JP2004258043A - Method and apparatus for detecting deterioration conditions of wide range air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for accurately detecting the deterioration conditions of a wide range air-fuel ratio sensor. <P>SOLUTION: A current is applied to an electromotive force cell 24 to detect a voltage V0 between electrodes (S10). Then, the application of the current is stopped (S16). After a lapse of 10μs to 1ms subsequent to the stoppage, the voltage drop Vsd1 between the electrodes on the both surfaces of the cell 24 is detected (S20), and a first resistance Rvs1 corresponding to the temperature of the cell 24 is detected from Vsd1 (S22). Then, after a lapse of 10ms to 50ms after the stoppage, a voltage drop Vsd2 of the cell 24 is detected (S26), and a second resistance Rvs2 corresponding to the internal resistance which includes the amount equivalent to the deterioration of the cell 24 is detected from the voltage drop Vsd2 (S28). Then, the deterioration condition of the wide range air/fuel ratio sensor is detected by comparing the resistance Rvs1 with the resistance Rvs2 (S30). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a deterioration state detection method and apparatus for detecting whether or not a full area air-fuel ratio sensor for detecting the concentration of oxygen contained in exhaust gas of an engine has deteriorated.

  An oxygen sensor is provided in the exhaust system to control the air-fuel ratio of the air-fuel mixture supplied to the engine to a target value and reduce CO, NOx, and HC in the exhaust gas. It is known that the fuel supply amount is feedback-controlled according to the concentration. As the oxygen sensor used for this feedback control, there are a λ sensor whose output changes stepwise at a specific oxygen concentration (particularly a stoichiometric air-fuel ratio atmosphere) and an oxygen sensor whose output continuously changes from a lean region to a rich region. A fuel ratio sensor is mainly used. The full range air-fuel ratio sensor can continuously measure the oxygen concentration in the exhaust gas as described above, and can improve the speed and accuracy of the feedback control, so it is used when higher speed and higher accuracy control is required. Have been.

  The full-range air-fuel ratio sensor has two cells of an oxygen ion conductive solid electrolyte body disposed opposite to each other with an interval therebetween, and one of the cells is used as a pump cell for extracting oxygen in the interval to the surroundings or incorporating oxygen from the surroundings. Further, the other cell is used as an electromotive force cell that generates a voltage due to a difference in oxygen concentration between the oxygen reference chamber and the space, and the pump cell is operated so that the output of the electromotive force cell becomes constant. Is measured as a measured oxygen concentration proportional value. The principle of operation of this full-range air-fuel ratio sensor is described in detail in Japanese Patent Application Laid-Open No. Sho 62-148849 filed by the present applicant.

  The reduction of exhaust gas by the feedback control is started after the warm-up of the full-range air-fuel ratio sensor is completed. This is because the whole region air-fuel ratio sensor cannot operate unless it has been heated to a predetermined temperature or higher to increase the activity of the oxygen ion conductive fixed electrolyte. For this reason, a heater for heating is arranged in the full range air-fuel ratio sensor, and the operation is started as soon as possible after the engine is started.

  Here, before the feedback control by the full-range air-fuel ratio sensor is started, the air-fuel ratio is often controlled to be slightly rich so as not to stop the engine. Has been exhausted. In order to complete the discharge of this high-concentration harmful exhaust gas in a short time, the electromotive force cell determines whether or not the entire area air-fuel ratio sensor has been activated so that the entire area air-fuel ratio sensor can operate from the earliest possible time. Judgment is made by applying a constant current or voltage and measuring the resistance value.

That is, since the electromotive force cell has negative temperature-resistance characteristics, the resistance value gradually decreases when heated by the heater. That is, the temperature of the electromotive force cell is estimated based on the resistance value, and based on reaching the temperature at which the electromotive force cell is activated, it is determined that the full area air-fuel ratio sensor can start measurement.
JP-A-62-148849

  Here, the oxygen ion conductive solid electrolyte constituting the electromotive force cell of the full range air-fuel ratio sensor does not deteriorate, but the porous electrode and the solid electrolyte made of platinum or the like attached to the electromotive force cell have a porous structure. Deterioration occurs at the interface with the quality electrode. That is, when the porous electrode is used, the porous electrode is peeled off from the oxygen ion conductive solid electrolyte body, or the oxygen permeability of the electrode decreases, and the internal resistance gradually increases and deteriorates.

