JPH11304758A - Control circuit unit for gas sensor and system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control circuit unit to which not only the function of a NOx sensor but also the function of an oxygen concentration sensor can be imparted when the unit is mounted on an already existing NOx sensor. SOLUTION: A control circuit unit 31 is used in a state where the unit 31 is connected to a NOx sensor 1. A first pump element control circuit 56 controls the partial pressure of oxygen in a first treating chamber 9, so that the output voltage of an oxygen concentration detecting element may be fixed by controlling the conducting voltage of a first pump element 3. A first pump current is detected by means of a current detecting resistor 101 and outputted through an A/D conversion circuit 65. A second pump element control circuit 57 impresses a constant voltage upon a second pump element 5 in the direction in which the element 5 pump up oxygen from a second treating chamber 10. A second pump current is detected by means of another current detecting resistor 107 and outputted through the A/D conversion circuit 65. The detecting signal of the first pump current is used for detecting the concentration of oxygen in a gas to be measured and the detecting signals of the first and second pump currents are used for detecting the concentrations of nitrogen oxides in the gas to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas sensor control circuit unit and a gas sensor system using the same.

[0002]

2. Description of the Related Art Conventionally, as a nitrogen oxide (hereinafter also referred to as NOx) concentration measuring device, for example, European Patent Application Publication No. 0678740A1, SAE paper
r No. 960334 P137-142 1996
As disclosed in Japanese Patent Application Laid-Open No. H11-163, the concentration of NOx in exhaust gas from an internal combustion engine or the like is detected using the following NOx sensor. In the NOx sensor, a first processing chamber communicated with the gas to be measured via a first diffusion-controlling part, and a second processing chamber communicated with the first processing chamber via a second diffusion-controlling part. Is formed in the oxygen ion conductive solid electrolyte layer. In the first processing chamber, a first pump element and an oxygen concentration measurement cell are formed by sandwiching the solid electrolyte layer between porous electrodes. Further, in the second processing chamber, a second pump element is formed by sandwiching the solid electrolyte layer with a porous electrode.

In this type of NOx concentration measuring device,
An electric current is supplied to the first pump element so that the output voltage from the oxygen concentration measurement cell becomes a preset constant value, thereby controlling the oxygen concentration in the first processing chamber to a constant concentration, while controlling the second pump element. A constant voltage is applied to pump out oxygen from the second processing chamber. Then, from the current value flowing through the second pump element, NOx in the gas to be measured is determined.
The concentration can be detected.

That is, in the exhaust gas from an internal combustion engine or the like, which is the gas to be measured, other gas components such as oxygen, carbon monoxide, and carbon dioxide exist in addition to NOx. Then, the first pumping element controls the low oxygen concentration in the first processing chamber to a very low level of oxygen. further,
By applying a constant voltage to the second pump element in the direction of pumping oxygen in the second processing chamber on the side of the second processing chamber into which the gas to be measured controlled to the low oxygen concentration flows, the second pump element is turned on. The NOx in the gas to be measured is decomposed into nitrogen and oxygen by the catalytic function of the porous electrode, and oxygen is extracted from the second processing chamber. Then, by detecting the pump current flowing through the second pump element at that time, the NOx concentration in the gas to be measured can be detected without being affected by other gas components in the gas to be measured.

On the other hand, in this type of NOx concentration measuring device,
In order to accurately detect the NOx concentration by the above detection method, it is necessary to heat the sensor to a predetermined activation temperature (for example, about 850 ° C.) to activate each cell. Therefore, a heater for heating the sensor is required. Is provided separately.

[0006]

For example, in a so-called lean burn engine that is operated at a lean air-fuel ratio in which the amount of air to fuel is large, the NOx component in the exhaust gas tends to increase. Therefore, the NOx concentration measuring device as described above is often used for the purpose of monitoring the state of the reduction catalyst in order to suppress NOx emission. Specifically, a NOx sensor is attached downstream of the reduction catalyst provided in the exhaust passage of the internal combustion engine to measure the NOx concentration,
The amount of NOx leaked from the catalyst is detected. When the amount of NOx leakage increases, the air-fuel ratio of the fuel mixture supplied to the internal combustion engine is temporarily controlled to a rich air-fuel ratio to discharge unburned gas from the internal combustion engine. And NOx accumulated in the catalyst,
It is used for control such as suppression of NOx emission.

In order to realize such NOx control, the NOx concentration measurement device cannot measure the air-fuel ratio of the fuel mixture supplied to the internal combustion engine. It is necessary to separately provide an air-fuel ratio measuring device for measuring the fuel ratio. In other words, when performing the above-described NOx control, it is necessary to also execute the air-fuel ratio control generally performed in the internal combustion engine. For this purpose, the NOx sensor and the oxygen A concentration sensor (so-called air-fuel ratio sensor) must be provided.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gas sensor control circuit unit which can be mounted on an existing gas sensor so that one gas sensor can function as a type capable of detecting a plurality of types of gas component concentrations. A gas sensor system is provided. More specifically, it is possible to easily provide not only a function as a NOx sensor but also a function as an oxygen concentration sensor simply by mounting the sensor on an existing NOx sensor.
It is an object of the present invention to provide a gas sensor control circuit unit which can simplify the configuration of a detection system for x concentration and oxygen concentration (or air-fuel ratio), or a gas sensor system using the same.

[0009]

Means for Solving the Problems and Functions / Effects The first aspect of the gas sensor control circuit unit (hereinafter also simply referred to as the control circuit unit) of the present invention is used by being connected to a gas sensor. And a signal detection circuit for detecting a plurality of signals capable of calculating the concentrations of at least two or more gas components from circuit parameters in the operation control circuit. According to this configuration,
By attaching the gas sensor to an existing gas sensor, one gas sensor can function as a device capable of detecting a plurality of types of gas component concentrations. Therefore, the number of necessary sensors can be reduced, which is economical. The circuit parameters are
For example, a current value or a voltage value of an electric signal generated by the detection unit of the gas sensor or another electric signal generated based on the electric signal. Further, a gas sensor system according to the present invention includes the gas sensor and the gas sensor control circuit unit connected thereto.

Specifically, the above-described control circuit unit for a gas sensor can be used by being connected to a NOx sensor having the following configuration. That is, the NOx sensor is partitioned from the surroundings, and the first processing chamber into which the gas to be measured is introduced via the first diffusion-controlling unit, and the NOx sensor is partitioned from the surroundings, and the gas in the first processing chamber is separated from the surroundings. A second processing chamber guided through the two diffusion-controlling sections, and a porous electrode formed on both surfaces and composed of an oxygen ion conductive solid electrolyte,
An oxygen concentration detection element that measures the oxygen concentration of gas in the first processing chamber, and a first pump element that is formed of an oxygen ion conductive solid electrolyte and has porous electrodes formed on both surfaces, and pumps oxygen from the first processing chamber And, a porous electrode formed on both sides and composed of oxygen ion conductive solid electrolyte, a second pump element that pumps oxygen from the second processing chamber, and a first pump element,
A heating element for heating the oxygen concentration detecting element and the second pump element is provided.

The gas sensor control circuit unit of the present invention used by being connected to the NOx sensor as described above controls the energizing voltage to the first pump element so that the output voltage of the oxygen concentration detecting element becomes substantially constant. A first pump element control circuit for controlling the oxygen partial pressure level in the first processing chamber,
A first pump current detection circuit for detecting a current (first pump current) flowing through the first pump element and outputting a detection signal; A second pump element control circuit for applying a constant voltage, and a current flowing through the second pump element (second pump current)
A second pump current detection circuit that detects the current and outputs a detection signal, and a heat generation control circuit that controls the heat generation of the heating element. And the detection signal of the first pump current and the detection signal of the second pump current are used for detecting the concentration of nitrogen oxides in the gas to be measured.

According to this configuration, by providing the first pump current detection circuit and the second pump current detection circuit, the detection signal of the first pump current can be used for detecting the oxygen concentration in the gas to be measured, and The detection signal of the first pump current and the detection signal of the second pump current can be used for detecting the nitrogen oxide concentration in the gas to be measured. Therefore, the function of not only the NOx sensor but also the function of the oxygen concentration sensor can be easily given to the existing NOx sensor only by attaching the NOx sensor to the existing NOx sensor. Easy to do.

On the other hand, according to the study of the present inventors, NOx
In general, in a sensor, when the oxygen concentration in the gas to be measured introduced into the first processing chamber fluctuates, the NO of the second pump current changes.
It has been found that the x-concentration dependency is affected, and it is impossible to detect the NOx concentration accurately only with the value of the second pump current as in the related art. In the gas sensor control circuit unit or gas sensor system of the present invention, the NOx concentration is detected based on both the first pump current detection signal reflecting the oxygen concentration in the gas to be measured and the second pump current detection signal. As a result, more accurate measurement is possible.

In this case, the first pump element control circuit controls the first pump so that the oxygen concentration in the gas guided from the first processing chamber through the second gas flow section to the second processing chamber becomes substantially constant. It can also be seen as controlling the energizing voltage to the element.

The control circuit unit includes an assembling means for integrally assembling the first pump element control circuit, the first pump current detection circuit, the second pump element control circuit, and the second pump current detection circuit. Can be provided. This makes the entire unit compact and facilitates attachment to the NOx sensor.

Further, the control circuit unit includes a control circuit for controlling the heat generation of the heating element so that the temperatures of the first pump element, the oxygen concentration detection element, and the second pump element approach a predetermined temperature target value. A microprocessor functioning at least as heat generation control instruction means for instructing control can be provided. This makes it possible to control the temperature of each element simply by mounting the control circuit unit on the NOx sensor, and to further reduce the configuration of the entire unit including the heat generation control command means. .

