WO2023188866A1 - NOx SENSOR - Google Patents

Abstract

A sensor (S) comprises: a sensor element (1) that has a first cell (1p) which outputs a first signal (Ip) correlated to an H2O concentration and a second cell (1s) which outputs a second signal (Is) in accordance with a NOx concentration and a H2O concentration; a heater (H); and a sensor control unit (10). The sensor control unit (10) has a NOx concentration reference value calculation unit (101) that calculates a NOx concentration reference value based on the second signal, a H2O concentration information detection unit (102) that detects H2O concentration information based on the first signal or external information, and a NOx concentration correction unit (103) that performs offset correction of the NOx concentration reference value. Offset correction information is based on the relation between the second signal and the H2O concentration information acquired at a predetermined reference environmental temperature. The reference environmental temperature is set to a steady temperature region of exhaust gas (G) in the environment in which the sensor element (1) is mounted.

Description

NOx sensor Cross-reference of related applications

This application is based on Patent Application No. 2022-052419 filed on March 28, 2022, and the contents thereof are incorporated herein.

The present disclosure relates to a NOx sensor for detecting NOx concentration in a gas to be measured.

NOx sensors for vehicles are equipped with a sensor element that uses a solid electrolyte body, and exhaust gas, which is the gas to be measured, is introduced into the sensor element, and the solid electrolyte body is dissolved due to the decomposition of nitrogen oxides (NOx). The NOx concentration is detected by measuring the current flowing through the sensor. Generally, a sensor element has a plurality of cells in which electrodes are formed on the surface of a solid electrolyte body, and for example, oxygen (O ₂ ) in the gas to be measured is pumped by a pump cell provided on the upstream side of the gas flow. After adjusting the oxygen concentration to a predetermined low oxygen concentration, a sensor cell provided on the downstream side detects NOx contained in the gas to be measured.

On the other hand, in the detection of NOx concentration, moisture (H ₂ O) contained in the gas to be measured may cause an error. As a countermeasure, Patent Document 1 describes a method of estimating the amount of moisture in exhaust gas from the excess air ratio or A/F value determined by the engine operating conditions, and correcting the gas concentration detection signal according to the estimated amount of moisture. is proposed. In addition, in a gas sensor that uses oxygen pumping, a second cell decomposes NOx by utilizing the correlation between the signal obtained from the first cell that pumps out oxygen and the oxygen concentration and water content in the exhaust gas. A method has been proposed for correcting the signal obtained from a map using a map or on an analog circuit.

Patent No. 3372186

The gas sensor of Patent Document 1 estimates the amount of moisture in exhaust gas or obtains a value corresponding to the amount of moisture from engine information or sensor information, and uses a correction amount corresponding to the amount of moisture to output NOx gas concentration detection output. is being corrected. The premise is that there is a linear relationship between the NOx gas concentration detection output and the NOx gas concentration, and if no correction is made based on moisture content, the offset will change although the sensitivity will not be affected. There is. However, it has been found that the offset based on the moisture content is not necessarily constant depending on the surrounding environment of the sensor, which varies depending on the mounting position and load conditions, and the sensor control state. This is presumed to be because the relationship between moisture content and offset is affected by the surrounding environmental temperature, and as the moisture content increases, the offset error increases, which may reduce the accuracy of NOx gas concentration correction. Ta.

An object of the present disclosure is to provide a NOx sensor that can improve the detection accuracy of NOx concentration by suppressing the influence of ambient environmental temperature and performing correction based on the amount of water contained in the gas to be measured with higher accuracy. It is.

One aspect of the present disclosure is
A sensor element that detects NOx contained in the gas to be measured, a heater that heats the sensor element, and controls the operation of the sensor element and the heater, and calculates the NOx concentration based on the signal from the sensor element. A NOx sensor comprising a sensor control section,
The above sensor element is
a gas chamber to be measured, into which the gas to be measured is introduced via a gas introduction part, and the chamber wall is a solid electrolyte body;
In the gas chamber to be measured, a first cell is disposed upstream of the gas flow to be introduced and outputs a first signal having a correlation with the H ₂ O concentration in the gas to be measured; and a second cell that is disposed on the downstream side and outputs a second signal according to the NOx concentration and H ₂ O concentration in the gas to be measured,
The above sensor control section is
a NOx concentration reference value calculation unit that calculates a NOx concentration reference value based on the second signal;
an H ₂ O concentration information detection unit that detects H 2 O concentration or H ₂ O concentration information including concentration information having a correlation with the _{H 2 O} concentration, based on the first signal or external information;
a NOx concentration correction unit that offset-corrects the NOx concentration reference value based on the H ₂ O concentration information;
The NOx concentration correction unit stores offset correction information of the second signal corresponding to the H ₂ O concentration information based on the output characteristics of the sensor element acquired at a predetermined reference environmental temperature. The reference environmental temperature is set in the NOx sensor in a steady temperature range of the gas to be measured in the environment in which the sensor element is mounted.

In the NOx sensor configured as described above, the sensor control section controls the operation of the sensor element and the heater, and calculates the NOx concentration based on the signal from the sensor element. When the second signal is input from the second cell, the NOx concentration reference value calculation section calculates the NOx concentration reference value based on a previously known relationship between the second signal and the NOx concentration. The H ₂ O concentration information detection section detects H ₂ O concentration information based on the first signal input from the first cell or external information of the sensor element. The NOx concentration correction section refers to offset correction information stored in advance, calculates an offset value corresponding to the detected H ₂ O concentration information, and corrects the NOx concentration reference value.

Here, the surrounding environment of the sensor element changes depending on the exhaust environment of the gas to be measured, and the amount of water contained in the gas to be measured also changes. At this time, the effect on the sensor output is small in areas where the amount of water is small or the temperature is low. However, for example, if the temperature at the mounting position of the sensor element changes significantly due to load conditions, etc., the sensor output will increase significantly in areas with high moisture content or high temperature, and the effect on sensor output cannot be ignored. Become. This is because even if the temperature of the sensor element is controlled by a heater, if the temperature of the second cell, which outputs the second signal, increases due to the influence of the high-temperature measured gas, the decomposition of water tends to proceed. It is assumed that this is because

Even in such a case, by using the offset correction information acquired in advance at the reference environmental temperature in the NOx concentration correction section, it becomes possible to perform correction that takes into account not only the H ₂ O concentration information but also the temperature characteristics. The reference environmental temperature at which the offset correction information is acquired is set to the steady temperature range of the gas to be measured that reflects the actual environment in which the sensor element _is mounted. A relationship between the concentration information and the second signal is obtained. By performing offset correction based on this relationship, variations in correction due to changes in moisture content and surrounding environmental temperature are alleviated, and under-correction or over-correction can be suppressed, making it possible to calculate NOx concentration with higher accuracy. .

