JP2009192289A - Gas concentration detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improving detection accuracy of gas concentration in a gas concentration detection device. <P>SOLUTION: A gas sensor equipped with a sensor element 20 having a pump cell 41, a monitor cell 44 and a sensor cell 45, adjusts an oxygen amount in detection gas introduced into the first chamber 24 by the pump cell 41 to a prescribed concentration level, detects the concentration of a specific component from gas after adjusting the oxygen amount by the pump cell 41 in the second chamber 26 by the sensor cell 45, and calculates the concentration of the specific component by the detection result. A microcomputer 51 in a sensor control device 50 acquires wall temperature information on the temperature of a gas passage wall on which the gas sensor is mounted, and corrects a cell output or cell application voltage of at least some of the pump cell 41, the monitor cell 44 and the sensor cell 45 based on the acquired wall temperature information. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas concentration detection device, and in particular, an oxygen pump cell that adjusts the amount of oxygen in a gas chamber (chamber) to a predetermined concentration level, and a concentration of a specific component (for example, nitrogen oxide ( The present invention relates to a gas concentration detection apparatus applied to a gas sensor having a sensor cell for detecting NOx) concentration).

  2. Description of the Related Art Conventionally, for example, a limit current type NOx sensor that detects nitrogen oxide (NOx) in exhaust of an in-vehicle engine is known. This NOx sensor has a two-cell structure including a pump cell and a sensor cell, or a three-cell structure including a pump cell, a sensor cell, and a monitor cell. Among these cells, the pump cell discharges or pumps oxygen in the exhaust gas introduced into the gas chamber, and the sensor cell detects the NOx concentration from the gas that has passed through the pump cell. In the monitor cell, the amount of excess oxygen in the gas chamber is detected.

Furthermore, the NOx sensor is provided with a heater for maintaining each of the above cells at a predetermined activation temperature. In this case, the resistance value (element impedance) of the solid electrolyte element provided with each cell is detected, and the energization of the heater is controlled so that the element impedance becomes a value corresponding to the activation temperature. More specifically, the element impedance is detected for either the pump cell or the monitor cell, and the heater energization is feedback controlled in accordance with the deviation between the detected value of the element impedance and the target value (see, for example, Patent Document 1).
JP 2000-171439 A

  When the NOx sensor is attached to the exhaust pipe of the engine, in the sensor element, heat release (heat shrinkage) to the exhaust pipe occurs at the sensor attachment portion of the element. In that case, a temperature gradient is generated between the distal end side of the sensor element and the proximal end side (exhaust pipe attachment site side), and the proximal end side is lower in temperature than the distal end side of the sensor element. It is possible. In addition, the temperature gradient may vary depending on the temperature change of the exhaust pipe temperature when the exhaust pipe temperature rises as the engine starts. Therefore, in the configuration in which the heater energization control is performed based on the element impedance of one cell as in Patent Document 1, the cell temperature varies with the change in the temperature gradient of the sensor element in the cell where the temperature is not controlled. May occur.

  On the other hand, the output characteristic of the sensor element has a temperature characteristic. For this reason, if the cell temperature varies, an error may occur in the sensor output, and the gas concentration detection accuracy may decrease. In particular, when the distance from the exhaust pipe is different in each cell, the degree of influence of fluctuations in the exhaust pipe temperature is different between the cells, and thus the above problem is likely to occur.

  The present invention has been made to solve the above-described problems, and has as its main object to provide a gas concentration detection device that can improve the detection accuracy of the gas concentration.

  The present invention employs the following means in order to solve the above problems.

  The gas concentration detection device of the present invention comprises a sensor element having a first cell and a second cell each comprising a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, After adjusting the amount of oxygen in the gas to be detected introduced into the gas chamber to a predetermined concentration level by applying a voltage to the electrode and after adjusting the amount of oxygen by the first cell by applying a voltage to the electrode of the second cell In a gas concentration detection device that is applied to a gas sensor that generates a second cell output according to a specific component in the gas and calculates the concentration of the specific component based on the second cell output, a gas passage wall to which the gas sensor is attached Based on the wall temperature information acquired by the wall temperature information acquisition means for acquiring the wall temperature information related to the temperature of the wall temperature information acquired by the wall temperature information acquisition means, at least of the first cell and the second cell And correcting means for correcting the cell output or cell applied voltage Zureka, it characterized in that it comprises a.

  In the gas sensor, the first cell and the second cell of the sensor element have temperature characteristics as their output characteristics. Further, heat is released to the gas passage wall at the attachment site of the gas sensor. In this case, when the temperature of the gas passage wall changes, the amount of heat released to the gas passage wall changes, and as a result, in each cell, the output value is affected according to the distance between each cell and the gas passage wall. . That is, in the sensor element, at least one of the cells has its temperature deviated from an appropriate temperature, resulting in an error in sensor output. In view of these points, in the present invention, wall temperature information related to the temperature of the gas passage wall at the attachment site of the gas sensor is acquired, and the cell output or the cell applied voltage is corrected according to the wall temperature information. As a result, even if there is a change in the temperature of the gas passage wall at the location where the gas sensor is attached, the cell output or cell applied voltage is corrected in consideration of the change in temperature of the exhaust pipe. The sensor output error accompanying this can be eliminated, and consequently the gas concentration detection accuracy can be improved.

  When the heater energization control is performed so that one cell is controlled and the cell temperature is kept constant, in the other cell where the temperature control is not performed, the change in the cell temperature due to the temperature change in the gas passage wall occurs. This causes a temperature deviation from the appropriate temperature. In this case, there is a concern that an output error may occur in the cell that is not temperature-controlled. In view of this point, in the invention according to claim 2, the cell output or the cell applied voltage that is not the target of the temperature control by the heater control unit is corrected based on the wall temperature information. By doing so, it is possible to eliminate a sensor output error caused by a temperature shift of a cell not subjected to temperature control.

  When temperature control is performed for the first cell of the first cell and the second cell, the residual oxygen concentration in the gas chamber is maintained at a desired oxygen concentration level. On the other hand, in the second cell, since the second cell is not subject to temperature control, a temperature deviation occurs due to a temperature fluctuation of the gas passage wall, and an output error corresponding to the temperature deviation occurs. Conceivable. In view of this point, in the invention according to claim 3, when the energization of the heater is controlled with the first cell as a control target, the cell output of the second cell is corrected based on the temperature of the gas passage wall. . By doing so, the output error due to the temperature shift of the second cell can be eliminated by the correction based on the temperature of the gas passage wall, and the concentration detection accuracy by the second cell can be improved.

  When the temperature control is performed for the second cell of the first cell and the second cell, the residual oxygen concentration in the gas chamber is shifted due to the temperature change of the gas passage wall, which is caused by the shift in the residual oxygen concentration. An error occurs in the second cell output. In view of this point, in the invention according to claim 4, when the energization of the heater is controlled with the second cell as a control target, the cell applied voltage of the first cell is corrected based on the temperature of the gas passage wall. To do. Thereby, the shift | offset | difference of the residual oxygen concentration in a gas chamber is suppressed, and the output error of a 2nd cell is eliminated by extension. As a result, the density detection accuracy by the second cell can be increased.

