cell current Is is detected in the first region and when the offset current Iso is detected in the second region, the offset current Iso is appropriately adjusted. Can be detected,
As a result, the detection accuracy of the gas concentration is improved.

(E) As the electrode configuration of the gas concentration sensor 100 applied to the gas concentration detection device, the porous diffusion layer 10
The electrodes (the pump second electrode 112 and the sensor first electrode 121) of each cell opposed to 1 are electrodes inactive with respect to NOx gas, thereby detecting the added current of the offset current component and the NOx gas component. A first region for detecting the offset current component and a second region for detecting only the offset current component are provided on the sensor cell characteristics. According to the gas concentration sensor 100, the offset current according to the residual oxygen amount near the second cell is directly detected by newly providing the second region with respect to the existing sensor having only the first region. It becomes possible. Therefore, a suitable sensor can be provided in the gas concentration detection device that performs the correction according to the residual oxygen amount.

(Fifth Embodiment) In the fourth embodiment, the electrode configuration of the gas concentration sensor 100 is changed so that the offset current can be directly detected, and the offset current is adjusted by adjusting the voltage applied to the sensor cell. The NOx concentration output was corrected based on the measured offset current, but this configuration is changed in the present embodiment.

In other words, focusing on the fact that when the amount of oxygen remaining in the sensor cell 120 differs, the electromotive force in the sensor cell 120 changes, the sensor cell electromotive force is measured, and the NOx concentration output is corrected based on the measured electromotive force. I do.

For example, if there is no residual oxygen in the sensor cell 120, the sensor cell 120 enters a stoichiometric state, and the electromotive force of the sensor cell becomes “about 0.45 V”. The sensor cell 120 enters a lean state, and the sensor cell electromotive force decreases. In this case, as shown in FIG. 26A, the difference in sensor cell electromotive force causes the NOx concentration output (output current) corresponding to the actual NOx concentration to fluctuate. For example, if the sensor cell electromotive force is 0.45V and the same electromotive force becomes 0.2V, NOx
The density output (output current) increases.

On the other hand, by performing correction in accordance with the sensor electromotive force, as shown in FIG. 26B, even if the sensor cell electromotive force changes from 0.45 V to 0.2 V, the NOx concentration output fluctuates. And an accurate NOx concentration output can be obtained. That is, the effect of the residual oxygen shown in FIG. 26A is canceled by the electromotive force correction.

FIG. 22 is a block diagram showing an outline of the gas concentration detecting apparatus according to the present embodiment. In FIG. 22, the sensor control circuit 270 includes the oxygen concentration detecting means 210 described above.
And an NOx concentration detecting means 220, and an electromotive force detecting means 280 for detecting the sensor cell electromotive force. The electromotive force detection means 280 outputs the detected value of the sensor cell electromotive force to the NOx current correction circuit 320 as a signal SG6.

NOx current correction circuit 32 as correction means
0 corrects the NOx concentration detection value (signal SG2) by the NOx concentration detection means 220 based on the electromotive force detection value (signal SG6) by the electromotive force detection means 280, and outputs the NOx concentration output obtained after the correction to the signal SG7. To an external device (not shown).

FIG. 23 shows the electrical configuration of the sensor control circuit 270 shown in FIG. The configuration of FIG. 23 is obtained by changing a part of the sensor control circuit 200 shown in FIG. 2 described above. The difference is that the amplifier circuit 222 in the NOx concentration detection means 220 and the current detection resistor 223 are different from each other. A normally closed switch SW1 is provided. Further, an electromotive force measurement circuit 281 for opening or closing the switch SW1 and measuring the sensor cell electromotive force when the switch is opened is provided.

Here, the switch SW1 and the electromotive force measurement circuit 281 correspond to the electromotive force detection means 280 in FIG. Further, the switch SW1 corresponds to the switch means in the claims, and the electromotive force measurement circuit 281 corresponds to the measurement means.

In this embodiment, it is not necessary to directly measure the offset current according to the residual oxygen amount, and the configuration of the gas concentration sensor 100 is the same as in the first to third embodiments. Of the electrodes 111, 112, 121 and 122, only the pump second electrode 112 is the NOx inactive electrode (A
u-Pt electrode).

When both the electromotive force measurement circuit 281 and the NOx current correction circuit 320 are constituted by microcomputers, the characteristic processing is shown in FIGS. 24 and 25.
This will be described with reference to the flowchart of FIG.

The CPU in the electromotive force measuring circuit 281 operates as shown in FIG.
Is started, at step 501, the switch SW
In step 502, the voltage on the sensor second electrode 122 side (the terminal voltage Vc on one side of the current detection resistor 223) is read by the A / D converter. Next, in step 503, the voltage Vc on the sensor second electrode 122 side is set.
(Detected value) and the voltage Va (fixed value) on the sensor first electrode 121 side, the electromotive force (Vc
-Va) is calculated.

