JP6700910B2 - Gas sensor controller - Google Patents

Description

  The present invention relates to a gas sensor control device for detecting a specific gas concentration in a gas to be measured.

  Conventionally, an air-fuel ratio sensor, a NOx sensor, and the like have been known as gas sensors capable of detecting the concentration of a specific gas (oxygen, NOx, etc.) contained in a measured gas such as exhaust gas of an internal combustion engine. For example, in the full-range air-fuel ratio sensor whose output changes linearly according to the oxygen concentration, between the electromotive force cell composed of a solid electrolyte body mainly composed of zirconia and the pump cell, it is possible to introduce a measured gas from the outside. Has a detection element in which a measurement chamber is formed. Then, the pump current flowing between the electrodes of the pump cell is controlled so that the electromotive force cell voltage generated between the electrodes of the electromotive force cell becomes the target voltage, and the oxygen in the gas in the measurement chamber introduced into the measurement chamber is pumped. Pumping is performed, and the oxygen concentration of the measured gas is detected by the magnitude of the pump current required for pumping. The target voltage is usually set to a value (specifically, target voltage=450 mV) at which the oxygen concentration in the measurement chamber gas becomes a stoichiometric air-fuel ratio (stoichiometry, hereinafter abbreviated as stoichiometry).

  By the way, it is known that the electromotive force cell and the pump cell which form the detection element of such a gas sensor increase in cell impedance as they deteriorate due to use or the like. That is, in a deteriorated electromotive force cell or the like, the cell impedance at the same temperature becomes relatively higher than that before deterioration. Some gas sensors have a heater for heating an electromotive force cell or the like, and in order to control the cell temperature at a constant level, feedback control is performed on the energization of the heater so that the cell impedance becomes constant. In such a gas sensor, when the electromotive force cell or the like is deteriorated and the cell impedance is increased, the energization of the heater is controlled in the direction of decreasing the cell impedance in order to bring the cell impedance closer to the target value, that is, in the direction of increasing the element temperature. It will be. Then, there is a problem that the gas sensor is overheated and the deterioration is further promoted and the output of the pump cell is biased.

  In order to solve this problem, for example, in Patent Document 1, it is determined that the deterioration determining unit determines the deterioration state in which the cell impedance of the detection element (electromotive force cell or the like) is increased, and the detection element is in the deterioration state. There is disclosed an oxygen concentration detection device including a target resistance changing unit that sometimes increases the target resistance. As a specific deterioration determination means, a heater supply power comparison means for comparing the heater supply power supplied to the heater with a predetermined determination value is shown.

  By the way, as described above, the target voltage is usually set to a value at which the oxygen concentration in the measurement chamber gas becomes the stoichiometric air-fuel ratio (specifically, target voltage=450 mV). That is, in the normal control state, the measurement chamber gas is controlled to the oxygen concentration of the stoichiometric air-fuel ratio. However, by changing the above-mentioned target voltage, it is possible to control the measurement chamber gas to a rich atmosphere or a lean atmosphere.

  On the other hand, it has been found that the detected cell impedance is also affected by the difference in oxygen concentration in the measurement chamber gas. Specifically, the cell impedance detected when the measurement chamber gas is rich is larger than the cell impedance detected when the measurement chamber gas is lean. Moreover, when the detection element deteriorates due to use, in addition to the cell impedance becoming relatively higher than that before the deterioration, the cell impedance detected when the measurement chamber gas is rich and the lean state It has been found that the difference with the cell impedance that is sometimes detected is larger than that before the deterioration.

  Therefore, in Patent Document 2, by changing the target voltage of the electromotive force cell voltage and controlling the pump current by the current control means, two states with different oxygen concentrations are created for the gas in the measurement chamber, and in these states, Disclosed is a gas sensor control device including a deterioration detecting unit that detects deterioration of a gas sensor by using a difference between a one-element resistance and a second element resistance.

JP, 10-26599, A JP, 2014-48279, A

  However, as described in Patent Document 1, when the heater supply power comparison means compares the heater supply power supplied to the heater with a predetermined determination value, the detection of deterioration of the detection element is indirect and accurate. Low. In addition, as described in Patent Document 2, when the target voltage is switched to change the oxygen concentration of the gas in the measurement chamber to detect deterioration, it takes time to detect and the oxygen concentration is appropriately detected during deterioration detection. It is difficult to detect (air-fuel ratio).

  The present invention has been made in view of such problems, and provides a gas sensor control device capable of appropriately detecting deterioration of an electromotive force cell or the like of a gas sensor in a short time.

  One embodiment of the present invention for solving the above-mentioned problems is to provide a first solid electrolyte body, a reference electrode formed on the first solid electrolyte body and exposed to a reference gas having a reference oxygen partial pressure, and a gas to be measured. An electromotive force cell that has a first measurement chamber electrode exposed to an inflowing measurement chamber gas and that generates an electromotive force according to a difference between the reference oxygen partial pressure and the oxygen partial pressure of the measurement chamber gas, And a second solid electrolyte body, a second measurement chamber electrode formed on the second solid electrolyte body and exposed to the measurement chamber gas, and a pump electrode exposed to the measurement gas or the outside air, A control device for a gas sensor, comprising a pump cell for pumping or pumping oxygen in the measurement chamber to the measurement gas or the outside air, wherein an electromotive force cell voltage generated between the reference electrode and the first measurement chamber electrode. A current control means for controlling a pump current flowing through the pump cell so that the gas in the measurement chamber has a stoichiometric voltage generated in the electromotive force cell when the gas is in stoichiometry; One current pulse is applied to the electromotive force cell to generate the first current pulse in the electromotive force cell during the application of the first current pulse and at a first time when 0.2 msec or more has elapsed from the start of application of the first current pulse. A first detection unit that detects a one-cell voltage; and a detection instruction unit that instructs the first detection unit to detect the first cell voltage when the electromotive force cell voltage is the stoichiometric voltage. It is a control device of a gas sensor.

  As described above, when the electromotive force cell and the pump cell of the gas sensor are deteriorated, the cell impedance increases. Moreover, the degree of increase depends on the frequency, and in the low frequency region, specifically, in the frequency region of 100 Hz or less, particularly in the frequency region of 50 Hz or less, the cell impedance greatly increases due to deterioration, and 0.2 msec ( (= 200 μsec) or more, it has been found that the effect becomes apparent when a pulse having a length of not less than 200 μsec is applied. In addition, as described above, the cell impedance is also affected by the difference in oxygen concentration in the measurement chamber gas.

Therefore, in the control device of the present gas sensor, under the condition that the electromotive force cell voltage is the stoichiometric voltage, that is, under the condition that the gas in the measurement chamber is controlled to be stoichiometric, the first current pulse that continues for 0.2 msec or more is generated. The voltage is applied to the power cell, and the first cell voltage generated in the electromotive force cell at the first time when 0.2 msec or more has elapsed from the start of application is detected. The first cell voltage is proportional to the magnitude of cell impedance generated in the electromotive force cell.
As a result, the first cell voltage corresponding to the first cell impedance of the electromotive force cell affected by the deterioration can be appropriately detected in a short time without being affected by the oxygen concentration of the measurement chamber gas. Then, by using this first cell voltage, the degree of deterioration of the gas sensor including the electromotive force cell can be appropriately detected in a short time.

  The timing at which the electromotive force cell voltage becomes the stoichiometric voltage and the first detecting means detects the first cell voltage is, for example, that the engine of the vehicle is started, the gas sensor is activated, and the electromotive force cell voltage is changed. Immediately after the energization control to the pump cell based on it is started, the fuel cut (hereinafter referred to as the fuel cut to the timing when the electromotive force cell voltage becomes the stoichiometric voltage or the fuel supply to the engine during vehicle traveling such as engine braking) In the period (also abbreviated as FC), the timing when the electromotive force cell voltage becomes the stoichiometric voltage can be mentioned. In addition, the electromotive force cell voltage becomes the stoichiometric voltage after a lapse of a predetermined period (for example, 30 days) or a lapse of a predetermined running time (for example, 1000 hours of running) since the previous acquisition of the first cell voltage. The timing and the timing when the electromotive force cell voltage becomes the stoichiometric voltage after the driver instructs the engine to stop by turning off the key switch are also included.

In addition, the first current pulse applied to the electromotive force cell has a square wave shape in which a constant first current is passed through the electromotive force cell. By passing the first current pulse through the electromotive force cell, the cell impedance of the electromotive force cell is increased. A corresponding cell voltage is generated. As described above, since the cell impedance has the frequency characteristic, the cell voltage generated after applying the first current pulse changes with time. For example, the cell voltage at 5000 μsec is higher than the cell voltage at 60 μsec from the start of application of the first current pulse. The cell impedance of the electromotive force cell at each time is obtained by subtracting the cell voltage at the application start time (start time t0) of the first current pulse from the cell voltage at that time and dividing by the first current. Be done.
After detecting the first cell voltage at the first time, it is preferable to quickly stop the application of the first current pulse, and the first time is 50 msec or less at the longest. Therefore, the length of the first current pulse is 50 msec or less. Good to do. This is because if it is too long, the change in the oxygen partial pressure in the measurement chamber due to the application of the first current pulse becomes large, and it becomes impossible to immediately return to the detection of the oxygen concentration after the end of the first current pulse.

  The first detection unit for detecting the first cell voltage includes a unit including a circuit and a process configured to directly acquire the first cell voltage, and a difference voltage between the first cell voltage and another voltage, etc. Means for indirectly obtaining the first cell voltage by obtaining an amount of

  In addition, in the above-described gas sensor control device, a second cell voltage that detects the second cell voltage generated in the electromotive force cell at a second time before an elapsed time of 0.2 msec has elapsed from the start of application of the first current pulse The gas sensor control device may include a detection unit and a deterioration determination unit that determines deterioration of the gas sensor based on a voltage difference between the first cell voltage and the second cell voltage.

The cell impedance of the electromotive force cell is affected by the above-mentioned difference in oxygen concentration in the measurement chamber gas as well as by disturbance factors such as temperature changes in the gas to be measured. It is desirable to do.
In this control device, the second cell voltage generated in the electromotive force cell at the second time at the same first current pulse that detects the first cell voltage is detected, and the difference between the first cell voltage and the second cell voltage is detected. Deterioration of the gas sensor is determined based on the voltage. Therefore, the influence of disturbance factors such as the oxygen concentration in the measurement chamber gas and the temperature change of the measured gas can be canceled to determine the deterioration, and the presence or the degree of the deterioration can be determined more appropriately. .
Moreover, in the case where the same first current pulse is applied, the difference voltage between the second cell voltage at the second time at the stage where the time is relatively short and the first cell voltage at the first time when the time is relatively long. Therefore, the change of the cell voltage due to the deterioration of the cell impedance in the low frequency region is likely to appear, and also from this point, the presence or absence and the degree of the deterioration can be more appropriately determined.

  As the second detection means for detecting the second cell voltage, similar to the first detection means described above, a means including a circuit and processing configured to directly obtain the second cell voltage, and the second cell It also includes means including circuitry and processing configured to indirectly obtain the second cell voltage by obtaining another quantity, such as a voltage difference between the voltage and the other voltage.

  Further, the deterioration determining means may determine the deterioration of the gas sensor based on the difference voltage between the first cell voltage and the second cell voltage. In addition to the difference voltage between the first cell voltage and the second cell voltage, this difference may be determined. The deterioration may be determined by using the cell impedance of the electromotive force cell obtained by dividing the voltage by the constant current passed by the first current pulse.

  Alternatively, in the control device for the gas sensor, the initial detection means for detecting the starting cell voltage generated in the electromotive force cell at the start time immediately before the application of the first current pulse, the first cell voltage and the start The gas sensor control device may include a deterioration determination unit that determines deterioration of the gas sensor based on a voltage difference from the hour cell voltage.

As described above, the cell impedance of the electromotive force cell is affected by disturbance factors such as the temperature change of the gas to be measured as well as the difference in the oxygen concentration of the gas in the measurement chamber described above. It is desirable to determine the presence or absence and the degree.
In this control device, the starting cell voltage generated in the electromotive force cell at the starting time at the same first current pulse is detected, and the deterioration of the gas sensor is determined based on the difference voltage between the first cell voltage and the starting cell voltage. To do. Therefore, it is possible to cancel the influence of a disturbance factor such as a change in the temperature of the gas to be measured and determine the deterioration, and it is possible to more appropriately determine the presence or absence and the degree of the deterioration.