The control circuit unit further includes a first pump current detection signal from the first pump current detection circuit,
An A / D conversion circuit for digitally converting the second pump current detection signal from the second pump current detection circuit can be provided. Accordingly, when the first pump current detection signal and the second pump current detection signal are to be digitally processed by a microprocessor or the like, a digital output can be directly taken out from the unit, which is convenient.

In the case where the above-mentioned microprocessor is mounted, the microprocessor converts the oxygen concentration information in the gas to be measured based on the first pump current detection signal digitally converted by the A / D conversion circuit. Nitrogen oxide concentration information generating means for functioning as generated oxygen concentration information generating means, and also generating nitrogen oxide concentration information in the gas to be measured based on the detection signal of the first pump current and the detection signal of the second pump current. It can function as a means. This makes it possible to extract oxygen concentration information and nitrogen oxide concentration information from the control circuit unit.

On the other hand, among the digital signals output from the microprocessor, oxygen concentration information, nitrogen oxide concentration information, air-fuel ratio information generated based on the oxygen concentration information, and excess generated based on the oxygen concentration information. It is also possible to provide a D / A conversion circuit that converts a digital signal related to at least one of the oxygen content information into an analog signal and outputs the analog signal as a corresponding analog signal. This makes it possible to extract the above information in the form of an analog output, so that it can be easily used as a control signal for an internal combustion engine such as an automobile engine. Further, based on the digital signal, the oxygen concentration, the nitrogen oxide concentration,
A display device for displaying at least one of the air-fuel ratio and the excess oxygen rate may be provided. This makes it possible to visually grasp the content of each piece of information.

Further, the NOx sensor to be connected is a temperature detecting section for detecting the temperature of at least one of a first pump element, an oxygen concentration detecting element, and a heating element for heating the second pump element. If you have
The microprocessor is configured to perform temperature-corrected oxygen concentration and nitrogen oxide concentration information (based on the temperature information detected by the temperature detection unit and the first pump current detection signal and the second pump current detection signal). Hereinafter, these may be collectively referred to as detected component concentration information) and function as detected component concentration information temperature correction means.

Thus, even if the temperature of the oxygen concentration detecting element temporarily changes due to a sudden change in the exhaust gas temperature, for example, the concentration information of the detected component is generated in a temperature-corrected form. Thus, the detection accuracy of the detection target component can be maintained satisfactorily. In this case, the temperature of the oxygen concentration detecting element may be measured by using a separately provided temperature sensor such as a thermistor or a thermocouple, but the value of the internal resistance of the solid electrolyte constituting each element changes according to the temperature. So
If this is used to measure the temperature, there is no need to provide a temperature sensor, and there is an advantage that the configuration of the measurement system can be simplified. In this case, the control unit may be provided with an internal resistance measurement control circuit for measuring the internal resistance of the oxygen concentration detecting element as a temperature detecting unit. In the case where a microprocessor is provided, the heat generation control command means realized by the microprocessor is configured to control each temperature of the first pump element, the oxygen concentration detection element, and the second pump element based on the measurement result of the internal resistance. May be commanded to the heat generation control circuit to control the heat generation of the heating element so that the temperature approaches a predetermined temperature target value.

The internal resistance measurement control circuit may include an internal resistance detection current supply circuit for supplying a constant internal resistance detection current to the oxygen concentration detection element. According to this, the internal resistance of the oxygen concentration detecting element can be easily measured from the applied voltage when the constant current is applied. In this case, the microprocessor detects a voltage applied to the oxygen concentration detection element when the internal resistance detection current is applied (hereinafter referred to as a resistance detection voltage) as internal resistance information of the oxygen concentration detection element. It can function as information detection means.

The internal resistance measurement control circuit applies an internal resistance detection current to the oxygen concentration detection element, measures the internal resistance, and then corrects the oxygen concentration detection element in a direction opposite to the internal resistance detection current. It can be configured to include a correction current supply circuit that supplies current. When a current for measuring internal resistance is supplied to the oxygen concentration detecting element, oxygen is transported in the oxygen concentration detecting element in a direction opposite to the direction of the current supply, and the oxygen concentration on both sides of the oxygen concentration detecting element changes. As a result, when the NOx sensor returns to the measurement of the concentration of the detected component, the change in the oxygen concentration may cause an error in the measurement accuracy of the concentration of the detected component. Further, when the internal resistance value of the oxygen concentration detecting element is high, oxygen ions in the oxygen concentration detecting element are difficult to move, and polarization may occur with the passage of current. Therefore, after the internal resistance detection current is applied to the oxygen concentration detecting element by the correction current applying means and the internal resistance is measured, the correction current is applied to the oxygen concentration detecting element in a direction opposite to the internal resistance detection current. If this is done, the oxygen is transported in the opposite direction by the energization, so that the changed oxygen concentration approaches the state before the internal resistance measurement, and the measurement accuracy of the concentration of the detected component after the return is improved, Also, the polarization state of the oxygen concentration detecting element can be eliminated. In this case, the magnitude and energizing time of the correction current are set so that approximately the same amount of oxygen that is considered to be transported when the internal resistance detection current is applied is reversely transported by the application of the correction current. For example, it is preferable to supply a current having substantially the same magnitude as the internal resistance detection current for approximately the same time as the internal resistance detection current.

Next, the control circuit unit or the gas sensor system is set in advance with respect to a characteristic representing the relationship between the value of the first pump current, the value of the second pump current, and the nitrogen oxide concentration in the gas to be measured. Standard characteristic information storage unit storing information on the standard characteristics thus obtained (hereinafter referred to as standard characteristic information), a value of the first pump current, a value of the second pump current, and nitrogen oxides in the gas to be measured. With respect to the characteristic indicating the relationship with the concentration, it is possible to provide a correction information storage unit that stores correction information for matching the previously measured characteristic of the NOx sensor to the standard characteristic. In the case where a microprocessor is provided, the nitrogen oxide concentration information generating means realized by the microprocessor detects the signals of the first pump current and the second pump current based on the correction information. After correcting each detected value, information on the nitrogen oxide concentration in the gas to be measured can be generated using the standard characteristic information.

According to this configuration, even if the NOx concentration of the same gas to be measured is measured using different NOx sensors, the variation of each NOx sensor is corrected by the unique correction information. The same measurement result can be obtained with high accuracy. In addition, instead of storing a characteristic representing a relationship between the value of the first pump current, the value of the second pump current, and the concentration of nitrogen oxide in the gas to be measured for each NOx sensor, a standard value is used. Since only correction data is stored in addition to the characteristics, the storage capacity is small.

[0026]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows a nitrogen oxide sensor (hereinafter, referred to as a NOx sensor) 1 as an example of a gas sensor. That is, the NOx sensor 1
Are a first heater 2, a first pump element 3, an oxygen concentration detection element 4, and a second pump element 5 each formed in a horizontally long plate shape.
And the second heater 8 are laminated and integrated in this order. A first processing chamber 9 is provided between the first pump element 3 and the oxygen concentration detecting element 4, and a second processing chamber 1 is provided between the oxygen concentration detecting element 4 and the second pump element 5.
0 is formed.

Each of the elements 3 to 5 is composed of a solid electrolyte having oxygen ion conductivity. Examples of such a solid electrolyte include Zr in which Y ₂ O ₃ or CaO is dissolved.
O ₂ is typical, but a solid solution of an oxide of another alkaline earth metal or rare earth metal and ZrO 2 may be used. The base ZrO ₂ contains Hf
O2 may be contained. In this embodiment, Y ₂ O ₃
It is assumed that a ZrO ₂ solid electrolyte ceramic in which CaO is dissolved is used. On the other hand, the first and second heaters 2 and 8 are configured by known ceramic heaters, and each element 3 to 5 is set to a predetermined operating temperature, for example, 750 to 8
50 ° C., desirably 780-830 ° C. (for example, 800
C). The heating temperature is set slightly lower than that of the conventional NOx sensor in order to improve the durability of the heaters 2 and 8.

The boundary between the elements 3 to 5 is made of Al ₂ O ₃
An insulating layer (such as the insulating layer 260 shown in FIG. 3; not shown in FIG. 1) mainly composed of an insulating material is interposed. The structure of such a sensor integrated by lamination can be manufactured by laminating and firing ceramic green sheets (ceramic molded bodies) to be the respective elements 3 to 5.

On both side wall portions of the first processing chamber 9, first gas circulation portions 11 for communicating the first processing chamber 9 with an external space to be measured are formed. As shown in FIG. 1 (b), the first gas flow portion 11 is formed in such a manner as to extend between the first pump element 3 and the oxygen concentration detection element 4 on both sides in the width direction of the first processing chamber 9. A porous ceramic body extending in the longitudinal direction of the first pump element 3 or the oxygen concentration detecting element 4 along the side edge of the first processing chamber 9 and having continuous ventilation holes made of a porous Al ₂ O ₃ fired body or the like. It is configured. As a result, the first gas flow section 11 functions as a diffusion control section that guides the exhaust gas from the outside into the first processing chamber 9 with a constant diffusion resistance.