As described above, according to the above aspect, there is provided a NOx sensor that can improve the detection accuracy of NOx concentration by suppressing the influence of the surrounding environment temperature and performing correction based on the amount of moisture contained in the gas to be measured with higher accuracy. can do.

The above objects and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing is
FIG. 1 is an overall schematic diagram showing the configuration of a NOx sensor in Embodiment 1, FIG. 2 is a longitudinal cross-sectional view and a cross-sectional view taken along line II of the sensor element, which is the main part of the NOx sensor, in Embodiment 1; FIG. 3 is a block diagram showing the main part configuration of the sensor control section of the NOx sensor in Embodiment 1, FIG. 4 is an overall configuration diagram and a partially enlarged sectional view showing the installation state of the NOx sensor in Embodiment 1, FIG. 5 is a diagram for explaining offset correction information in the first embodiment, and is a diagram showing the relationship between NOx output and H ₂ O concentration in a steady temperature range, FIG. 6 is a diagram showing the temperature characteristics of the NOx output of the sensor element in Embodiment 1, FIG. 7 is a diagram for explaining an offset correction method based on an offset correction value calculation map in the first embodiment, FIG. 8 is a diagram for explaining the NOx concentration calculation procedure of the NOx concentration calculation section of the sensor control section in the first embodiment, FIG. 9 is an engine map diagram showing the relationship between engine speed and torque obtained from a running test in Embodiment 1; FIG. 10 is a diagram comparing and showing NOx output before and after offset correction based on offset correction information in Embodiment 1, FIG. 11 is a diagram showing the relationship between NOx output error and H ₂ O concentration acquired by multiple sensor elements in Embodiment 1, FIG. 12 is a schematic configuration diagram of the main parts of the NOx sensor in Embodiment 2, FIG. 13 is a diagram showing the relationship between pump cell voltage variation and NOx output error in Embodiment 2, FIG. 14 is a schematic configuration diagram when the detection control section of the sensor control section includes a command voltage correction section in Embodiment 2, FIG. 15 is a schematic configuration diagram in the second embodiment when the detection control section of the sensor control section does not include the command voltage correction section.

(Embodiment 1)
Embodiment 1 of the NOx sensor will be described with reference to the drawings.
As shown in FIG. 1, the NOx sensor S of this embodiment includes a sensor element 1, a heater H that heats the sensor element 1, and a sensor control section 10. As shown in the overall view (right figure) of FIG. 4, the sensor main body 1A in which the sensor element 1 is housed is installed, for example, in the exhaust gas passage EX of an internal combustion engine such as a vehicle engine, and the sensor element 1 is used to Nitrogen oxides (ie, NOx) contained in exhaust gas G, which is a gas to be measured, is detected. The sensor control unit 10 is installed outside the exhaust gas passage EX, controls the detection operation by the sensor element 1 and the heating operation by the heater H, and calculates the NOx concentration based on the output from the sensor element 1.

As shown in FIGS. 1 and 2, the sensor element 1 is configured, for example, as a limiting current type sensor using a solid electrolyte body 11, and includes a pump cell 1p as a first cell and a sensor cell 1s as a second cell. It has . In the sensor element 1, a gas chamber 2 to be measured having a solid electrolyte body 11 as a chamber wall is formed inside one end side (for example, the lower end side in the right diagram of FIG. 4) that serves as a gas detection section. Exhaust gas G is introduced from the outside of the element 1 into the gas chamber 2 to be measured via the gas introduction section 3 . The sensor element 1 can also include a monitor cell 1m as a third cell arranged in parallel with the sensor cell 1s.

As shown in the left diagram of FIG. 4, the exhaust gas G is introduced into the gas chamber 2 to be measured from the gas introduction part 3 provided at the tip of the sensor element 1, with the longitudinal direction of the sensor element 1 being the gas flow direction X. In the gas chamber 2 to be measured, the pump cell 1p is arranged on the upstream side of the gas flow, and while adjusting the oxygen concentration in the exhaust gas G, generates a signal corresponding to the oxygen concentration in the exhaust gas G, which is correlated with the H ₂ O concentration. The first signal is configured to output a first signal having a first signal. The sensor cell 1s is arranged downstream of the pump cell 1p, and outputs a second signal corresponding to the NOx concentration and _H2O concentration in the exhaust gas G whose oxygen concentration has been adjusted. A reference gas chamber 4 is arranged on the opposite side of the gas chamber 2 to be measured with the solid electrolyte body 11 in between. A porous protective layer 5 is formed on the outer surface of the sensor element 1, covering the entire gas detection section.

As shown in FIG. 2, specifically, the pump cell 1p has a pump electrode 21, which is a first cell electrode, on the surface of the solid electrolyte body 11 facing the gas chamber 2 to be measured, and performs oxygen pumping. , adjust the oxygen concentration in the exhaust gas G to a predetermined low concentration. At this time, due to the catalytic action of the pump electrode 21, oxygen (i.e., O ₂ ) contained in the exhaust gas G is reduced to become oxide ions (i.e., O ^2- ), which are conducted inside the solid electrolyte body 11 . , is discharged to the reference gas chamber 4 side. At this time, the current Ip flowing through the pump cell 1p (hereinafter referred to as pump cell current) corresponds to the oxygen concentration in the exhaust gas G before adjustment (hereinafter referred to as O ₂ concentration as appropriate), and the H ₂ O concentration and It is output to the sensor control unit 10 as a first signal having a correlation.

The sensor cell 1s has a sensor electrode 22, which is a second cell electrode, on the surface of the solid electrolyte body 11 facing the gas chamber 2 to be measured, and detects NOx contained in the exhaust gas G whose O ₂ concentration has been adjusted. At this time, if the exhaust gas G contains H ₂ O, the catalytic action of the sensor electrode 22 decomposes NOx and H ₂ O, and oxide ions resulting from NOx and H ₂ O are decomposed. , conducts inside the solid electrolyte body 11 and is discharged to the reference gas chamber 4 side. At this time, the current Is flowing through the sensor cell 1s (hereinafter referred to as sensor cell current) corresponds to the NOx concentration and H ₂ O concentration in the exhaust gas G, and is outputted to the sensor control unit 10 as a second signal.