Next, in step 504, the calculated sensor cell electromotive force is output to the NOx current correction circuit 320 as a signal SG6.
Return W1 to the closed state.

On the other hand, CP in the NOx current correction circuit 320
When U starts the processing in FIG. 25, in step 601,
For example, the correction value ΔIk is calculated according to the sensor cell electromotive force using the relationship in FIG. In FIG. 27, a negative correction value ΔIk is set at a lower voltage side than the sensor cell electromotive force = 0.45 V (stoichiometric state).

Next, at step 602, the corrected sensor cell current Isf is calculated by adding the correction value ΔIk to the sensor cell current Is at that time (Isf = Is + ΔI
k). In the following step 603, the calculated corrected sensor cell current Isf is output as a NOx concentration output (signal SG7).
Is output by a D / A converter or serial communication, and then this routine ends.

However, when the electromotive force measurement circuit 281 and the NOx current correction circuit 320 are constituted by the same microcomputer, the processing in FIGS. 24 and 25 may be executed as a series of processing.

According to the fifth embodiment, the sensor cell electromotive force is detected as a reflection of the residual oxygen amount, and the sensor cell current Is is corrected according to the detected sensor cell electromotive force. Thus, even if the residual oxygen amount changes, highly accurate gas concentration detection can be performed.

(Sixth Embodiment) In the above-described first to third embodiments, correction reflecting the oxygen concentration dependency such that the NOx concentration output fluctuates according to the oxygen concentration in the exhaust gas is performed. In the fourth and fifth embodiments, the correction reflecting the effect of the residual oxygen in the sensor cell is performed. In the present embodiment, the correction reflecting the oxygen concentration dependency and the effect of the residual oxygen are performed. A device that can implement both the correction and the reflection reflecting the above is proposed.

FIG. 28 is a block diagram showing an outline of the gas concentration detecting device according to the present embodiment. In FIG. 28, FIG.
The difference from the configuration of the first embodiment is that the NOx current correction circuit 330 as the correction means performs a correction corresponding to the oxygen concentration dependency and a correction corresponding to the influence of the residual oxygen, and obtains the NOx concentration obtained after the correction. The output is output as a signal SG8 to an external device (not shown).

The NOx current correction circuit 330 operates in the first to
What is necessary is just to realize by appropriately combining the requirements in the fifth embodiment. Here, an example is described below. FIG. 29 is a flowchart showing a calculation process by the NOx current correction circuit 330 (microcomputer).

In FIG. 29, at step 701, the pump cell current Ip and the sensor cell current Is are calculated.
In the following step 702, a correction value ΔIs is calculated based on the pump cell current Ip. This correction value ΔIs corrects a current error due to oxygen concentration dependency, and is calculated using, for example, the relationship shown in FIG. Here, step 701 is equivalent to steps 201 to 206 in FIG.
Step 702 corresponds to the processing of step 301 in FIG.

Further, at step 703, the offset current Iso corresponding to the residual oxygen amount near the sensor cell 120 is determined.
Is calculated. In practice, the offset current Iso is calculated by executing the processing of steps 401 to 413 of FIG. However, in order to apply the processing of FIGS. 19 and 20 (the fourth embodiment), it is necessary to partially change the configuration of the sensor cell electrode. That is, each electrode 111, 112, 121, 122 of the gas concentration sensor 100
Among them, the pump second electrode 112 and the sensor first electrode 121
Are used as NOx inactive electrodes (Au-Pt electrodes) so that the offset current according to the residual oxygen amount can be directly measured.

Thereafter, in step 704, the sensor cell current Is is corrected based on the calculated correction value ΔIs and the offset current Iso. That is, the sensor cell current Isf after correction using an arithmetic expression such as Isf = Is + ΔIs−Iso
Is calculated. In step 705, the corrected sensor cell current Isf is output as a NOx concentration output by a D / A converter or serial communication.

On the other hand, in the correction according to the oxygen concentration dependency, the structure constant Ka uniquely determined from the structure of the gas concentration sensor 100 instead of the map calculation of the correction value ΔIs.
And an arithmetic expression based on the correction coefficient Kb calculated from the NOx sensitivity, and Isf = Is · Kb / (Ka · Ip + Kb). That is, in step 704 of FIG. 29, the sensor cell current Is is corrected using the above-mentioned arithmetic expression. Actually, Isf = (Is−Iso) · Kb / (Ka · Ip + K
b) is calculated to obtain the corrected sensor cell current Isf.