  Then, when the deterioration has progressed to a certain degree or more, there has been a problem that an accurate air-fuel ratio cannot be detected. However, a method for accurately detecting the deterioration of the sensor is not known at present.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a deterioration state detection method and apparatus capable of accurately detecting deterioration of an air-fuel ratio sensor in all regions.

In order to achieve the above object, a first aspect of the present invention is to dispose two cells having porous electrodes provided on both sides of an oxygen ion conductive solid electrolyte body heated by a heater, facing each other with a gap therebetween. One of the cells is used as a pump cell that pumps or pumps oxygen in the gap to the surroundings, and the other cell is used as an electromotive force cell that generates a voltage due to the difference in oxygen concentration between the oxygen reference chamber and the gap. In the full range air-fuel ratio sensor that measures the fuel ratio,
A first step of applying a current or voltage to the electromotive force cell;
A second step of detecting a voltage Vs0 between electrodes on both surfaces of the electromotive force cell;
A third step of stopping the application of the current or voltage applied to the electromotive force cell;
A fifth step of detecting a voltage Vs2 between the electrodes on both surfaces of the electromotive force cell after a lapse of 10 ms to 50 ms after the third step;
A ninth step of detecting the activation state of the full area air-fuel ratio sensor from the Vs0 and Vs2;
A tenth step of detecting a time Ts from when the energization of the heating heater is started to when the ninth step detects that the all-area air-fuel ratio sensor is active;
An eleventh step of detecting a deterioration state of the full area air-fuel ratio sensor from the time Ts detected in the tenth step;
Is a technical feature.

  According to a second aspect of the present invention, in the method for detecting the deterioration state of the full-area air-fuel ratio sensor, the third step may be executed after a predetermined time has elapsed after the energization of the heating heater is started. Features.

  According to a third aspect of the present invention, in the first aspect, the third step is started after Vs0 detected in the second step becomes equal to or smaller than a predetermined value. This is a technical feature.

In order to achieve the above object, a fourth aspect of the present invention is to dispose two cells in which porous electrodes are provided on both sides of an oxygen ion conductive solid electrolyte body heated by a heater, facing each other with a gap therebetween. One cell is used as a pump cell that pumps or pumps oxygen in the gap to the surroundings, and the other cell is used as an electromotive force cell that generates a voltage due to the difference in oxygen concentration between the oxygen reference chamber and the gap, and An all-area air-fuel ratio sensor for measuring a fuel ratio,
Application means for applying a current or voltage to the electromotive force cell,
Vs0 voltage detecting means for detecting a voltage Vs0 between electrodes on both surfaces of the electromotive force cell;
From the start of energization to the heating heater, application stop means for stopping the application of the current or voltage applied to the electromotive force cell after the elapse of a predetermined time,
Vs2 voltage detecting means for detecting a voltage Vs2 between the electrodes on both surfaces of the electromotive force cell after a lapse of 10 ms to 50 ms after stopping the application of the current or the voltage;
Active state detecting means for detecting an active state of the full area air-fuel ratio sensor from the Vs0 and Vs2;
Activation time detection means for detecting an activation time from when the heater is energized to when the full area air-fuel ratio sensor is activated,
Deterioration state detection means for detecting the deterioration state of the entire area air-fuel ratio sensor from the activation time,
Technical features are provided.

  In the first aspect, a current or a voltage is applied to the electromotive force cell, and a voltage Vs0 between the electrodes on both surfaces of the electromotive force cell is detected. Further, the application of the current or the voltage applied to the electromotive force cell is stopped, and the voltage Vs2 between the electrodes on both surfaces of the electromotive force cell is detected after a lapse of 10 to 50 ms from the stop. Then, the activation state of the full range air-fuel ratio sensor is detected from Vs0 and Vs2. Thereafter, a time Ts from when the heating heater is energized to when the whole area air-fuel ratio sensor detects that it is active is detected. Here, when the entire area air-fuel ratio sensor is deteriorated, the temperature at which the activity is reached increases. That is, the heating time required for activation becomes longer. Therefore, the deterioration state of the air-fuel ratio sensor in all regions is detected from the time Ts until activation.