The NOx sensor S is used, for example, in a selective catalytic reduction (SCR) system for purifying NOx, detects the NOx concentration downstream of the catalyst, and directs the reducing agent to the upstream side of the catalyst. Used for supply amount control, etc. In that case, if NOx and moisture (that is, H ₂ O) are mixed in the exhaust gas G, the output from the sensor element 1 will be the output based on H ₂ O added to the original output based on NOx. . H ₂ O in the exhaust gas G is mainly caused by combustion of fuel in the engine, and has a correlation with O ₂ in the exhaust gas G. Therefore, it is possible to correct the NOx concentration by estimating the offset amount of NOx output using the H ₂ O concentration or O ₂ concentration, and furthermore, it is possible to correct the NOx concentration by taking into account the temperature characteristics of the output based on H ₂ O. By doing so, offset correction can be appropriately performed.

As shown in FIGS. 1 and 3, the sensor control section 10 is configured to be able to communicate with the sensor element 1 or an external device, and functionally includes a NOx concentration calculation section 100, a detection control section 200, and a heater. A control unit 300 is provided. The NOx concentration calculation unit 100 corrects an error in NOx output caused by H ₂ O (hereinafter referred to as NOx output error) based on the first signal, the second signal output from the sensor element 1, and external information. Then, calculate the NOx concentration. The detection control unit 200 controls the detection operation by the sensor element 1 to be performed appropriately, and the heater control unit 300 controls the heating by the heater H so that the sensor element 1 has a temperature suitable for detection. Control behavior. Details of the control by the detection control section 200 and the heater control section 300 will be described later.

The NOx concentration calculation section 100 includes a NOx concentration reference value calculation section 101, an H ₂ O concentration information detection section 102, and a NOx concentration correction section 103. The sensor cell current Is, which is a second signal, is input to the NOx concentration reference value calculation unit 101, and the NOx concentration reference value C1 is calculated based on the sensor cell current Is. The pump cell current Ip as a first signal or external information is input to the H ₂ O concentration information detection unit 102, and the H ₂ O concentration or a concentration having a correlation with the H ₂ O concentration is detected based on the pump cell current Ip or the external information. H ₂ O concentration information Ci containing information is detected. The NOx concentration correction unit 103 offset-corrects the NOx concentration reference value C1 calculated by the NOx concentration reference value calculation unit 101 using the H ₂ O concentration information Ci detected by the H ₂ O concentration information detection unit 102. Then, the value after offset correction is output as the calculated value of NOx concentration.

Specifically, the NOx concentration correction unit 103 stores offset correction information based on the relationship between the second signal and the H ₂ O concentration information Ci obtained at a predetermined reference environmental temperature. This reference environmental temperature is set to be in the steady temperature range of the exhaust gas G in the environment in which the sensor element 1 is mounted. The steady temperature range is the temperature range that the exhaust gas G that reaches the mounting position of the sensor element 1 can be in when the engine is in a steady operating state, and is based on the assumed operating state of the engine and the sensor in the engine and exhaust gas passage EX. It varies depending on the distance to the element 1, etc.

At this time, the offset correction information used for NOx concentration correction corresponds to the reference environmental temperature that is the steady temperature range of the exhaust gas G, and reflects the surrounding environmental temperature in the actual environment in which the NOx sensor S is installed. As a result, offset correction based on the detected H ₂ O concentration information Ci can be performed more appropriately, and NOx output errors in NOx detection can be reduced. The temperature characteristics of NOx output and offset correction will be explained next.

FIG. 5 shows the relationship between NOx output and H ₂ O concentration information Ci in a steady temperature range as an example. As shown on the horizontal axis of _the figure, there is a correlation between the H ₂ O concentration and the O ₂ concentration, which is the H ₂ O concentration information Ci. The lower the H 2 O concentration (eg, 0% to about 13%), the higher the H ₂ O concentration (eg, 0% to about 13%). Further, as shown on the vertical axis of the figure, for example, the NOx output known from the sensor cell current Is corresponds to the NOx concentration (unit: ppm). At this time, the NOx output includes an offset corresponding to the H ₂ O concentration or O ₂ concentration, and specifically, the higher the H ₂ O concentration or the lower the O ₂ concentration, the more the offset increases. The rate of increase increases. Therefore, even if NOx is not substantially included, the NOx output varies depending on the H ₂ O concentration or O ₂ concentration.

Furthermore, the relationship between the NOx output and the H ₂ O concentration information Ci has a temperature characteristic, and varies depending on the environmental temperature at the mounting position of the sensor element 1. Here, the temperature range in which the temperature of the exhaust gas G at the mounting position of the sensor element 1 reaches a stable running state after the engine starts is defined as the steady temperature range, and the NOx output characteristics in that range are compared. There is. At this time, the NOx output characteristics change greatly between the lower limit temperature T1 (eg, 300° C.) and the upper limit temperature T2 (eg, 700° C.) of the steady temperature range, and the higher the temperature, the more the offset increases. Although this difference in offset due to temperature characteristics is relatively small in a region where the H ₂ O concentration is low, it becomes a large difference as the H ₂ O concentration increases or the O ₂ concentration decreases.

As shown in FIG. 6, the NOx output gradually increases as the gas temperature of the exhaust gas G changes (for example, from 0° C. to 800° C.), and the higher the temperature, the higher the rate of increase in the offset becomes. Therefore, when performing offset correction using a fixed value according to the H ₂ O concentration, as in the past, based on characteristics obtained through general tests that do not take temperature characteristics into account, it is necessary to sufficiently reduce the NOx output error. There is a possibility that it will not be possible to reduce the Therefore, the NOx concentration correction section 103 selects optimal offset correction information from the offset characteristics of the NOx output shown in FIG. 5, for example, and performs correction based on the offset correction information.

In FIG. 5, it is assumed that the NOx concentration correction unit 103 has acquired offset correction information for correcting the NOx concentration reference value C1 in advance at a reference environmental temperature T0 in the steady temperature range of the exhaust gas G. The steady temperature range is a temperature range that the exhaust gas G reaching around the sensor element 1 can have when the engine is in a steady operating state, and indicates the range of the environmental temperature around the sensor element 1. The steady temperature range is determined by the type of engine, the mounting position of the gas sensor S in the exhaust gas pipe, and other conditions, and is determined appropriately depending on the state of each sensor element 1 or multiple sensor elements 1 of the same type used under the same conditions. A standard environmental temperature T0 can be determined.