  When the temperature control is performed for the second cell of the first cell and the second cell, the residual oxygen concentration in the gas chamber is shifted due to the temperature change of the gas passage wall, which is caused by the shift in the residual oxygen concentration. An error occurs in the second cell output. In view of this point, in the invention according to claim 5, when the energization of the heater is controlled with the second cell as a control target, the cell output of the second cell is corrected based on the temperature of the gas passage wall. . Thereby, the output error of the second cell due to the deviation of the residual oxygen concentration can be eliminated by correction based on the temperature of the gas passage wall. As a result, the density detection accuracy by the second cell can be increased.

  In a gas sensor that is provided in an exhaust pipe of an internal combustion engine and detects the concentration (NOx concentration, etc.) of a specific component in the exhaust gas, the sensor element of the gas sensor is attached to the exhaust pipe so as to protrude into the center of the exhaust pipe. Further, in the configuration in which the sensor element is provided with the first cell and the second cell at different positions on the tip side and the exhaust pipe attachment side of the sensor element, based on the temperature of the exhaust pipe wall of the internal combustion engine The cell output or the cell applied voltage may be corrected. In particular, when the first cell and the second cell are arranged at different positions from the exhaust pipe attachment site (for example, the first cell is on the tip side of the sensor element and the second cell is on the exhaust pipe attachment side). In each cell, the degree of change in cell temperature due to heat release to the exhaust pipe is different. For this reason, in the said structure, since the temperature gradient in a sensor element changes easily with the change of exhaust pipe temperature, this invention can be applied preferably.

  When the internal combustion engine is started, the exhaust pipe temperature rises from the normal temperature as the internal combustion engine is started. Therefore, the temperature gradient of the sensor element changes depending on the temperature change of the exhaust pipe, and this tends to cause a temperature shift of the cell. In view of this point, in the invention according to claim 7, the cell output or the cell applied voltage is corrected in a predetermined start period of the internal combustion engine. As a result, even if a cell temperature deviation occurs due to a change in the temperature of the exhaust pipe, the cell output or cell applied voltage is corrected in consideration of the temperature change of the exhaust pipe. The sensor output error can be preferably eliminated.

  As the temperature of the gas passage wall deviates from a predetermined temperature (for example, 350 ° C. when the gas sensor is attached to the exhaust pipe of the internal combustion engine), the temperature deviation of each cell increases, and as a result, the gas concentration detection accuracy decreases. In view of this point, in the invention according to the eighth aspect, the sensor output is corrected when the temperature of the gas passage wall is in the correction temperature range. When the temperature deviation of each cell is large, the output error of the sensor element increases with the temperature deviation. Therefore, it is desirable to correct the sensor output.

  Here, for example, when the gas sensor is attached to the exhaust pipe of the internal combustion engine, the correction temperature range is such that the temperature of the exhaust gas passing through the exhaust pipe is a low temperature range (for example, 25 ° C. or less) and an excessively high temperature range (for example, 600 for a gasoline vehicle). It is desirable that the exhaust pipe temperature range in the case of a temperature higher than 0 ° C. or 400 ° C. or higher in a diesel vehicle) or a temperature range that deviates from the exhaust pipe temperature after warming up the internal combustion engine (for example, 350 ° C. ± 10 ° C.).

  When the gas sensor has a three-cell structure including the first cell, the second cell, and the third cell, that is, the sensor element in the gas sensor includes a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, When the gas sensor further includes a third cell for detecting the residual oxygen concentration in the gas chamber from the gas after adjusting the oxygen amount in the first cell, the gas sensor detects the concentration in the third cell from the concentration of the specific component detected in the second cell. Based on the value obtained by subtracting the residual oxygen concentration, the concentration of the specific component in the detection gas is calculated. In this case, as described in claim 9, the current value of the second cell and the current value of the third cell may be corrected based on the temperature of the gas passage wall. As a result, even if the degree of influence due to the temperature difference is different between the second cell and the third cell, it is possible to perform correction according to the degree of influence, and to calculate the concentration of the specific component with high accuracy. it can.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a NOx concentration detection system that uses a NOx sensor provided in an exhaust pipe of an in-vehicle engine and detects the NOx concentration in the exhaust based on the output of the NOx sensor will be described. The in-vehicle engine is, for example, a diesel engine, and a NOx purification catalyst (such as a NOx storage reduction catalyst or an ammonia selective reduction catalyst) as an exhaust purification device provided in the exhaust pipe of the engine is based on the output of the NOx sensor. Abnormal diagnosis etc. are to be implemented. For example, a NOx sensor is provided downstream of the NOx purification catalyst, and the NOx purification catalyst is abnormal when the NOx concentration (NOx purification rate) calculated from the output of the NOx sensor exceeds a predetermined abnormality determination value. Diagnosed.

  The configuration of the NOx sensor 10 will be described with reference to FIGS. 1 and 2. First, the overall configuration of the NOx sensor 10 will be described with reference to FIG.

  As shown in FIG. 2, the NOx sensor 10 has a distal end side cover 11, a housing 12, and a proximal end side cover 13, and has a substantially cylindrical shape as a whole. And the elongate sensor element 20 is accommodated in the inside. The NOx sensor 10 is attached to the wall portion of the exhaust pipe EP by the housing 12, and in the attached state, the front end side cover 11 is arranged in the exhaust pipe EP and is provided on the front end side cover 11. Exhaust gas is supplied to the sensor element 20 through a plurality of small holes (vent holes) 11a. That is, the NOx sensor 10 is attached to the exhaust pipe EP so that the sensor element 20 protrudes to the central part in the exhaust pipe. In the figure, “PS” indicates a pump cell described later, and “SS” indicates a sensor cell described later.

  The sensor element 20 has a so-called stacked structure. Although not shown, the front end side cover 11 has an inner / outer double structure, and the inner / outer covers are provided at alternate positions on the inside / outside of the cover (ie, the maze) as a measure for preventing the sensor element 20 from getting wet. A plurality of small holes 11a are provided.

  Next, the configuration of the sensor element 20 will be described with reference to FIG. FIG. 1 shows the internal structure of the sensor element 20, and the left-right direction in the figure corresponds to the longitudinal direction of the element. That is, the right side of the figure is the element base end side (exhaust pipe attachment site side), and the left side of the figure is the element tip side.

  The sensor element 20 has a so-called three-cell structure including a pump cell, a sensor cell, and a monitor cell, and each cell is laminated and configured. Since the monitor cell has a function of discharging oxygen in the gas like the pump cell, the monitor cell may be referred to as an auxiliary pump cell or a second pump cell.

  In the sensor element 20, the solid electrolyte bodies 21 and 22 made of an oxygen ion conductive material such as zirconia are formed in a sheet shape, and are stacked at a predetermined interval above and below the figure via spacers 23 made of an insulating material such as alumina. ing. Among these, an exhaust inlet 21a is formed in the solid electrolyte body 21 on the upper side of the figure, and exhaust around the sensor element is introduced into the first chamber 24 through the exhaust inlet 21a. The first chamber 24 communicates with the second chamber 26 via the throttle unit 25. On the upper surface of the solid electrolyte body 21 in the figure, a porous diffusion layer 27 for taking in and out the exhaust gas with a predetermined diffusion resistance is provided, and an insulating layer 29 for defining an air passage 28 is provided.

  Further, an insulating layer 31 made of alumina or the like is provided on the lower surface of the solid electrolyte body 22 in the figure, and an atmospheric passage 32 is formed by the insulating layer 31. A heater (heating element) 33 for heating the entire sensor is embedded in the insulating layer 31. In this case, the pump cell 41, the monitor cell 44, and the sensor cell 45 are heated by the heater 33, and each of these cells 41, 44, 45 is activated. The heater 33 generates heat energy by power supply from a battery power source (not shown).