  According to the second aspect, the application of the current or the voltage applied to the electromotive force cell is stopped after a lapse of a predetermined time from the start of energization of the heating heater. That is, the current is continuously supplied to the electromotive force cell (or the voltage is applied) without interruption until the possibility of reaching the active state occurs.

  According to the third aspect, the application of the current or the voltage applied to the electromotive force cell is stopped after the detected Vs0 becomes equal to or smaller than a predetermined value. That is, the current is continuously supplied to the electromotive force cell (or the voltage is applied) without interruption until the possibility of reaching the active state occurs.

  In claim 4, the applying means applies a current or a voltage to the electromotive force cell, and the Vs0 voltage detecting means detects the voltage Vs0 between the electrodes on both surfaces of the electromotive force cell. Then, the application stopping means stops applying the current or the voltage applied to the electromotive force cell after a lapse of a predetermined time after the energization of the heating heater is started, and the Vs2 voltage detecting means stops applying the current or the voltage. A voltage Vs2 between the electrodes on both surfaces of the electromotive force cell after a lapse of 10 to 50 ms from the stop is detected. Thereafter, the activation state detection means detects the activation state of the full area air-fuel ratio sensor from Vs0 and Vs2, and the activation time detection means starts energizing the heating heater. Activating time until becomes. Here, when the entire area air-fuel ratio sensor is deteriorated, the temperature at which the activity is reached increases. That is, the heating time required for activation becomes longer. For this reason, the deterioration state detecting means detects the deterioration state of the entire area air-fuel ratio sensor based on the activation time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a full area oxygen sensor according to one embodiment of the present invention. The sensor element 10 in which two cells are joined is disposed in an exhaust gas system. The sensor element 10 is connected to a controller 50 that measures the oxygen concentration in the exhaust gas and the temperature of the sensor element 10. A heater 70 controlled by a heater control circuit 60 is attached to the sensor element 10 via a ceramic bonding agent (not shown). The heater 70 is made of ceramic such as alumina as an insulating material, and has a heater wiring 72 disposed therein. The heater control circuit 60 functions to apply electric power to the heater 70 so as to maintain the temperature of the sensor element 10 measured by the controller 50 at the target value, and to maintain the temperature of the sensor element 10 at the target value.

  The sensor element 10 is configured by stacking a pump cell 14, a porous diffusion layer 18, an electromotive force cell 24, and a reinforcing plate 30. The pump cell 14 is made of stabilized or partially stabilized zirconia (ZrO 2), which is an oxygen ion conductive solid electrolyte material, and has porous electrodes 12 and 16 mainly made of platinum on its front and rear surfaces, respectively. I have. The porous electrode 12 on the front side exposed to the measurement gas is referred to as an Ip + electrode because an Ip + voltage is applied to flow an Ip current. The porous electrode 16 on the back side is referred to as an Ip-electrode because an Ip-voltage is applied to flow an Ip current.

  The electromotive force cell 24 is also formed of stabilized or partially stabilized zirconia (ZrO2), and has porous electrodes 22 and 28 mainly formed of platinum on the front and back surfaces, respectively. A gap 20 surrounded by the porous diffusion layer 18 is formed between the pump cell 14 and the electromotive force cell 24. That is, the gap 20 is communicated with the measurement gas atmosphere via the porous diffusion layer 18. In this embodiment, the porous diffusion layer 18 filled with a porous substance is used, but small holes may be provided instead. The porous electrode 22 disposed on the gap (measurement chamber) 20 side is referred to as a Vs-electrode because a negative voltage of the electromotive force of the electromotive force cell 24 is generated, and is disposed on the reference oxygen chamber 26 side. The porous electrode 28 is referred to as a Vs + electrode because a positive voltage of the electromotive force of the electromotive force cell 24 is generated. The reference oxygen in the reference oxygen chamber 26 is generated by pumping a certain amount of oxygen from the porous electrode 22 to the porous electrode 28.

  Here, oxygen corresponding to the difference between the oxygen concentration of the measurement gas and the oxygen concentration in the gap 20 diffuses toward the gap 20 via the porous diffusion layer 18. Here, when the atmosphere in the gap 20 is maintained at the stoichiometric air-fuel ratio, the oxygen concentration difference between the reference oxygen chamber 26 where the oxygen concentration is kept substantially constant and the Vs + electrode 28 of the electromotive force cell 24 A potential of about 0.45 V is generated between the Vs-electrode 22. Therefore, the controller 50 maintains the atmosphere in the gap 20 at the stoichiometric air-fuel ratio by adjusting the current Ip flowing through the pump cell 14 so that the electromotive force Vs of the electromotive force cell potential 24 becomes 0.45 V. The oxygen concentration in the measurement gas is measured based on the pump cell current amount Ip for maintaining the stoichiometric air-fuel ratio.