Preferably, the reference environmental temperature T0 is set in a temperature range higher than the lower limit temperature T1 in the steady temperature range. For example, when the temperature of the exhaust gas G is defined as a steady temperature range of 300°C or more and 700°C or less, the reference environmental temperature T0 is set to be higher than the lower limit temperature T1 of 300°C. . Preferably, the reference environmental temperature T0 is set to be in a temperature range lower than 700° C., which is the upper limit temperature T2 in the steady temperature range. More preferably, the reference environmental temperature is set so that the offset characteristic in a low temperature range including the lower limit temperature T1 and the offset characteristic in a high temperature range including the upper limit temperature T2 become an intermediate temperature that exhibits an intermediate offset characteristic between them. It is desirable that T0 be set.

Specifically, a predetermined intermediate temperature range including an intermediate temperature (for example, 500°C) between the lower limit temperature T1 and upper limit temperature T2 of the steady temperature range is set as the reference temperature range, and the reference environmental temperature T0 is set within that range. I can do it. The reference environmental temperature T0 may be an intermediate temperature of 500° C., or may be a temperature exhibiting a more intermediate offset characteristic, and can be arbitrarily set. Preferably, an intermediate temperature range centered around 500°C, for example, a range from 400°C to 600°C, can be set as the reference temperature range, so that errors due to the mounting environment can be further reduced according to the offset characteristics. The reference environmental temperature T0 can be set as appropriate. In that case, the low temperature range is, for example, a range of 300°C or more and less than 400°C, and the high temperature range is, for example, a range of 600°C or more and less than 700°C.

Further, the steady temperature range is not limited to a temperature range of 300°C or more and 700°C or less, but can be set as appropriate depending on the mounting position of the sensor element 1, such as a temperature range lower than 300°C or higher than 700°C. It may include a temperature range. In that case, the ranges of the low temperature range, reference temperature range, and high temperature range are also changed as appropriate depending on the set steady temperature range.

In FIG. 3, the NOx concentration correction unit 103 includes an offset correction value calculation unit 103A, and can store a correction map or a correction formula based on the output characteristics at the reference environmental temperature T0 as offset correction information. The offset correction value calculation unit 103A uses the H ₂ O concentration information Ci detected by the H ₂ O concentration information detection unit 102. Calculate offset correction value C2. The NOx concentration correction unit 103 uses this offset correction value C2 to correct the NOx concentration reference value C1 and outputs it as the NOx concentration.

As shown in FIG. 7, by using the offset correction information acquired in this way, the influence of the surrounding environment temperature can be suppressed to a minimum. The middle diagram in FIG. 7 shows the result of correcting NOx output using a correction map based on offset correction information acquired in a reference temperature range (for example, reference environmental temperature: 500°C), and When the temperature is within the reference temperature range, almost no output error occurs. Further, even in a low temperature range or a high temperature range, when the H ₂ O concentration increases, the NOx output shifts to the plus side or the minus side, but the overall magnitude (absolute value) of the output error becomes relatively small. Therefore, as long as the H ₂ O concentration is in the normal range, stable NOx output can be obtained in a steady operating state even if the temperature approaches the lower limit temperature T1 or the upper limit temperature T2 of the steady temperature range.

On the other hand, as shown in the upper diagram of FIG. 7, when a correction map is used for NOx output based on offset correction information acquired in a low temperature range (for example, lower limit temperature T1: 300°C), On the high temperature side from the low temperature range, as the H ₂ O concentration increases, the NOx output shifts significantly to the positive side. On the other hand, as shown in the lower part of FIG. ₂ As the O concentration increases, the NOx output shifts significantly to the negative side. Therefore, if a correction map for a low temperature range is used, there will be insufficient correction, and if a correction map for a high temperature range is used, it will be overcorrected.

In this way, by setting the appropriate reference environmental temperature T0 and acquiring the offset correction information, the NOx concentration correction unit 103 can perform more appropriate correction. That is, the offset correction value calculation unit 103A obtains the offset correction value C2 that reflects the temperature characteristics based on the offset correction information and the H ₂ O concentration information Ci from the H ₂ O concentration information detection unit 102. , by offset-correcting the NOx concentration reference value C1 using this, it is possible to reduce the influence of the surrounding environment temperature on NO concentration detection.

Here, the H ₂ O concentration information Ci detected by the H ₂ O concentration information detection unit 102 includes the H ₂ O concentration or concentration information having a correlation with the H ₂ O concentration, for example, information on the O ₂ concentration. That's fine. Information on the O ₂ concentration can be acquired based on the pump cell current Ip input from the sensor element 1, and can be converted into the O ₂ concentration based on the relationship between the pump cell current Ip and the O ₂ concentration, which is known in advance. I can do it. Note that the information on the O ₂ concentration may be the pump cell current Ip input from the sensor element 1, or the air-fuel ratio (A/F), which has a certain relationship with the O ₂ concentration (%) in the exhaust gas G. , excess air ratio (λ=air-fuel ratio/stoichiometric air-fuel ratio), equivalence ratio (φ=1/λ), etc.

Further, the H ₂ O concentration information Ci is not limited to information based on internal information of the sensor element 1 such as the pump cell current Ip, but may be external information acquired outside the sensor element 1. The external information includes information such as engine operating information and mounting environment, and the H 2 O concentration may be calculated in the H ₂ O concentration information detection unit 102 based on this external information, or the H ₂ O concentration may be calculated based on this external information. The H ₂ O concentration or the estimated value of the O ₂ concentration estimated based on the above may be acquired as external information.

In the H ₂ O concentration information detection unit 102, external information is input to the sensor control unit 10 as, for example, information from a vehicle engine control unit (namely, an Engine Control Unit; hereinafter referred to as ECU), not shown. The sensor control unit 10 is configured as a sensor control unit that includes a communication unit, a microcomputer (hereinafter referred to as a microcomputer), various terminals connected to the sensor element 1 and the ECU, and receives internal information from the sensor element 1 or The NOx concentration is calculated in the NOx concentration calculating section 100 based on external information from the ECU.

Note that the ECU receives inputs such as intake air amount detected by an air flow meter (not shown), detection signals from an engine rotation speed sensor, an accelerator opening sensor, etc., and operates the engine E based on these input information. It knows the status and controls the entire vehicle.
Hereinafter, a configuration example of the NOx sensor S and details of control by the sensor control unit 10 will be described.