  The solid electrolyte body 22 on the lower side of the figure is provided with a pump cell 41 so as to face the first chamber 24, and the pump cell 41 takes in and out oxygen in the exhaust gas introduced into the first chamber 24. The residual oxygen concentration in the chamber 24 is adjusted to a predetermined concentration. The pump cell 41 has a pair of upper and lower electrodes 42 and 43 provided with the solid electrolyte body 22 sandwiched therebetween, and in particular, the electrode 42 on the first chamber 24 side is a NOx inactive electrode (an electrode that hardly decomposes NOx). Yes. The pump cell 41 decomposes oxygen present in the first chamber 24 in a state where a voltage is applied between the electrodes 42 and 43 and discharges it from the electrode 43 to the atmosphere passage 32 side.

  Further, a monitor cell 44 and a sensor cell 45 are provided in the upper solid electrolyte body 21 in the drawing so as to face the second chamber 26. After the surplus oxygen is discharged by the pump cell 41 described above, the monitor cell 44 generates a current output in accordance with the electromotive force or voltage application according to the residual oxygen concentration in the second chamber 26. The sensor cell 45 detects the NOx concentration from the gas in the second chamber 26.

  The monitor cell 44 and the sensor cell 45 are arranged side by side at positions close to each other, and have the electrodes 46 and 47 on the second chamber 26 side and the common electrode 48 on the atmosphere passage 28 side. That is, the monitor cell 44 is configured by the solid electrolyte body 21, the electrode 46 and the common electrode 48 disposed so as to face each other, and the sensor cell 45 is similarly configured to face the solid electrolyte body 21 and the electrode 47 disposed so as to face it. And the common electrode 48. The electrode 46 (electrode on the second chamber 26 side) of the monitor cell 44 is made of a noble metal such as Au—Pt that is inactive to NOx, whereas the electrode 47 (electrode on the second chamber 26 side) of the sensor cell 45 is active on NOx. It consists of noble metals such as platinum Pt and rhodium Rh. For convenience, in the drawing, the monitor cell 44 and the sensor cell 45 are shown side by side with respect to the exhaust flow direction, but in actuality, the cells 44 and 45 are arranged at the same position with respect to the exhaust flow direction. Yes.

  Here, the pump cell 41, the monitor cell 44, and the sensor cell 45 are provided side by side in the longitudinal direction of the sensor element 20. The pump cell 41 is provided on the distal end side of the sensor element 20, and the base end side (exhaust pipe attachment side). ) Is provided with a monitor cell 44 and a sensor cell 45.

  In the sensor element 20 (NOx sensor 10) configured as described above, the exhaust is introduced into the first chamber 24 through the porous diffusion layer 27 and the exhaust introduction port 21a. Then, when this exhaust gas passes through the vicinity of the pump cell 41, a decomposition reaction occurs by applying a pump cell applied voltage Vp between the pump cell electrodes 42 and 43. Thereby, oxygen is taken in and out through the pump cell 41 according to the oxygen concentration in the first chamber 24. Since the electrode 42 on the first chamber 24 side is a NOx inactive electrode, NOx in the exhaust gas is not decomposed in the pump cell 41, but only oxygen is decomposed and discharged from the electrode 43 to the atmosphere passage 32. By such a function of the pump cell 41, the inside of the first chamber 24 is maintained in a predetermined low oxygen concentration state.

  The gas that has passed in the vicinity of the pump cell 41 flows into the second chamber 26, and the monitor cell 44 generates an output corresponding to the residual oxygen concentration in the gas. The output of the monitor cell 44 is detected as a monitor cell current Im when a predetermined monitor cell application voltage Vm is applied between the monitor cell electrodes 46 and 48. Further, when a predetermined sensor cell applied voltage Vs is applied between the sensor cell electrodes 47 and 48, NOx in the gas is reduced and decomposed, and oxygen generated at that time is discharged from the electrode 48 to the atmospheric passage 28. At this time, the NOx concentration in the exhaust gas is finally detected by the current (sensor cell current Is) flowing through the sensor cell 45.

  Here, the output characteristics of the NOx sensor 10 will be described with reference to FIG. 3A shows the output characteristic (V-I characteristic) of the pump cell 41, and FIG. 3B shows the output characteristic (VI characteristic) of the sensor cell 45. FIG. In FIG. 3, the horizontal axis represents applied voltages Vp and Vs, and the vertical axis represents cell currents Ip and Is.

  In FIG. 3A, a flat portion parallel to the voltage axis (horizontal axis) is a limit current region that specifies the pump cell current Ip. The pump cell current Ip in the limit current region is associated with the oxygen concentration in the exhaust gas. That is, the pump cell current Ip increases as the oxygen concentration in the exhaust gas increases. This limit current region shifts to the higher voltage side as the oxygen concentration in the exhaust gas increases. As the limit current region shifts to the high temperature side, the applied voltage characteristic (applied voltage line Vp0) for determining the pump cell applied voltage Vp also shifts to the high temperature side.

  In FIG. 3B, the flat portion parallel to the voltage axis (horizontal axis) is a limit current region for specifying the sensor cell current Is. The sensor cell current Is in the limit current region is associated with the NOx concentration in the exhaust gas. That is, the sensor cell current Is increases as the NOx concentration in the exhaust gas increases. The sensor cell applied voltage Vs is set at a predetermined value Vs0 that allows the sensor cell current Is corresponding to a predetermined NOx concentration to be detected in the limit current region.

  Returning to the description of FIG. 1, the sensor control circuit 50 includes a microcomputer 51 which is a main body of sensor control. The microcomputer 51 receives the pump cell voltage Vp applied between the electrodes 42 and 43 of the pump cell 41, the monitor cell voltage Vm applied between the electrodes 46 and 48 of the monitor cell 44, and the sensor cell voltage Vs applied between the electrodes 47 and 48 of the sensor cell 45, respectively. Control. Further, the microcomputer 51 sequentially inputs measured values of the current flowing through the pump cell 41 (pump cell current Ip), the current flowing through the monitor cell 44 (monitor cell current Im), and the sensor cell current Is. Then, the NOx concentration in the exhaust gas is calculated from the difference between the input monitor cell current Im and the sensor cell current Is. Further, the microcomputer 51 controls the energization of the heater 23 so that the pump cell 41 is controlled and the pump cell temperature is kept constant at a target activation temperature (for example, 750 ° C.).

  The ECU 70 is an in-vehicle engine ECU, and has a microcomputer (not shown) which is a main body for controlling them. The ECU 70 controls the fuel injection amount of the fuel injection valve and the ignition timing by the ignition device based on each operation state. In addition, NOx in the exhaust gas is monitored based on the NOx concentration value input from the sensor control circuit 50.

  By the way, in the NOx sensor 10, the heat of the sensor element 20 is released from the base end side to the exhaust pipe EP by being attached to the exhaust pipe EP. In such a case, the temperature at the base end side of the sensor element 20 is lower than that at the tip end side. That is, in the sensor element 20, there is a temperature gradient (temperature distribution) in the longitudinal direction, the pump cell 41 disposed on the distal end side becomes relatively high temperature, and the monitor cell 44 and sensor cell disposed on the proximal end side. 45 becomes relatively low temperature.