Next, a portion sandwiched between the first processing chamber 9 and the second processing chamber 10 is a partition wall 12 made of an oxygen ion conductive solid electrolyte. In other words, the two processing chambers 9 and 10 are arranged adjacent to each other with the partition wall 12 interposed therebetween. The partition 12 is provided with a second gas flow section 13 for communicating the first processing chamber 9 and the second processing chamber 10 with each other.
Is buried. The second gas flow section 13 is also configured as a porous ceramic body similarly to the first gas flow section 11, and the gas in the first processing chamber 9 is diffused into the second processing chamber 10 under a certain diffusion resistance. Functions as a guiding diffusion-controlling part. In addition, the said diffusion rate-controlling part may be comprised with a small hole or slit instead of forming with a porous ceramic body (or metal body).

On the other hand, a first electrode 15 is formed on the surface of the partition wall 12 facing the first processing chamber 9.
And a partition part 12 sandwiched between the electrodes 15 and 14
a. On the other hand, the second pump element 5
The electrodes 17 and 18 are formed on both surfaces of the first pump element 3, respectively, and the electrodes 19 and 20 are formed on both surfaces of the first pump element 3, respectively. The electrodes 15 and 14 are formed so as to be shifted from each other in the longitudinal direction of the oxygen concentration detecting element 4.

Each of the electrodes 14, 15, 17 to 20 is for dissociating oxygen molecules for injecting oxygen into the solid electrolyte constituting each of the elements 3 to 5, and for releasing oxygen from the solid electrolyte. Is configured as a porous electrode (for example, a Pt porous electrode) having a reversible catalytic function (oxygen dissociation catalytic function) for the oxygen recombination reaction. Such a porous electrode is prepared, for example, by mixing an appropriate amount of a solid electrolyte ceramic powder of the same material as the base to improve the adhesion strength between the metal or alloy powder and the base solid electrolyte ceramic to form a paste. An electrode pattern is printed and formed on a ceramic green sheet to be used as a base using this, and is formed by integrally firing.

As shown in FIG. 1, the electrodes 14, 15, 17 to 20 of the elements 3 to 5 extend from the electrodes 14, 15, 17 to 20 to the base end side of the NOx sensor 1 along the longitudinal direction of the element. The leads 14a, 15a, 17a to 20a (only 14a, 15a, 20a are shown in FIG. 1) are formed integrally, and the connection terminals 14b, 15b, One end of each of 17b to 20b is embedded. Then, as shown in FIG. 2, each connection terminal (20b) is connected to the end of the electrode lead portion (20a) by a conductive portion (20c) formed in the thickness direction of the element as a sintered body of a metal paste. (In the figure, the case of the electrode lead portion 20a is shown as a representative).

Further, as shown in FIG.
4 is formed at a position that does not interfere with the second gas flow portion 13. Thereby, the detection output of the NOx concentration can be further stabilized. On the other hand, the first electrode 15 of the oxygen concentration detecting element 4 is formed at a position overlapping with the second gas flow part 13, and at a position corresponding to the second gas flow part 13, to secure gas flow. Is formed with a through hole 15h.

Next, as shown in FIG. 3 (b), in the first processing chamber 9 and the second processing chamber 10, a column 210 for preventing the space of the processing chamber from being collapsed at the time of sintering is provided in the form of a spot. It is formed in a staggered pattern. A method of manufacturing such a structure will be described by taking the first processing chamber 9 as an example. That is, as shown in FIG. 3A, the first processing chamber is formed on each of the opposing surfaces of the ceramic green sheet 220 to be the first pump element 3 and the ceramic green sheet 230 to be the oxygen concentration detecting element 4. In a region scheduled for 9, a ceramic powder paste (for example, a porous Al ₂ O ₃ powder paste)
, The support part pattern 26 to be the support part 210
6a and 266b are formed. Further, in a region not overlapping with the column part patterns 266a and 266b, an auxiliary support pattern 267a is formed by powder paste (for example, carbon paste) of a material which burns or decomposes during firing in a region which is also planned in the first processing chamber 9. And 26
7b is formed. Further, in an area other than the area planned for the first processing chamber 9, a bonding coat 269 as an insulating layer pattern is formed of an Al ₂ O ₃ powder paste or the like so as to have a thickness smaller than the height of the pillar pattern 210. Is formed. Further, although not shown, on both sides of a region to be the first processing chamber 9, a communicating portion pattern for forming the first gas flowing portion 11 (FIG. 1) made of a porous Al ₂ O ₃ fired body. Is formed by a porous Al ₂ O ₃ powder paste.

By firing this, as shown in FIG. 3B, between the first pump element 3 and the oxygen concentration detecting element 4, the auxiliary support patterns 267a and 267 are provided.
b disappears, and the above-mentioned strut pattern 266a,
The pillars 210 are formed by integrating the 266b by firing. Further, the first processing chamber 9 is formed in a shape of which the size is defined by the support portion 210, and the first gas flow portion 11 made of a porous ceramic body as shown in FIG. Is formed. On the other hand, in the other region except the first processing chamber 9, the oxygen concentration detecting element 4 and the first pump element 3 are combined with the insulating layer 2 based on the bonding coat 269.
60 are joined to each other.

Here, as shown in FIG. 4, the support part patterns 266a, 266b and the auxiliary support patterns 267a, 267a,
267b is formed complementarily so as to almost completely fill the plane. For example, the green sheets 220 and 2 shown in FIG.
30 are stacked together, the auxiliary support pattern 267
Based on the reinforcing effect by the a and 267b, the strut portion patterns 266a and 266b are prevented or suppressed from being crushed between them. Also, the green sheets 220 and 230
Is flexible, and as shown in an exaggerated manner in FIG. 3 (a), the bonding coat 269 is used for supporting column patterns 266a, 266b.
Even if formed much thinner than the total thickness of
When the green sheets 220 and 230 are slightly bent, they can be adhered to each other via the bonding coat 269 and can be integrated without any trouble by firing.

FIG. 5 is a block diagram showing an electrical configuration of an example of the gas sensor system (hereinafter simply referred to as a sensor system) of the present invention using the NOx sensor 1. That is, the sensor system 30 includes the NOx sensor 1
And a NOx sensor control circuit unit (hereinafter simply referred to as a control circuit unit) 31 according to an embodiment of the present invention connected to the NOx sensor 1. The control circuit unit 31 includes a microprocessor 52 and N
The peripheral circuit 51 connects the Ox sensor 1 and the microprocessor 52. The microprocessor 52 includes an I / O port 52a as an input / output interface, and a CPU 53, a RAM 55,
It is composed of a ROM 54 and the like. The CPU 53 calculates
With the control program stored in the ROM 54 using the AM 55 as a work area, it functions as an oxygen concentration information generation unit and a nitrogen oxide concentration information generation unit.

The peripheral circuit 51 includes a first pump element control circuit 56, a second pump element control circuit 57, a reference constant current power supply circuit 58, a limiter circuit 59, and an internal resistance measurement control circuit 6.
A / A which converts the detection output from the heater control circuit (heat generation control circuit) 72 and the internal resistance measurement control circuit 60 into a digital signal
It is configured to include a D conversion circuit 64, an A / D conversion circuit 65 for digitally converting detection outputs from the first pump element control circuit 56 and the second pump element control circuit 57, and the like. Digital outputs from the A / D conversion circuits 64 and 65 are input to the microprocessor 52 from the I / O port 52a.

The I / O port 52a of the microprocessor 52 has a data storage unit 66 and a D / A converter for converting a digital output signal from the microprocessor 52 into an analog signal.
The A conversion circuit 67 is connected. D / A conversion circuit 67
Are based on the analog-converted output, based on the nitrogen oxide (hereinafter also referred to as NOx) concentration, oxygen (hereinafter also referred to as O2) concentration, and air-fuel ratio (hereinafter also referred to as A / F) of the detected gas. An output circuit 68 for generating an analog signal output reflecting information such as the above is connected. Further, the I / O port 52a is connected to a display device 69 that displays values (for example, numerical values) such as NOx concentration, O2 concentration, and A / F based on a digital output signal from the microprocessor 52. I have.

FIG. 6 is a circuit diagram showing details of the peripheral circuit 51. First, the reference constant current power supply circuit 58 is connected to the oxygen reference electrode 14 side of the oxygen concentration detection element 4 and has a resistance value sufficiently larger than the internal resistance value of the oxygen concentration detection element 4 at the sensor operating temperature (for example, the internal resistance value). 1000 of resistance value
The power supply voltage AVcc is applied to the oxygen concentration detecting element 4 through a resistor 90 having a resistance of about 5000 times. As a result, a substantially constant minute current I0 is applied to the oxygen concentration detecting element 4 in a direction in which oxygen is pumped from the first processing chamber 9 side to the oxygen reference electrode 14 side. With a reference gas having an oxygen concentration close to 100%.

The first pump element control circuit 56 includes a pump current control unit 62 and a PID control unit 63. The input side of the PID control unit 63 has an internal resistance measurement control circuit 60, a reference constant current power supply circuit 58, Is connected to the oxygen reference electrode 14 (positive electrode side) of the oxygen concentration detection element 4 via the. On the other hand,
The output side of the PID control unit 63 is connected to the outer electrode 20 (positive electrode side) of the first pump element 3 via the operational amplifier 102 of the pump current control unit 62 and the limiter circuit 59. Further, the first pump element 3 and the oxygen concentration detecting element 4
The electrodes 19 and 15 facing the first processing chamber 9 are
0 is commonly connected to the output side of the PID control unit 63.

The main part of the PID control section 63 is composed of two operational amplifiers 104 and 105 and peripheral resistors and capacitors. Of these, the operational amplifier 104 at the former stage functions as an inverting amplifier having a low-pass filter function together with the resistor 104a and the capacitor 104b. The reference voltage Vr1 (for example, 2.5 V) is input to the positive side, and connected to the oxygen reference electrode 14 on the negative side. The input voltage on the negative side is the output voltage of the oxygen concentration detection element 4, and the output voltage is the same as the oxygen concentration on the oxygen reference electrode 14 side and the first processing chamber 9.
The concentration cell electromotive force generated in the oxygen concentration detection element 4 is mainly based on the difference from the oxygen concentration on the side.