As a correction reflecting the effect of the residual oxygen near the sensor cell 120, a correction value ΔIk corresponding to the sensor cell electromotive force is obtained using, for example, the relationship shown in FIG.
It is of course possible to correct the sensor cell current Is using the correction value ΔIk.

As described above, according to the sixth embodiment, the first method for correcting the sensor cell current Is while reflecting the oxygen concentration dependency.
Since the correction and the second correction for correcting the sensor cell current Is based on the residual oxygen amount near the sensor cell are performed, both the effect of the oxygen concentration dependency and the effect of the residual oxygen amount are eliminated. Therefore, even if the oxygen concentration in the exhaust gas changes or the amount of oxygen remaining near the sensor cell changes, highly accurate gas concentration detection can be performed.

The embodiments of the present invention can be embodied in the following forms other than the above. (Other Embodiment 1) In each of the above embodiments, the pump voltage command circuit 211 and the sensor voltage command circuit 221 are configured using a microcomputer (see FIG. 7), but the command circuits 211 and 221 are configured by hardware. May be. FIG. 30 shows a circuit configuration of the instruction circuits 211 and 221. However, since the pump voltage command circuit 211 and the sensor voltage command circuit 221 can be realized by the same configuration, only the configuration of the pump voltage command circuit 211 is shown in FIG.

Referring to FIG. 30, pump voltage command circuit 21
1 includes a reference voltage circuit 241, an amplification circuit 242, amplification resistors 245 and 246, an LPF (low-pass filter) 243, and a current detection circuit 247. Current detection circuit 2
47 takes in both terminal voltages Vd and Vb of the current detection resistor 213 for detecting the pump cell current Ip, and applies the voltage (Vd−Vb) processed by the current detection circuit 247 to the non-inverting input terminal of the amplifier circuit 242. Is output. Amplifier circuit 2
The inverting input terminal of 42 is connected to amplification resistors 245 and 246 for determining the amplification factor. A primary LPF 243 including a resistor 243a and a capacitor 243b is connected to an output terminal of the amplifier circuit 242, and the LPF 243
The command voltage Vb is output via.

Here, the reference voltage circuit 241 generates an offset voltage (applied voltage at 0 mA) of the applied voltage line LX1, and the amplifying circuit 242 and the amplifying resistors 245 and 246 generate the inclination of the applied voltage line LX1 (to increase the pump cell current). Accompanying increase in applied voltage). In such a case, an applied voltage along the applied voltage line LX1 shown in FIG. According to the applied voltage line LX1, a positive feedback system in which the applied voltage increases with an increase in the pump cell current Ip is formed, and the applied voltage to be output tends to oscillate. However, by providing the LPF 243 in the feedback system, Voltage oscillation is prevented. With the above configuration and operation, it is possible to control the applied voltage of the present apparatus by hardware.

(Other Embodiment 2) In each of the above embodiments, the common negative terminal (the pump second electrode 112 and the sensor first electrode 121) of the pump cell 110 and the sensor cell 120 is connected to the G
Although the reference voltage Va is higher than the ND voltage (0 V voltage), this configuration is changed. For example, only the negative terminal of one cell (for example, the sensor cell 120 in FIG. 2) is floated from the GND voltage, and the other cell (the pump cell 11 in FIG.
The negative terminal of 0) may be grounded to GND, or the negative terminals of both cells may be grounded to GND.

(Other Embodiment 3) In the sixth embodiment, the "first correction" reflecting the oxygen concentration dependency and the "second correction" reflecting the effect of residual oxygen are both performed. However, the configuration of the device is changed as follows. In many cases, the first correction is required at any time according to, for example, a change in the oxygen concentration in the exhaust gas, whereas the second correction is required when an individual difference between sensors or a change with time occurs.

Therefore, the necessity of the first correction and the second correction are determined, and each correction is selectively performed according to the determination result. For example, the second correction is performed only when it is necessary to eliminate variations due to individual sensor differences and aging. Actually, in the routine of FIG. 29, the necessity of correction is first determined, and the correction in steps 702 and 703 is enabled or disabled according to the result. Unnecessary processing may be bypassed.

Alternatively, the frequency of performing the second correction is lower than the frequency of performing the first correction. In practice, the frequency of calculating the correction amount of the second correction (for example, the offset current Iso) is lower than the frequency of calculating the correction amount of the first correction (for example, the correction value ΔIs based on FIG. 13). In this case, the correction amount calculation of the first correction is performed every several msec, while the correction amount calculation of the second correction is performed every several seconds.
Alternatively, the correction amount calculation of the second correction is performed only at the timing when the ignition key of the engine is turned ON.
When the frequency of calculating the correction amount in the second correction is reduced, the correction amount is stored and updated in the backup memory each time,
When performing the correction, the correction amount data in the same memory is read and used.