  Alternatively, in the above-described gas sensor control device, deterioration determination for determining deterioration of the gas sensor based on a difference voltage between the first cell voltage and the previously stored new first cell voltage when the gas sensor is new. And a gas sensor control device.

  In this control device, the deterioration of the gas sensor is determined based on the voltage difference between the first cell voltage and the previously stored gas sensor when it is new, that is, before the deterioration. Therefore, it is possible to cancel the variation of the new first cell voltage in each gas sensor, clarify the increase in the first cell voltage due to deterioration, and more appropriately determine the presence or absence and degree of deterioration.

  The gas sensor control device according to any one of the preceding three items, comprising: deterioration warning means for warning deterioration of the gas sensor when the deterioration judgment means judges that the gas sensor has deteriorated. Is good.

  This control device warns of the deterioration of the gas sensor when it is determined that the gas sensor has deteriorated. Therefore, appropriate processing such as replacement of the gas sensor can be performed according to the warning.

  Examples of the warning include urging the driver to replace the gas sensor by turning on a warning light on an instrument panel (instrument panel) in the driver's seat of the vehicle or issuing a warning by voice.

  The gas sensor control device according to any one of the above, wherein the pump current correction means corrects a quantity value corresponding to the pump current with an amount based on the first cell voltage, and the corrected pump current. It is advisable to use a control device for the gas sensor that includes an output unit that outputs the value to the outside.

When the gas sensor deteriorates, not only the cell impedance of the electromotive force cell and the pump cell increases, but also the characteristics of the electromotive force cell and the pump cell deteriorate such that the responsiveness of the pump cell decreases. Along with this, the output of the gas sensor (pump current value) changes (drifts).
On the other hand, in this gas sensor control device, since the amount corresponding to the acquired pump current is corrected by the amount based on the detected first cell voltage, even if the gas sensor is deteriorated, it can be corrected appropriately. Various gas detection signals can be output to the outside.

An example of the amount corresponding to the pump current is a gas detection signal obtained by converting the pump current into a voltage with a resistor.
The amount based on the first cell voltage may be, for example, the difference voltage between the first cell voltage and the second cell voltage, the difference voltage between the first cell voltage and the start cell voltage, or the first cell voltage. And the voltage difference between the new first cell voltage and the like. Further, an impedance difference obtained by dividing these difference voltages by the first current can also be mentioned.

  Furthermore, in the gas sensor control device according to any one of the above, the gas sensor includes a heater that heats the electromotive force cell and the pump cell, and a constant second current shorter than the first current pulse. Is applied to the electromotive force cell, and the electromotive force cell is in the middle of applying the second current pulse and at a third time 0.2 msec after the start of application of the second current pulse. Based on the first cell voltage detected by the first detection means, the third detection means for detecting the third cell voltage, the heater control means for controlling the energization of the heater by using the third cell voltage. The gas sensor control device may include a heater control correction unit that corrects the control by the heater control unit based on the amount.

In the heater control unit that controls the energization of the heater using the third cell voltage, it seems as if the element temperature is low when the third cell voltage of the electromotive force cell increases due to the deterioration of the gas sensor. For this reason, the heater control means controls the heater so as to raise the heater temperature. That is, the temperature of the electromotive force cell (gas sensor) is maintained at a value higher than the setting. Then, the amount of the gas to be measured introduced into the measurement chamber, and thus the amount of oxygen to be discharged by the pump current, increases. Therefore, even if the oxygen concentration of the measured gas introduced is the same, the pump current passed through the pump cell increases as compared with that before deterioration due to the increase in the amount of oxygen introduced.
On the other hand, in this gas sensor control device, the heater control correction means corrects the control of the heater control means by an amount based on the first cell voltage. As a result, the heater temperature shift due to the deterioration of the gas sensor is eliminated, the increase in pump current due to the heater temperature shift is corrected, and an appropriate gas detection signal can be output to the outside.

The second current pulse has a square wave shape in which a constant second current is passed through the electromotive force cell. By passing the second current pulse through the electromotive force cell, a cell voltage corresponding to the cell impedance of the electromotive force cell is generated. Occur.
The magnitude of the second current may be different from that of the first current, but it may be the same. This is because the circuit configuration that allows the first current (second current) to flow can be facilitated.
The third time for detecting the third cell voltage may be before 0.2 msec has elapsed from the start of application of the second current pulse. However, when the second detecting means is provided, the above-mentioned second cell voltage is obtained. It may be the same as the second time for detecting the. By doing so, the detection of the second cell voltage and the detection of the third cell voltage can be performed by the same circuit. The cell impedance of the electromotive force cell at the third time can be obtained by subtracting the cell voltage at the time of starting the application of the second current pulse from the third cell voltage at the third time and dividing by the second current. Be done.

  As a method of correcting the control in the heater control means, for example, the detected third cell voltage increases with deterioration, so that the first resistance voltage is canceled (lowered) by the resistance increase due to deterioration. The heater control is performed by the amount based on the first cell voltage detected by the detection unit, and the amount based on the first cell voltage in accordance with the method of correcting the obtained third cell voltage or the increase in the third cell voltage due to deterioration. Examples include a method of correcting the target value of the means.

  Further, in the above-described gas sensor control device, the heater control correction means is a gas sensor control device that corrects a target value in the heater control means by an amount based on the first cell voltage.

As a correction method in the heater control means, a method of correcting the detected third cell voltage can also be adopted. However, in this case, it is necessary to perform the correction process every time the third cell voltage is detected.
On the other hand, in the above-described gas sensor control device, the target value in the heater control means is corrected by the amount based on the first cell voltage. Therefore, once the correction is made, the target value is corrected next (the first It is not necessary to perform correction until the cell voltage is acquired), and the process is easy. Specifically, there is a method of estimating a change (increase) in the third cell voltage due to deterioration from the increase in the first cell voltage due to deterioration, adding the increased amount to a target value, and increasing this. The target value can also be multiplied by the correction coefficient corresponding to the acquired first cell voltage.

It is explanatory drawing which shows the whole structure at the time of equipping an exhaust pipe with the gas sensor control apparatus and gas sensor which concern on embodiment, and using it for engine control. It is explanatory drawing which shows schematic structure of the gas sensor control apparatus which concerns on embodiment. It is a section explanatory view showing a schematic structure of a gas sensor. 6 is a graph showing a relationship between a current pulse application time t and a detected cell voltage Vs of an electromotive force cell for a new product and a deteriorated product. 6 is a flowchart showing a processing operation of 2-1 differential voltage DVs21 detection/storage processing in the microprocessor of the gas sensor control device according to the embodiment. 6 is a flowchart showing a processing operation of a detection process of a difference voltage ΔVs02D, ΔVs01D in the 2-1 difference voltage DVs21 detection process shown in FIG. 5, according to the embodiment. 6 is a flowchart showing a processing operation of deterioration detection and deterioration warning processing in the microprocessor of the gas sensor control device according to the embodiment. 6 is a flowchart showing a processing operation of correcting deterioration of a gas detection signal in the microprocessor of the gas sensor control device according to the embodiment. 7 is a flowchart showing a target differential voltage correction processing operation for heater temperature control in the microprocessor of the gas sensor control device according to the embodiment. 6 is a flowchart showing a heater temperature control processing operation in the microprocessor of the gas sensor control device according to the embodiment. 9 is a flowchart according to Modification 1 and showing a processing operation of 0-1 difference voltage ΔVs01 detection/storage processing in the microprocessor of the gas sensor control device. 12 is a flowchart according to the first modification, which shows a processing operation of a detection process of a cell voltage Vs1D in the 0-1 difference voltage ΔVs01 detection process shown in FIG. 9 is a flow chart showing a processing operation of deterioration detection and deterioration warning processing in the microprocessor of the gas sensor control device according to the first modification. 11 is a flowchart according to the first modification, showing a processing operation of correcting a deterioration of a gas detection signal in the microprocessor of the gas sensor control device. 11 is a flowchart according to the first modification, showing a processing operation of a target differential voltage correction for controlling a heater temperature in a microprocessor of the gas sensor control device. 14 is a flowchart according to the second modification, which shows the processing operation of the first differential voltage SVs1 detection/storage processing in the microprocessor of the gas sensor control device. 14 is a flowchart according to the second modification, showing the processing operation of deterioration detection and deterioration warning processing in the microprocessor of the gas sensor control device. 11 is a flowchart according to the second modification, which illustrates a processing operation of correcting deterioration of a gas detection signal in the microprocessor of the gas sensor control device. 9 is a flowchart according to Modification 2 and showing a target differential voltage correction processing operation for heater temperature control in the microprocessor of the gas sensor control device.

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an overall configuration when the gas sensor control device 1 and the gas sensor 2 according to the present embodiment are used for controlling an engine. Further, FIG. 2 is a diagram showing a schematic configuration of the gas sensor control device 1.
The gas sensor 2 is attached to the exhaust pipe EP of the engine ENG of the vehicle (not shown), detects the oxygen concentration (air-fuel ratio) in the exhaust gas EG (measured gas), and is used for air-fuel ratio feedback control in the engine ENG. It is a full-range air-fuel ratio sensor (oxygen sensor). As shown in FIG. 2, the gas sensor 2 has a sensor unit 3 that detects the oxygen concentration, and a heater unit 4 that heats the sensor unit 3.
The gas sensor control device 1 is connected to the gas sensor 2 and controls it. Further, the gas sensor control device 1 is connected to the CAN bus 102 of the vehicle via the connection bus 101, and is capable of transmitting/receiving data to/from the ECU 100. The gas sensor control device 1 includes a microprocessor 50, a sensor control circuit 60 that controls the sensor unit 3 of the gas sensor 2, and a heater control circuit 70 that controls energization of the heater unit 4.

  First, the gas sensor 2 will be described. FIG. 3 is a cross-sectional explanatory view showing a schematic configuration of the gas sensor 2. The gas sensor 2 includes a sensor unit 3 and a heater unit 4 laminated on the sensor unit 3. Of these, the sensor unit 3 is formed by stacking the pump cell 10, the porous layer 18, and the electromotive force cell 20 in this order, and the heater unit 4 is stacked on the electromotive force cell 20.

The electromotive force cell 20 has a plate-shaped electrolyte layer 21 made of a solid electrolyte body mainly composed of zirconia and having oxygen ion conductivity as a base body, and a pair of electrodes 22, 23 (made mainly of porous platinum) on both surfaces thereof. Porous electrode). Specifically, the reference electrode 23 is provided on the reference chamber side surface 21e which is one surface (lower surface in the figure) of the electrolyte layer 21, and the first measurement chamber is provided on the measurement chamber side surface 21i which is the other surface (upper surface in the figure). The electrodes 22 are respectively formed.
In addition, the pump cell 10 also has an electrolyte layer 11 made of a plate-like solid electrolyte body mainly composed of zirconia and having oxygen ion conductivity as a base, and a pair of electrodes 12, 13 (made mainly of porous platinum) on both surfaces thereof. A porous electrode) is formed. Specifically, the outer electrode 12 is on the outer surface 11e, which is one surface (the upper surface in the drawing) of the electrolyte layer 11, and the second measurement chamber electrode is on the measurement chamber side surface 11i, which is the other surface (the lower surface in the drawing). 13 are formed respectively.

  The measurement chamber side surface 11i of the electrolyte layer 11 of the pump cell 10 faces the measurement chamber side surface 21i of the electrolyte layer 21 of the electromotive force cell 20, and the porous layer 18 is interposed between the electrolyte layer 11 and the electrolyte layer 21. There is. The porous layer 18 is provided in a form having a predetermined length (depth direction dimension) on the left and right sides in FIG. 3 among the peripheral edges of the measurement chamber side surface 11i of the electrolyte layer 11 and the measurement chamber side surface 21i of the electrolyte layer 21. There is. In addition to the porous layer 18, an insulating layer (not shown) mainly containing alumina is provided between the electrolyte layer 11 and the electrolyte layer 21. Thus, the hollow space surrounded by the inner surface of the insulating layer, the inner surface of the porous layer 18, the measurement chamber side surface 11i, and the measurement chamber side surface 21i can introduce the exhaust gas EG through the porous layer 18. Measuring chamber 3S.