(Overall configuration of NOx sensor S)
In FIG. 4, in a sensor body 1A of a NOx sensor S, a sensor element 1 is inserted and held inside a cylindrical housing S1, and an outer peripheral threaded portion of the housing S1 is fixed to a passage wall EX1 of an exhaust gas passage EX. The sensor main body 1A is housed in an element cover S2 with the distal end of the sensor element 1 protruding into the exhaust gas passage EX, and housed in the element cover S2 with the proximal end of the sensor element 1 protruding outside the exhaust gas passage EX. It is accommodated in S3. The sensor control unit 10 is electrically connected to the sensor element 1 via a lead wire S4 drawn out to the base end side of the sensor main body 1A.

The element cover S2 has a double cylinder structure with a bottom surface, and a plurality of gas flow holes (not shown) are provided on the side and bottom surfaces of the outer cover and the inner cover. Thereby, the exhaust gas G flowing through the exhaust gas passage EX is taken into the inside of the element cover S2, and the tip side of the sensor element 1, which serves as the gas detection section, is exposed to the exhaust gas G, which is the gas to be measured. Further, a plurality of gas flow holes (not shown) are provided on the side surface of the cylindrical atmospheric cover S3. Thereby, the atmosphere A, which is the reference gas, is taken into the atmosphere cover S3 and can reach the base end side of the sensor element 1.

As shown in an enlarged view in FIG. 4, the exhaust gas G that has reached the distal end side of the sensor element 1 is taken into the gas chamber 2 to be measured from the gas introduction section 3 and moves toward the proximal end side. In the gas chamber 2 to be measured, a pump cell 1p is arranged on the upstream side in the gas flow direction X, and a sensor cell 1s and a monitor cell 1m are arranged on the downstream side. Detect NOx. Note that the current Im flowing through the monitor cell 1m (hereinafter referred to as monitor cell current) is output to the sensor control unit 10 as a third signal.

(Configuration of sensor element 1)
In FIG. 2, the sensor element 1 is a stacked element with a three-cell structure, and the stacking direction is a direction perpendicular to the gas flow direction X (that is, the vertical direction in FIG. 2). Electrolyte body 11 and heater insulating layer 61 are arranged in this order. A spacer layer 12 and a shielding layer 13 are arranged on one surface side of the solid electrolyte body 11 to form a space that will become the gas chamber 2 to be measured. Further, on the other surface side of the solid electrolyte body 11, a space serving as the reference gas chamber 4 is formed between the solid electrolyte body 11 and the heater insulating layer 61 constituting the heater H.

The gas chamber 2 to be measured is connected to the inside of the element cover S2 (see, for example, FIG. 4) where the exhaust gas G exists via the diffusion resistance layer 31 embedded in the front end surface (i.e., the left end surface in FIG. 2) of the spacer layer 12. It communicates with the space of The diffusion resistance layer 31, together with a part of the porous protective layer 5 arranged on the outside thereof, constitutes a gas introduction section 3 into the gas chamber 2 to be measured, so that the exhaust gas G is introduced under a predetermined diffusion resistance. has been adjusted to. The porous protective layer 5 is formed to cover the entire surface of the tip side of the sensor element 1, which is the gas detection section, and protects the sensor element 1 from poisonous substances and the like.

The gas detection section of the sensor element 1 is provided with a pump cell 1p, a sensor cell 1s, and a monitor cell 1m, and each cell has a pair of electrodes facing each other with a solid electrolyte body 11 in between. In the gas chamber 2 to be measured, the pump electrode 21 of the pump cell 1p is arranged on the surface of the solid electrolyte body 11 on the upstream side in the gas flow direction X, and the sensor electrode 22 of the sensor cell 1s and the monitor cell 1m are arranged on the downstream side thereof. A monitor electrode 23 is arranged. In the reference gas chamber 4, a reference electrode 41 serving as a common electrode is provided on the surface of the solid electrolyte body 11 at a position facing these electrodes 21, 22, and 23.

The reference gas chamber 4 in which the common reference electrode 41 is arranged extends to the base end side (for example, the right end side in FIG. 2) of the sensor element 1, and through a reference gas inlet opening at an end surface (not shown), It communicates with the space within the atmosphere cover S3 (see, for example, FIG. 4) where the atmosphere A exists. A heating element 62 that generates heat when energized is buried inside a heater insulating layer 61 that forms the bottom wall of the reference gas chamber 4, and constitutes a heater H. The heating element 62 is disposed corresponding to the portion where the electrodes of the pump cell 1p, the sensor cell 1s, and the monitor cell 1m are formed, and is capable of heating the entire tip side of the element, which becomes the gas detection section.

As a result, one electrode 21, 22, 23 of each cell is exposed to the exhaust gas G introduced into the gas chamber 2 to be measured, and the other electrode 41 is exposed to the exhaust gas G introduced into the reference gas chamber 4. exposed to atmosphere A. At this time, by applying a voltage between a pair of electrodes in each cell, oxygen contained in the exhaust gas G is pumped out to the reference gas chamber 4 side via the solid electrolyte body 11 having oxide ion conductivity or the reference gas Oxygen pumping from the chamber 4 side becomes possible. Further, by operating the heater H, each cell is heated to a temperature higher than the temperature at which it becomes active, and oxygen pumping can be performed stably.

In the gas chamber 2 to be measured, the pump electrode 21 of the pump cell 1p is formed on the upstream side in the gas flow direction X with a large area. When the exhaust gas G that has passed through the diffusion resistance layer 31 comes into contact with the pump electrode 21, oxygen is decomposed by its catalytic action and is discharged to the reference electrode 41 side. The exhaust gas G adjusted to have a low oxygen concentration by the pump cell 1p reaches the sensor electrode 22 and monitor electrode 23 on the downstream side, and at the sensor electrode 22, oxygen caused by NOx is discharged together with residual oxygen by oxygen pumping. Further, residual oxygen at the monitor electrode 23 is exhausted by oxygen pumping.

The sensor electrode 22 and the monitor electrode 23 are arranged in parallel at the same position in the gas flow direction X, and are formed in the same shape with a smaller area than the pump electrode 21. As a result, the sensor electrode 22 and the monitor electrode 23 have the same conditions with respect to the flow of exhaust gas G, and by comparing the outputs of the sensor cell 1s and the monitor cell 1m, it is possible to remove the influence of residual oxygen contained in the NOx output. .

The solid electrolyte body 11 is composed of a zirconia-based solid electrolyte material having oxide ion conductivity. As the zirconia-based solid electrolyte material, for example, partially stabilized zirconia or stabilized zirconia containing a stabilizer such as yttria can be used. Further, the diffusion resistance layer 31 and the porous protective layer 5 are made of a ceramic material such as alumina, for example. The heater insulating layer 61, the shielding layer 13, and the spacer layer 12 can be constructed using an insulating ceramic material such as alumina.