According to the above configuration, it is possible to carry out a correction as required, and a more appropriate gas concentration detecting device can be realized. In this case, for example, when a microcomputer is used, the calculation load can be reduced.

(Other Embodiment 4) As a gas concentration sensor having a two-cell structure, a part of the configuration may be changed. For example, a pump cell that discharges excess oxygen in exhaust gas while applying a voltage and supplies a current corresponding to the oxygen concentration while applying a voltage, and a sensor cell that also supplies a current corresponding to the NOx concentration from a gas component after the excess oxygen is discharged along with the application of a voltage. In the configuration provided, the installation locations of the pump cell and the sensor cell are reversed. That is,
A pump cell is provided between the porous diffusion layer 101 and the air duct 102, and a sensor cell is provided between the porous diffusion layer 101 and the exhaust gas space. Also in this case, the gas concentration can be detected by the same principle as the gas concentration sensor 100 described above.

In order to obtain the sensor cell characteristics shown in FIG. 6, among the electrodes of each cell, only the pump electrode on the porous diffusion layer 101 side is a NOx inert electrode (an electrode which is difficult to decompose NOx gas). . In order to obtain the sensor cell characteristics shown in FIG. 16, among the electrodes of each cell, the pump cell electrode and the sensor cell electrode on the porous diffusion layer 101 side are connected to NOx.
Inactive electrodes (electrodes that are difficult to decompose NOx gas) are used.

(Other Embodiment 5) In each of the above embodiments, 2
A specific example of the gas concentration sensor having a cell structure has been described. In addition to the sensor having a two-cell structure, a gas concentration sensor having a three-cell structure, a pump cell and a sensor cell are provided by dividing into a plurality of cells, thereby providing four or more cells. It can also be applied to gas concentration sensors having Hereinafter, an example of application to a gas concentration detection device using a gas concentration sensor having a three-cell structure will be described.

One configuration of the gas concentration sensor 400 having a three-cell structure will be described with reference to FIG. Gas concentration sensor 40
0 is a main configuration, a pump cell 410 (first cell) for detecting oxygen concentration by discharging oxygen in exhaust gas.
A reference cell 430 for detecting the oxygen partial pressure;
NOx is decomposed by decomposing Ox gas and discharging its oxygen ions.
a sensor cell 420 (second cell) for detecting the x concentration.

The exhaust gas discharged from the engine is introduced into the first chamber 405 via the first porous diffusion layer 401. The pump cell 410 includes the first reference electrode 43.
Based on the voltage of the reference cell 430 monitored by the voltage between the first and reference second electrodes 432, the first
The oxygen present in the chamber 405 is pumped and controlled at a level at which NOx is not decomposed. That is, oxygen is pumped by applying a voltage between the first pump electrode 411 and the second pump electrode 412, and the oxygen concentration is detected by measuring the current flowing at this time.

The exhaust gas from which oxygen has been pumped out is introduced into the second chamber 406 via the second porous diffusion layer 404. The NOx gas present in the second chamber 406 is controlled to be decomposed and pumped out using the sensor cell 420. That is, the sensor first electrode 421 and the sensor second
NOx gas is pumped out by applying a voltage between the electrode 422 and the current flowing at this time is measured.
Ox concentration is detected.

For example, as the exhaust gas in the first chamber 405 is leaner (a state where more oxygen is contained), the electromotive force of the reference cell 430 is reduced, and the voltage of the reference second electrode 432 is reduced. At this time, the first chamber 4
Oxygen in 05 is discharged to the exhaust gas side (upper side in the figure) through the pump cell 410. When the oxygen concentration of the exhaust gas in the first chamber 405 is extremely low, the electromotive force of the reference cell 430 increases, and the reference second electrode 432
Voltage rises. At this time, the discharge of oxygen in the first chamber 405 is reduced. By measuring the pump cell current at that time, the oxygen concentration in the exhaust gas can be detected.

On the other hand, the gas from which oxygen in the exhaust gas has been discharged is passed through the second porous diffusion layer 404 to the second chamber 40.
6 is introduced. When a predetermined voltage is applied to the sensor cell 420, the sensor cell 420 decomposes NOx gas,
Oxygen ions are transferred from the second chamber 406 to the air duct 407.
Discharge to the side. By measuring the sensor cell current at that time, the NOx concentration in the exhaust gas can be detected.