  The second measurement chamber electrode 13 of the pump cell 10 and the first measurement chamber electrode 22 of the electromotive force cell 20 are exposed in the measurement chamber 3S. These measurement chamber electrodes 13 and 22 are electrically connected to each other and are connected to the terminal COM of the sensor unit 3. The outer electrode 12 of the pump cell 10 is connected to the terminal Ip+ of the sensor unit 3, and the reference electrode 23 of the electromotive force cell 20 is connected to the terminal Vs+ of the sensor unit 3. Exhaust gas EG is introduced into the measurement chamber 3S through the porous layer 18.

  Further, the entire outer electrode 12 of the pump cell 10 is covered with a protective layer 15 that suppresses poisoning of the outer electrode 12. The protective layer 15 is made of porous ceramic or the like and is exposed to the exhaust gas EG.

  The heater portion 4 is laminated on the reference chamber side surface 21e (lower side in the figure) of the electrolyte layer 21 of the electromotive force cell 20, and a heater resistor 41 made of platinum is sandwiched between a pair of alumina layers 42 and 43. Have a configuration. By heating the sensor unit 3 by the heater unit 4, the electrolyte layers 11 and 21 of the sensor unit 3 are activated, and oxygen ions can move in the electrolyte layers 11 and 21. The heater part 4 (alumina layers 42 and 43) covers the reference electrode 23 of the electromotive force cell 20 to seal the reference electrode 23. The space (holes) inside the porous reference electrode 23 constitutes a reference oxygen chamber 24 that functions as an internal reference oxygen source described below.

  Next, the gas sensor control device 1 will be described with reference to FIG. The sensor control circuit 60 is mainly composed of an ASIC, and has three terminals Vs+, Ip+, and Ip+ of the sensor unit 3 via connection wirings 81, 82, and 83 (specifically, wirings and lead wires on the circuit board). Each connected to COM. The sensor control circuit 60 generates a minute current Icp having a predetermined magnitude in the electromotive force cell 20 of the sensor unit 3, and generates the electromotive force cell 20 at both ends (between the first measurement chamber electrode 22 and the reference electrode 23) of the electromotive force cell 20. The pump current Ip flowing in the pump cell 10 is feedback-controlled so that the electromotive force cell voltage Vs becomes 450 mV (=target voltage Vrf (described later)), and oxygen in the measurement chamber gas EGS in the measurement chamber 3S is pumped. Pump in and out. Here, the magnitude of the pump current Ip flowing in the pump cell 10 and the direction of the current should change according to the oxygen concentration (air-fuel ratio) in the exhaust gas EG introduced into the measurement chamber 3S through the porous layer 18. Therefore, the oxygen concentration in the exhaust gas EG can be detected by detecting the current value (magnitude and positive/negative) of the pump current Ip. The minute current Icp is a current in the direction in which oxygen in the measurement chamber 3S is pumped out toward the reference electrode 23 (porous electrode) from the electromotive force cell 20. Therefore, the reference oxygen chamber 24 formed by the holes of the porous reference electrode 23 serves as an internal reference oxygen source having the reference gas RG having a predetermined oxygen partial pressure.

In the sensor control circuit 60, the electric potentials of the terminal COM and the terminal Vs+ of the sensor unit 3 are input to the microprocessor 50 through the COM port 55 and the Vs port 56 by circuits (not shown), respectively. The electromotive force cell voltage Vs is calculated in the microprocessor 50 as a voltage difference between the potentials input to the Vs port 56 and the COM port 55.
Further, the magnitude of the pump current Ip is detected by the differential amplifier circuit 61 as the gas detection signal Vip converted into the voltage signal, and is output from the output terminal 60b to the microprocessor 50.
In addition to the detection of the gas detection signal Vip, the sensor control circuit 60 uses a current pulse as described later to change the differential voltage ΔVs that changes according to the cell impedance Rvs of the electromotive force cell 20 of the sensor unit 3. Is detected and output from the differential voltage output terminal 60c. The microprocessor 50 can input the gas detection signal Vip and the difference voltage ΔVs through the A/D input ports 51 and 52. The value of the detected gas detection signal Vip is sent to the ECU 100 via the connection bus 101.

  The heater control circuit 70 is connected to the battery BT and the ground potential GND, is connected to the heater unit 4 of the gas sensor 2 via two lead wires 71 and 72, and is connected to the PWM output port 54 of the microprocessor 50. It is connected to the. The heater control circuit 70 performs PWM control of energization to the heater unit 4 by the PWM pulse output from the PWM output port 54.

Next, the operation of the sensor control circuit 60 when measuring the oxygen concentration using the sensor unit 3 of the gas sensor 2 will be described. The sensor control circuit 60 includes, in addition to the detection resistor R1, first to fifth operational amplifiers OP1 to OP5, a first switch SW1, three second switches SW2, two third switches SW3, a PID control circuit 69, and differential amplification. The circuit 61, the Icp supply circuit 62, the current sources 63, 64, 65, 66, the control unit 67, and the like.
The terminal COM of the sensor unit 3 is connected to the Vcent point via the connection wiring 83. Further, the terminal Ip+ is connected to the output terminal of the second operational amplifier OP2 via the connection wiring 82. Further, the terminal Vs+ is connected to the non-inverting input terminal + of the fourth operational amplifier OP4 via the connection wiring 81. The terminal Vs+ is also connected to the Icp supply circuit 62. The Icp supply circuit 62 is a constant current circuit that causes the minute current Icp having the predetermined value described above to flow in the electromotive force cell 20. Further, the Icp supply circuit 62, the connection wiring 81, the electromotive force cell 20, and the connection wiring 83 are connected in this order to form a current path through which the minute current Icp flows.

  When measuring the oxygen concentration, the controller 67 turns on the first switch SW1 (turns off the second and third switches SW2 and SW3). As a result, the potential of the terminal Vs+ of the sensor unit 3 is input to the input terminal IT of the PID control circuit 69 via the connection wiring 81 and the fourth operational amplifier OP4 and the first operational amplifier OP1 that form the voltage follower circuit. The control unit 67 is a logic circuit configured in the ASIC forming the sensor control circuit 60. The control unit 67 is connected to the serial transmission port 53 of the microprocessor 50 through the command reception port 60d of the sensor control circuit 60, and based on a command from the microprocessor 50, the first switch SW1 to the third switch SW3. ON/OFF control of

  One input terminal of the second operational amplifier OP2 is connected to the Vcent point, and the reference voltage Vc (=+3.6V) is applied to the other input terminal. The output terminal of the second operational amplifier OP2 is connected to the terminal Ip+ of the sensor unit 3 via the connection wiring 82. The Vcent point is also connected to the reference terminal RT of the PID control circuit 69.

  The PID control circuit 69 has an output terminal OT in addition to the above-mentioned input terminal IT and reference terminal RT, and has the potential (Vs+ of the terminal Vs+ of the sensor unit 3 input via the fourth operational amplifier OP4 and the first operational amplifier OP1. The magnitude of the pump current Ip is PID controlled so that the potential difference between the input terminal IT) and the potential at the Vcent point (reference terminal RT) becomes the target voltage Vrf (=450 mV). Specifically, in the PID control circuit 69, the deviation between the target voltage Vrf (=450 mV) and the electromotive force cell voltage Vs generated between both electrodes 22 and 23 of the electromotive force cell 20 is PID-calculated, and the second operational amplifier is operated. By being fed back to OP2, the second operational amplifier OP2 causes the pump current Ip to flow through the pump cell 10.

  Further, the sensor control circuit 60 includes a detection resistor R1 that detects the magnitude of the pump current Ip and converts it into a voltage signal. The voltage across the detection resistor R1 (the difference voltage between the potential Vcent and the potential Vpid) is the difference. The signal is differentially amplified by the dynamic amplification circuit 61, and is output from the output terminal 60b to the microprocessor 50 as the gas detection signal Vip. As described above, since the magnitude of the pump current Ip and the direction of the current change according to the oxygen concentration (air-fuel ratio) of the exhaust gas EG, the exhaust gas is detected from the gas detection signal Vip obtained by converting the pump current Ip into a voltage signal. The oxygen concentration of the gas EG can be detected. In the microprocessor 50, this gas detection signal (oxygen concentration signal) Vip is converted into a digital value through the A/D input port 51 and acquired, and the acquired value is sent out to the ECU 100 through the connection bus 101.

Next, detection of the cell impedance Rvs (first cell impedance Rivs, second cell impedance Rpvs) of the electromotive force cell 20 of the sensor unit 3 using the sensor control circuit 60 will be described. However, in the sensor control circuit 60 of the present embodiment, instead of detecting the cell impedance Rvs itself, the difference voltage ΔVs that changes according to the cell impedance Rvs is detected.
In the sensor control circuit 60, the first operational amplifier OP1 forms a sample hold circuit together with the first switch SW1 and the capacitor C1. When detecting the cell impedance Rvs (detecting the difference voltage ΔVs), the first switch SW1 is switched from on to off by the control unit 67. As a result, this sample-hold circuit causes the potential of the terminal Vs+ (reference electrode 23 of the electromotive force cell 20) of the sensor unit 3 (output of the fourth operational amplifier OP4) immediately before the detection operation of the difference voltage ΔVs (start time t0). Hold. Therefore, while the detection operation of the difference voltage ΔVs described later is being performed (while the first switch SW1 is off), the potential of the terminal Vs+ immediately before the detection operation of the difference voltage ΔVs (the first operational amplifier OP1 is held. Hold voltage) is input to the input terminal IT of the PID control circuit 69 and used for PID control. Further, the gas detection signal Vip that is PID-controlled using this hold voltage is output from the output terminal 60b.

  Further, the control unit 67 switches off the first switch SW1 and then switches the three second switches SW2 from off to on. The third switch SW3 remains off. The current source 65, the second switch SW2, the connection wiring 83, the terminal COM (the first measurement chamber electrode 22), the electromotive force cell 20, the terminal Vs+ (the reference electrode 23) are temporarily provided only while the respective second switches SW2 are turned on. ), the connection wiring 81, the second switch SW2, and the current source 63 are formed in this order, and a square wave current pulse that applies a constant constant current −Iconst to the electromotive force cell 20 is applied.

The third operational amplifier OP3 constitutes a differential amplifier circuit, and a hold voltage (potential of the immediately preceding terminal Vs+) held by the first operational amplifier OP1 and a current pulse of a constant current −Iconst flow to the electromotive force cell 20. In doing so, a voltage corresponding to the difference between the potential of the terminal Vs+ (reference electrode 23) and the potential (output of the fourth operational amplifier OP4) generated in response to this is output. This output voltage is the difference voltage ΔVs. The difference voltage ΔVs is obtained when the constant current −Iconst is not applied to the electromotive force cell 20 (immediately before turning on each second switch SW2) and when the constant current −Iconst is applied (on each second switch SW2 is turned on). , And the difference between the electromotive force cell voltages Vs generated in the electromotive force cell 20. The difference voltage ΔVs has a magnitude proportional to the cell impedance Rvs of the electromotive force cell 20 in which the constant current −Iconst is applied.
When the current pulse is continuously applied to the electromotive force cell 20 after the start time t0, the electromotive force cell voltage Vs tends to gradually increase as shown in FIG. Further, in FIG. 4, as shown by two graphs of a new product (broken line) and a deteriorated product (solid line), the electromotive force cell voltage Vs (and therefore the cell impedance Rvs and the differential voltage ΔVs) is the gas sensor 2 (the sensor unit 3). ), that is, its size tends to increase with use.