Here, the above-mentioned negative side input is a bias voltage V
Biased by r2. The bias voltage Vr2 is
The target value Vemf0 of the output voltage Vemf of the oxygen concentration detecting element 4
Is subtracted from the reference voltage Vr1 (that is, Vr1
−Vemf0). Therefore, the operational amplifier 104 inverts and differentially amplifies the difference Vemf-Vemf0 between Vemf and Vemf0 and outputs the result. The reference voltage Vr1 and the bias voltage Vr2 are obtained by connecting the power supply voltage AVcc (for example, 8 V in this embodiment) to the resistor 104g, 104h or 104.
i, 104j to adjust the partial pressure.

Next, the operational amplifier 105 in the second stage forms a PID operation section together with the peripheral resistors or capacitors 105a to 105f, and performs the PID operation according to the difference between the input voltage from the operational amplifier 104 and the reference voltage Vr1. Do. Here, the resistors 105e and 105b represent the proportional terms, the resistor 105f and the capacitor 105a represent the integral terms,
The resistor 105e and the capacitor 105d are for forming a differential term. Note that the capacitor 105
“c” is for providing a low-pass filter function to the PID operation unit.

The output of the PID operation section is input to a current control operational amplifier 102 which is a main part of the pump current control section 62. The operational amplifier 102 is of a single power supply type, and its output varies from 0 to a maximum value (power supply voltage AVcc in this embodiment) according to the difference between the input voltage Vk from the PID operation unit and the reference voltage Vr1. , And a pump voltage (energization voltage) Vp for pumping oxygen from the first processing chamber 9 is applied to the first pump element 3. Thereby, the oxygen partial pressure in the first processing chamber 9 is changed to the second processing chamber 10 through the second gas flow unit 13 based on the output voltage of the oxygen concentration detecting element 4 (based on the electromotive force of the oxygen concentration cell generated in itself). The current value to be supplied to the first pump element 3, that is, the first pump current Ip1 'is controlled so that the PID control is performed while maintaining the target value Vemf0 while the PID control is performed. The Rukoto.

Here, the limiter circuit 59 serves to limit the upper limit of the first pump element 3 so that an excessive pump voltage Vp is not applied. Although the function of the limiter circuit 59 can be realized by various circuit configurations, the present embodiment employs the following circuit configuration. That is, the main parts of the circuit are two voltage-follower operational amplifiers 59d and 59e connected to the voltage control point PC via the diodes 59f and 59g, respectively. Then, for example, 6 V) and the lower limit voltage Vmin (for example, 2 V in the present embodiment) are maintained on the output side. It should be noted that Vmax and Vmin are formed in such a manner that the power supply voltage AVcc is divided and adjusted by resistors 59a to 59c. When the voltage at the control point PC is going to exceed Vmax, the diode 59f conducts and balances with the output voltage of the operational amplifier 59d.
maintained at max. On the other hand, when going to fall below Vmin, the diode 59g is balanced with the output voltage of the operational amplifier 59e, and the value is maintained at Vmin.

In the pump current control section 62, for example, a current detecting resistor 101 is provided on the output path of the PID operating section. This resistor 101 is a main component of the first pump current detection circuit, and the difference between the voltages across the two ends is the detection of the first pump current Ip1 ′ (however, a second pump current Ip2 described later is superimposed). The signal is taken out in the form of a voltage signal by an operational amplifier 103 constituting a differential amplifier together with the peripheral resistors 103a to 103d, further digitized by an A / D conversion circuit 65, and input to the microprocessor 52 of FIG. You. However, the voltage between both ends of the current detecting resistor 101 may be individually A / D converted and input to the microprocessor 52, and the difference may be calculated by the internal processing of the microprocessor 52 to detect the current value.

Next, the second pump element control circuit 57 is for applying a constant second pump voltage Vp2 to the second pump element 5 in the direction of pumping oxygen from the second processing chamber 10. Yes, it includes an applied voltage generator 75 and a second pump current detection circuit 76. The applied voltage generator 75 includes resistors 75a and 75b that generate an intended applied voltage by dividing the power supply voltage AVcc and adjusting the voltage, and an operational amplifier 106 for a voltage follower. The pump voltage to be applied is maintained at Vp2. The second pump current detection circuit 76 includes, for example, the current detection resistor 1 provided on the input path of the second pump voltage Vp2.
07. The difference between the voltages at both ends of the resistor 107 is taken out as a detection signal of the second pump current Ip2 in the form of a voltage signal by the operational amplifier 108 constituting a differential amplifier together with the peripheral resistors 108a to 108d, and further subjected to A / D conversion. The data is digitized by the circuit 65 and input to the microprocessor 52 of FIG. However, in this case as well, the voltage across the current detection resistor 107 may be individually A / D converted and input to the microprocessor 52.

Here, the target value Vemf0 of the output voltage of the oxygen concentration detecting element 4 is adjusted within a range of, for example, 300 to 500 mV (for example, 350 mV in the present embodiment). This corresponds to a range of 10 ⁻¹⁰ to 10 ⁻⁶ atm (approximately 10 ⁻⁷ atm in the present example) in terms of an oxygen partial pressure value calculated based on the Nernst equation. This means that the first processing chamber 9 detected by the oxygen concentration detecting element 4
In other words, it means that the partial pressure of oxygen in the gas introduced into the second processing chamber 10 through at least the second gas flow section 13 is adjusted within the above range.

When the oxygen partial pressure is less than 10 ⁻¹⁰ atm (or the output voltage target value Vemf0 is 500 mV or more), the decomposition of NOx in the gas to be measured in the first processing chamber 9 proceeds too much, and the detection of the NOx is performed. Accuracy may decrease. On the other hand, when the oxygen partial pressure exceeds 10 ⁻⁶ atm,
In some cases, the concentration of oxygen remaining in the gas introduced into the second processing chamber 10 becomes too high, and the offset current value of the second pump element 5 described later becomes excessively large, thereby lowering the NOx detection accuracy. On the other hand, according to the study of the present inventors, the partial pressure of oxygen in the first processing chamber 9 is set to a level at which NOx in the introduced gas to be measured decomposes to some extent. It has been found that it is important for ensuring the stability of the NOx detection output with respect to changes in the oxygen concentration in the gas to be measured and the oxygen concentration in the gas to be measured. Therefore, the oxygen partial pressure is 10
^If it exceeds ^-6 atm, decomposition of NOx hardly occurs, and the stability of the detection output of NOx may not be secured.

Next, the internal resistance measurement control circuit 60 includes a bipolar analog switch circuit 79 composed of, for example, a CMOS-IC or the like. It is arranged on the route to 56. Further, a sample and hold circuit (hereinafter, referred to as an S & H circuit) 1 is provided between the analog switch circuit 79 and the first pump element control circuit 56.
20 are provided. On the other hand, the analog switch circuit 7
Nine Sw2 and Sw3 are connected to constant current power supply circuits 77 and 78 having current values IC and different polarities, respectively. Further, an internal resistance detection signal ΔVS, which will be described later, output through the S & H circuit 120, is digitally converted by the A / D conversion circuit 64 and input to the microprocessor 52.

The first pump current control circuit 56, the second pump current control circuit 57, and the analog switch circuit 7
9, the switches Sw1 to Sw3 are connected to the microprocessor 5
It turns on / off in response to a control signal from the control unit 2 (see FIG. 10).

FIG. 7 shows an example of the heater control circuit 72. The heater control circuit 72 shown in FIG. 9A includes a D / A conversion circuit 80 for converting a heater control value given from the microprocessor 52 into an analog signal, and a transistor 82 connected thereto. And 8 are connected. The transistor 82 operates in the active region and increases the current flowing through the heaters 2 and 8 according to the applied heater control value.

On the other hand, FIG. 2B shows a PWM (pulse width).
h modulation) heater control circuit 72 employing a control method
This is an example. The main component of the circuit 72 is a PWM control circuit 85, which converts a heater control voltage value supplied from the microprocessor 52 into an analog signal.
It is configured to include an A converter 86, a triangular wave (or sawtooth wave) generating circuit 87, and an operational amplifier 88 to which outputs from the D / A converter 86 and the triangular wave generating circuit 87 are input. The operational amplifier 88 is of a single power supply type, and operates as a comparator that outputs either zero or a non-zero predetermined voltage V according to the magnitude relationship between the heater control voltage value and the triangular wave input value. In this case, the duty ratio of the comparator output changes according to the heater control voltage value, and the heat generation of the heaters 2 and 8 is adjusted.

In FIG. 5, the first pump element control circuit 56, the second pump element control circuit 57, the reference constant current power supply circuit 58, the limiter circuit 59, the internal resistance measurement control circuit 60, the heater control circuit 72, A / D conversion circuits 64, 6
5. The microprocessor 52, the D / A conversion circuit 67, the output circuit 68, and the like are mounted on the circuit board 32 and integrated with each other. Then, as shown in FIG. 8, the substrate 32 is accommodated in the case 31a, and the control circuit unit 31
Is composed. The control circuit unit 31 is detachably attached to the NOx sensor 1 via a cable 89 and a connector 90.