In the gas concentration sensor 400 having the above-described configuration, the sensor cell current Is is corrected using the arithmetic expression: Isf = Is · Kb / (Ka · Ip + Kb). The above sensor 4
In the case of 00, the first and second porous diffusion layers 401 and 404 and the first and second chambers 405 and 406 correspond to diffusion resistance portions, and the structure constant Ka is set based on the structure of the diffusion resistance portions and the like. The correction coefficient Kb is set based on the NOx sensitivity of the sensor cell 420. Actually, the diffusion resistance portion (members 401 and 404)
To 406), the structural constant Ka is determined based on the diffusion coefficient, the shape and volume of the diffusion resistance portion, and the electrode positions of the cells 410, 420, and 430.

According to the present embodiment, as described above, the influence of the oxygen concentration dependence is canceled, and the gas concentration can be detected with high accuracy regardless of the change in the oxygen concentration in the exhaust gas. In addition, it is of course possible to implement the correction method described in the second to sixth embodiments in combination with the gas concentration sensor 400 as appropriate.

Incidentally, in order to obtain the sensor cell characteristics shown in FIG. 16 in order to directly detect the offset current according to the residual oxygen amount, the first chamber 405 of the electrodes of each cell is required.
The pump second electrode 412 on the side and the sensor first electrode 421 on the side of the second chamber 406 may be a NOx inactive electrode (an electrode that hardly decomposes NOx gas).

(Other Embodiment 6) As a gas concentration sensor (NOx sensor) having a three-cell structure, the structure shown in FIG. 32 may be applied. In the gas concentration sensor 500 of FIG. 32, the oxygen pump cell 510 (first cell) includes a solid electrolyte SEA and a pair of electrodes 511 and 512 on both surfaces thereof. A pinhole 513 having a predetermined size is formed in the solid electrolyte SEA and the electrodes 511 and 512. Reference numeral 514 is a porous protective layer.

The oxygen sensing cell 520 has a solid electrolyte SEB
And a pair of electrodes 521 and 522 on both surfaces thereof. The electrode 521 is made of, for example, a porous Pt electrode, and the electrode 522 is made of an electrode, like the electrode 512 of the oxygen pump cell 510, so as to be inactive for NOx reduction and active for oxygen reduction. Also, the NOx detection cell 530
The (second cell) includes a solid electrolyte SEB common to the oxygen sensing cell 520 and a pair of electrodes 531 and 532 on both surfaces thereof. The electrode 531 is made of, for example, a porous Pt electrode,
The electrode 532 is formed of, for example, a porous Pt electrode that is active for NOx reduction.

The first internal space 541 and the second internal space 541 adjacent to each other through the communication hole 543 are provided between the solid electrolytes SEA and SEB.
An internal space 542 is formed. An air passage 544 is formed on the back surface side of the solid electrolyte SEB, and a heater 545 for heating each cell is further laminated.

In the gas concentration sensor 500 having the above configuration, the exhaust gas passes through the pinhole 513 and passes through the first internal space 5.
41 is introduced. In the oxygen sensing cell 520, the electrode 52
An electromotive force is generated based on the oxygen concentration difference between the two sides of the first and the second 522. By measuring the magnitude of the electromotive force, the oxygen concentration in the first internal space 541 is detected.

In the oxygen pump cell 510, the electrodes 511, 5
When a voltage is applied between the first internal space 541 and the first internal space 541,
Oxygen inside is taken in and out, and the oxygen concentration in the internal space 541 is controlled to a predetermined low concentration. Oxygen pump cell 510
The amount of electricity supplied to the electrodes 521 and 52
Feedback control is performed so that the electromotive force generated between the two becomes a predetermined constant value. Here, since the electrodes 512 and 522 facing the first internal space 541 are inactive with respect to the reduction of NOx, NOx is not decomposed in the first internal space 541 and NOx in the first internal space 541 is reduced. The amount does not change.

Oxygen pump cell 510 and oxygen detection cell 5
The exhaust gas having a constant low oxygen concentration due to 20 is introduced into the second internal space 542 through the communication hole 543. The NOx detection cell 530 facing the second internal space 542 has N
Since it is active against Ox, when a predetermined voltage is applied between the electrodes 531 and 532, NOx is reduced and decomposed on the electrode 532, and an oxygen ion current flows. By measuring this current value (sensor cell current Is), the concentration of NOx contained in the exhaust gas is detected.

In the gas concentration sensor 500 having the above-described configuration, the sensor cell current Is is corrected using the arithmetic expression: Isf = Is · Kb / (Ka · Ip + Kb). The above sensor 5
In the case of 00, the pinhole 513, the first and second internal spaces 541, 542, and the communication hole 543 correspond to a diffusion resistance portion, and a structure constant Ka is set based on the structure of the diffusion resistance portion and the like.
The correction coefficient Kb is set based on the NOx sensitivity of the NOx detection cell 530. Actually, the diffusion resistance portion (members 513, 541)
To 543), the structural constant Ka is determined based on the diffusion coefficient, the shape and volume of the diffusion resistance portion, and the electrode positions of the cells 510, 520, and 530.