Subsequently, the operation of the activity detection by the controller 50 will be described with reference to FIGS.
After starting the engine, the controller 50 supplies a current to the heater 70 via the heater control circuit 60 to heat and activate the sensor element 10. Then, the current Icp is caused to flow through the electromotive force cell 24 to detect whether or not the temperature of the electromotive force cell 24 is increased and activated based on the voltage Vs of the electromotive force cell 24, and measurement of the oxygen concentration is started. At the same time, the deterioration of the entire area air-fuel ratio sensor 10 is detected. This operation will be described in detail with reference to the flowchart of FIG. 2, FIG. 3A showing the voltage Vs of the electromotive force cell 24, and FIG. 3B showing the current Icp to the electromotive force cell 24.

  First, after starting the engine, the controller 50 starts applying a current to the heater 70 via the heater control circuit 60, and supplies a constant current Icp to the electromotive force cell 24, The voltage between the porous electrodes 22 and 28 is measured (S10). Then, it is determined whether or not the voltage Vs of the electromotive force cell 24 has become equal to or lower than the potential Vss (see FIG. 3A) at which the possibility of reaching the activation is generated (S12). That is, until the possibility of reaching the active state occurs, the current continues to flow through the electromotive force cell 24 without interruption as described later.

  When the voltage Vs of the electromotive cell 24 becomes equal to or lower than the potential Vss at which the possibility of reaching the activation is generated (Yes in S12), a predetermined interval has elapsed after measuring the potential Vs0 of the electromotive cell 24 (S15). It is determined (S14), and at time t2, which is a predetermined interval shown in FIGS. 3A and 3B (S14: Yes), the current Icp to the electromotive force cell 24 is cut off (S16). FIG. 4 is an enlarged waveform diagram at the time of current interruption shown in FIG.

  At the time t3 immediately after the current interruption (after 10 μs to 10 ms has elapsed) (Yes at S18), the controller 50 measures the potential Vs1 of the electromotive force cell 24 at the time t3, and thereby the potential Vs0 immediately before the voltage interruption and the potential Vs0 The difference from the potential Vs1 at time t3, that is, the voltage drop Vsd1 is calculated (S20). Then, the internal resistance Rvs1 of the electromotive force cell 24 is calculated, and then the element temperature is searched from a prepared map (S22). Thereafter, at time t4 after 10 to 50 ms has elapsed from time t2 when the current Icp was cut off (Yes at S24), the potential Vs2 of the electromotive force cell 24 at the time t4 is measured to determine the potential immediately before the voltage cutoff. A difference between Vs0 and the potential Vs2 at the time t4, that is, a voltage drop Vsd2 is calculated (S26). After that, the internal resistance Rvs2 including the deterioration component of the electromotive force cell 24 is calculated or searched from a prepared map (S28).

ここで、Ｒｖｓは起電力セル２４の内部抵抗を、また、ＥＭＦは起電力セル２４の内部起電力を示している。 Here, the voltage Vs of the electromotive force cell 24 when the current Icp is cut off will be described with reference to FIG. First, the voltage Vs of the electromotive force cell 24 is represented by the following equation.

Here, Rvs indicates the internal resistance of the electromotive force cell 24, and EMF indicates the internal electromotive force of the electromotive force cell 24.

  When the current Icp is turned off, the voltage Vs of the electromotive force cell 24 drops sharply, and becomes the internal electromotive force EMF. Here, since the current Icp is a known value, the internal resistance Rvs1 of the electromotive force cell 24 can be obtained by measuring the voltage drop Vsd1 as described above and dividing this value by the current Icp. Since the internal resistance Rvs1 is a value that changes depending on the temperature of the electromotive force cell 24, the temperature of the electromotive force cell 24 can be obtained by searching the map as described above (S20 and S22). Note that the voltage drop Vsd1 immediately after the current interruption depends only on the temperature of the electromotive force cell 24, and is not directly affected by the deterioration of the electromotive force cell 24 as described later.