Returning to FIG. 5, the data storage section 66 is configured as a semiconductor memory device detachably mounted on the microprocessor 52 (hereinafter also referred to as the semiconductor memory device 66). In the present embodiment, as shown in FIG. 8, as the data storage unit, a substantially button-shaped semiconductor memory device (for example, a touch memory button (DS1995) manufactured by Dallas Semiconductor Corporation) having a button shape is configured as an EPROM. Is used. This semiconductor memory device 66 is small, having a diameter of less than 2 cm, and has a substantially diamond-shaped mount 66a.
(Touch memory mount products (D
S9093x)), and the mount 66a is screwed to the outer surface of the case 31a.

Hereinafter, the operation of the NOx sensor system 30 will be described. The outline is as follows. First,
In FIG. 6, the switch S of the analog switch circuit 79
w1 is turned on and the switches Sw2 and Sw3 are turned off to operate the first pump element control circuit 56 and the second pump element control circuit 57 (these are operation commands from the microprocessor 52 as shown in FIG. 5). Activated in response to a signal). The gas to be measured is introduced into the first processing chamber 9 via the first gas flow section 11, where the first pump element 3
Oxygen is pumped out by the operation of the oxygen concentration detecting element 4
The oxygen concentration is adjusted so that the output voltage of the above maintains a constant target value Vemf0. The detection signal of the first pump current value Ip1 'at this time is input to the microprocessor 52 via the A / D conversion circuit 64.

The gas to be measured after the oxygen concentration is adjusted flows into the second processing chamber 10 through the second gas flow section 13. At this time, the second pump current Ip2 flowing through the second pump element 5 changes according to the NOx concentration in the gas to be measured. However, the relationship between the value of the second pump current Ip2 and the NOx concentration is
Since it changes depending on the oxygen concentration level originally contained in the gas to be measured, NOx is determined by specifying both the oxygen concentration level and the second pump current Ip2.
You can know the concentration.

In this case, since the first pump current value Ip1 'changes according to the oxygen concentration in the gas to be measured, the oxygen concentration can be known based on the value of the first pump current value Ip1'. However, in the circuit configuration of FIG. 6, the current value Ip1 ′ detected by the current detection resistor 101 is such that the second pump current value Ip2 is superimposed on the true current value Ip1 flowing through the first pump element 3 as described above. Ip1'-
The oxygen concentration is determined based on the value of Ip2 (hereinafter, this value is referred to as Ip1, and this is referred to as a first pump current value). However, in general, compared with the current level of Ip1,
Since the current level of p2 is small, if it can be determined that the influence of the superposition of Ip2 can be ignored, the above-mentioned Ip1 'can be used approximately as the first pump current value.

The procedure for determining the oxygen concentration and the NOx concentration by the microprocessor 52 in FIG. 5 is as follows. First, Ip1 is obtained from Ip1 'and Ip2, and the data storage unit 66
The value of the oxygen concentration COX is determined by referring to the relationship (numerical table or mathematical expression) between Ip1 and the oxygen concentration COX stored in the storage device. On the other hand, the value of the NOx concentration CNX is determined with reference to the relationship (for example, a two-dimensional numerical table 200 as shown in FIG. 9) between Ip1, Ip2 and the NOx concentration CNX stored in the data storage unit 66. The two-dimensional numerical table 200
Is determined by experiment for each NOx sensor.

The value of COX or CNX determined above is
Through a D / A conversion circuit 67 and an output circuit 68, they are output to the outside as analog output signals of the oxygen concentration and the NOx concentration. (Including a display unit), and the density value is visually displayed by numerical values or the like. It should be noted that Ip1
The A / F and the excess oxygen concentration may be calculated based on the value of (i) and output.

Incidentally, in order to ensure the detection accuracy of the NOx concentration, the temperature of each of the above elements 3 to 5, especially the temperature of the oxygen concentration detecting element 4 for detecting the oxygen concentration in the first processing chamber 9, is controlled to be constant. For this purpose, it is necessary to control the amount of current supplied from the heater control circuit 72 to each of the heaters 2 and 8 so that the temperature of the oxygen concentration detecting element 4 becomes the target temperature. Therefore, in this embodiment, the microprocessor 52
As a result, the switch S of the analog switch circuit 79 in FIG.
By switching on / off states of w1 to Sw3, the temperature of the oxygen concentration detecting element 4 is detected from its internal resistance RVS, and the detected internal resistance RVS is a constant value (that is, the temperature of the oxygen concentration detecting element 4 is the target temperature). Thus, the amount of electricity supplied from the heater control circuit 72 to the heaters 2 and 8 is controlled.

Hereinafter, the operation in this case will be described with reference to FIGS.
FIG. 16 is described using the flowchart. First,
In S1 of FIG. 14, the activation process of the NOx sensor 1 is performed. The purpose of the activation process is to start energization of the heaters 2 and 8 and to stabilize the elements 3 to 5 at a predetermined operating temperature. The element temperature is detected by measuring the internal resistance of the oxygen concentration detecting element 4 and utilizing the fact that the internal resistance RVS exhibits a constant temperature dependence as shown in FIG.

FIG. 15 shows the details of the processing. That is, in S101, an initial set value Vh0 is set in the heater control circuit 72 as a control value Vi. At this time, Sw1 to Sw3 of the analog switch circuit 79 are all turned off.
In this state, the power supply to the heater is started by outputting the initial setting value Vh0 of the heater control voltage value Vi to the heater control circuit 72 in S102. Then, in step S103, when a predetermined time t0 has elapsed from the start of energization, a temperature control process is started. First, the activation determination counter value N is cleared in S105.

Next, the routine proceeds to S106, where the internal resistance measurement processing is performed. The flow will be described with reference to the flowchart of FIG. 16 (however, only S201 to S208 indicated by LF here) and the circuit diagram of FIG. further,
FIG. 11 shows an analog switch circuit 79 in the processing.
The operation timing chart of Sw1 to Sw3 in FIG. 6 is shown in association with the voltage signal VS on the oxygen reference electrode 14 side of the oxygen concentration detecting element 4. First, in FIG. 10, the S & H circuit 120 is a switch Sw1 of the analog switch circuit 79.
Is turned off, a capacitor 121 for holding the value immediately before the output voltage VS on the oxygen reference electrode 14 side of the oxygen concentration detecting element 4 and an operational amplifier 122 (hereinafter, voltage follower 1) functioning as a voltage follower
22) and an operational amplifier 123 (hereinafter referred to as a differential amplifier 123) for amplifying the difference between the output voltage of the voltage follower 122 and the output voltage VS directly input from the oxygen reference electrode 14.

In the processing flow of FIG.
At 201, S of the analog switch circuit 79 of FIG.
Turn on w1. Thus, the output voltage signal VS of the oxygen concentration detection element 4 on the oxygen reference electrode 14 side is output to the first pump element control circuit 56 via the operational amplifier 122 as a voltage follower. At this time, the capacitor 1
The terminal voltage at 21 changes according to the level of VS. Then, when the measurement timing of the internal resistance comes, S202
Then, Sw1 is turned off, and Sw2 is turned on instead. Then, the output voltage VS1 immediately before Sw1 is turned off is held by the capacitor 121. The held output voltage signal VS1 is supplied to the first pump element control circuit 56 via the voltage follower 122. This allows
The first pump element control circuit 56 receives the held output voltage VS1 and keeps operating even while Sw1 is turned off for measuring the internal resistance. Therefore, the first processing of the NOx sensor 1 is performed. The problem that the oxygen concentration in the chamber 9 changes greatly does not occur.

On the other hand, when Sw 2 is turned on, a constant current IC for detecting internal resistance is supplied to the oxygen concentration detecting element 4.
When IC is energized, the value of the output voltage VS of the oxygen concentration detecting element 4 drops by a value corresponding to its internal resistance. The difference ΔVS between this value and the previously held value of VS1 (that is, the output voltage before the IC is energized) is amplified by the differential amplifier 123 and input to the microprocessor 52 via the A / D conversion circuit 64. You. Then, the value of the output voltage VS of the oxygen concentration detecting element 4 after a lapse of a fixed time t1 from the start of the supply of the constant current IC is set to VS2, and the differential amplifier 12
3, the output ΔVS = VS1-VS2 (internal resistance detection signal)
The measured value is stored in the measured value memory area of the RAM 55. And
The internal resistance RVS is calculated as a value obtained by dividing ΔVS by the above-described value of the constant current IC, and is stored in the measured value memory area of the RAM 55 (S204).

Here, the reason why VS is measured after a lapse of a fixed time t1 from the start of energization of the constant current IC is as follows. That is, when a constant current IC is applied to the oxygen concentration detecting element 4, oxygen is transported in the oxygen concentration detecting element 4 in a direction opposite to the direction of the current supply, and the oxygen concentration on both sides of the oxygen concentration detecting element 4 changes. As a result, as shown in FIG. 11, the value of the concentration cell electromotive force Em and thus the value of VS also change with the continuation of the current IC. Here, in order to ensure the accuracy of the internal resistance measurement, it is important that the change in VS unavoidably caused by energization is always substantially constant. And
Since a constant current IC is used as the current for measuring the internal resistance, if the energization time until the VS measurement is controlled so as to be always t1, the oxygen transport amount, that is, the oxygen on both sides of the oxygen concentration detecting element 4, The change in the concentration is also substantially constant, and the change in the electromotive force Em of the concentration cell and thus the change in VS can be made substantially constant.

Next, the energization of the constant current IC causes a change in the oxygen concentration on both sides of the oxygen concentration detection element 4. Another problem is that when the NOx sensor 1 returns to the measurement of the NOx concentration, the oxygen concentration changes. May affect the measurement accuracy. Further, when the internal resistance value of the oxygen concentration detecting element 4 is high, oxygen ions in the oxygen concentration detecting element 4 are difficult to move, and polarization may occur with the passage of current.