The electrodes of the pump cell 1p, the sensor cell 1s, and the monitor cell 1m can be porous cermet electrodes containing a noble metal or noble metal alloy material and a zirconia-based solid electrolyte. The sensor electrode 22 of the sensor cell 1s is constructed using an electrode material that has decomposition activity for NOx to be detected. As such an electrode, for example, an electrode containing platinum and rhodium (hereinafter appropriately referred to as a Pt-Rh electrode) can be used.

The pump electrode 21 of the pump cell 1p is constructed using an electrode material that has oxygen decomposition activity and does not have NOx decomposition activity. As such an electrode, for example, an electrode containing platinum and gold (hereinafter appropriately referred to as a Pt-Au electrode) can be used. The monitor electrode 23 of the monitor cell 1m is also constructed using the same electrode material as the pump electrode 21. Further, the reference electrode 41 can be configured as, for example, an electrode containing platinum (hereinafter, appropriately referred to as a Pt electrode).

As a result, NOx in the exhaust gas G is adjusted to a predetermined low oxygen concentration in the pump cell 1p by heating the sensor element 1 to a predetermined temperature by the heater H and applying a predetermined voltage between the electrodes of each cell. can be detected by the sensor cell 1s. Furthermore, by utilizing the difference in gas adsorption between the Pt-Rh electrode used for the sensor electrode 22 and the Pt-Au electrode used for the monitor electrode 23, the difference value between the currents output from the sensor cell 1s and the monitor cell 1m is calculated. By setting the output to NOx, the influence of oxygen remaining in the exhaust gas G can be canceled.

However, since Rh contained in the Pt-Rh electrode constituting the sensor electrode 22 has decomposition activity against H ₂ O in addition to NOx and O ₂ , H If ₂ O is included, an output error will occur due to these decompositions. This output error is corrected by the NOx concentration calculation unit 100 of the sensor control unit 10 using offset correction information acquired in advance. Control of each section and output correction by the sensor control section 10 will be described next.

(Configuration of sensor control unit 10)
In FIG. 1, the sensor control unit 10 includes a current detection unit 10A that detects the output current from each cell of the sensor element 1, a pump cell current Ip, a sensor cell current Is, and a monitor cell current Im detected by the current detection unit 10A. and a NOx concentration calculation unit 100 that calculates the NOx concentration based on the NOx concentration. The sensor control unit 10 also includes a detection control unit 200 that controls NOx detection by the sensor element 1, and a heater control unit 300 that controls heating of the sensor element 1 by the heater H.

Each cell of the sensor element 1 is connected to the sensor control unit 10 via a detection terminal P- and a detection terminal S-, M-, and both ends of the heating element 62 of the heater H are connected to a pair of heater terminals H+, H-. It is connected to the. The sensor control unit 10 is connected to an ECU (not shown) via a pair of communication terminals CAN+ and CAN-, and is capable of receiving commands from the ECU, performing NOx detection processing, and outputting the detection results. There is. Further, the sensor control unit 10 is connected to a vehicle battery and ground (not shown) via a power supply terminal VB and a ground terminal GND, respectively, and is connected to various circuits of the sensor control unit 10, a heater H of the sensor element 1, etc. power supply is possible.

The NOx concentration calculation unit 100 is composed of a microcomputer or the like having a storage unit and a calculation unit, and executes a pre-stored program using internal information of the sensor element 1 input from the current detection unit 10A. A predetermined calculation is performed to calculate the NOx concentration. The current detection unit 10A is connected to the pump electrode 21 of the pump cell 1p via the detection terminal P-, and is connected to the sensor electrode 22 of the sensor cell 1s and the monitor electrode 23 of the monitor cell 1m via detection terminals S- and M-. It is connected to the. The current detection unit 10A includes, for example, a detection circuit using a resistor for current detection, and is configured to be able to detect the output current of each cell from the potential difference between both ends of the resistor. The detected output current is converted into a digital signal in an analog/digital conversion circuit and input to each part of the NOx concentration calculation section 100.

The detection control unit 200 controls the detection operations of the pump cell 1p, the monitor cell 1m, and the sensor cell 1s, respectively. The detection control unit 200 includes, for example, a voltage application circuit for applying a voltage between a pair of electrodes of each cell, generates a predetermined voltage signal based on a control command, and generates a predetermined voltage signal via a common terminal COM+. It can be applied to the common reference electrode 41 side. The applied voltage is adjusted within a range in which the current flowing through each cell exhibits a limiting current characteristic so that the O ₂ concentration in the gas chamber 2 to be measured becomes a predetermined low concentration by, for example, oxygen pumping in the pump cell 1p.

The heater control unit 300 controls energization of the heater H built into the sensor element 1. The heater control unit 300 includes, for example, a switch circuit connected to a power supply terminal VB, and the switch circuit is turned on and off based on a control command, thereby supplying power to the heater H via the heater terminals H+ and H-. The power supply can be controlled. Thereby, each cell of the sensor element 1 heated by the heater H is maintained at a temperature suitable for NOx detection.

In FIG. 3, the NOx concentration calculation unit 100 calculates the NOx concentration reference value C1 (unit: ppm) based on the sensor cell current Is and monitor cell current Im detected by the current detection unit 10A in the NOx concentration reference value calculation unit 101. Calculate. Specifically, as shown in the upper diagram of FIG. 8, the relationship between the difference value [Is-Im] (unit: nA) between the sensor cell current Is and the monitor cell current Im and the corresponding NOx concentration reference value C1 is , it is possible to calculate the NOx concentration reference value C1 based on the outputs from the sensor cell 1s and the monitor cell 1m by mapping and storing the map in advance. At this time, the NOx concentration reference value C1 increases in accordance with the output of the sensor cell 1s, and includes the influence of H ₂ O when present.

The H ₂ O concentration information detection unit 102 detects the O ₂ concentration that becomes the H ₂ O concentration information Ci based on the input pump cell current Ip (unit: mA). Specifically, as shown in the middle diagram of FIG. 8, the relationship between pump cell current Ip and O ₂ concentration is mapped and stored in advance, and based on the detected value of pump cell current Ip, H It is possible to calculate the O ₂ concentration (unit: %) that has a correlation with the ₂ O concentration. As mentioned above, since the relationship between the H ₂ O concentration and O ₂ concentration in the exhaust gas G due to combustion etc. is known, the calculated O ₂ concentration can be used as the H ₂ O concentration information Ci. . At this time, as the pump cell current Ip increases, the O ₂ concentration increases while the H ₂ O concentration decreases.