  After drastically decreasing as described above, the voltage Vs of the electromotive force cell 24 further decreases gradually. This gradual decrease in potential mainly depends on the deterioration of the electromotive force cell 24, that is, the deterioration of the sensor element 10. The electromotive force cell 24 of the sensor element 10 has the porous platinum electrodes 22 and 28 attached to the front and back surfaces of the partially stabilized zirconia plate as described above. Separation occurs between the porous electrodes 22 and 28, and the oxygen permeability of the porous electrodes 22 and 28 decreases, and the internal resistance increases. However, in the full-range air-fuel ratio sensor made of partially stabilized zirconia, the internal resistance due to this deterioration does not directly appear immediately after the above-described current interruption. At time t4 when 〜50 ms has elapsed, the voltage drop Vsd2 is measured, and the internal resistance Rvs2 including the degradation is calculated.

  In the next step (S30), it is determined whether or not Rvs2 is equal to or less than a predetermined value. If Rvs2 is equal to or less than the predetermined value, it is determined that the element is activated, and the process proceeds to the next step. If the value is equal to or smaller than the predetermined value, it is determined that the element is not activated, and the activation determination processing routine is repeated again.

  If it is determined that the element has been activated, a map stored in advance is searched in S32, and deterioration of the element is determined using Rvs1 and Rvs2 obtained in the above step (S32). FIG. 7 shows an example of the map.

On the other hand, the deterioration can be determined from the calculation using Rvs1 and Rvs2. In a simple model, the difference between Rvs2 and Rvs1 is considered to be the resistance component at the interface between the porous electrode and the solid electrolyte. Then, it is determined that the resistance component has deteriorated when the resistance component is larger than a certain value. The resistance component at this interface also basically has temperature dependency. Therefore, a method is used in which the temperature is compensated using the following equation, and the deterioration is determined based on whether or not the magnitude is larger than a predetermined value Rr.

If it is determined that the sensor has deteriorated by using a map or a mathematical expression, the result is recorded in the memory, and the air-fuel ratio detection operation of the full-range air-fuel ratio sensor does not start (S34). On the other hand, if the sensor has not deteriorated, the measurement of the oxygen concentration is started (S36), and the program for determining the activity ends.
In the first embodiment, in addition to being able to detect the activity of the air-fuel ratio sensor in all regions, it is possible to accurately determine the deterioration of the electromotive force cell 24 due to aging.

  Next, an operation of detecting activation and deterioration by the controller of the full range air-fuel ratio sensor according to the second embodiment of the present invention will be described with reference to FIG. The configuration of the full-range air-fuel ratio sensor and the method of interrupting the current according to the second embodiment are the same as those of the first embodiment described above with reference to FIGS. And its description is omitted.

  After starting the engine, the controller 50 of the second embodiment supplies a current to the heater 70 via the heater control circuit 60 to heat and activate the sensor element 10. Then, the current Icp is caused to flow through the electromotive force cell 24 to detect whether or not the temperature of the electromotive force cell 24 has risen and has been activated based on the voltage Vs of the electromotive force cell 24, to start measuring the oxygen concentration, and at the same time, Determine deterioration. This operation is shown in the flowchart of FIG. 5, FIG. 3A showing the voltage Vs of the electromotive force cell 24, FIG. 3B showing the current Icp to the electromotive force cell 24, and the waveform when the current Icp is cut off. This will be described in detail with reference to FIG.

  First, after the engine is started, the controller 50 starts applying a current to the heater 70 via the heater control circuit 60. At the same time, a constant current Icp is applied to the electromotive force cell 24, and the voltage between the porous electrodes 22 and 28 on both surfaces of the electromotive force cell 24 is measured (S50). Then, after starting the timer for measuring the time until activation (S52), the time when the possibility that the voltage Vs of the electromotive force cell 24 reaches the activation occurs, that is, the time when the activation can be reached in the shortest time (FIG. A)) It is determined whether T5 has elapsed (S54). That is, until the possibility of reaching the active state occurs, the current continues to flow through the electromotive force cell 24 without interruption as described later.

  Then, when it is time to reach the activity (Yes in S54), it is determined whether a predetermined interval has elapsed (S56), and a time t2 at which the predetermined interval shown in FIGS. 3A and 3B is reached. (Yes in S56), the potential Vs0 of the electromotive force cell 24 is measured (S57), and the current Icp to the electromotive force cell 24 is cut off (S58). FIG. 6 is an enlarged waveform diagram at the time of current interruption shown in FIG.