  Since the temperature of the exhaust pipe EP rises when the engine is cold started, this temperature gradient changes as the temperature rises. That is, the wall temperature of the exhaust pipe EP is different immediately after the start of the engine start and after the engine warm-up is completed. At this time, the monitor cell 44 and the sensor cell 45 are closer to the exhaust pipe EP than the pump cell 41. Susceptible to changes in tube wall temperature. For this reason, if the temperature of the exhaust pipe wall is relatively low when the engine is started, the monitor cell 44 and the sensor cell 45 are also relatively low temperature. If the temperature of the exhaust pipe wall increases as the engine warms up, the monitor cell 44 And the temperature of the sensor cell 45 also rises. As a result, in the sensor element 20, the temperature gradient in the longitudinal direction changes depending on the temperature of the exhaust pipe wall.

  In particular, in the heater energization control of the present embodiment, the energization control of the heater 33 is performed so that the pump cell 41 is controlled and the temperature is kept constant at the target activation temperature. On the other hand, in the monitor cell 44 and the sensor cell 45, the heater 23 is energized and controlled based on the pump cell temperature, so that the normal cell temperature without the cause of temperature fluctuation (disturbance) is the target activation temperature (for example, 700 ° C.). ) To be held. When the pump cell 41 is controlled as described above, if a temperature variation factor occurs in the monitor cell 44 and the sensor cell 45, the temperature variation is likely to occur due to the temperature variation factor.

  FIG. 4 is a time chart showing changes in pump cell temperature, monitor cell temperature, and exhaust pipe temperature with the passage of time from the start of engine start. Since the monitor cell 44 and the sensor cell 45 are arranged close to each other, the cell temperatures of both are the same.

  In FIG. 4, when the energization control of the heater 33 is executed after the engine is started, the pump cell temperature and the monitor cell temperature are increased. Further, the exhaust pipe EP is heated by the exhaust heat, so that the exhaust pipe temperature also gradually increases from around the normal temperature. At this time, as described above, since heat is released from the sensor element 20 to the exhaust pipe, a temperature difference (that is, a temperature gradient of the sensor element 20) between the pump cell 41, the monitor cell 44, and the sensor cell 45 is formed. Further, the temperature gradient fluctuates with the fluctuation of the exhaust pipe temperature. That is, the temperatures of the monitor cell 44 and the sensor cell 45 are not controlled by the energization control of the heater 33, and thus become lower than the target temperature due to heat release to the exhaust pipe.

  Each cell 41, 44, 45 has a temperature characteristic as its output characteristic, and suitable sensor control is realized by making each cell temperature an activation temperature. For this reason, if the cell temperature fluctuates due to heat release to the exhaust pipe EP due to fluctuations in the exhaust pipe temperature and deviates from the activation temperature, an error occurs in the sensor output, which may lead to a decrease in detection accuracy of the NOx concentration.

  Therefore, in the present embodiment, the wall temperature of the exhaust pipe EP is detected, and the sensor output is corrected based on the wall temperature. Specifically, the sensor control circuit 50 according to the present embodiment detects the values of the monitor cell current Im and the sensor cell current Is, and corrects the detected values according to the wall temperature of the exhaust pipe EP. Then, the NOx concentration is calculated from the difference between the corrected monitor cell current Im and sensor cell current Is.

  FIG. 5 is a functional block diagram showing the overall configuration of the sensor control circuit 50 in the present embodiment. As shown in FIG. 5, the sensor control circuit 50 includes an Ip detection unit 52 that detects the pump cell current Ip, an Im detection unit 53 that detects the monitor cell current Im, and an Is detection unit 54 that detects the sensor cell current Is. ing. The Ip detector 52 detects a pump cell current Ip that flows between the electrodes 42 and 43 in a state where the pump cell applied voltage Vp is applied to the pump cell electrodes 42 and 43. The Im detector 53 detects a monitor cell current Im flowing between the electrodes 46 and 48 in a state where the monitor cell application voltage Vm is applied to the monitor cell electrodes 46 and 48. The Is detector 54 detects a sensor cell current Is flowing between the electrodes 47 and 48 in a state where the sensor cell applied voltage Vs is applied to the sensor cell electrodes 47 and 48.

  The sensor control circuit 50 includes a heater control unit 55 that controls energization of the heater 33. The heater control unit 55 controls energization of the heater 33 so that the temperature of the pump cell 41 is kept constant. Specifically, the pump cell impedance detection unit 56 detects the element impedance for the pump cell 41, and the heater control unit 55 sets the detection value of the element impedance detected by the pump cell impedance detection unit 56 to the target value. Impedance feedback control is executed to match.

  The method for detecting the element impedance is not particularly limited. In the present embodiment, the element impedance is detected by using a so-called sweep method. Specifically, the pump cell impedance detection unit 56 commands to temporarily change the applied voltage of the pump cell electrodes 42 and 43 in an alternating manner, and the element impedance of the pump cell 41 is determined based on the current change amount at that time. calculate. At this time, the sensor applied voltage is changed to a positive / negative side (or either positive or negative) with a predetermined width (for example, 0.2 V) by a sweep circuit (not shown), and a change in element current accompanying the change in the applied voltage is measured. . Then, the element impedance is calculated from the applied voltage change amount ΔV and the current change amount ΔI at that time (impedance = ΔV / ΔI). In detecting impedance, it is also possible to change the current passed through the pump cell 41 in an alternating manner and calculate the element impedance from the amount of change in current or voltage at that time.

  Thus, in the pump cell 41, the cell temperature is controlled to be constant by feedback control of the element impedance, and the sensor control circuit 50 outputs the pump cell current Ip detected by the Ip detection unit 52 to the ECU 70 as it is. On the other hand, in the monitor cell 44 and the sensor cell 45, since the cell temperature is not directly controlled by the heater control unit 55, when the exhaust pipe temperature varies, the cell temperature varies depending on the temperature variation. For this reason, in the monitor cell 44 and the sensor cell 45, a temperature shift occurs between the target activation temperature and the actual cell temperature. Therefore, in order to eliminate the cell output error due to the temperature deviation, the sensor control circuit 50 exhausts the monitor cell current Im detected by the Im detection unit 53 and the sensor cell current Is detected by the Is detection unit 54. Corrections are made according to the wall temperature of the exhaust pipe (exhaust pipe temperature Tex) detected by the pipe wall temperature sensor 71, and the NOx concentration is calculated based on the corrected value.

  Specifically, the sensor control circuit 50 includes an Im correction unit 57 that corrects the monitor cell current Im detected by the Im detection unit 53 and an Is correction unit 58 that corrects the sensor cell current Is detected by the Is detection unit 54. ing. The Im correction unit 57 inputs the Im correction amount calculated by the Im correction amount calculation unit 59, and corrects the monitor cell current Im using the Im correction amount. The Is correction unit 58 receives the Is correction amount calculated by the Is correction amount calculation unit 61 and corrects the monitor cell current Im using the Is correction amount.

  In the Im correction amount calculation unit 59 and the Is correction amount calculation unit 61, for example, an output correction map indicating the relationship between the exhaust pipe temperature and the correction amount (Im correction amount and Is correction amount) is stored in advance, and the maps are stored. To calculate the correction amount.