The NOx concentration correction unit 103 corrects the NOx concentration reference value C1 input from the NOx concentration reference value calculation unit 101 using the offset correction value C2 calculated by the offset correction value calculation unit 103A. Specifically, as shown in the lower diagram of FIG. 8, the relationship between the O ₂ concentration as H ₂ O concentration information Ci and the offset correction value C2 is obtained as offset correction information at a predetermined reference environmental temperature T0. , can be stored as an offset correction map. Based on this map, an offset correction value C2 corresponding to the detected O ₂ concentration is calculated and subtracted from the NOx concentration reference value C1, thereby making it possible to calculate the offset-corrected NOx concentration.

A test to obtain offset correction information can be performed, for example, using a model gas bench and evaluated by varying the H ₂ O concentration in the model gas within a predetermined range (for example, 0% to about 13%). can. Specifically, a model gas simulating exhaust gas was supplied from the gas supply unit at a predetermined flow rate to the gas passage where the gas sensor S was installed, and the H ₂ O concentration was changed at a predetermined reference environmental temperature T0. The offset characteristics were evaluated based on the NOx output of the sensor element 1 at that time. The reference environmental temperature T0 is set from the gas temperature range that reaches the mounting position of the sensor element 1 during steady operation in the actual vehicle environment. The temperature was adjusted to T0.

FIG. 9 is an engine map showing the results of a driving test in an actual vehicle environment, and shows the engine speed and torque in certified driving patterns (WLTC mode, RDE mode) stipulated by law, and the surrounding environment at the mounting position of sensor element 1. It shows the relationship between temperature. The gas temperature range obtained from this result (for example, 300° C. to 700° C.) was defined as a steady temperature range, and its center value (for example, 500° C.) was defined as the reference environmental temperature T0.

FIG. 10 shows the offset characteristic (before correction) obtained in this way and the NOx output after correction based on the offset correction information obtained from this characteristic line. The offset correction information may be a correction map, but it can also be expressed as a correction equation that approximates the relationship between the NOx output and O ₂ concentration before correction using a linear equation ₍ y=Ax+b), and By calculating the offset correction value C2 and subtracting it from the NOx concentration reference value C1, the corrected NOx concentration can be calculated. In the NOx output after such correction, NO output errors due to changes in the O ₂ concentration or H ₂ O concentration are reduced, allowing highly accurate NOx detection.

Note that the offset correction information may be information based on output characteristics acquired individually for the sensor elements 1, or may be information obtained by averaging a plurality of output characteristics acquired for a plurality of sensor elements 1. good. Specifically, the offset correction information can be acquired for each NOx sensor S, for example, at the time of product production, taking into consideration the mounting environment of each NOx sensor, applied vehicle information, etc. In this way, by acquiring the characteristics for each product individually, it is possible to perform correction based on appropriate offset correction information.

Alternatively, common offset correction information may be acquired for a plurality of NOx sensors S of the same type at the time of design, etc., and applied to all of the NOx sensors S of the same type. In that case, as shown in FIG. 11, for example, the H ₂ O Obtain characteristic data of NOx output error with respect to concentration. By calculating an average value from these data, even when offset correction information is shared, offset correction can be performed based on more average characteristics.

As described above, according to the present embodiment, in the sensor control unit 10 of the NOx sensor S, the NOx concentration calculation unit 100 includes the NOx concentration correction unit 103, and uses offset correction information that takes temperature characteristics into consideration. The NOx concentration can be calculated by appropriately correcting the NOx output error caused by moisture.

(Embodiment 2)
A second embodiment of the NOx sensor will be described based on the drawings. In this embodiment, an example of a specific procedure for the detection control performed by the detection control section 200 by the sensor control section 10 described above will be described. As shown in FIG. 12, the detection control unit 200 includes a voltage application circuit 201 and a voltage application instruction unit 202, and controls the pump cell voltage Vp applied to the pump cell 1p for oxygen pumping. In the NOx sensor S of this embodiment, the basic configuration of the sensor element 1 and the basic control of the sensor control unit 10 are the same as those in the first embodiment, and the differences will be mainly described below.
Note that among the symbols used in the second embodiment and subsequent embodiments, the same symbols as those used in the previously described embodiments represent the same components as those in the previously described embodiments, unless otherwise specified.

In FIG. 12, the sensor control unit 10 causes the detection control unit 200 to apply a predetermined pump cell voltage Vp between the pump electrode 21 and the reference electrode 41 of the pump cell 1p, and also causes the heater control unit 300 (not shown, for example, 1) controls the power supply to the heater H so that the pump cell 1p reaches a predetermined temperature. Based on the instruction voltage V0 from the voltage application instruction section 202, the detection control section 200 generates a voltage signal corresponding to the instruction voltage V0 in the voltage application circuit 201, and applies it to the reference electrode 41 side of the pump cell 1p. The same voltage is also applied to the sensor cell 1s and the monitor cell 1m. As a result, in the exhaust gas G introduced into the gas chamber 2 to be measured, oxide ions generated by reductive decomposition of oxygen at the pump electrode 21 move toward the reference electrode 41 side, so that a pump cell current Ip flows. NOx and H ₂ O in the exhaust gas G move on the pump electrode 21 and head toward the downstream side.

Here, for example, when the actual voltage applied to the pump cell 1p becomes larger than the command voltage V0 to the voltage application circuit 201, the catalytic reaction at the pump electrode 21 is further activated, and H ₂ in the exhaust gas G is Some of the O is decomposed. At this time, it is considered that as the applied voltage increases, the amount of H ₂ O that reaches the sensor cell 1s decreases. These reactions cause variations in the sensor cell current Is and the monitor cell current Im, and there is a possibility that the NOx output based on the sensor cell current Is and the monitor cell current Im may vary. Moreover, when detecting H ₂ O concentration information Ci based on the pump cell current Ip, it also affects the calculation of the offset correction value C2.

On the other hand, even when the detection control unit 200 controls the voltage application circuit 201 to output a predetermined instruction voltage V0, the product itself has a predetermined variation (for example, about ±20 mV at 20° C.). The actual applied voltage may vary with respect to the command voltage V0. Therefore, when comparing multiple NOx sensors S, as shown in _FIG . When offset correction based on values is standardized, it is difficult to ensure correction accuracy.