  When 10 to 50 ms have elapsed since the current was interrupted and time t4 is reached (Yes in S60), the potential Vs2 of the electromotive force cell 24 at the time t4 is measured to determine the potential Vs0 immediately before the voltage interruption and the time t4. Is calculated, that is, the voltage drop Vsd2 (S62). Then, the internal resistance (resistance value Rvs3 including the degradation component) of the electromotive force cell 24 is calculated or retrieved from a prepared map (S64). Thereafter, the activation of the element is determined based on whether the calculated internal resistance Rvs3 of the electromotive force cell 24 has reached a predetermined value (S66).

  If the activity has not been reached (No in S66), the heating is further continued, and the process returns to step 56 to determine whether or not the above-mentioned interval has elapsed. Icp is cut off (S58), and the above-described processing is restarted.

  On the other hand, when it is determined in step 66 that the activation temperature has been reached (Yes in S66), the timer for measuring the time until activation is stopped, and the application of the current Icp, that is, the heating from the start of heating by the heater 70, is stopped. The time Ts until the area air-fuel ratio sensor is activated is measured (S68). Then, it is determined whether or not the time Ts exceeds the maximum time until activation (S70). That is, as described above, if the electromotive force cell 24 is deteriorated, the temperature for activation becomes higher, and the heating time until activation becomes longer. For this reason, in the second embodiment, the longest time that is predicted to be necessary for the activation of the element when the element that has not deteriorated is properly heated is set in advance as the maximum heating time, and the time Ts exceeds this maximum time. Whether or not the element has deteriorated is determined based on whether or not.

  Here, if the time Ts does not exceed the maximum time (No in S70), the application of the current to the pump cell 14 is started, and the measurement of the oxygen concentration in the exhaust gas by the full area air-fuel ratio sensor is started (S74). ). On the other hand, when the time Ts exceeds the maximum time (Yes in S70), the deterioration of the full-range air-fuel ratio sensor is recorded in a memory provided in the engine control unit or the like for storing the state of the vehicle ( S72) Thereafter, the detection of the oxygen concentration by the full-range air-fuel ratio sensor does not start. Based on the record in this memory, the air-fuel ratio sensor in all areas is replaced with a new one at the time of periodic inspection or the like, and thereafter the air-fuel ratio of the engine can be appropriately controlled.

  In the second embodiment, in addition to being able to detect the presence / absence of activation of the full-range air-fuel ratio sensor, it is possible to accurately determine the deterioration of the electromotive force cell 24 due to aging.

  In the first embodiment described above, in step 12 shown in FIG. 2, after determining whether or not the voltage Vs of the electromotive force cell 24 has become equal to or lower than a predetermined value, the current interruption is started to detect the activity. Further, in the second embodiment, after it is determined in step 54 shown in FIG. 5 that the predetermined time has elapsed, the current interruption is started to detect the activity. However, the method (S54) of starting the current interruption for detecting the activity after a predetermined time has elapsed in the second embodiment is determined in step 13 as shown in FIG. 8 showing a modification of the first embodiment. It is also possible to apply to the first embodiment. Similarly, the method (S12) of starting the current cutoff for detecting the activity when the voltage becomes equal to or lower than the predetermined voltage in the first embodiment is changed in step 55 as shown in FIG. 9 showing a modification of the second embodiment. The determination can be applied to the second embodiment.

  Further, in the first and second embodiments, a constant current is applied to the electromotive force cell 24. Alternatively, a constant voltage may be applied and cut off at predetermined intervals. In the above embodiment, the deterioration is detected when the air-fuel ratio sensor in the entire region is warmed up. However, the deterioration state is similarly detected by interrupting the current flowing through the electromotive force cell even during normal operation. You can do it.

  As described above, in the deterioration state detecting device for the full range air-fuel ratio sensor according to claim 1 and claim 4, the electromotive force 10 ms to 50 ms after the application of the current or the voltage to the electromotive force cell is stopped. Whether the electromotive force cell is activated is detected from the voltage of the cell and whether or not the electromotive force cell has deteriorated is determined based on the time required until the activation. Therefore, the deterioration state of the entire area air-fuel ratio sensor can be accurately detected.