In order to solve this problem, this embodiment employs the following method. That is, S in FIG.
In steps 205 to S208, after a certain time t2 has elapsed after the detection of VS, the switch SW2 is turned off to terminate the supply of the constant current IC, while the switch Sw3 is turned on instead. The correction current IA having the same magnitude in the opposite direction to IC by the current applying means)
Is energized for a time t3 substantially equal to the total energizing time t1 + t2, and then Sw3 is turned off (S208). As a result, almost the same amount of oxygen is transported in the oxygen concentration detection element 4 in the opposite direction to the above, and the change in oxygen concentration caused by the IC energization is eliminated, making it possible to approach the state before the internal resistance measurement. In the case where it is determined that the influence on the oxygen concentration change on both sides of the oxygen concentration detecting element 4 is small, for example, when the energizing time of the current IC for measuring the internal resistance of the oxygen concentration detecting element 4 can be sufficiently shortened, FIG. , Correction current I
It is also possible to omit the constant current power supply 78 for generating A (corresponding to this, an analog switch circuit 79 having a small number of switch channels may be used).

Returning to FIG. 15, as described above, the value of RVS has a fixed relationship with the element temperature T of the oxygen concentration detecting element 4, and the relation is used as correction information in the data storage section 66 (FIG. 5). , The element temperature T can be determined from the value of RVS. Further, the value of RVS itself can be used as temperature information. In the present embodiment, a map indicating the values of the various internal resistances RVS and the values of the element temperatures T in association with each other is stored in the data storage unit 66. T is determined (S107). The calculated value of the internal resistance RVS is stored in the RAM 55 (FIG. 5), and is overwritten and updated when a new internal resistance RVS is detected and calculated.

The determined element temperature T is equal to the upper limit value Tma
It is determined in S108 and S110 whether or not the temperature falls within the set temperature range of x and the lower limit value Tmin. When the element temperature T is higher than the upper limit value Tmax, the heater control voltage value Vi decreases by a certain value ΔVi to suppress the heat generation of the heaters 2 and 8, and conversely, when the heater control voltage value Vi is lower than the lower limit value Tmin. The heater control voltage value Vi increases by ΔVi and the heaters 2, 8
Is promoted (S109, S111). Also, T
If min ≦ T ≦ Tmax, the current value of Vi is maintained, and the activation determination counter value N is incremented (S112,
S113).

Then, the value of the activation determination counter value N becomes
For example, until the set value NS is reached, the above S106 to S1
13 is repeated at fixed time intervals ta (S114,
S115) If N reaches NS, it is considered that the element temperature T has been substantially maintained within the set temperature range, and in FIG. 6, Sw2 of the analog switch circuit 79 is turned off, and Sw1
Is turned on to warm up for a predetermined time tw, and then the activation process ends (S116, S117).

Returning to FIG. 14, when the activation process S1 is completed, the process proceeds to S2, where the values of the pump currents Ip1 and Ip2 are detected.
The oxygen concentration COX and the NOx concentration CNX are determined. However, since the values of the pump currents Ip1 and Ip2 fluctuate depending on the element temperature T, the correction is performed as follows (S
3). First, the value of the internal resistance value RVS of the oxygen concentration detecting element 4 stored in the RAM 55 (FIG. 5) is read, and the corresponding temperature T is determined with reference to the aforementioned map 301. Since the pump current correction amounts ΔIp1 and ΔIp2 for each temperature with respect to the values of the pump currents Ip1 and Ip2 can be determined experimentally in advance, the respective ΔIp1 and ΔIp2
Based on this, a map showing the value of Ip2 and the value of the element temperature T in association with each other is created, and this is stored in the data storage unit 66.
, Each pump current correction amount ΔIp can be determined by an interpolation method with reference to this map.
Then, the pump current correction amounts ΔIp1 and ΔIp2 are added to the actually measured Ip1 and Ip2 to correct them, and the oxygen concentration COX and the NOx concentration CNX corresponding to the corrected pump current values Ip1 and Ip2 are determined. (S4). These values are output in S5. Thereafter, the process returns to S2 and the subsequent processes are repeated.

Next, after the element temperature T is set at the time of the activation processing, the same internal resistance measurement processing as described above is performed, so that the element temperature T is set in parallel with the hydrocarbon concentration detection processing. Control is continued. FIG. 16 shows the flow of the processing. This processing routine is periodically executed by the CPU 53 (FIG. 5) by time measurement based on a clock pulse (by a clock circuit not shown) as an interruption processing routine for the routine of FIG. The cycle of the execution can be set, for example, in the range of 0.3 to 1 ms. If the execution cycle exceeds 1 ms, it may not be possible to sufficiently secure the temperature measurement and hence the concentration detection accuracy by the sensor. On the other hand, if it is less than 0.3 ms, the ratio of the temperature measurement processing to the processing time of the CPU 53 becomes too large, and it may not be possible to sufficiently secure the density detection accuracy. However, by using a CPU 53 that can perform high-speed processing, such as one with a high clock frequency, the execution cycle may be less than the above value.

First, S201 relating to the measurement of the internal resistance RVS
The processing of steps S208 to S208 has already been described in the sensor activation processing, and a description thereof will be omitted. The processing from S210 to S215, in which the element temperature T is determined from RVS and the heater control voltage value Vi is determined based on the element temperature T, is shown in FIG.
5 is almost the same as the process from S107 to S112 of the sensor activation process, and the description is also omitted. Then, after waiting for a time t4 in S216, S217 is executed in S217.
w1 is turned on, and the internal resistance measurement process ends. Thereafter, the density measurement processing routine of FIG. 14 is executed again.
The measured value of the element temperature T is updated every time the internal resistance measurement processing is performed, and the information of the updated element temperature T is always
It is also used in the concentration measurement processing routine of FIG.
Further, the heater temperature is also periodically corrected based on the measured value of the element temperature T.

Thus, the temperature of the oxygen concentration detecting element 4 is accurately maintained at the set value by the heaters 2 and 8, and the measurement accuracy of the carbide concentration in the gas to be detected is improved. When the detected gas is an exhaust gas of an automobile engine, FIG.
As shown in FIG. 1A, even when the temperature of the exhaust gas rapidly changes when the engine rapidly accelerates and decelerates, and the temperature T of the oxygen concentration detecting element 4 correspondingly changes suddenly, as shown in FIG.
As shown in FIG. 3 (b), by compensating the temperature change of the oxygen pump current Ip, it is possible to continue relatively accurate measurement of the carbide concentration without waiting for the return of the element temperature T. Become.

The internal resistance measurement processing is not an interruption routine to the concentration measurement processing routine.
It can also be executed as a subroutine of the concentration measurement processing routine. An example of a flowchart in this case is shown in FIG.
FIG. The process of determining and outputting the densities of S1 to S5 is shown in FIG.
However, the difference is that by adding steps S301 to S303, the measurement counter Nm is counted up each time one determination is completed. Then, when Nm reaches the predetermined count number Ng in S302, the same internal resistance measurement processing as that shown in FIG. 16 is executed as S304.
After the execution of the internal resistance measurement process, the process returns to S301, where the measurement counter Nm returns to 1, and the same process is repeated thereafter. This method does not change in that the internal resistance measurement processing is performed periodically, but is characterized in that the concentration measurement processing is not necessarily performed at regular time intervals, but is performed every time the concentration measurement processing is completed a predetermined number of times. This prevents the measurement process of the NOx concentration or the oxygen concentration from being interrupted halfway for the internal resistance measurement process, and reduces the frequency of occurrence of errors and the like.

Further, a constant current generating circuit 77 shown in FIG.
Instead of using the two units 78 and 78, one unit may be used by switching the polarity as needed using a polarity switching circuit (not shown). The microprocessor 52
A circuit (for example, including a voltage / current conversion circuit) that can generate a current according to the current value and the polarity instructed from the side may be used.

Although the control circuit unit 31 shown in FIG. 5 has a form in which the microprocessor 52 is mounted, as shown in FIG. 22, this may be omitted. In this case, the input terminal 72 to the heater control circuit 72
t, output terminals 64t from the A / D conversion circuits 64 and 65,
65t, input terminals 56t, 60t, 5 for each control command signal
7t and the like are collected into a connector (or a card edge provided on the substrate 32) 91, and an external (for example, mounted on an automobile side) microprocessor is detachably mounted and used here. . On the other hand, in the example shown in FIG. 21, the microprocessor 52 is mounted, but this functions only as a control command means to the heater control circuit 72, and the output terminals 64t, 65t from the A / D conversion circuits 64, 65. , Input terminals 56t, 6 for each control command signal
0t, 57t, and the like are collected in a connector 91, and another external microprocessor is connected to the connector 91 for use.

Next, another method of determining the oxygen concentration COX from Ip1 and the NOx concentration CNX from Ip1 and Ip2 will be described. First, a standard product is determined in advance for the NOx sensor 1 of FIG. 1, and the characteristic of the second pump current Ip2 with respect to the NOx concentration (first pump current Ip1
(Corresponding to the NOx concentration output characteristic in the case where is substantially zero), and this is stored in the ROM 54 (FIG. 18) of the microprocessor 52 as a standard current parameter characteristic. Then, the microprocessor 52 detects the first pump current Ip1 and the second pump current Ip2, and obtains the NOx concentration in the gas to be measured from the detected values based on the standard current parameter characteristics. When the test gas containing no oxygen is the gas to be measured, the rate of change of the second pump current Ip2 with respect to the NOx concentration is substantially constant,
Hereinafter, this is referred to as a gain.