  FIG. 6 is an example of an output correction map. 6A shows the Im correction amount, and FIG. 6B shows the Is correction amount. In the map of FIG. 6, when the exhaust pipe temperature is a predetermined temperature Tex0, the Im correction amount and the Is correction amount are zero. Further, the exhaust pipe temperature and the correction amount are associated with each other so that the Im correction amount and the Is correction amount increase as the exhaust pipe temperature decreases. At this time, with the predetermined temperature Tex0 as a boundary, the correction amount is a positive value when the exhaust pipe temperature is the low temperature side, and the correction amount is a negative value when the exhaust pipe temperature is the high temperature side. Here, it is desirable that the predetermined temperature Tex0 is an exhaust pipe temperature (for example, 350 ° C.) at the completion of engine warm-up.

  In FIG. 5, an Ip detection unit 52, an Im detection unit 53, and an Is detection unit 54 each include a current measurement resistor that measures a current flowing through each cell, and an amplification circuit that amplifies and outputs a measurement value by the current measurement resistor. It is implement | achieved by the electrical circuit (Ip measuring circuit, Im measuring circuit, Is measuring circuit) which has. In addition, the Im correction unit 57, the Is correction unit 58, the Im correction amount calculation unit 59, and the Is correction amount calculation unit 61 are realized by the microcomputer 51.

  Next, the NOx concentration calculation process executed by the microcomputer 51 will be described. FIG. 7 is a flowchart showing the processing procedure of the NOx concentration calculation processing in the NOx sensor 10. This process is repeatedly executed by the microcomputer 51 at a predetermined time period.

  In FIG. 7, in step S11, first, the monitor cell current Im measured by the Im measuring circuit and the sensor cell current Is measured by the Is measuring circuit are input. Subsequently, in step S12, it is determined whether or not the sensor element 20 is in an active completion state. Here, it is determined that the sensor element 20 has been activated when a predetermined time T0 (for example, 10 min) has elapsed since the start of engine start. Note that the activation completion state of the sensor element 20 may be determined based on, for example, the engine water temperature, element impedance, or sensor output value. Then, the process proceeds to step S13 on condition that it is determined that the sensor element 20 has been activated.

  In step S13, it is determined whether a condition (correction execution condition) for executing correction of the monitor cell current Im and the sensor cell current Is is satisfied. In the present embodiment, the correction execution condition is that the time is within a predetermined time T1 (for example, ten times min) from the start of engine start (start of cranking). The predetermined time T1 is desirably a time from when the exhaust pipe temperature reaches a temperature after normal warming-up of the engine (for example, 350 ° C.) during cold start of the engine. If the correction execution condition is satisfied in step S13, the process proceeds to step S14.

  In step S14, the exhaust pipe temperature Tex detected by the exhaust pipe wall sound sensor 71 is input. In the subsequent step S15, an Im correction amount and an Is correction amount corresponding to the input exhaust pipe temperature Tex are obtained using the correction map shown in FIG. In step S16, the monitor cell current Im and the sensor cell current Is are corrected using the calculated Im correction amount and Is correction amount, respectively. In the present embodiment, correction is performed by adding an Im correction amount and an Is correction amount to the monitor cell current Im and the sensor cell current Is, respectively. Thereafter, in step S17, the NOx concentration is calculated from the difference between the corrected monitor cell current Im and the corrected sensor cell current Is.

  The correction method is not limited to this. For example, instead of the correction map of FIG. 6, a correction coefficient set according to the exhaust pipe temperature is stored in advance as a map or table, and the exhaust pipe temperature is stored. Correction may be performed by multiplying the monitor cell current Im and the sensor cell current Is by a correction coefficient corresponding to. At this time, the correction coefficient is preferably set to a value of 1 when the exhaust pipe temperature is the predetermined temperature Tex0, and is set so that the correction coefficient increases as the exhaust pipe temperature decreases.

  FIG. 8 is a time chart showing the temperature transition of the pump cell 41 and the like after the engine is started and the transition of the sensor cell output. 8A shows the pump cell temperature, the monitor cell temperature, and the exhaust pipe temperature, FIG. 8B shows the correction execution time, and FIG. 8C shows the sensor cell output (= Is). In FIG. 8C, the solid line shows the transition of the sensor cell output when it is corrected based on the exhaust pipe temperature Tex, and the alternate long and short dash line shows the transition of the sensor cell output when it is not corrected based on the exhaust pipe temperature Tex.

  In FIG. 8, after the start of the engine, the sensor output increases as the output value increases due to the discharge of excess oxygen in the chamber (including the discharge of adsorbed oxygen from the electrode), and then the excess oxygen is discharged to output the sensor output value. Becomes smaller. The activation is completed when the output value corresponds to the NOx concentration in the exhaust gas. At this time, when the NOx sensor 10 enters the active completion state at a time t11 when a predetermined time T0 has elapsed from the start of engine start, as shown in FIG. 8C, in this embodiment, the monitor cell current Im and the sensor cell after the time t11. Correction of the current Is is performed. Then, this correction is continuously performed until the exhaust pipe temperature Tex is stabilized (that is, until a predetermined time T1 elapses from the start of engine start). By correcting the monitor cell current Im and the sensor cell current Is in this way, the sensor cell output is stabilized at the output Nop earlier than the prior art and without depending on the exhaust pipe temperature.

  According to the embodiment described above, the following excellent effects can be obtained.

  Since the temperature (wall temperature) of the exhaust pipe to which the NOx sensor 10 is attached is detected and the monitor cell current Im and the sensor cell current Is are corrected according to the wall temperature, the monitor cell 44 is caused by fluctuations in the exhaust pipe temperature. And when the temperature shift of the sensor cell 45 arises, the sensor output error accompanying the temperature shift can be eliminated. That is, in the prior art that does not take into account fluctuations in the exhaust pipe temperature, a temperature shift between the monitor cell 44 and the sensor cell 45 occurs due to fluctuations in the exhaust pipe temperature, which causes a sensor output error. In this embodiment, The monitor cell current Im and the sensor cell current Is are corrected according to the exhaust pipe temperature, and the sensor output error due to the temperature deviation of each cell is eliminated. As a result, the detection accuracy of the NOx concentration can be improved.

  In order to correct the monitor cell current Im and the sensor cell current Is, even if the monitor cell 44 and the sensor cell 45 are not subjected to the energization control of the heater 33 and a temperature shift occurs in those cells, the temperature shift It is possible to suitably eliminate the sensor output error associated with.

  Since the correction of the monitor cell current Im and the sensor cell current Is according to the exhaust pipe temperature is performed in the engine start period between the cranking start and the predetermined time T1, it is possible to cope with a change in the exhaust pipe temperature accompanying the engine start. Thus, the correction of the NOx sensor output can be suitably realized.

  Since both the monitor cell current Im and the sensor cell current Is are targeted for correction, the detection accuracy can be improved as compared with the case where only one of them is corrected. In addition, since the correction amount of the monitor cell current Im and the correction amount of the sensor cell current Is are set separately according to the exhaust pipe temperature, the tendency of the change in cell output with respect to the change in cell temperature is different between the two cells. (For example, when the tendency of the change in cell output with respect to the change in cell temperature differs due to the difference in material between the monitor cell 44 and the sensor cell 45), the difference can be reflected in the corrected value, and the correction accuracy Can be improved.