  The difference voltage ΔVs output from the third operational amplifier OP3 is input to the sample hold circuit including the second switch SW2, the resistor R2, the capacitor C2, and the fifth operational amplifier OP5. The output voltage ΔVs of the sample-hold circuit (fifth operational amplifier OP5) changes similarly to the difference voltage ΔVs input from the third operational amplifier OP3 when the second switch SW2 is on, but the second switch SW2 Is turned off, the difference voltage ΔVs at the time when the second switch SW2 is turned off is held by the capacitor C2 and continues to be output from the output terminal 60c. That is, during the operation of detecting the difference voltage ΔVs by turning on the second switch SW2, the difference voltage ΔVs generated by the third operational amplifier OP3 is directly output from the fifth operational amplifier OP5. On the other hand, after the second switch SW2 is turned off and the detection operation of the difference voltage ΔVs is completed, a constant difference voltage ΔVs output at the time when the second switch SW2 is turned off, which is held in the fifth operational amplifier OP5, is output. Continue to be done.

The microprocessor 50 converts the differential voltage ΔVs output from the output terminal 60c into a digital value at predetermined time intervals through the A/D input port 52 and acquires the digital value. As a result, the microprocessor 50 can detect (calculate) the cell impedance Rvs of the electromotive force cell 20 from the difference voltage ΔVs.
Note that the control unit 67 controls the second switch SW2 to be turned on during a period in which a current pulse of the constant current −Iconst is passed, that is, a period for detecting the difference voltage ΔVs (start time t0 and end time of application of the current pulse). Controlled. In the present embodiment, as will be described later, two types of application end time are used, that is, first time t1=5000 μsec (=5.0 msec) and third time t3=60 μsec.

  Further, as described above, even after the second switch SW2 is turned off, the fifth operational amplifier OP5 continues to output the difference voltage ΔVs at the time point when the second switch SW2 is turned off. Therefore, the microprocessor 50 does not need to acquire the difference voltage ΔVs during the operation of detecting the difference voltage ΔVs, and the fifth operational amplifier OP5 holds the difference voltage ΔVs at an arbitrary timing after the second switch SW2 is turned off. The output difference voltage ΔVs can be acquired.

  When the operation of detecting the difference voltage ΔVs is completed, the control unit 67 turns off the second switch SW2 and then turns on the third switch SW3 for a predetermined period. During this time, the first switch SW1 remains off. By turning on the third switch SW3, the current source 64, the third switch SW3, the connection wiring 81, the terminal Vs+ (reference electrode 23), the electromotive force cell 20, the terminal COM (first measurement chamber electrode 22), the connection wiring A current path in which 83, the third switch SW3, and the current source 66 are arranged in this order is formed, and a reverse current pulse of constant current +Iconst is applied to the electromotive force cell 20 for a predetermined time.

  The reverse current pulse of the constant current +Iconst has the opposite polarity to the current pulse of the constant current −Iconst described above. In this embodiment, the length of the predetermined period during which the third switch SW3 is turned on is 60 μsec. In this way, by flowing the current pulse of the opposite polarity to the electromotive force cell 20, the time until the electromotive force cell voltage Vs+ generated in the electromotive force cell 20 returns to a normal value is shortened. By applying the current pulse of the constant current −Iconst to the electromotive force cell 20, the orientation phenomenon of the electrolyte layer (solid electrolyte body) forming the electromotive force cell 20 occurs, and the electromotive force cell voltage Vs+ generated in the electromotive force cell 20 is increased. Due to the influence, the correct electromotive force cell voltage to be generated between the reference electrode 23 and the first measurement chamber electrode 22 cannot be output according to the oxygen concentration of the measurement chamber gas EGS. This is to forcibly cancel the orientation phenomenon of the electrolyte layer (solid electrolyte body) by the reverse current pulse.

  Therefore, the control unit 67 turns on the third switch SW3, supplies a reverse current pulse of constant current +Iconst to the electromotive force cell 20 for 60 μsec, and then turns off the third switch SW3. Then, after a predetermined stabilization waiting time until the electromotive force cell 20 outputs the electromotive force cell voltage Vs+ according to the oxygen concentration of the measurement chamber gas EGS, the first switch SW1 is turned back on.

  As described above, the sensor control circuit 60 can detect the gas detection signal Vip according to the oxygen concentration of the exhaust gas EG, and temporarily switch from the state of detecting the gas detection signal Vip to the electromotive force cell. It is possible to detect the differential voltage ΔVs that changes according to the cell impedance Rvs of 20, and then to return to the state in which the gas detection signal Vip is detected again. While the differential voltage ΔVs is being detected, the PID-controlled value is output as the gas detection signal Vip using the electromotive force cell voltage Vs+ immediately before switching. Further, after the detection of the differential voltage ΔVs is completed, when returning to the state of detecting the gas detection signal Vip again, the differential voltage ΔVs is held. This series of operations is performed by the microprocessor 50 transmitting an instruction signal for instructing switching of the switches SW1, SW2, SW3 to the control unit 67 through the serial transmission port 53.

  As described above, the difference voltage ΔVs is output from the output terminal 60c of the sensor control circuit 60 and input to the microprocessor 50 through the A/D input port 52. Thus, the microprocessor 50 periodically detects the value of the difference voltage ΔVs. Note that the cell impedance Rvs of the electromotive force cell 20 can be obtained by dividing the difference voltage ΔVs by the constant current Iconst flowing as a current pulse.

  In the gas sensor control device 1 of the present embodiment, the heater unit 4 (heater resistor 41) of the gas sensor 2 is energized by using the heater control circuit 70 to bring the sensor unit 3 to a predetermined holding temperature (720° C. in the present embodiment). The heating is controlled. Thereby, oxygen ion conductivity is expressed (activated) in the electrolyte layers 11 and 21, respectively.

  The cell impedance Rvs of the electrolyte layer 21 of the electromotive force cell 20 changes depending on the temperature thereof. Specifically, the higher the temperature, the smaller the cell impedance Rvs. Therefore, in the present embodiment, in the gas sensor control device 1, when the heater control circuit 70 is used for control, a second current pulse of constant current −Iconst having a length of 60 μsec is applied to the electromotive force cell 20 to obtain the cell impedance Rvs as The third cell impedance Rpvs is acquired at the third time t3 when 60 μsec has elapsed from the start of application of the second current pulse, and feedback control of the heater unit 4 (heater resistor 41) is performed using this.

  Specifically, in the state where the oxygen concentration is being detected, that is, in the state where the pump current Ip is controlled so that the electromotive force cell voltage Vs becomes the target voltage Vrf (=450 mV), the sensor control circuit as described above. The switches SW1 and SW2 of 60 are switched, and a second current pulse having a length of 60 μsec and a magnitude of constant current −Iconst, which is shorter than a first current pulse described later, is applied to the electromotive force cell 20. Then, in the microprocessor 50, the start-time cell voltage Vs0 that is the electromotive force cell voltage at the start time t0 and the third cell voltage that is the electromotive force cell voltage at the third time t3 when 60 μsec has elapsed from the start of the application of the second current pulse. The difference voltage ΔVs (=Vs3−Vs0) from Vs3 is acquired through the A/D input port 52. The microprocessor 50 causes the target impedance Rtg generated in the electromotive force cell 20 when the difference voltage ΔVs (0-3 difference voltage ΔVs03 described later) corresponding to the third cell impedance Rpvs is a predetermined holding temperature (720° C.). The electric power applied to the heater unit 4 is feedback-controlled so as to be equal to ΔVstg corresponding to. Specifically, the duty ratio of the PWM pulse to be applied to the heater unit 4 is calculated through the heater control circuit 70 according to the difference voltage ΔVs (0-3 difference voltage ΔVs03), and the heater output circuit 54 outputs the duty ratio to the heater control circuit. The PWM pulse of the duty ratio calculated toward 70 is output. As a result, the heater control circuit 70 turns on/off the power supply to the heater unit 4 (heater resistor 41), and feedback control is performed by the PWM method. Thus, the gas sensor 2 is heated and controlled so that the sensor portion 3 thereof has a predetermined holding temperature, and it becomes possible to appropriately detect the oxygen concentration of the exhaust gas EG. In the gas sensor control device 1 of the present embodiment, the second cell impedance Rpvs, specifically, the 0-3 difference voltage ΔVs03 is detected by applying the second current pulse every 100 msec. In order to frequently perform feedback control of the duty ratio during energization of the heater unit 4 (heater resistor 41) and maintain the temperature of the sensor unit 3 (electromotive force cell 20, pump cell 10) at a predetermined holding temperature more accurately. is there.

By the way, it has been found that the impedances of the pump cell 10 and the electromotive force cell 20 of the gas sensor 2 increase when they deteriorate due to the use of the gas sensor 2. That is, when the constant current −Iconst current pulse is continuously applied to the electromotive force cell 20 of the new gas sensor 2 from the start time t0, the electromotive force cell voltage Vs generated in the electromotive force cell 20 is indicated by a thick broken line in FIG. Thus, it increases with an increase in the application time t of the current pulse.
On the other hand, for the deteriorated gas sensor 2 in which the sensor unit 3 (electromotive force cell 20 and pump cell 10) has deteriorated after long-term use, the current pulse of constant current −Iconst is continuously applied from the start time t0. However, the electromotive force cell voltage Vs generated in the electromotive force cell 20 increases as the application time t of the current pulse increases, as indicated by the thick solid line in FIG.

  However, comparing the changes in the electromotive force cell voltage Vs between the new product and the deteriorated product, the electromotive force cell voltage Vs of the deteriorated gas sensor 2 indicated by the thick solid line is larger than that of the new product indicated by the thick broken line. Moreover, for example, the new second cell voltage Vs2N of the new product at the second time t2 (the same applies to the third time t3) 60 μsec after the start of the application of the current pulse (start time t0) and the deterioration first of the deteriorated product Compared to the difference voltage SVs2 (=Vs2D-Vs2N) between the two-cell voltage Vs2D, the new first cell voltage Vs1N of the new product at the first time t1 after 5000 μsec (=5 msec), and the deterioration of the deteriorated product The difference voltage SVs1 (=Vs1D-Vs1N) from the one-cell voltage Vs1D becomes large (SVs1>SVs2). That is, it can be seen that the difference voltage SVs between the cell voltages Vs of the new product and the deteriorated product increases with the passage of time t.

Regarding the new gas sensor 2, at the second time t2=60 μsec, the new 0-2 difference voltage ΔVs02N obtained from the fifth operational amplifier OP5 is the new start cell voltage Vs0N which is the electromotive force cell voltage at the start time t0. And the new second cell voltage Vs2N which is the electromotive force cell voltage at the second time t2.
In the deteriorated gas sensor 2, the deterioration 0-2 differential voltage ΔVs02D obtained from the fifth operational amplifier OP5 at the second time t2=60 μsec is the deterioration start cell voltage which is the electromotive force cell voltage at the start time t0. It is a voltage difference between Vs0D and the deteriorated second cell voltage Vs2D which is the electromotive force cell voltage at the second time t2.
The second cell impedance Rpvs (RpvsN, RpvsD) of the electromotive force cell 20 at the second time t2 is obtained by dividing the new 0-2 difference voltage ΔVs02N or the deteriorated 0-2 difference voltage ΔVs02D by the constant current −Iconst. Obtainable.

In addition, in FIG. 4, as described above, by applying the second current pulse to the gas sensor 2, at the third time t3=60 μsec (the same as the second time t2 in the present embodiment), from the fifth operational amplifier OP5. The resulting 0-3 differential voltage ΔVs03 is also shown. As described above, the 0-3 difference voltage ΔVs03 is the difference voltage between the start cell voltage Vs0 and the third cell voltage Vs3.
In addition, the third cell impedance Rpvs of the electromotive force cell 20 at the third time t3 can be obtained by dividing the 0-3 difference voltage ΔVs03 by the constant current −Iconst flowing at the second pulse current.