By the way, in this embodiment, the oxygen concentration in the first processing chamber 9 is adjusted to the aforementioned partial pressure range (10 ⁻¹⁰⁾ so that the NOx component in the gas to be measured is not excessively decomposed.
Since the pressure is controlled within the range of 10 ⁻⁶ atm), not only the NOx in the gas to be measured but also the oxygen remaining in the first processing chamber 9 inevitably flows into the second processing chamber 10. Therefore, although the second pump current Ip2 changes according to the NOx concentration in the gas to be measured, it is also affected by the oxygen concentration in the gas to be measured. That is, even when the NOx component in the measured gas is zero, the second pump current Ip2 changes depending on the oxygen concentration remaining in the measured gas. For this reason,
Regarding the NOx sensor 1 as a standard product, the characteristic of the second pump current (hereinafter, referred to as offset current) with respect to the oxygen concentration when the test gas having zero NOx component is used as the gas to be measured (hereinafter, referred to as offset characteristic). Is measured in advance (see FIG. 19), and this is set as a standard offset characteristic (see FIG. 19).
54 (FIG. 18). Then, by subtracting the offset current Ip2OFF corresponding to the oxygen concentration at that time (measured from the first pump current Ip1) from the detected second pump current Ip2, in other words, the second pump current Ip2 and the first A new current parameter Ipx is determined based on the pump current Ip1, and the NOx concentration is determined based on the new current parameter Ipx and the standard current parameter characteristics.

The first pump current Ip1 during the pump current control
Varies depending on the oxygen concentration in the gas to be measured. Therefore, for the NOx sensor 1 as the standard product, the first pump current with respect to the oxygen concentration when the test gas having no NOx component is the gas to be measured. Characteristics (referred to as Ip1 characteristics) are measured in advance, and are measured as standard Ip1 characteristics (see FIG. 19).
As the ROM 54 of the microprocessor 52 (FIG. 18)
To memorize it. Then, the detected first pump current I
The oxygen concentration is detected from p1 based on the standard Ip1 characteristics. From the oxygen concentration, the offset current Ip2OFF can be obtained as described above.

Since the second pump current Ip2 changes with a change in the temperature of the NOx sensor 1 (hereinafter referred to as the element temperature), the detected second pump current Ip2 is determined according to the element temperature by the above-described method. It is preferable to correct. Here, when the temperature of the gas to be measured suddenly changes, the temperature control cannot follow the temperature change of the gas to be measured, and the element temperature may change due to the temperature change of the gas to be measured. In this case, the second pump current Ip2 changes according to the element temperature. For this reason, the characteristic of the second pump current Ip2 with respect to the temperature (hereinafter referred to as temperature characteristic) of the NOx sensor 1 as the standard product is measured in advance, and this is set as the standard temperature characteristic (see FIG. 19). (FIG. 18). Then, a correction amount is obtained based on the standard temperature characteristics from the element temperature obtained from the internal resistance RVS by the same method as described above, and the temperature is corrected for the detected second pump current Ip2.

In detecting the NOx concentration, the gain changes depending on the oxygen concentration in the gas to be measured.
Preferably, the standard current parameter characteristics are modified according to the oxygen concentration. In this embodiment, NOx as the standard product is used.
For the sensor, a gain at a certain oxygen concentration (for example, zero) and a gain at another oxygen concentration are measured in advance to calculate a linear function characteristic of the gain with respect to the oxygen concentration (hereinafter, referred to as a gain characteristic). This is stored in the ROM 54 (FIG. 18) of the microprocessor 52 as a standard gain characteristic (see FIG. 19). And
From the oxygen concentration detected from the first pump current Ip1, a gain correction amount is obtained based on the standard gain characteristic, and gain correction is performed on the detected second pump current Ip2. In addition,
The ROM 54 corresponds to standard characteristic storage means.

Each of the above-mentioned characteristics, ie, the Ip1 characteristic, the offset characteristic, the temperature characteristic, the gain characteristic, and the Ip2 characteristic
Each x sensor 1 is slightly different. For this reason, which NOx
NOx is constantly used for the sensor using the above standard characteristics.
If the concentration has been detected, sufficient detection accuracy cannot be obtained. Therefore, in the present embodiment, each of the above characteristics is measured in advance for each NOx sensor, and each correction data (Ip1 characteristic correction data, offset characteristic correction data, temperature characteristic Correction data,
Gain characteristic correction data) is created and stored in the data storage unit 66.

The procedure for detecting the NOx concentration in this case will be described with reference to the flowchart of FIG. This NO
In the x concentration detection processing, first, in S400, the sensor activation processing is executed by processing exactly the same as that in FIG. When the activation is completed, the flow shifts to S410, where the internal resistance RVS of the oxygen concentration detecting element 4 is read. In S420, the second pump current Ip2 and the first pump current Ip1 are detected. Then, in S430, a temperature correction amount for the second pump current Ip2 is calculated based on the internal resistance RVS read in S410, and the temperature is corrected.

That is, even if the temperature of the gas to be measured suddenly changes, the internal resistance RVS of the oxygen concentration detecting element 4 is used to detect the NOx concentration accurately from the second pump current Ip2. Of the element, that is, the element temperature, and a temperature correction amount corresponding to the element temperature is stored in the ROM 54.
It is determined based on the standard temperature characteristics stored in (FIG. 18). Then, for the temperature correction amount thus obtained,
The temperature is corrected using the temperature characteristic correction data read from the data storage unit 66 to obtain a corrected temperature correction amount, and the temperature is corrected using the corrected temperature correction amount. When the NOx sensor 1 is a standard product, the corrected temperature correction amount matches the temperature correction amount obtained from the standard temperature characteristics.

After the temperature correction is performed, the process proceeds to S440, and the current parameter Ipx is calculated by subtracting the offset current value from the temperature-corrected second pump current Ip2.
That is, the Ip1 characteristic correction data stored in the data storage unit 66 is read out, and the first pump current Ip1 is corrected with the Ip1 characteristic correction data to obtain a corrected first pump current Ip1. Ip1 to standard Ip1
The oxygen concentration in the gas to be measured is obtained using the characteristics as they are. Then, the offset current value Ip2OFF is obtained from the oxygen concentration using the standard offset characteristic as it is, and the offset current value Ip2OFF is corrected with the offset characteristic correction data read from the data storage unit 66 to obtain the corrected offset current value Ip2OFF. I do. A value obtained by subtracting the corrected offset current value Ip2OFF from the second pump current Ip2 is used as a current parameter Ipx.

At S450, gain correction is performed on the current parameter Ipx. That is, in S440, a gain is obtained from the oxygen concentration obtained from the first pump current Ip1 using the standard gain characteristic as it is, and this gain is corrected by the gain correction data read from the data storage unit 66 to obtain a corrected gain. A gain correction coefficient (for example, a corrected gain / a gain in the standard current parameter characteristic) is obtained, and the gain correction of the current parameter Ipx is performed using the correction coefficient. When the NOx sensor 1 is a standard product, the corrected gain and the gain obtained from the standard gain characteristics match.

Then, in S460, the NOx concentration is obtained from the current parameter Ipx after the gain correction by using the standard current parameter characteristics, and the NOx concentration is calculated from the NOx concentration in the gas to be measured.
Output as Ox concentration.

Since each of the above correction data is unique to each NOx sensor, a data storage section 66 is attached to each NOx sensor. Then, the connector 9 shown in FIG.
When removing NOx and replacing it with another NOx sensor 1, the NOx sensor 1 is replaced with the data storage unit 66 attached thereto, and the nitrogen oxide concentration is detected.

The gas sensor to which the present invention is applied is not limited to the NOx sensor, but may be applied to, for example, an HC sensor for detecting hydrocarbon (HC).
In this case, the plurality of gas components to be detected are, for example, 2
The above HC component can be used, or oxygen and one or more HC components can be used. Also. Other than the HC sensor, the present invention can be applied to a CO sensor, an ammonia sensor, and the like.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing an example of a NOx sensor to which the present invention is applied, and an AA sectional view thereof.

FIG. 2 is a sectional view showing an example of a connection structure between an electrode lead portion and a terminal portion.

FIG. 3 is an explanatory view showing a method of forming a processing chamber in the NOx sensor of FIG. 1;

FIG. 4 is another explanatory view of the same.

FIG. 5 is a block diagram showing an example of an electric configuration of a gas sensor control circuit unit of the present invention and a gas sensor system using the same.

FIG. 6 is a circuit diagram showing the main part in detail.

FIG. 7 is a circuit diagram showing some examples of a heater control circuit.

FIG. 8 shows a control circuit unit for a NOx sensor of the present invention;
FIG. 2 is a perspective view showing the appearance of a NOx sensor system using the same.

FIG. 9 shows Ip1, Ip2 and NO stored in a data storage unit.
FIG. 3 is a conceptual diagram of a two-dimensional table for giving a relation of x density.

FIG. 10 is a block diagram showing a circuit operating system when measuring the internal resistance of the oxygen concentration detecting element.

FIG. 11 is an operation timing chart of each switch when measuring the internal resistance of the oxygen concentration detecting element.

FIG. 12 is a conceptual diagram of a graph showing an example of a relationship between an element temperature and an internal resistance of an oxygen concentration detecting element, and a map showing a relationship between an internal resistance of the oxygen concentration detecting element and an element temperature.

FIG. 13 is a graph showing an example of a measurement example of a pump current change accompanying rapid acceleration or deceleration of an engine, and a graph showing an example of a relationship between an element temperature and a corrected pump current value.