According to the present embodiment, the influence of the oxygen concentration dependence is canceled as described above, and highly accurate gas concentration detection can be performed regardless of the change in the oxygen concentration in the exhaust gas. In addition, it is of course possible to implement the correction method described in the second to sixth embodiments and the gas concentration sensor 500 appropriately in combination.

Incidentally, in order to obtain the sensor cell characteristics shown in FIG. 16 in order to directly detect the offset current according to the residual oxygen amount, the first internal space 541 of the electrodes of each cell is required.
Side oxygen pump cell electrode 512 and oxygen sensing cell electrode 5
22 and the NOx detection cell electrode 5 on the second internal space 542 side
32 may be a NOx inactive electrode (an electrode that hardly decomposes NOx gas).

(Other Embodiment 7) The present invention is applicable not only to a gas concentration sensor capable of detecting the oxygen concentration and the NOx concentration, but also to a gas concentration sensor capable of detecting the oxygen concentration and the HC concentration or the CO concentration. When detecting the HC concentration or the CO concentration, excess oxygen in the exhaust gas (gas to be detected) is discharged by a pump cell, and HC or CO is extracted from a gas component after discharging the excess oxygen by a sensor cell.
Decompose. Thus, the HC concentration or the CO concentration can be detected in addition to the oxygen concentration.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of a gas concentration detection device according to a first embodiment.

FIG. 2 is a circuit diagram showing an electrical configuration of a sensor control circuit.

FIG. 3 is a sectional view of a main part showing a configuration of a gas concentration sensor.

FIG. 4 is a diagram for explaining the operation principle of the gas concentration sensor.

FIG. 5 is a diagram showing pump cell characteristics of a gas concentration sensor.

FIG. 6 is a diagram showing sensor cell characteristics of a gas concentration sensor.

FIG. 7 is a diagram showing a configuration of a pump (sensor) voltage command circuit.

FIG. 8 is a diagram showing a configuration of a NOx current correction circuit.

FIG. 9 is a flowchart showing an applied voltage control procedure.

FIG. 10 is a flowchart showing a NOx current correction procedure.

FIG. 11 is a diagram showing a relationship between NOx concentration and output current.

FIG. 12 is a flowchart showing a NOx current correction procedure in the second embodiment.

FIG. 13 is a diagram showing a relationship between an oxygen concentration and a correction value ΔIs.

FIG. 14 is a circuit diagram showing an electrical configuration of a NOx current correction circuit according to the third embodiment.

FIG. 15 is a block diagram illustrating an outline of a gas concentration detection device according to a fourth embodiment.

FIG. 16 is a diagram showing sensor cell characteristics of a gas concentration sensor.

FIG. 17 is a circuit diagram showing an electrical configuration of a sensor control circuit according to a fourth embodiment.

FIG. 18 is a diagram showing a configuration of a NOx current correction circuit.

FIG. 19 is a flowchart showing a NOx current correction procedure.

FIG. 20 is a flowchart showing a NOx current correction procedure following FIG. 19;

FIG. 21 is a diagram showing a relationship between NOx concentration and output current.

FIG. 22 is a block diagram illustrating an outline of a gas concentration detection device according to a fifth embodiment.

FIG. 23 is a circuit diagram showing an electrical configuration of a sensor control circuit according to the fifth embodiment.

FIG. 24 is a flowchart showing a procedure for detecting a sensor cell electromotive force.

FIG. 25 is a flowchart showing a NOx current correction procedure.

FIG. 26 is a graph showing the relationship between NOx concentration and output current.

FIG. 27 is a diagram showing a relationship between a sensor cell electromotive force and a correction value ΔIk.

FIG. 28 is a block diagram illustrating an outline of a gas concentration detection device according to a sixth embodiment.

FIG. 29 is a flowchart showing a NOx current correction procedure.

FIG. 30 is a circuit diagram showing a configuration of a pump voltage command circuit.

FIG. 31 is a cross-sectional view showing a main part of a gas concentration sensor having a three-cell structure in another embodiment.

FIG. 32 is a cross-sectional view showing a main part of a gas concentration sensor having a three-cell structure in another embodiment.

FIG. 33 is a view showing a configuration of a diffusion resistance section by a simple model.