Further, regarding the new gas sensor 2, at the first time t1=5000 μsec, the new product 0-1 difference voltage ΔVs01N obtained from the fifth operational amplifier OP5 is the new start cell voltage Vs0N which is the electromotive force cell voltage at the start time t0. And the new first cell voltage Vs1N which is the electromotive force cell voltage at the first time t1.
Further, regarding the deteriorated gas sensor 2, at the first time t1=5000 μsec, the deterioration 0-1 difference voltage ΔVs01D obtained from the fifth operational amplifier OP5 is the deterioration start cell voltage which is the electromotive force cell voltage at the start time t0. It is a voltage difference between Vs0D and the deteriorated first cell voltage Vs1D which is the electromotive force cell voltage at the first time t1.
Further, the first cell impedance Rivs (RivsN, RivsD) of the electromotive force cell 20 at the first time t1 is obtained by dividing the new 0-1 difference voltage ΔVs01N or the deteriorated 0-1 difference voltage ΔVs01D by the constant current −Iconst. Can be obtained at

  Therefore, as can be understood from FIG. 4, the second impedance difference SRpvs (or the difference between the new 0-2 difference voltage ΔVs02N and the deterioration 0-2 difference voltage ΔVs02D) between the second cell impedances RpvsN and RpvsD for the new product and the deteriorated product. Voltage SVs2), the first impedance difference SRivs between the first cell impedances RivsN and RivsD of the new and deteriorated products (or the difference voltage SVs1 between the new 0-1 difference voltage ΔVs01N and the deterioration 0-1 difference voltage ΔVs01D). ) Becomes larger. This is because the degree of deterioration of the electromotive force cell 20 and the pump cell 10 (the degree of increase of the cell impedance Rvs (difference voltage SVs) due to deterioration) has frequency dependency, and in the low frequency region, specifically, 100 Hz or less. It is shown that the increase of the cell impedance due to the deterioration significantly appears in the frequency region, particularly in the frequency region of 50 Hz or less.

Therefore, in the gas sensor control device 1 of the present embodiment, the switches SW1 and SW2 of the sensor control circuit 60 are switched, and the electromotive force cell 20 has a length of 5000 μsec (=5.0 msec) and a constant current of −Iconst. Apply a current pulse. Then, in the microprocessor 50, the deterioration 0-2 difference voltage ΔVs02D obtained at the second time t2, which is 60 μsec after the start of the application of the first current pulse (start time t0), and the first time t1, which is 5000 μsec, are obtained. The deteriorated 0-1 difference voltage ΔVs01D is obtained through the A/D input port 52 (or these are divided by the constant current −Iconst to obtain the deteriorated second cell impedance RpvsD and the deteriorated first cell impedance RivsD). .. As a result, the degree of deterioration of the gas sensor 2 (sensor unit 3, electromotive force cell 20) can be detected.
In the present embodiment, the first time t1 is set to t1=5000 μsec, but the first time t1 is set to a time larger than 200 μsec, and the first cell impedance Rivs is 200 μsec or more after the application of the current pulse. You should get it later. Considering the change in the frequency characteristics due to the deterioration of the cell impedance Rvs, the cell impedance becomes large in the low frequency region of 50 Hz or less. This is because if the magnitude of deterioration is evaluated using 0-2 difference voltage ΔVs02D), the deterioration can be evaluated appropriately and in a short time.

  By the way, as described above, the cell impedance Rvs of the electromotive force cell 20 is also affected by the difference in the oxygen concentration of the measurement chamber gas EGS. Specifically, even if the first current pulse having the same length of 5000 μsec is applied and the first cell impedance Rivs is similarly detected, the value of the cell impedance Rvs detected when the measurement chamber gas EGS is in the rich state. Becomes larger than the value of the cell impedance Rvs detected when the measurement chamber gas EGS is in the lean state. Therefore, in the present embodiment, in order to suppress this influence, the first current pulse is applied to the electromotive force cell under the condition that the measurement chamber gas EGS in the measurement chamber 3S is in the stoichiometric state, and the 2-1 differential voltage DVs21D is applied. , Or 2-1 Impedance difference ΔRvs is detected.

  When the engine ENG is driven and the gas sensor 2 is detecting the oxygen concentration of the exhaust gas EG, the application of the second current pulse and the second cell impedance Rpvs are performed every 100 msec, as described above. It is not preferable to apply a long first current pulse during the process to detect the second cell impedance Rpvs and the first cell impedance Rivs. This is because the actual oxygen concentration detection of the exhaust gas EG becomes impossible while the first current pulse is being applied. Further, unlike the case where the second cell impedance Rpvs is repeatedly detected at short time intervals (for example, every 100 msec in this embodiment) for detecting the temperature of the electromotive force cell 20 and controlling the energization of the heater unit 4, unlike the gas sensor. It is not required to repeatedly detect the degree of deterioration of 2 in a short time.

  Therefore, in the gas sensor control device 1 of the present embodiment, the deterioration is evaluated when the driver turns off the key switch of the vehicle and stops the engine ENG. That is, even after the engine ENG is stopped, the control of the gas sensor 2 by the gas sensor control device 1 is continued for a while, and the measurement chamber gas EGS is in the stoichiometric state, that is, the electromotive force cell voltage Vs of the electromotive force cell 20 is When the stoichiometric voltage Vss (specifically, Vs=Vss=450 mV), which is a predetermined electromotive force cell voltage, indicating that the measurement chamber gas EGS is in the stoichiometric state is reached, as described above, The deterioration 0-2 difference voltage ΔVs02D (second cell impedance RpvsD) is detected at the second time t2=60 μsec, and further the deterioration 0-1 difference voltage ΔVs01D (first cell impedance RivsD) is detected at the first time t1=5000 μsec. Then, after the deterioration 2-1 difference voltage DVs21D (2-1 impedance difference ΔRvs) is stored, the gas sensor control device 1 is stopped. Further, when the engine ENG is started next time, the deterioration of the gas sensor 2 is evaluated using the deterioration 2-1 difference voltage DVs21D (2-1 impedance difference ΔRvs) after the previous operation.

That is, in the gas sensor control device 1 of the present embodiment, for the gas sensor 2 that is not new and is in use, the microprocessor 50 detects the 2-1 differential voltage DVs21D (or 2-1 impedance difference ΔRvs) as follows. Then, the DVs21D detection and storage processing is performed (see FIG. 5). This processing is executed by calling from the main routine executed by the microprocessor 50. In the microprocessor 50, in addition to the process of obtaining the gas detection signal Vip and the process of controlling the energization of the heater unit 4, the DVs21D detection/storage process, the deterioration detection/deterioration warning process (described later), and the gas detection signal deterioration correction process ( Target difference voltage correction processing (described later) and the like are performed.
Note that, in the following, apart from the above-mentioned comparison between the new product and the deteriorated product, the cell impedance, the cell voltage, the differential voltage, etc. of the gas sensor 2 in use are denoted by the respective symbols including the character of deterioration in the sense that it is not a new product. It will be diverted and explained.

  In the DVs21D detection/storage process, first, in step S1, initial setting of a treatment such as resetting of a timer described later is performed. After that, the process proceeds to step S2, and it is detected whether or not an instruction to stop the engine is issued. Specifically, it is detected whether the driver has turned off the key switch (not shown) of the vehicle (whether the ON state during driving is changed to the OFF state). Here, the process waits until the key switch of the vehicle is turned off (No), and when the key switch is turned off (Yes), the process proceeds to step S3. In step S3, the first timer is started. As indicated by the broken line in step S4, in the vehicle (engine), the engine stop process is performed by turning off the key switch.

  Since the supply of the exhaust gas EG in which the fuel is burned to the exhaust pipe EP is stopped with the stop of the engine, the fluctuation of the oxygen concentration in the exhaust gas EG due to the driving of the engine is eliminated. On the other hand, in the gas sensor 2, the control is continued so that the measurement chamber gas EGS in the measurement chamber 3S becomes stoichiometric, so that the measurement chamber gas EGS quickly becomes stoichiometric in the measurement chamber 3S. That is, the electromotive force cell voltage Vs becomes the stoichiometric voltage Vss (specifically, Vss=450 mV) indicating that the measurement chamber gas EGS is in the stoichiometric state. Therefore, in step S5, it is detected whether or not the electromotive force cell voltage Vs is Vs=Vss. Note that, as described above, the electromotive force cell voltage Vs is the voltage difference between the potentials input to the Vs port 56 and the COM port 55 of the microprocessor 50. Here, when Vs=Vss is not satisfied (No, that is, when Vs≠Vss), the process proceeds to step S6, and the first timer detects whether 5 seconds or more has elapsed. If it is less than 5 seconds, the process returns to step S5. That is, steps S5 and S6 are repeated, and the process waits until Vs=Vss. However, when the first timer has passed 5 seconds or more, it is determined that Vs=Vss does not hold for some reason, and the process proceeds to step S12. On the other hand, if Yes in step S5, that is, Vs=Vss, the process proceeds to step S7. This step S5 corresponds to the detection instruction means.

  In step S7, as described above, the control unit 67 of the sensor control circuit 60 is operated through the serial transmission port 53 of the microprocessor 50 to switch the switches SW1 and SW2 to the electromotive force cell 20 at a constant current of 5000 μsec in length. -Apply a square-wave-shaped first current pulse having a magnitude of Iconst.

  In a succeeding step S8, the deterioration 0-2 difference voltage ΔVs02D obtained from the fifth operational amplifier OP5 at the time point when the second time t2=60 μsec has elapsed from the start of the application of the first current pulse (start time t0), is set to the A/D input port 52. Through the microprocessor 50. Specifically, as shown in FIG. 6, together with the application of the first pulse, the second timer is started in step S81, the second timer T2 is waited until T2≧60 μsec in step S82, and the deterioration 0 in step S83. −2 The difference voltage ΔVs02D is acquired. Instead of the acquired deterioration 0-2 difference voltage ΔVs02D, this may be divided by the constant current Iconst to obtain the value of the deterioration second cell impedance RpvsD.

The obtained deterioration 0-2 differential voltage ΔVs02D (or the deterioration second cell impedance RpvsD) is affected by the impedance deterioration of the electromotive force cell 20 (gas sensor 2) (deterioration 0-1 described below due to the frequency characteristics of the cell impedance). Less than the difference voltage ΔVs01D.
The deterioration 0-2 difference voltage ΔVs02D is a difference voltage between the deterioration start cell voltage Vs0D and the deterioration second cell voltage Vs2D (ΔVs02D=Vs2D−Vs0D), and thus step S83 indirectly determines the deterioration second cell voltage Vs2D. Is being detected. That is, step S83 corresponds to the second detecting means.

  In the following step S9, the deteriorated 0-1 difference voltage ΔVs01D obtained from the fifth operational amplifier OP5 at the time point when the first time t1=5000 μsec has elapsed from the start of the application of the first current pulse (start time t0), the A/D input port 52 Through the microprocessor 50. Specifically, as shown in FIG. 6, in step S91, the second timer T2 waits until T2≧5000 μsec, and in step S92, the degraded 0-1 difference voltage ΔVs01D is acquired. The acquired deterioration 0-1 difference voltage ΔVs01D may be divided by the constant current Iconst to obtain the value of the deterioration first cell impedance RivsD.

The obtained deterioration 0-1 difference voltage ΔVs01D (or the deterioration first cell impedance RivsD) includes many influences due to the impedance deterioration of the electromotive force cell 20 (gas sensor 2) on the frequency characteristic of the cell impedance, and the deterioration 0-2 difference. The value is larger than the voltage ΔVs02D (or the deteriorated first cell impedance RivsD).
The deterioration 0-1 difference voltage ΔVs01D is a difference voltage between the deterioration start cell voltage Vs0D and the deterioration first cell voltage Vs1D (ΔVs01D=Vs1D−Vs0D), and thus step S92 indirectly determines the deterioration first cell voltage Vs1D. Is being detected. That is, step S92 corresponds to the first detecting means.

  Then, in step S10, the 2-1 differential voltage DVs21D is calculated by the equation DVs21D=ΔVs01D−ΔVs02D and stored in the memory (not shown) in the microprocessor 50. As can be easily understood from FIG. 4, the 2-1 difference voltage DVs21D is DVs21D=ΔVs01D−ΔVs02D=Vs1D−Vs2D, and becomes a difference voltage between the deteriorated first cell voltage Vs1D and the deteriorated second cell voltage Vs2D. There is. Instead of calculating the 2-1 difference voltage DVs21D, the 2-1 impedance difference ΔRvs may be calculated by the formula ΔRvs=RivsD−RpvsD=(ΔVs01D−ΔVs02D)/Iconst and stored in the memory.

In the following step S11, the application of the applied first current pulse is stopped. Further, in step S12, since the key switch has already been turned off (see step S2), a stop process for turning off the gas sensor 2 and the gas sensor control device 1 is performed.
In this way, in this embodiment, every time the key switch is turned off, the 2-1 difference voltage DVs21D (2-1 impedance difference ΔRvs) is stored in the memory in the microprocessor 50.