FIG. 14 is a flowchart showing a control flow on the microprocessor side in the apparatus of FIG. 5;

FIG. 15 is a flowchart showing details of the sensor activation process.

FIG. 16 is a flowchart showing details of an internal resistance measurement process.

FIG. 17 is a flowchart showing the flow of another control mode on the microprocessor side in the system of FIG. 5;

FIG. 18 is an explanatory diagram showing storage contents of a ROM and a data storage unit of a microprocessor, which are used in another method for determining the NOx concentration.

FIG. 19 is an explanatory diagram showing a procedure for detecting a NOx concentration in the alternative method.

FIG. 20 is a flowchart showing the flow of the processing.

FIG. 21 is a block diagram showing a first modification of the control circuit unit for the NOx sensor.

FIG. 22 is a block diagram showing a second modified example.

[Description of Signs] 1 Nitrogen oxide sensor (NOx sensor) 2 First heater (heating element) 3 First pump element 4 Oxygen concentration detection element 5 Second pump element 8 Second heater (heating element) 9 First processing chamber DESCRIPTION OF SYMBOLS 10 2nd processing chamber 11 1st gas flow part (diffusion rate control part) 12 Partition wall 13 2nd gas flow part (diffusion rate control part) 14 Oxygen reference electrode 15, 17, 18, 19, 20 electrode 30 Nitrogen oxide sensor Unit 31 Control circuit unit for nitrogen oxide sensor 52 Microprocessor 53 CPU (oxygen concentration information generating means, nitrogen oxide concentration information generating means) 54 ROM 55 RAM 56 First pump element control circuit 57 Second pump element control circuit 58 Reference Constant current power supply circuit 60 Internal resistance measurement control circuit 64, 65 A / D conversion circuit 66 Data storage unit 67 D / A conversion circuit 69 Table 72 heater control circuit (heating control circuit) 77 and 78 constant-current power supply circuit

Claims (16)

[Claims] 1. A plurality of signals which are used in connection with a gas sensor and which can calculate concentrations of at least two or more gas components from an operation control circuit of the gas sensor and circuit parameters in the operation control circuit. A control circuit unit for a gas sensor, comprising: a signal detection circuit. 2. A first processing chamber, which is partitioned from the surroundings and into which a gas to be measured is introduced via a first diffusion-controlling unit, and is partitioned from the surroundings and the gas in the first processing chamber is a second processing chamber. A second processing chamber guided through the diffusion-controlling portion, and an oxygen concentration detecting element configured of an oxygen ion conductive solid electrolyte, having porous electrodes formed on both surfaces thereof, and measuring an oxygen concentration of gas in the first processing chamber. And a first pump element for pumping oxygen from the first processing chamber, wherein the first pump element is formed of an oxygen ion conductive solid electrolyte, and porous electrodes are formed on both sides thereof. And a heating element for heating the second pump element, wherein the second pump element pumps oxygen from the second processing chamber, the first pump element, the oxygen concentration detection element, and the second pump element. Equipped gas sensor A control circuit unit for a gas sensor to be connected and used, comprising controlling an energization voltage to the first pump element, and controlling an oxygen in the first processing chamber so that an output voltage of the oxygen concentration detection element becomes substantially constant. A first pump element control circuit that controls a partial pressure level; a first pump current detection circuit that detects a current flowing through the first pump element (hereinafter, referred to as a first pump current) and outputs a detection signal thereof; A second pump element control circuit for applying a constant voltage to the second pump element in a direction of pumping oxygen from the second processing chamber; and a current flowing through the second pump element (hereinafter, referred to as a second pump current) A second pump current detection circuit that detects the current and outputs a detection signal; and a heat generation control circuit that controls heat generation of the heating element. For detecting a concentration of oxygen in the gas, wherein the detection signal of the first pump current and the detection signal of the second pump current are used for detecting the concentration of nitrogen oxides in the gas to be measured. Control circuit unit. 3. Assembling means for integrally assembling the first pump element control circuit, the first pump current detection circuit, the second pump element control circuit, and the second pump current detection circuit with each other. The control circuit unit for a gas sensor according to claim 2, further comprising: 4. The heat generation control circuit controls the heat generation of the heating element so that the temperatures of the first pump element, the oxygen concentration detection element, and the second pump element approach a predetermined temperature target value. The control circuit unit for a gas sensor according to claim 2 or 3, further comprising a microprocessor functioning as at least a heat generation control commanding unit for commanding. 5. An A / D conversion circuit for digitally converting a first pump current detection signal by the first pump current detection circuit and a second pump current detection signal by the second pump current detection circuit. Item 5. A control circuit unit for a gas sensor according to any one of Items 2 to 4. 6. The A / D converter according to claim 1, wherein
Based on the first pump current detection signal digitally converted by the conversion circuit, functions as oxygen concentration information generating means for generating oxygen concentration information in the measured gas, the detection signal of the first pump current and the same 6. The gas sensor control circuit unit according to claim 5, wherein the control circuit unit functions as a nitrogen oxide concentration information generating means for generating nitrogen oxide concentration information in the gas to be measured based on a detection signal of the second pump current. 7. A digital signal output from the microprocessor based on the oxygen concentration information, the nitrogen oxide concentration information, air-fuel ratio information generated based on the oxygen concentration information, and the oxygen concentration information. 7. The gas sensor control circuit unit according to claim 6, further comprising a D / A conversion circuit that converts a digital signal related to at least one of the generated excess oxygen rate information into an analog signal and outputs the analog signal as a corresponding analog signal. 8. A digital signal output by the microprocessor, based on the oxygen concentration information, the nitrogen oxide concentration information, air-fuel ratio information generated based on the oxygen concentration information, and the oxygen concentration information. A display device for displaying at least one of the oxygen concentration, the nitrogen oxide concentration, the air-fuel ratio, and the excess oxygen rate of the measured gas based on a digital signal related to at least one of the generated excess oxygen rate information is provided. The control circuit unit for a gas sensor according to claim 6 or 7, wherein: 9. The gas sensor to be connected is a temperature that detects a temperature of at least one of the first pump element, the oxygen concentration detection element, and a heating element that heats the second pump element. A microprocessor, wherein the microprocessor corrects a temperature based on information on a temperature detected by the temperature detector, the first pump current detection signal, and the second pump current detection signal. Each information of oxygen concentration and nitrogen oxide concentration
9. The gas sensor control circuit unit according to claim 4, wherein said control circuit unit functions as a detected component concentration information temperature correction means for generating detected component concentration information. 10. The oxygen concentration detecting element functions as the temperature detecting section that changes the internal resistance according to the element temperature, and an internal resistance measurement control circuit for measuring the internal resistance is provided. Item 10. A control circuit unit for a gas sensor according to item 9. 11. The heat generation control command means, which is implemented by the microprocessor, controls a temperature of the first pump element, the oxygen concentration detection element, and the second pump element based on a measurement result of the internal resistance. 11. The heat control circuit instructs the heat control circuit to control heat generation of the heating element so as to approach a predetermined temperature target value.
A control circuit unit for a gas sensor as described in the above. 12. The gas sensor according to claim 10, wherein the internal resistance measurement control circuit includes an internal resistance detection current supply circuit that supplies a constant internal resistance detection current to the oxygen concentration detection element. Control circuit unit. 13. The microprocessor according to claim 1, wherein a voltage (hereinafter referred to as a resistance detection voltage) applied to said oxygen concentration detecting element when said internal resistance detecting current is supplied is used as internal resistance information of said oxygen concentration detecting element. 13. The control circuit unit for a gas sensor according to claim 12, which functions as an internal resistance information detecting means for detecting. 14. The internal resistance measurement control circuit supplies the internal resistance detection current to the oxygen concentration detection element, measures the internal resistance, and then applies the internal resistance detection current to the oxygen concentration detection element. The control circuit unit for a gas sensor according to claim 12, further comprising a correction current supply circuit that supplies a correction current in a direction opposite to that of the control circuit. 15. A first processing chamber, which is partitioned from the surroundings and into which a gas to be measured is introduced via a first diffusion-controlling unit, A second processing chamber guided through the diffusion-controlling section, and an oxygen concentration detecting element configured of an oxygen ion-conductive solid electrolyte and having porous electrodes formed on both surfaces thereof, and measuring an oxygen concentration of gas in the first processing chamber. A first pump element for pumping oxygen from the first processing chamber, and a first pump element for pumping oxygen from the first processing chamber; and a porous electrode formed on both surfaces, the first pump element being formed of an oxygen ion conductive solid electrolyte. 15. A gas sensor comprising: a gas electrode; a second pump element for pumping oxygen from the second processing chamber; and a gas sensor control circuit unit according to claim 2 connected to the gas sensor. A gas sensor system comprising: 16. A characteristic representing a relationship between the value of the first pump current, the value of the second pump current, and the concentration of nitrogen oxides in the gas to be measured relates to a standard characteristic set in advance. A standard characteristic information storage unit storing information (hereinafter, referred to as standard characteristic information); a relationship between a value of the first pump current, a value of the second pump current, and a nitrogen oxide concentration in the gas to be measured. And a correction information storage unit that stores correction information for matching the previously measured characteristics of the gas sensor to the standard characteristics, wherein the nitrogen oxide concentration information realized by the microprocessor is provided. The generation unit detects each signal of the first pump current and the second pump current, corrects each detection value based on the correction information, and then uses the standard characteristic information to perform the measurement. Gas sensor system of claim 15, wherein which is configured to generate the information of the nitrogen oxide concentration in the gas.