[Explanation of symbols]

100: gas concentration sensor, 101: porous diffusion layer as a diffusion resistance part, 110: pump cell as a first cell,
111: pump first electrode, 112: pump second electrode, 1
20: sensor cell as a second cell, 121: sensor first electrode, 122: sensor second electrode, 200, 250, 2
70: sensor control circuit, 210: oxygen concentration detecting means as first detecting means, 220, 260 ... NOx concentration detecting means as second detecting means, 280 ... electromotive force detecting means, 2
81 ... Electromotive force measurement circuit as measurement means, 300, 31
0, 320, 330: NOx current correction circuit as correction means, 400: gas concentration sensor, 401: first porous diffusion layer, 404: second porous diffusion layer, 405: first chamber, 406: second chamber , 410... A pump cell as a first cell, 420... A sensor cell as a second cell, 5
00: gas concentration sensor, 513: pinhole, 541 ...
First internal space, 542: second internal space, 543: communication hole, 510: oxygen pump cell as the first cell, 530
... NOx detection cell as second cell, SW1. Switch as switch means.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Satoshi Haneda 1-1-1 Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Co., Ltd. 72) Inventor Satoshi Nakamura 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Pref. Japan Automobile Parts Research Institute Co., Ltd. (56) References JP-A-9-288084 (JP, A) JP-A-9-288087 (JP, A) JP-A-9-329578 (JP, A) JP-A-9-318596 (JP, A) JP-A-10-38845 (JP, A) JP-A-10-90222 (JP, A) JP-A-10-129494 (JP, A) JP-A-10-142194 (JP, A) JP-A-10-185866 (JP, A) Kaihei 10-227760 (JP, A) JP-A-10-253586 (JP, A) JP-A-10-267893 (JP, A) JP-A-10-282053 (JP, A) JP-A-11-2620 (JP, A) JP-A-11-2621 (JP) JP-A-11-14589 (JP, A) JP-A-11-14592 (JP, A) JP-A-11-14587 (JP, A) JP-A-11-23523 (JP, A) 11-37972 (JP, A) JP-A-11-94794 (JP, A) JP-A-8-27146 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/416 G01N 27/419

Claims (17)