  Since the heater energization control is performed with the pump cell 41 as the control target, the detection accuracy of the NOx sensor 10 is high and preferable as compared with the case where the monitor cell 44 or the sensor cell 45 is the control target. That is, when the pump cell 41 is a target for temperature control, the residual oxygen concentration in the second chamber 26 can be maintained at a desired oxygen concentration level, whereas the monitor cell 44 and the sensor cell 45 are targeted for temperature control. In this case, the residual oxygen concentration in the second chamber 26 cannot be maintained at a desired oxygen concentration level. At this time, if the residual oxygen concentration in the second chamber 26 can be maintained at a desired oxygen concentration level, the output error (Is error) of the sensor cell 45 becomes a temperature deviation of the sensor cell 45 due to the temperature fluctuation of the exhaust pipe wall. . Here, as shown in FIG. 3, the scale of the cell output is greatly different between the pump cell 41 and the sensor cell 45. For this reason, it is considered that the temperature deviation of the sensor cell 45 is smaller than the output error caused by the residual oxygen concentration deviation in the second chamber 26. Therefore, by controlling the temperature of the pump cell 41 among the pump cell 41, the monitor cell 44 and the sensor cell 45, the output error level of the sensor cell 41 can be reduced, thereby improving the detection accuracy.

  Since the pump cell 41 is disposed on the front end side of the sensor element 20 and the monitor cell 44 and the sensor cell 45 are disposed on the exhaust pipe attachment side, the degree of heat release to the exhaust pipe differs between the pump cell 41, the monitor cell 44 and the sensor cell 45. . In such a configuration, a temperature gradient is likely to be generated in the sensor element 20, and thus the above-described effect becomes remarkable.

(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on differences from the first embodiment. In the first embodiment, the monitor cell current Im and the sensor cell current Is are corrected with the correction execution condition being within a predetermined time T1 from the start of engine start (cranking start). These corrections are performed under the condition that the temperature is within a predetermined correction temperature range as a correction execution condition.

  Specifically, in step S13 of FIG. 7, the exhaust pipe temperature Tex is input, and it is determined whether or not the exhaust pipe temperature Tex is in the correction temperature range. This correction temperature range is the range of the exhaust pipe temperature when the exhaust gas temperature in the exhaust pipe is in a low temperature range (for example, 25 ° C. or lower) and an excessively high temperature range (for example, 600 ° C. or higher for gasoline vehicles, 400 ° C. or higher for diesel vehicles). In addition, it is desirable that the exhaust pipe temperature Tref (for example, 350 ° C.) after engine warm-up is within a temperature range that is outside of ± α ° C. (for example, 10 ° C.). If the exhaust pipe temperature Tex is in the correction temperature range, the NOx concentration is calculated by correcting the monitor cell current Im and the sensor cell current Is according to the exhaust pipe temperature Tex in step S15 and subsequent steps.

  FIG. 9 is a time chart showing the temperature transition of the pump cell 41 and the like, the transition of the sensor cell output, etc. after the engine is started. 9A shows the pump cell temperature, the monitor cell temperature, and the exhaust pipe temperature, FIG. 9B shows the correction execution timing, and FIG. 9C shows the sensor cell output (= Is). In FIG. 9C, the solid line shows the transition of the sensor cell output when it is corrected based on the exhaust pipe temperature Tex, and the alternate long and short dash line shows the transition of the sensor cell output when it is not corrected based on the exhaust pipe temperature Tex.

  In FIG. 9A, when the exhaust pipe temperature decreases after a long period of time has elapsed since the engine was started (for example, after a lapse of several tens of minutes), and the correction temperature range is reached at time t21, the monitor cell current Im and sensor cell current Is are corrected. The process is started (see FIG. 9B). As a result, the sensor cell output is stabilized at the output Nop without depending on the exhaust pipe temperature, as shown by the solid line in FIG. 9C.

  According to the embodiment described above, the following excellent effects can be obtained.

  Since the monitor cell current Im and the sensor cell current Is are corrected according to the exhaust pipe temperature when the exhaust pipe temperature deviates from the temperature range Tref ± α, the change in the exhaust pipe temperature can be suitably dealt with, and the sensor cell 45 It is possible to improve the density detection accuracy due to. Further, the monitor cell current Im and the sensor cell current Is can be corrected according to the exhaust pipe temperature not only after the engine start period but also after the engine start period has elapsed (for example, during idle control). As a result, it is possible to suitably improve the sensor detection accuracy.

(Third embodiment)
Next, a third embodiment of the present invention will be described focusing on differences from the above embodiment. In the above embodiment, the energization control of the heater 33 is executed by the feedback control of the pump cell temperature. However, in this embodiment, the energization control of the heater 33 is executed by the feedback control of the monitor cell temperature. Since the monitor cell 44 and the sensor cell 45 are arranged close to each other, the element impedances are substantially the same. Therefore, in the present embodiment, the energization control may be executed based on the sensor cell temperature instead of the monitor cell temperature.

  FIG. 10 is a functional block diagram showing the overall configuration of the sensor control circuit 50 in the present embodiment. The sensor control circuit 50 of FIG. 10 is different from FIG. 5 in that a monitor cell impedance detection unit 62 is provided instead of the pump cell impedance detection unit 56 in FIG. That is, the heater control unit 55 controls the energization of the heater 33 so that the temperature of the monitor cell 44 (and the sensor cell 45) is kept constant, specifically, the element impedance detected by the monitor cell impedance detection unit 62. Impedance feedback control is executed so that the detected value matches the target value.

  Thus, in a system in which the cell temperature of the monitor cell 44 (and sensor cell 45) is controlled to be constant by feedback control of the element impedance of the monitor cell 44, when heat is released to the exhaust pipe at the site where the sensor element 20 is attached, Since the monitor cell 44 and the sensor cell 45 are close to the exhaust pipe, the cell temperature is lowered due to heat release to the exhaust pipe. Heater energization control is performed so as to cancel the temperature change. In this case, the temperature of the pump cell 41 becomes higher than the target temperature due to the heating of the sensor element 20 by the heater 33.

  FIG. 11 shows changes in pump cell temperature, monitor cell temperature, and exhaust pipe temperature with the elapsed time from the start of engine start. In FIG. 11, when the energization control of the heater 33 is executed after the engine is started, the pump cell temperature and the monitor cell temperature are increased. Further, the exhaust pipe is heated by the exhaust heat, so that the exhaust pipe temperature gradually increases from around normal temperature. At this time, since the sensor element 20 is heated in order to suppress the temperature drop of the monitor cell 44 and the sensor cell 45 due to heat release to the exhaust pipe, the monitor cell temperature (and sensor cell temperature) depends on the change of the exhaust pipe temperature. The target temperature is maintained. On the other hand, in the pump cell 41, the cell temperature becomes higher than the target temperature due to the heating of the sensor element 20. Therefore, the oxygen in the exhaust gas is excessively exhausted in the pump cell 41, so that the offset current Is0 (see FIG. 3B) of the sensor cell 45 is only the oxygen excessive exhaust amount (the oxygen concentration decrease amount) in the second chamber 26. Get smaller. As a result, an output error occurs in the monitor cell current Im and the sensor cell current Is, and as a result, the NOx concentration detection accuracy may be lowered.

  Therefore, in the present embodiment, as in the first embodiment, the sensor control circuit 50 detects the values of the monitor cell current Im and the sensor cell current Is, respectively, and according to the exhaust pipe temperature for these detected values. Make corrections. Then, the NOx concentration is calculated from the difference between the corrected sensor cell current Is and the monitor cell current Im.