  The sensor control circuit 60 that performs the PID control of the gas sensor 2 corresponds to the current control means. Further, step S92 corresponds to the first detection means.

  Next, the processing when the vehicle is started (engine ENG is started) after that, for example, the next day, will be described. First, the deterioration detection/degradation warning process will be described with reference to FIG. 7. When the driver changes the key switch from OFF to ON, that is, when the engine ENG is started, the microprocessor 50 is activated, and in step SS1, the 2-1 differential voltage DVs21D(2 stored in the microprocessor 50 is stored. −1 impedance difference ΔRvs) is read.

  In the subsequent step SS2, it is determined whether or not the 2-1 difference voltage DVs21D (2-1 impedance difference ΔRvs) becomes equal to or higher than the first threshold value TH1 (DVs21D≧TH1) (or ΔRvs≧TH1′. Determine whether). Here, in the case of No, that is, DVs21D<TH1 (or ΔRvs<TH1'), it is considered that the deterioration of the gas sensor 2 has not progressed so much. Therefore, the microprocessor 50 does not notify the ECU 100. As a result, in step SS5, the ECU 100 performs the normal engine drive processing and does not turn on the deterioration warning lamp.

On the other hand, if Yes in step SS2, that is, if DVs21D≧TH1 (or ΔRvs≧TH1′), it is considered that the deterioration of the gas sensor 2 progresses and the 2-1 difference voltage DVs21D becomes equal to or higher than the first threshold value TH1. Be done. Therefore, the process proceeds to step SS3, and the microprocessor 50 notifies the ECU 100 of the deterioration abnormality of the gas sensor 2. In response to this, in step SS4 indicated by a broken line, the ECU 100 turns on the deterioration warning lamp and prompts the driver to replace the gas sensor 2 or the like.
The above-mentioned step SS2 corresponds to the deterioration determination means, and step SS3 corresponds to the deterioration warning means.

The cell impedance Rvs of the electromotive force cell 20 is affected by disturbance factors such as the temperature of the exhaust gas EG as well as the difference in oxygen concentration of the measurement chamber gas EGS. It is desirable to determine the presence or absence and the degree.
The controller 1 of the present embodiment detects the deteriorated second cell voltage Vs2D generated in the electromotive force cell at the second time t2 and the deteriorated first cell voltage Vs1D generated at the first time t1 in the same first current pulse. Then, the deterioration of the gas sensor is determined based on the 2-1 difference voltage DVs21D that is the difference voltage. Therefore, it is possible to cancel the influence of the disturbance factors of the electromotive force cell 20, such as the temperature of the exhaust gas EG, to determine the deterioration, and it is possible to more appropriately determine the presence or absence and the degree of the deterioration.
Moreover, in the case where the same first current pulse is applied, the second cell voltage Vs2D at the second time t2 (=60 μsec) in a relatively short time period and the first time t1 (= Since the 2-1 difference voltage DVs21D with the first cell voltage Vs1D at 5000 μsec) is used for the determination, the change of the cell voltage due to the deterioration of the cell impedance in the low frequency region is likely to be reflected, and from this point as well, it is more appropriate. It is possible to determine the presence and degree of deterioration.

  Furthermore, in the present embodiment, the gas detection signal Vip is corrected using the acquired 2-1 difference voltage DVs21D (or 2-1 impedance difference ΔRvs) (see FIG. 8). As described above, in the sensor control circuit 60, the magnitude of the pump current Ip is detected by the differential amplifier circuit 61 as the gas detection signal Vip converted into the voltage signal, and the microprocessor 50 detects the gas through the output terminal 60b. The signal Vip is acquired (step ST1).

  In the present embodiment, prior to the output of the gas detection signal Vip, the gas detection signal Vip is a 2-1 difference voltage DVs21D (or 2-1 impedance difference ΔRvs) which is an amount based on the deteriorated first cell voltage Vs1D. To correct (step ST2). Specifically, for example, a table in which the corrected gas detection signal Vip is obtained from the 2-1 difference voltage DVs21D (or the 2-1 impedance difference ΔRvs) and the acquired gas detection signal Vip is created in advance, Using this, the corrected gas detection signal Vip is acquired.

After that, the microprocessor 50 outputs the corrected gas detection signal Vip to the ECU 100 (step ST3). The ECU 100 uses the corrected gas detection signal Vip to perform drive control of the engine ENG and the like. As described above, in the present embodiment, it is possible to obtain and output the corrected gas detection signal Vip in which the influence due to the deterioration of the gas sensor 2 is suppressed.
The above-mentioned step ST2 corresponds to pump current correction means, and step ST3 corresponds to output means.

  As described above, the microprocessor 50 uses the sensor control circuit 60 to apply the second pulse current to the electromotive force cell 20 every 100 msec, and starts the application of the second pulse current (start time t0) to the second time. After the lapse of the third time t3=60 μsec, which is the same as t2, the 0-3 difference voltage ΔVs03 (or further the third cell impedance RpvsD) is acquired, and the 0-3 difference voltage ΔVs03 becomes the target difference voltage ΔVstg (or The heater control circuit 70 is used to control the energization of the heater unit 4 (heater resistor 41) of the gas sensor 2 so that the 3-cell impedance RpvsD becomes the target impedance Rtg). The temperature is controlled. However, if the third cell impedance RpvsD of the electromotive force cell 20 (electrolyte layer 21) increases due to the deterioration of the gas sensor, it appears that the third cell impedance RpvsD increases because the element temperature is low. Therefore, the microprocessor 50 controls the energization of the heater unit 4 so that the temperature of the heater unit 4 becomes high. As a result, the temperature of the electromotive force cell 20 (gas sensor) is maintained at a value higher than the set value. Along with this, the pump current Ip flowing through the pump cell 10 increases as compared with that before the deterioration, and the pump current Ip (gas detection signal Vip) is biased.

  In the gas sensor control device 1 of the present embodiment, in order to suppress this, the heater control correction means has a 2-1 difference voltage DVs21D (or 2-1) which is an amount obtained based on the acquired first cell voltage Vs1D. The control of the heater control means SV2 is corrected by the impedance difference ΔRvs). Specifically, as shown in FIG. 9, first, by using the acquired 2-1 difference voltage DVs21D (or 2-1 impedance difference ΔRvs), a target difference voltage ΔVstg (or a target value used for temperature control of the gas sensor 2 (or The target impedance Rtg) is corrected (step SU1). In the present embodiment, a correction value determined for each value of the acquired 2-1 difference voltage DVs21D is added to the target difference voltage ΔVstg to obtain the corrected target difference voltage ΔVstg (or the acquired 2-1 impedance difference ΔRvs. A predetermined correction value is added to the target impedance Rtg to obtain the corrected target impedance Rtg).

  After that, the heater temperature control is performed as usual using the corrected target difference voltage ΔVstg (or the corrected target impedance Rtg). That is, as shown in FIG. 10, first, the microprocessor 50 uses the sensor control circuit 60 to acquire the 0-3 difference voltage ΔVs03 (or the third cell impedance Rpvs) (step SV1). Next, using the heater control circuit 70, the gas sensor is adjusted so that the 0-3 difference voltage ΔVs03 becomes the corrected target difference voltage ΔVstg (or the third cell impedance Rpvs becomes the corrected target impedance Rtg). The energization of the second heater unit 4 (heater resistor 41) is controlled (step SV2). Thus, even if the gas sensor 2 is deteriorated, the heater control can be performed so that the electromotive force cell 20 (gas sensor 2) has a predetermined temperature.

In the gas sensor control device 1 of the present embodiment, the target difference voltage ΔVstg is corrected with the 2-1 difference voltage DVs21D (or the target impedance Rtg is corrected with the 2-1 impedance difference ΔRvs). Specifically, a correction value according to the 2-1 difference voltage DVs21D was added to the target difference voltage ΔVstg (or a correction value according to the 2-1 impedance difference ΔRvs was added to the target impedance Rtg). Therefore, once the correction is performed, the key switch is specifically turned off and a new 2-1 difference voltage DVs21D( until the next correction value of the target difference voltage ΔVstg (or target impedance Rtg) is changed. Alternatively, it is not necessary to correct the target difference voltage ΔVstg (or the target impedance Rtg) until the 2-1 impedance difference ΔRvs) is calculated and then the key switch is turned on, and the process is easy.
The above-mentioned step SV1 corresponds to the third detection means, and step SV2 corresponds to the heater control means. Further, step SU1 corresponds to the heater control correction means.

(Modification 1)
Next, the control device 1A of the gas sensor 2 according to the first modification will be described with reference to the flowcharts of FIGS.
In detecting the deterioration of the gas sensor 2, the control device 1 of the above-described embodiment applies the first current pulse to the electromotive force cell 20 at the timing when the electromotive force cell voltage Vs is the stoichiometric voltage Vss in step S5. .. Then, the deterioration 0-2 difference voltage ΔVs02D which is the difference voltage between the deterioration start cell voltage Vs0D and the deterioration second cell voltage Vs2D, and the deterioration which is the difference voltage between the deterioration start cell voltage Vs0D and the deterioration first cell voltage Vs1D. 0-1 difference voltage ΔVs01D was obtained. Then, a 2-1 difference voltage DVs21D (or a 2-1 impedance difference ΔRvs) that is the difference between them is calculated, and the presence or absence of deterioration of the gas sensor 2 (electromotive force cell 20) is determined using this, or The detection signal Vip and heater temperature control were corrected.

On the other hand, in the control device 1A of the gas sensor 2 according to the first modification, when detecting the deterioration of the gas sensor 2, in step S5, the first current pulse is generated at the timing when the electromotive force cell voltage Vs is the stoichiometric voltage Vss. Although the same points are applied, the gas sensor 2 (electromotive force is generated by using only the deteriorated 0-1 difference voltage ΔVs01D acquired at the first time t1 without acquiring the deteriorated 0-2 difference voltage ΔVs02D at the second time t2. Others are the same except that the presence or absence of deterioration of the cell 20) is determined, or the gas detection signal Vip and the heater temperature control are corrected.
Therefore, in the following description, the portions different from the embodiment will be mainly described, and the description of the similar portions will be omitted or simplified.

The ΔVs01D detection/storing process shown in FIG. 11 is almost the same as the DVs21D detection/storing process of the embodiment shown in FIG. 5, but step S8 is not provided and steps S9a and 10a are different. Therefore, these will be described.
In step S9a, the deteriorated 0-1 difference voltage ΔVs01D obtained from the fifth operational amplifier OP5 at the time point at which the first time t1=5000 μsec has elapsed from the start of the application of the first current pulse (start time t0) is passed through the A/D input port 52. It is acquired by the microprocessor 50. Specifically, as shown in FIG. 12, together with the application of the first pulse, the second timer is started in step S90a, the second timer T2 is waited until T2≧5000 μsec in step S91, and the deterioration 0 in step S92. The −1 difference voltage ΔVs01D is acquired. The acquired deteriorated 0-1 difference voltage ΔVs01D may be divided by the constant current Iconst to obtain the deteriorated first cell impedance RivsD.

  Then, in step S10a, the deteriorated 0-1 difference voltage ΔVs01D acquired in step S9a is stored in the memory (not shown) in the microprocessor 50. Instead of calculating the 2-1 difference voltage DVs21D, the deteriorated first cell impedance RivsD may be stored in the memory. After that, similarly to the embodiment, the stop process of stopping the application of the first current pulse and turning off the gas sensor 2 and the gas sensor control device 1 is performed (steps S11 and S12).

Further, the deterioration detection/deterioration warning process shown in FIG. 13 is almost the same as the deterioration detection/degradation warning process of the embodiment shown in FIG. 7, but steps SS1a and SS2a are different.
When the engine ENG is started, the microprocessor 50 is activated, and in step SS1a, the deteriorated 0-1 difference voltage ΔVs01D (or the deteriorated first cell impedance RivsD) stored in the microprocessor 50 is read.

  In the subsequent step SS2a, it is determined whether or not the deterioration 0-1 difference voltage ΔVs01D (or the deterioration first cell impedance RivsD) is equal to or more than the second threshold value TH2 (ΔVs01D≧TH2) (or RivsD≧TH2. 'Determine whether or not). In the case of No, the microprocessor 50 does not notify the ECU 100, etc., and in step SS5 the ECU 100 performs normal engine drive processing and does not turn on the deterioration warning lamp.