(57) [Claims] 1. A diffusion resistance portion for introducing the gas to be detected within the interior space, with the voltage applied, via the diffusion resistance portion
To decompose the oxygen of the detected gas introduced Te discharged
An oxygen pump cell through which a current according to the oxygen concentration in the gas to be detected flows, and a gas after oxygen is exhausted by the oxygen pump cell.
An oxygen detection cell for detecting the oxygen concentration of oxygen, and N 2
Decompose Ox, HC or CO and discharge oxygen ions
In a gas concentration detection device using a gas concentration sensor including a specific gas detection cell that flows a current corresponding to the NOx concentration, the HC concentration, or the CO concentration , a first detection unit that detects a current value flowing through the oxygen pump cell; A second detection unit for detecting a current value flowing through the specific gas detection cell; a current value detected by the second detection unit while reflecting oxygen concentration dependency based on the current value detected by the first detection unit A gas concentration detecting device, comprising: 2. A current value detected by the first detecting means is Ip, a current value detected by the second detecting means is Is,
The current value of the specific gas detection cell obtained after the correction is Isf,
Assuming that a structural constant uniquely determined from the structure of the gas concentration sensor is Ka and a correction coefficient determined from the detection sensitivity of the specific gas detection cell is Kb, the correction means: Isf = Is · Kb / ( The gas concentration detection device according to claim 1, wherein the current value of the specific gas detection cell is corrected using a relationship represented by an arithmetic expression of (Ka · Ip + Kb). 3. The gas concentration detection device according to claim 2, wherein the structural constant is a diffusion coefficient in the diffusion resistance portion;
The shape and volume of the diffusion resistance part, and the oxygen pump cell,
A gas concentration detection device determined by the position of an electrode provided in a specific gas detection cell. 4. The relation between the oxygen concentration in the gas to be detected and the correction data required corresponding to the oxygen concentration in advance reflecting the oxygen concentration dependence is stored in advance. The gas concentration detection device according to claim 1, wherein the current value of the specific gas detection cell is corrected according to the correction data on the dependency. 5. The gas concentration detection device according to claim 4, wherein the stored correction data decreases the gas concentration detected by the specific gas detection cell as the oxygen concentration in the detected gas increases. A gas concentration detection device to be corrected. 6. A diffused resistor portion for introducing the gas to be detected within the interior space, with the voltage applied, via the diffusion resistance portion
To decompose the oxygen of the detected gas introduced Te discharged
An oxygen pump cell through which a current according to the oxygen concentration in the gas to be detected flows, and a gas after oxygen is exhausted by the oxygen pump cell.
An oxygen detection cell for detecting the oxygen concentration of oxygen, and N 2
Decompose Ox, HC or CO and discharge oxygen ions
In a gas concentration detection device using a gas concentration sensor including a specific gas detection cell that flows a current corresponding to the NOx concentration, the HC concentration or the CO concentration , based on the amount of oxygen remaining near the specific gas detection cell, A gas concentration detection device comprising a correction means for correcting a current value of a specific gas detection cell. 7. An offset current detecting means for detecting an offset current flowing through the specific gas detection cell in accordance with an amount of residual oxygen in the vicinity of the specific gas detection cell, wherein the correction means detects the offset current based on the detected offset current. The gas concentration detection device according to claim 6, wherein the current value of the specific gas detection cell is corrected. 8. An output characteristic of the specific gas detection cell,
A first region for detecting an addition current of an offset current component and a specific gas component after oxygen is exhausted by the oxygen pump cell; and a second region for detecting only an offset current component. The gas concentration detection device according to claim 7, wherein the offset current is detected using two regions. 9. The output characteristic of the specific gas detection cell is as follows:
A first region for detecting an addition current of an offset current component and a specific gas component after oxygen is exhausted by the oxygen pump cell; and a second region for detecting only an offset current component. Detect the value,
The gas concentration detection device according to claim 6, wherein an offset current is detected in the second region, and the correction unit corrects the detected current value before correction by an offset current. 10. The gas concentration detecting apparatus according to claim 9, wherein a voltage is applied in said first area when detecting a current value before correction, and said second area is used when detecting an offset current. A gas concentration detection device comprising a voltage switching means for selectively switching an applied voltage of a specific gas detection cell so that a voltage is applied in the gas concentration detection device. 11. An electromotive force detection means for detecting an electromotive force of the specific gas detection cell, wherein the correction means changes a current value of the specific gas detection cell according to the detected electromotive force of the specific gas detection cell. The gas concentration detection device according to claim 6, wherein the correction is performed. 12. The gas concentration detecting device according to claim 11, wherein said electromotive force detecting means includes a switch for opening an electric path for applying a voltage to the specific gas detecting cell, and the specific gas detecting cell by the switch. And a measuring means for measuring an electromotive force generated in the specific gas detection cell when an electric path for applying a voltage to the cell is opened. 13. A gas to be detected an internal diffusion resistance portion for introducing into the space, with the voltage applied, via the diffusion resistance portion
Decompose and discharge oxygen in the detected gas introduced
An oxygen pump cell through which a current corresponding to the oxygen concentration in the gas to be detected flows, and after the oxygen is exhausted by the oxygen pump cell,
Oxygen detection cell for detecting the oxygen concentration of the gas, and with the application of voltage, from the gas after oxygen is exhausted by the oxygen pump cell.
Decompose NOx, HC or CO and release oxygen ions
And a gas concentration sensor using a gas concentration sensor having a specific gas detection cell for flowing a current corresponding to the NOx concentration, the HC concentration or the CO concentration. A second detection unit for detecting a current value flowing through the specific gas detection cell; and a current detected by the second detection unit while reflecting oxygen concentration dependency based on the current value detected by the first detection unit. A correction unit that performs a first correction that corrects a value and a second correction that corrects a current value of the specific gas detection cell based on the amount of oxygen remaining near the specific gas detection cell. Gas concentration detector. 14. The gas concentration detecting device according to claim 13, wherein the correction means determines whether each of the first correction and the second correction is necessary, and selectively performs each correction according to the result of the determination. Gas concentration detector. 15. The gas concentration detection device according to claim 13, wherein the correction means calculates the first and second correction amounts, and at that time, the frequency at which the first correction amount is calculated. On the other hand, a gas concentration detection device that reduces the frequency of calculating the correction amount of the second correction. 16. A gas to be detected an internal diffusion resistance portion for introducing into the space, with the voltage applied, via the diffusion resistance portion
To decompose and exhaust oxygen in the gas to be detected
An oxygen pump cell through which a current corresponding to the oxygen concentration in the gas to be detected flows, and after the oxygen is exhausted by the oxygen pump cell,
Oxygen detection cell for detecting the oxygen concentration of the gas, and with the application of voltage, from the gas after oxygen is exhausted by the oxygen pump cell.
Decompose NOx, HC or CO and release oxygen ions
NOx concentration in the, in the gas concentration sensor and a specific gas detection cell to flow a current corresponding to the HC concentration or CO concentration, as an output characteristic of the specific gas sensing cell, after oxygen discharge by the oxygen pump cell and the offset current component A gas concentration sensor comprising a first region for detecting an addition current with a specific gas component and a second region for detecting only an offset current component. 17. The gas concentration sensor according to claim 16, wherein each electrode of the oxygen pump cell and the specific gas detection cell facing the diffusion resistance section is adapted to a specific gas component after oxygen is exhausted by the oxygen pump cell . Gas concentration sensor with inert electrodes.