  FIG. 12 is a time chart showing the temperature transition of the pump cell 41 and the like, the transition of the sensor cell output, etc. after the engine is started. 12A shows the pump cell temperature, the monitor cell temperature, and the exhaust pipe temperature, FIG. 12B shows the correction execution timing, and FIG. 12C shows the sensor cell output (= Is). In FIG. 12C, the solid line indicates the transition of the sensor cell output when corrected based on the exhaust pipe temperature Tex, and the alternate long and short dash line indicates the transition of the sensor cell output when not corrected based on the exhaust pipe temperature Tex.

  In FIG. 12, when the activation of the NOx sensor 10 is completed at time t31 when a predetermined time T0 has elapsed from the start of engine start, as shown in FIG. 12C, in this embodiment, the monitor cell current Im and By performing the correction of the sensor cell current Is, the NOx sensor output is stabilized at the output Nop earlier than before and without depending on the exhaust pipe temperature.

  According to the embodiment described above, the following excellent effects can be obtained.

  When a temperature shift occurs in the pump cell 41 as a result of heating the sensor element 20 in order to suppress a temperature shift in the monitor cell 44 due to fluctuations in the exhaust pipe temperature, a sensor output error associated with the temperature shift is eliminated. Can do. That is, in the conventional technology that does not consider the fluctuation of the exhaust pipe temperature, when the exhaust pipe temperature fluctuates, a temperature shift occurs in the pump cell 41, and accordingly, a residual oxygen concentration shift in the second chamber 26 occurs. Further, a sensor output error occurs due to the residual oxygen concentration shift. On the other hand, in the present embodiment, the sensor cell error Im and the sensor cell current Is are corrected according to the exhaust pipe temperature, thereby eliminating the sensor output error due to the temperature deviation of the pump cell 41. As a result, the detection accuracy of the NOx concentration can be improved.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described focusing on differences from the third embodiment. In the third embodiment, energization control of the heater 33 is executed by feedback control of the monitor cell temperature, and the monitor cell current Im and the sensor cell current Is are corrected according to the exhaust pipe temperature. However, in this embodiment, the monitor cell current Im and the sensor cell are corrected. Instead of correcting the current Is, the pump cell applied voltage Vp is corrected.

  That is, in the system in which the cell temperature of the monitor cell 44 (and the sensor cell 45) is controlled to be constant by feedback control of the element impedance, when heat is released to the exhaust pipe at the attachment site of the sensor element 20, as described above, Due to heat release to the exhaust pipe, the temperature of the monitor cell 44 and the sensor cell 45 decreases. When energization control of the heater 33 is performed to cancel the temperature change and the sensor element 20 is heated, the temperature of the pump cell 41 becomes higher than the target temperature. In such a case, it is considered that the oxygen in the exhaust gas is excessively discharged from the pump cell 41. Therefore, in the present embodiment, in order to suppress excessive oxygen discharge by the pump cell 41, the pump cell applied voltage Vp is corrected to be small. That is, in the pump cell output characteristic (VI characteristic) of FIG. 3A, in the limit current region, the current value slightly increases as the applied voltage increases (that is, slightly right in FIG. 3A). Therefore, by correcting the pump cell applied voltage Vp to be small, the pump cell current Ip becomes small, and as a result, excessive oxygen discharge by the pump cell 41 is suppressed.

  FIG. 13 is a functional block diagram showing the overall configuration of the sensor control circuit 50 in the present embodiment. The sensor control circuit 50 in FIG. 13 includes a Vp correction amount calculation unit 63 instead of the Im correction unit 57, Is correction unit 58, Im correction amount calculation unit 59, and Is correction amount calculation unit 61 in FIG. The Vp correction amount calculation unit 63 stores in advance an output correction map indicating the relationship between the exhaust pipe temperature and the Vp correction amount, for example, in accordance with the exhaust pipe temperature input from the exhaust pipe wall temperature sensor 71. Is used to calculate the Vp correction amount.

  FIG. 14 is an example of an output correction map. In the map of FIG. 14, the Vp correction amount is zero when the exhaust pipe temperature is a predetermined temperature Tex0 (for example, the exhaust pipe temperature at the completion of engine warm-up). Further, the exhaust pipe temperature and the Vp correction amount are associated so that the Vp correction amount decreases as the exhaust pipe temperature decreases. At this time, with the predetermined temperature Tex0 as a boundary, the correction amount is a negative value when the exhaust pipe temperature is a low temperature side, and the correction amount is a positive value when the exhaust pipe temperature is a high temperature side.

  Returning to the description of FIG. 13, the Vp correction amount calculation unit 63 outputs the calculated Vp correction amount to the pump cell driving unit 65. In the pump cell driving unit 65, the pump cell applied voltage Vp input from the Ip detecting unit 52 is corrected by adding the Vp correction amount input from the Vp correction amount calculating unit 63, and the corrected pump cell applied voltage Vp is the pump cell electrodes 42, 43. The pump cell 41 is driven and controlled to be applied to.

  In FIG. 13, in the configuration related to the pump cell 41, the Vp correction amount calculation unit 63 and the pump cell driving unit 65 are realized by the microcomputer 51, and the Ip detection unit 52 is realized by an electric circuit (Ip measurement circuit).

  Next, the pump cell driving process executed by the microcomputer 51 will be described. FIG. 15 is a flowchart showing a processing procedure of pump cell driving processing in the NOx sensor 10. This process is repeatedly executed by the microcomputer 51 at a predetermined time period.

  In FIG. 15, first, in step S21, the pump cell current Ip measured by the Ip measuring circuit is input, and in step S22, the pump cell applied voltage Vp is calculated from the VI characteristic (see FIG. 3A). Subsequently, the process proceeds to Step 25 on condition that the sensor element 20 is in the active completion state (Step S23) and that the correction execution condition is satisfied (Step S24).

  In step S25, the exhaust pipe temperature Tex is input, and the Vp correction amount corresponding to the temperature is set using the correction map shown in FIG. In step S27, the pump cell application voltage Vp is corrected by the Vp correction amount, and in step S28, the pump cell 41 is driven and controlled so that the corrected pump cell application voltage Vp is applied to the pump cell electrodes 42 and 43.

  According to the embodiment described above, the following excellent effects can be obtained.

  When the sensor element 20 is heated to suppress the temperature shift in the monitor cell 44 due to the fluctuation of the exhaust pipe temperature, when the temperature shift occurs in the pump cell 41, the sensor output error due to the temperature shift is eliminated. be able to. That is, in the conventional technology that does not consider the fluctuation of the exhaust pipe temperature, when the exhaust pipe temperature fluctuates, a temperature shift occurs in the pump cell 41, and accordingly, a residual oxygen concentration shift in the second chamber 26 occurs. Further, a sensor output error occurs due to the residual oxygen concentration shift. On the other hand, in the present embodiment, the residual oxygen concentration in the second chamber 26 is adjusted to an appropriate concentration by correcting the pump cell applied voltage Vp according to the exhaust pipe temperature. As a result, it is possible to eliminate the sensor output error associated with the temperature shift of the pump cell 41, and consequently improve the detection accuracy of the NOx concentration.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  In the above embodiment, the sensor cell current Is that is the cell output, the monitor cell current Im, or the pump cell application voltage Vp that is the cell application voltage is corrected continuously using the map, but the present invention is not limited to this. For example, a correction value corresponding to one or a plurality of exhaust pipe temperature ranges is set in advance, a correction amount corresponding to a measured value of the exhaust pipe temperature is calculated, and then correction is performed step by step using the correction amount. May be.