Therefore, as shown in FIG. 14, an instruction voltage correction section 203 is provided in the voltage application instruction section 202 of the detection control section 200, and outputs a corrected instruction voltage V2 obtained by correcting the instruction voltage V0 to the voltage application instruction section 202. . Specifically, the command voltage correction unit 203 uses a voltage detection unit 203a that detects the actual voltage V1 actually applied to each cell from the voltage application command unit 202, and a difference value between the actual voltage V1 and the command voltage V0. A correction value calculation unit 203b that calculates and outputs it as a correction value V1-V0 is provided. The command voltage V0 from the voltage application command section 202 is outputted to the voltage application circuit 201 as a corrected corrected command voltage V2 by subtracting the correction value V1-V0 in the command voltage correction section 203.

FIG. 15 shows a configuration that does not include the command voltage correction section 203, and the voltage application circuit 201 of the detection control section 200 changes the voltage applied to each cell of the sensor element 1 to the command voltage V0 from the voltage application instruction section 202. It is configured so that it can be generated according to the requirements. For example, the voltage application instruction unit 202 outputs a pulse signal corresponding to a preset instruction voltage V0 so that the oxygen pumping operation in the pump cell 1p is appropriate, and the voltage application circuit 201 outputs a pulse signal corresponding to the pulse signal. Voltage is output. As a result, a predetermined voltage is applied to each cell via the common terminal COM+ of the sensor control unit 10 shown in FIG. 1 described above. In this configuration, if the actual voltage V1 output from the voltage application circuit 201 varies with respect to the command voltage V0, as described above, there is a risk that the NOx output error due to the increase in voltage will increase.

On the other hand, when the instruction voltage correction section 203 is provided, a correction instruction voltage V2 expressed by the following equation is applied.
Correction instruction voltage V2 = instruction voltage V0 - correction value [actual voltage V1 - instruction voltage V0]
By outputting the corrected instruction voltage V2 corrected in this way to the voltage application circuit 201, the actual applied voltage becomes the original instruction voltage V0. Then, the decomposition reaction of H ₂ O in the pump cell 1p is suppressed, and variations in the sensor cell current Is and the monitor cell current Im are suppressed, thereby making it possible to reduce the NOx output error.

Note that the command voltage V0 to the pump cell 1p can be arbitrarily set so that it can be adjusted to a desired low oxygen concentration by oxygen pumping and the decomposition reaction of H ₂ O in the pump cell 1p can be suppressed. Preferably, by setting the instruction voltage V0 without variations between individual voltage application circuits 201, the effect of suppressing variations in the decomposition reaction of H ₂ O is increased, and output errors due to variations in applied voltage, etc. Can be suppressed.

The present disclosure is not limited to the embodiments described above, and can be applied to various embodiments without departing from the spirit thereof. For example, the NOx sensor S can be applied to NOx detection using not only exhaust gas G from a vehicle engine but also gases discharged from various internal combustion engines as the gas to be measured. Further, the structure of each part of the sensor element 1 of the NOx sensor S, the control procedure of each part in the sensor control section 10, etc. can be changed as appropriate.

Although the present disclosure has been described based on the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also includes various modifications and equivalent modifications. In addition, various combinations and configurations, as well as other combinations and configurations that include only one, more, or fewer elements, are within the scope and scope of the present disclosure.

Claims (8)

1. A sensor element (1) that detects NOx contained in the gas to be measured (G), a heater (H) that heats the sensor element, and controls the operation of the sensor element and the heater, and A NOx sensor (S) comprising a sensor control unit (10) that calculates a NOx concentration based on a signal,
   The above sensor element is
   A gas to be measured chamber (2) into which the gas to be measured is introduced via a gas introduction part (3) and has a solid electrolyte body (11) as a chamber wall;
   A first cell (1p) that is arranged in the upstream side of the gas flow to be introduced in the measurement gas chamber and outputs a first signal (Ip) that has a correlation with the H ₂ O concentration in the measurement gas; , a second cell (1s) that is disposed downstream of the first cell and outputs a second signal (Is) according to the NOx concentration and H ₂ O concentration in the gas to be measured. Ori,
   The above sensor control section is
   a NOx concentration reference value calculation unit (101) that calculates a NOx concentration reference value (C1) based on the second signal;
   an H ₂ O concentration information detection unit (102) that detects H 2 O concentration or H ₂ O concentration information (Ci _{) including concentration information having a correlation with the H 2 O} concentration, based on the first signal or external information; ,
   a NOx concentration correction unit (103) that offsets and corrects the NOx concentration reference value based on the H ₂ O concentration information;
   The NOx concentration correction unit calculates offset correction information of the second signal corresponding to the H ₂ O concentration information based on the output characteristics of the sensor element acquired at a predetermined reference environmental temperature (T0). The NOx sensor stores the reference environmental temperature in a steady temperature range of the gas to be measured in an environment in which the sensor element is mounted.
2. The sensor element is installed in an exhaust gas passage (EX) of the internal combustion engine through which the gas to be measured is discharged, and the steady temperature range is determined when the sensor element is installed when the internal combustion engine is in a steady operating state. The NOx sensor according to claim 1, wherein the temperature range of the gas to be measured that reaches the position is within a possible temperature range.
3. The NOx sensor according to claim 1 or 2, wherein the reference environmental temperature is set in a temperature range higher than the lower limit temperature of the steady temperature range.
4. The above reference environmental temperature is based on the output characteristics obtained by the sensor element in a low temperature range including the lower limit temperature of the above steady temperature range, and the output characteristic obtained by the above sensor element in a high temperature range including the upper limit temperature of the above steady temperature range. The NOx sensor according to any one of claims 1 to 3, wherein the NOx sensor is set to a reference temperature range exhibiting an intermediate output characteristic.
5. The NOx sensor according to any one of claims 1 to 4, wherein the reference environmental temperature is set in a range of 300°C or more and 700°C or less.
6. The NOx sensor according to any one of claims 1 to 4, wherein the offset correction information is information based on output characteristics individually acquired for the sensor element.
7. The NOx sensor according to any one of claims 1 to 4, wherein the offset correction information is information obtained by averaging a plurality of output characteristics obtained for a plurality of the sensor elements.
8. The sensor control unit includes a detection control unit (200) that controls voltages applied to the first cell and the second cell,
   The detection control section includes a voltage application circuit (201) that generates a voltage according to an instruction voltage (V0) input from a voltage application instruction section (202), and an instruction voltage correction section (203), and includes an instruction voltage correction section (203). The voltage correction section includes a voltage detection section (203a) that detects the actual voltage (V1) generated by the voltage application circuit, and corrects the indicated voltage based on a difference value between the indicated voltage and the actual voltage. The NOx sensor according to any one of claims 1 to 7, further comprising a correction value calculation unit (203b) that performs the correction value calculation section (203b).

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