On the other hand, if Yes in step SS2a, that is, if ΔVs01D≧TH2 (or RivsD≧TH2′), it is considered that the deterioration of the gas sensor 2 has progressed. Therefore, the process proceeds to step SS3, and the deterioration abnormality of the gas sensor 2 is sent to the ECU 100. Notice. In response to this, in step SS4 indicated by a broken line, the ECU 100 turns on the deterioration warning lamp and prompts the driver to replace the gas sensor 2 or the like.
The above-mentioned step SS2a also corresponds to the deterioration determining means.

As described in the embodiment, the cell impedance Rvs of the electromotive force cell 20 is affected not only by the difference in oxygen concentration of the measurement chamber gas EGS but also by disturbance factors such as the temperature of the exhaust gas EG.
Also in the control device 1A of the first modification, the difference voltage between the deterioration start cell voltage Vs0D generated in the electromotive force cell at the start time t0 and the deterioration first cell voltage Vs1D generated at the subsequent first time is 0−. The deterioration of the gas sensor is determined based on the 1-difference voltage ΔVs01D. Therefore, it is possible to cancel the influence of the disturbance factor of the electromotive force cell 20 and determine the deterioration, and it is possible to more appropriately determine the presence or absence and the degree of the deterioration.
Moreover, in one of the first current pulses, the 0-1 difference between the starting cell voltage Vs0D at the starting time t0 and the first cell voltage Vs1D at the first time t1 (=5000 μsec) where a relatively long time has elapsed is obtained. Since the voltage ΔVs01D is used for the determination, the change of the cell voltage due to the deterioration of the cell impedance in the low frequency region is likely to be reflected, and from this point as well, the presence or absence and the degree of the deterioration can be determined more appropriately.

  Further, in the first modification, as in the embodiment (see FIG. 8), the gas detection signal Vip is corrected, but in step ST2a, the 0-1 difference voltage ΔVs01D (or the deteriorated first cell impedance RivsD) acquired in advance is acquired. Is used to correct the gas detection signal Vip (see FIG. 14). That is, in step ST2a, prior to the output of the gas detection signal Vip, the gas detection signal Vip is the amount based on the deteriorated first cell voltage Vs1D, that is, the 0-1 difference voltage ΔVs01D (or the deteriorated first cell impedance RivsD) is used. To correct. Specifically, for example, a table in which the corrected gas detection signal Vip is obtained from the 0-1 difference voltage ΔVs01D (or the deteriorated first cell impedance RivsD) and the acquired gas detection signal Vip is created in advance, By using this, the corrected gas detection signal Vip is acquired. The above-mentioned step ST2a corresponds to pump current correction means.

  In addition, in the gas sensor control device 1A according to the first modification, the heater control is performed using the corrected target difference voltage ΔVstg (see FIG. 10) as in the embodiment (see FIGS. 9 and 10), but step SU1a is performed. , The target difference voltage ΔVstg (or the target impedance Rtg) is corrected by the 0-1 difference voltage ΔVs01D (or the deteriorated first cell impedance RivsD) (see FIG. 15). That is, in this modification 1, in step SU1a, the corrected target difference voltage ΔVstg (or target impedance Rtg) corrected by the 0-1 difference voltage ΔVs01D (or the deteriorated first cell impedance RivsD) is obtained. Then, using the corrected target difference voltage ΔVstg (or target impedance Rtg), heater control is performed as in the embodiment (see FIG. 10).

(Modification 2)
Next, the control device 1B of the gas sensor 2 of Modification 1 will be described with reference to the flowcharts of FIGS. 16 to 19.
In detecting the deterioration of the gas sensor 2, in the control devices 1 and 1A of the above-described embodiment and modification 1, the electromotive force cell 20 is first subjected to the step S5 at the timing when the electromotive force cell voltage Vs is the stoichiometric voltage Vss. One current pulse was applied. Then, in the embodiment, the deterioration 0-2 difference voltage ΔVs02D and the deterioration 0-1 difference voltage ΔVs01D are obtained, the 2-1 difference voltage DVs21D (or the 2-1 impedance difference ΔRvs) is calculated, and this is used. No. 2 (electromotive force cell 20) was checked for deterioration, or the gas detection signal Vip and heater temperature control were corrected. In the first modification, only the deterioration 0-1 difference voltage ΔVs01D is obtained, and the presence or absence of deterioration of the gas sensor 2 (electromotive force cell 20) is determined using this, or the gas detection signal Vip or heater temperature control is performed. Corrected.

In detecting the deterioration of the gas sensor 2, the control device 1B of the second modification also applies the first current pulse to the electromotive force cell 20 at the timing when the electromotive force cell voltage Vs is the stoichiometric voltage Vss in step S5. The points are the same as those of the embodiment and the modification 1. Further, the point that only the deterioration 0-1 difference voltage ΔVs01D (or the deterioration first cell impedance RivsD) is obtained is the same as in the first modification.
However, in the control device 1B of the present second modified embodiment, the new product 0-1 difference voltage ΔVs01N (or the new product first cell impedance RivsN) for the new gas sensor 2 obtained in advance is stored. Then, the first differential voltage SVs1 (or the deteriorated first cell impedance RivsD and the new first voltage difference SVs1) which is the difference voltage between the deteriorated 0-1 difference voltage ΔVs01D acquired at each time point and the stored new 0-1 difference voltage ΔVs01N. Using the first impedance difference SRivs, which is the voltage difference from the cell impedance RivsN, it is determined whether the gas sensor 2 (electromotive force cell 20) is deteriorated, or the gas detection signal Vip and heater temperature control are corrected. , But the others are the same.
Therefore, in the following, a description will be given focusing on a part different from the embodiment or the first modification, and the description of the similar part will be omitted or simplified.

The SVs1 detection/storing process shown in FIG. 16 is almost the same as the DVs21D detection/storing process of the embodiment shown in FIG. 5 and the ΔVs01D detection/storing process of the modified embodiment 1 shown in FIG. Since it is different, this will be explained.
As in the first modification (see FIGS. 11 and 12), under the condition that the electromotive force cell voltage Vs is the stoichiometric voltage Vss (Yes in step S5), the fifth operational amplifier OP5 is obtained in step S9a (step S92). The deteriorated 0-1 difference voltage ΔVs01D (or the deteriorated first cell impedance RivsD) is acquired.

  After that, in step S10b, the first difference voltage SVs1 which is the difference voltage between the deteriorated 0-1 difference voltage ΔVs01D and the previously stored new 0-1 difference voltage ΔVs01N of the new gas sensor 2 is calculated (SVs1= ΔVs01D−ΔVs01N), which is stored in a memory (not shown) in the microprocessor 50. Instead of calculating the first difference voltage SVs1, the first impedance difference SRivs, which is the difference voltage between the deteriorated first cell impedance RivsD and the previously stored new first cell impedance RivsN, is calculated (SRivs=RivsD -RivsN), may be stored in memory. After that, as in the case of the embodiment and the modified embodiment 1, the stop process of stopping the application of the first current pulse and turning off the gas sensor 2 and the gas sensor control device 1 is performed (steps S11 and 12).

The deterioration detection/deterioration warning process shown in FIG. 17 is almost the same as the deterioration detection/deterioration warning process of the embodiment and the modification 1 shown in FIGS. 7 and 13, but steps SS1b and SS2b are different. Will be described.
When the engine ENG is started, the microprocessor 50 is started, and in step SS1b, the first difference voltage SVs1 (or the first impedance difference SRivs) stored in the microprocessor 50 is read.

In the following step SS2b, it is determined whether or not the first difference voltage SVs1 (or the first impedance difference SRivs) becomes equal to or larger than the third threshold value TH3 (SVs1≧TH3) (or whether SRivs≧TH3′ or not). To determine). In the case of No here, in step SS5, the normal engine driving process is performed in the ECU 100, and the deterioration warning lamp is not lit. On the other hand, if Yes in step SS2b, that is, if SVs1≧TH3 (or Rivs≧TH3′), the process proceeds to step SS3 to notify the ECU 100 of the abnormality abnormality of the gas sensor 2.
The above-mentioned step SS2b also corresponds to the deterioration determining means.

As described in the first embodiment and the first modification, the cell impedance Rvs of the electromotive force cell 20 is affected not only by the difference in oxygen concentration of the measurement chamber gas EGS but also by disturbance factors such as the temperature of the exhaust gas EG.
Also in the control device 1B of the second modification, the deterioration of the gas sensor is determined based on the 0-1 difference voltage ΔVs01D that is the difference voltage between the deterioration start cell voltage Vs0D and the deterioration first cell voltage Vs1D. The influence can be canceled and the deterioration can be determined, and the presence or absence and the degree of the deterioration can be determined more appropriately.
Moreover, in one of the first current pulses, the 0-1 difference between the starting cell voltage Vs0D at the starting time t0 and the first cell voltage Vs1D at the first time t1 (=5000 μsec) where a relatively long time has elapsed is obtained. Since the first differential voltage SVs1 based on the voltage ΔVs01D is used for the determination, the change in the cell voltage due to the deterioration of the cell impedance in the low frequency region is likely to be reflected. From this point as well, the presence or absence and the degree of the deterioration can be determined more appropriately. You can
Further, since the first difference voltage SVs1 is obtained by subtracting the new 0-1 difference voltage ΔVs01N from the deterioration 0-1 difference voltage ΔVs01D, the new 0-1 difference voltage ΔVs01N (according to the new first cell voltage The variation of Vs1N) can be canceled, the increase in the cell impedance of the electromotive force cell 20 caused by the deterioration can be clarified, and the presence or absence and the degree of the deterioration can be more appropriately determined.

  Further, in the second modification, the gas detection signal Vip is corrected similarly to the embodiment (see FIG. 8) and the first modification (see FIG. 14), but in step ST2b, the first difference voltage SVs1( Alternatively, it is different in that the gas detection signal Vip is corrected using the first impedance difference SRivs) (see FIG. 18). That is, in step ST2b, prior to the output of the gas detection signal Vip, the gas detection signal Vip is corrected using the first difference voltage SVs1 (or the first impedance difference SRivs) which is an amount based on the deteriorated first cell voltage Vs1D. To do. Specifically, for example, a table in which the corrected gas detection signal Vip is obtained from the first difference voltage SVs1 (or the first impedance difference SRivs) and the acquired gas detection signal Vip is created in advance, and this table is prepared. The corrected gas detection signal Vip is acquired by using. The above step ST2b also corresponds to the pump current correction means.

  In addition, also in the gas sensor control device 1B of the present second modified example, as in the embodiment (see FIGS. 9 and 10) and the first modified example (see FIGS. 15 and 10), the heater uses the corrected target difference voltage ΔVstg. The control is performed (see FIG. 10), but the difference is that in step SU1b, the target difference voltage ΔVstg (or the target impedance Rtg) is corrected with the first difference voltage SVs1 (or the first impedance difference SRivs) (see FIG. 19). . That is, in the second modified example, in step SU1b, the corrected target difference voltage ΔVstg (or the target impedance Rtg) corrected by the first difference voltage SVs1 (or the first impedance difference SRivs) is obtained. Then, using the corrected target difference voltage ΔVstg (or target impedance Rtg), heater control is performed as in the embodiment (see FIG. 10).

In the above, the gas sensor control device of the present invention has been described according to the embodiment and the first and second modifications, but the present invention is not limited to the above-described embodiments and the like, and within the scope not departing from the gist thereof. Needless to say, it can be applied with appropriate changes.
For example, in the embodiment and the like, an example in which the present invention is applied to the air-fuel ratio sensor that detects the oxygen concentration (air-fuel ratio) in the exhaust gas EG as the gas sensor 2 is shown, but the “gas sensor” is not limited to the air-fuel ratio sensor. Instead, a NOx sensor that detects the concentration of nitrogen oxides (NOx) may be used.
The gas sensor is not limited to the one mounted on the exhaust pipe, and the present invention may be applied to a gas sensor mounted on the intake pipe of an engine having an EGR device to detect the oxygen concentration in the intake gas.