  In the above embodiment, the exhaust pipe temperature detected by the exhaust pipe wall temperature sensor 71 is used as wall temperature information, and the sensor cell current Is, the monitor cell current Im, or the cell applied voltage, which is a cell applied voltage, is applied based on the sensor detection value. Although the voltage Vp is corrected, the wall temperature information is not limited to this. For example, the exhaust pipe temperature may be estimated from the engine operating state, the elapsed time from the start of engine start, etc., and the estimated exhaust pipe temperature may be used as the wall temperature information. Examples of the engine operating state include an engine water temperature and an engine rotation speed. In these cases, the exhaust temperature is estimated from the engine water temperature or the like, and the temperature of the exhaust pipe wall is estimated from the exhaust temperature.

  In the third and fourth embodiments, the sensor cell current Is and the monitor cell current Im or the pump cell applied voltage Vp are corrected in the heater energization control for the monitor cell 44 (and the sensor cell 45), respectively. The correction may be executed. As described above, in the heater energization control with the monitor cell 44 (and the sensor cell 45) as a control target, the sensor element 20 is heated in order to suppress the temperature shift in the monitor cell 44. As a result, the pump cell 41 has a temperature shift. Further, a sensor output error occurs in the pump cell 41 with the temperature shift. Therefore, by correcting the pump cell current Ip, the pump cell output error due to the temperature shift of the pump cell 41 can be eliminated. For example, it is suitable for detecting the oxygen concentration in the exhaust gas from the pump cell output.

  In the above embodiment, the sensor cell current Is and the monitor cell current Im are individually corrected, and the NOx concentration is calculated from the difference between the corrected sensor cell current Is and the monitor cell current Im, but the sensor cell current Is and the monitor cell are calculated. After obtaining the difference from the current Im, the NOx concentration may be calculated by correcting the difference.

  In the first embodiment, the monitor cell application voltage Vm and the sensor cell application voltage Vs may be corrected. That is, in the heater energization control with the pump cell 41 as a control target, a temperature shift occurs in the monitor cell 44 and the sensor cell 45, and an output error occurs in the monitor cell current Im and the sensor cell current Is due to the temperature shift. Therefore, the output errors of the monitor cell current Im and the sensor cell current Is can be eliminated by correcting the monitor cell applied voltage Vm and the sensor cell applied voltage Vs according to the VI characteristic.

  In the first embodiment, the cell output is corrected in the period of the predetermined time T1 from the start of the engine start. However, the cell output may be corrected after the period has elapsed.

The block diagram which shows the internal structure of a sensor element, and a sensor control circuit. The figure which shows the whole structure of a NOx sensor. The figure which shows the output characteristic of a NOx sensor. The time chart which shows transition of the pump cell temperature, monitor cell temperature, and exhaust pipe temperature with progress of time from engine starting start. The functional block diagram which shows the whole structure of a sensor control circuit. The figure which shows an example of the map for output correction. The flowchart which shows the process sequence of a NOx density | concentration calculation process. The time chart which shows transition of the cell temperature and exhaust pipe temperature with the passage of time from the engine starting start in 1st Embodiment, and a sensor cell output. The time chart which shows transition of the cell temperature and exhaust pipe temperature with the passage of time from the engine starting start in 2nd Embodiment, and a sensor cell output. The functional block diagram which shows the whole structure of a sensor control circuit. The time chart which shows transition of the pump cell temperature, monitor cell temperature, and exhaust pipe temperature with progress of time from engine starting start. The time chart which shows transition of the cell temperature and exhaust pipe temperature with progress of time after engine starting, and a sensor cell output. The functional block diagram which shows the whole structure of a sensor control circuit. The figure which shows an example of the map for output correction. The flowchart which shows the process sequence of a pump cell drive process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... NOx sensor (gas sensor), 20 ... Sensor element, 21 ... Solid electrolyte body, 24 ... 1st chamber (gas chamber), 26 ... 2nd chamber (gas chamber), 33 ... Heater, 41 ... Pump cell (1st cell) ), 42, 43 ... electrodes, 44 ... monitor cell (third cell), 45 ... sensor cell (second cell), 46-48 ... electrodes, 50 ... sensor control circuit, 51 ... microcomputer, EP ... exhaust pipe.

Claims (9)

A sensor element having a first cell and a second cell each composed of a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, and applying a voltage to the electrode of the first cell to form a gas According to the specific component in the gas after adjusting the oxygen amount by the first cell by adjusting the oxygen amount in the gas to be detected introduced into the room to a predetermined concentration level and applying a voltage to the electrode of the second cell. In a gas concentration detection apparatus that is applied to a gas sensor that generates a second cell output and calculates the concentration of the specific component based on the second cell output,
Wall temperature information acquisition means for acquiring wall temperature information related to the temperature of the gas passage wall to which the gas sensor is attached;
Correction means for correcting a cell output or a cell applied voltage of at least one of the first cell and the second cell based on the wall temperature information acquired by the wall temperature information acquisition means;
A gas concentration detection device comprising: The gas sensor controls energization of the heater so that a cell temperature becomes a target temperature with one of the first cell and the second cell of the sensor element being controlled and a heater for heating the sensor element. Heater control means,
The correction means corrects a cell output or a cell applied voltage of a cell whose temperature is not controlled by the heater control means based on the wall temperature information acquired by the wall temperature information acquisition means. The gas concentration detection apparatus according to 1. The heater control means controls energization of the heater with the first cell as a control target,
The gas concentration detection device according to claim 2, wherein the correction unit corrects a cell output of the second cell based on the wall temperature temperature acquired by the wall temperature information acquisition unit. The heater control means controls energization of the heater with the second cell as a control target,
The gas concentration detection device according to claim 2, wherein the correction unit corrects the applied voltage of the first cell based on the wall temperature information acquired by the wall temperature information acquisition unit. The gas sensor includes a heater for heating the sensor element, and heater control means for controlling energization of the heater so that the cell temperature becomes a target temperature with the second cell in the sensor element as a control target.
The gas concentration detection device according to claim 1, wherein the correction unit corrects the cell output of the second cell based on the wall temperature information acquired by the wall temperature information acquisition unit. The gas passage wall is an exhaust pipe wall of an internal combustion engine;
The gas sensor is attached to the exhaust pipe so that the sensor element protrudes to a central portion in the exhaust pipe,
The sensor element is provided with the first cell and the second cell at different positions on the tip side and the exhaust pipe attachment side of the element,
6. The gas concentration detection apparatus according to claim 1, wherein the correction unit corrects the cell output or the cell applied voltage based on a temperature of an exhaust pipe wall of the internal combustion engine.   The gas concentration detection device according to claim 7, wherein the correction unit corrects the cell output or the cell applied voltage during a predetermined start period of the internal combustion engine. The wall temperature information acquisition means acquires a detection value of a temperature sensor provided on the gas passage wall as the wall temperature information,
8. The gas according to claim 1, wherein when the temperature of the gas passage wall is in a correction temperature range, the correction unit performs correction of a cell output or a cell applied voltage. Concentration detector. The sensor element comprises a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, and a third cell for detecting a residual oxygen concentration in the gas chamber from a gas after adjusting the oxygen amount of the first cell. Furthermore, it is applied to the gas sensor provided,
The concentration of the specific component is calculated based on the difference between the cell output of the second cell and the cell output of the third cell, and the second cell is based on the temperature of the gas passage wall by the correction means. 9. The cell output of the third cell and the cell output of the third cell are corrected, and the concentration of the specific component is calculated based on each cell output after the correction. Gas concentration detector.

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