  Further, in the embodiment and the like, the target difference voltage ΔVstg (or the target impedance Rtg) is corrected in controlling the temperature of the heater unit 4 (see step SU1), but instead, the target difference voltage ΔVstg (or the target impedance Rtg) is used. For example, every 100 msec, every time the third cell impedance Rpvs is acquired, the third cell impedance Rpvs is corrected by the 2-1 difference voltage DVs21D, the deterioration 0-1 difference voltage ΔVs01D, the first difference voltage SVs1, and the like, and is corrected. The temperature of the heater unit 4 may be controlled by using the third cell impedance Rpvs. Furthermore, in the embodiment and the like, an example is shown in which whether or not the gas sensor 2 is deteriorated is determined, and when the deterioration is detected, both the gas detection signal Vip and the heater temperature control are corrected. However, when the deterioration of the gas sensor 2 is detected, only one of the correction of the gas detection signal Vip and the correction of the heater temperature control may be performed.

  Further, in the embodiment, the timing at which the 2-1 differential voltage DVs21D, the deterioration 0-1 differential voltage ΔVs01D, the first differential voltage SVs1 and the like are detected and stored, after the operation of the vehicle is finished, the driver turns off the key switch. After that, the timing when the electromotive force cell voltage Vs is the stoichiometric voltage Vss is set (see FIGS. 5, 11, and 16, steps S2 to S5). However, the timing for detecting the 2-1 difference voltage DVs21D or the like may be appropriately set during the timing when the electromotive force cell voltage Vs is the stoichiometric voltage Vss.

  Further, in the embodiment and the like, the mode in which the gas sensor control device 1 and the like are provided separately from the ECU 100 has been shown (see FIG. 1), but the “gas sensor control device” of the present invention is not limited to this. For example, a mode in which the functional components (specifically, the sensor control circuit 60, the heater control circuit 70, the microprocessor 50) in the gas sensor control device 1 of the embodiment are installed in the ECU 100 and the gas sensor 2 is connected to the ECU 100, that is, The ECU 100 may also be used as a “gas sensor control device”.

1, 1A, 1B Gas sensor control device (gas sensor control device)
2 Gas sensor 3 Sensor part 3S Measuring chamber 4 Heater part (heater)
10 Pump Cell 11 Electrolyte Layer (Second Solid Electrolyte Body)
12 Outer electrode (pump electrode)
13 2nd measurement chamber electrode 20 electromotive force cell 21 electrolyte layer (1st solid electrolyte body)
22 first measurement chamber electrode 23 reference electrode 24 reference oxygen chamber Ip pump current Vs electromotive force cell voltage Vss (electromotive force cell voltage when gas in measurement chamber is in stoichiometric state) stoichiometric voltage Vs1N (at first time t1) , New electromotive force cell voltage) new first cell voltage Vs2N (new electromotive force cell voltage at second time t2) new second cell voltage Vs0N (new electromotive cell voltage at start time t0 The cell voltage Vs1D at the start of new product (which is the electromotive force cell voltage of the deteriorated product at the first time t1) deteriorated first cell voltage (first cell voltage)
Vs2D (which is the electromotive force cell voltage of the deteriorated product at the second time t2) Degradation second cell voltage Vs0D (which is the electromotive force cell voltage of the deteriorated product at the start time t0) Degradation start cell voltage Vs0 (Start time t0 At the start time), the start cell voltage Vs3 (which is the electromotive force cell voltage at the third time t3), the third cell voltage ΔVs, the difference voltage ΔVstg, the target difference voltage (the target value of the heater control means).
ΔVs01N (0st cell voltage Vs1N and starting cell voltage Vs0N) new 0-1 difference voltage ΔVs02N (2nd cell voltage Vs2N and starting cell voltage Vs0N) new 0-2 difference voltage ΔVs01D (first cell voltage Degradation 0-1 difference voltage ΔVs02D (of Vs1D and starting cell voltage Vs0D) Degradation 0-2 difference voltage ΔVs03 (of second cell voltage Vs2D and starting cell voltage Vs0D) (Third cell voltage Vs3D and starting cell voltage 0-3 differential voltage DVs21D (with Vs0D) 2-1 differential voltage SVs1 (with first cell voltage Vs1D and second cell voltage Vs2D) first difference (with first cell voltage Vs1D and new first cell voltage Vs1N) Voltage SVs2 (between second cell voltage Vs2D and new second cell voltage Vs2N) Second differential voltage Rvs Cell impedance Rivs, RivsN, RivsD (at first time t1 of electromotive force cell) First cell impedance RivsN New first cell Impedance RivsD Degraded first cell impedance Rpvs, RpvsN, RpvsD Second cell impedance (at second time t2, third time t3) of electromotive force cell, Third cell impedance RpvsN New second cell impedance RpvsD Degraded second cell impedance ΔRvs (between the cell impedance RpvsD at the second time t2 of the electromotive force cell and the cell impedance RivsD at the first time t1) 2-1 Impedance difference SRivs (new cell impedance RivsN and deterioration of the electromotive force cell at the first time t1) First impedance difference (with cell impedance RivsD) DVs21D, ΔVs01D, SVs1, ΔRvs, RivsD, SRivs Amount based on the first cell voltage Vip Gas detection signal (amount corresponding to oxygen concentration signal, pump current)
50 Microprocessor 60 Sensor control circuit (current control means, first detection means, second detection means)
70 heater control circuits 81, 82, 83 connection wiring t0 start time t1 first time t2 second time t3 third time ENG engine EP exhaust pipe EG exhaust gas (measured gas)
EGS measurement chamber gas RG reference gas 100 ECU
Vrf target voltage TH1 first threshold TH2 second threshold TH3 third threshold)
Rtg target impedance (target value of heater control means)
S92 First detection means S8 Second detection means S7 Initial detection means S5 Detection instruction means SS2, SS2a, SS2b Deterioration determination means SS3, SS4 Degradation warning means ST2, ST2a, ST2b Pump current correction means ST3 Output means SV1 Third detection means SV2 Heater control means SU1, SU1a, SU1b Heater control correction means

Claims (7)

A first solid electrolyte body,
Reference electrodes each formed on the first solid electrolyte body and exposed to a reference gas having a reference oxygen partial pressure, and
A first measurement chamber electrode exposed to the measurement chamber gas in the measurement chamber into which the gas to be measured flows,
An electromotive force cell that generates an electromotive force according to the difference between the reference oxygen partial pressure and the oxygen partial pressure of the measurement chamber gas, and
A second solid electrolyte body,
Second measurement chamber electrodes formed on the second solid electrolyte body and exposed to the measurement chamber gas, and
Having a pump electrode exposed to the measured gas or the outside air,
A pump cell for pumping or pumping oxygen in the measurement chamber into the gas to be measured or the outside air
A control device for a gas sensor,
The pump cell is set so that the electromotive force cell voltage generated between the reference electrode and the first measurement chamber electrode becomes the stoichiometric voltage generated in the electromotive force cell when the measurement chamber gas is in stoichiometry. Current control means for controlling the flowing pump current,
A first current pulse for flowing a constant first current is applied to the electromotive force cell, and the first current pulse is being applied, and at a first time when 0.2 msec or more has elapsed from the start of application of the first current pulse. A first detection means for detecting a first cell voltage generated in the electromotive force cell,
A control device for a gas sensor , comprising: a detection instruction means for instructing detection of the first cell voltage by the first detection means when the electromotive force cell voltage is the stoichiometric voltage .
Second detecting means for detecting a second cell voltage generated in the electromotive force cell at a second time before an elapsed time of 0.2 msec has elapsed from the start of application of the first current pulse;
A gas sensor control device, comprising: a deterioration determination unit that determines deterioration of the gas sensor based on a voltage difference between the first cell voltage and the second cell voltage. A first solid electrolyte body,
Reference electrodes each formed on the first solid electrolyte body and exposed to a reference gas having a reference oxygen partial pressure, and
A first measurement chamber electrode exposed to the measurement chamber gas in the measurement chamber into which the gas to be measured flows,
An electromotive force cell that generates an electromotive force according to the difference between the reference oxygen partial pressure and the oxygen partial pressure of the measurement chamber gas, and
A second solid electrolyte body,
Second measurement chamber electrodes formed on the second solid electrolyte body and exposed to the measurement chamber gas, and
Having a pump electrode exposed to the measured gas or the outside air,
A pump cell for pumping or pumping oxygen in the measurement chamber into the gas to be measured or the outside air
A control device for a gas sensor,
The pump cell is set so that the electromotive force cell voltage generated between the reference electrode and the first measurement chamber electrode becomes the stoichiometric voltage generated in the electromotive force cell when the measurement chamber gas is in stoichiometry. Current control means for controlling the flowing pump current,
A first current pulse for flowing a constant first current is applied to the electromotive force cell, and the first current pulse is being applied, and at a first time when 0.2 msec or more has elapsed from the start of application of the first current pulse. A first detection means for detecting a first cell voltage generated in the electromotive force cell,
A control device for a gas sensor , comprising: a detection instruction means for instructing detection of the first cell voltage by the first detection means when the electromotive force cell voltage is the stoichiometric voltage .
Initial detecting means for detecting a starting cell voltage generated in the electromotive force cell at a starting time immediately before the application of the first current pulse;
On the basis of the first cell voltage and the difference voltage between the start cell voltage, the control device of a gas sensor comprising a degradation determiner means a deterioration of the gas sensor, the. A first solid electrolyte body,
Reference electrodes each formed on the first solid electrolyte body and exposed to a reference gas having a reference oxygen partial pressure, and
A first measurement chamber electrode exposed to the measurement chamber gas in the measurement chamber into which the gas to be measured flows,
An electromotive force cell that generates an electromotive force according to the difference between the reference oxygen partial pressure and the oxygen partial pressure of the measurement chamber gas, and
A second solid electrolyte body,
Second measurement chamber electrodes formed on the second solid electrolyte body and exposed to the measurement chamber gas, and
Having a pump electrode exposed to the measured gas or the outside air,
A pump cell for pumping or pumping oxygen in the measurement chamber into the gas to be measured or the outside air
A control device for a gas sensor,
The pump cell is set so that the electromotive force cell voltage generated between the reference electrode and the first measurement chamber electrode becomes the stoichiometric voltage generated in the electromotive force cell when the measurement chamber gas is in stoichiometry. Current control means for controlling the flowing pump current,
A first current pulse for flowing a constant first current is added to the electromotive force cell, and the first current pulse is being applied, and at a first time when 0.2 msec or more has elapsed from the start of application of the first current pulse. A first detection means for detecting a first cell voltage generated in the electromotive force cell,
A control device for a gas sensor , comprising: a detection instruction means for instructing detection of the first cell voltage by the first detection means when the electromotive force cell voltage is the stoichiometric voltage .
A control device for a gas sensor, comprising: a deterioration determination unit that determines deterioration of the gas sensor based on a voltage difference between the first cell voltage and the previously stored new first cell voltage when the gas sensor is new. It is a control device of the gas sensor according to any one of claims 1 to 3 ,
A control device for a gas sensor, comprising: deterioration warning means for warning deterioration of the gas sensor when the deterioration judgment means judges that the gas sensor has deteriorated. The control device for a gas sensor according to any one of claims 1 to 4 ,
Pump current correction means for correcting an amount corresponding to the pump current with an amount based on the first cell voltage;
A control device for a gas sensor, comprising: an output unit that outputs an amount corresponding to the corrected pump current to the outside. A control device for a gas sensor according to any one of claims 1 to 5 , wherein:
The gas sensor has a heater that heats the electromotive force cell and the pump cell,
A second current pulse, which is shorter than the first current pulse and flows a constant second current, is applied to the electromotive force cell, the second current pulse is being applied, and 0. Third detection means for detecting a third cell voltage generated in the electromotive force cell at a third time before 2 msec has passed,
Heater control means for controlling energization of the heater using the third cell voltage;
A controller for a gas sensor, comprising: a heater control correction unit that corrects the control in the heater control unit by an amount based on the first cell voltage detected by the first detection unit. The gas sensor control device according to claim 6 ,
The heater control correction means,
A gas sensor control device for correcting a target value in the heater control means by an amount based on the first cell voltage.

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