  In the method for detecting the deterioration state of the full-range air-fuel ratio sensor according to claim 2 or 3, the current is continuously supplied to the electromotive force cell without interruption until the possibility of reaching the activation state is reached. The activation and degradation can be detected with a small amount of operation without performing the operation of detecting.

FIG. 2 is an explanatory diagram illustrating a configuration of an entire area air-fuel ratio sensor, a heater control circuit, and a controller according to the first embodiment of the present invention. 2 is a flowchart illustrating a process performed by a controller illustrated in FIG. 1. FIG. 3A is a waveform diagram illustrating the voltage of the electromotive force cell, and FIG. 3B is a waveform diagram of the current applied to the electromotive force cell 24. FIG. 4 is an enlarged waveform diagram showing the waveform at the time of current interruption shown in FIG. It is a flowchart which shows the process by the controller which concerns on 2nd Embodiment. FIG. 6 is an enlarged waveform diagram showing the waveform at the time of current interruption shown in FIG. 3 is a map used for a map determination in a process S32 in the flowchart of FIG. 2. 5 is a flowchart illustrating a modified example of a process performed by the controller according to the first embodiment. It is a flowchart which shows the example of a change of the process by the controller which concerns on 2nd Embodiment.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 Sensor element 14 Pump cell 20 Interval 22 and 28 Porous electrode 24 Electromotive force cell 50 Controller 60 Heater control circuit 70 Heater Vs Electromotive force cell voltage Icp Electromotive force cell current

Claims (4)

Two cells having porous electrodes provided on both sides of an oxygen ion conductive solid electrolyte body heated by a heater are disposed to face each other with a gap therebetween, and one of the cells is provided with oxygen in the gap surrounding the cell. A pump cell that pumps or pumps oxygen, the other cell is used as an electromotive force cell that generates a voltage due to a difference in oxygen concentration between the oxygen reference chamber and the gap, and in an all-area air-fuel ratio sensor that measures the air-fuel ratio,
A first step of applying a current or voltage to the electromotive force cell;
A second step of detecting a voltage Vs0 between electrodes on both surfaces of the electromotive force cell;
A third step of stopping the application of the current or voltage applied to the electromotive force cell;
A fifth step of detecting a voltage Vs2 between the electrodes on both surfaces of the electromotive force cell after a lapse of 10 ms to 50 ms after the third step;
A ninth step of detecting the activation state of the full area air-fuel ratio sensor from the Vs0 and Vs2;
A tenth step of detecting a time Ts from when the energization of the heating heater is started to when the ninth step detects that the all-area air-fuel ratio sensor is active;
A tenth step of detecting a deterioration state of the full area air-fuel ratio sensor from the time Ts detected in the ninth step;
A method for detecting the deterioration state of the full-range air-fuel ratio sensor comprising: 2. The method according to claim 1, wherein the third step is performed after a lapse of a predetermined time from the start of energization of the heater. The method according to claim 1, wherein the third step is started after Vs0 detected in the second step becomes equal to or smaller than a predetermined value. Two cells having porous electrodes provided on both sides of an oxygen ion conductive solid electrolyte body heated by a heater are disposed to face each other with a gap therebetween, and one of the cells is provided with oxygen in the gap surrounding the cell. A pump cell that pumps or pumps oxygen, the other cell is used as an electromotive force cell that generates a voltage due to an oxygen concentration difference between the oxygen reference chamber and the gap, and is a full area air-fuel ratio sensor that measures the air-fuel ratio,
Application means for applying a current or voltage to the electromotive force cell,
Vs0 voltage detecting means for detecting a voltage Vs0 between electrodes on both surfaces of the electromotive force cell;
From the start of energization to the heating heater, application stop means for stopping the application of the current or voltage applied to the electromotive force cell after the elapse of a predetermined time,
Vs2 voltage detecting means for detecting a voltage Vs2 between the electrodes on both surfaces of the electromotive force cell after a lapse of 10 ms to 50 ms after stopping the application of the current or the voltage;
Active state detecting means for detecting an active state of the full area air-fuel ratio sensor from the Vs0 and Vs2;
Activation time detection means for detecting an activation time from when the heater is energized to when the full area air-fuel ratio sensor is activated,
Deterioration state detection means for detecting the deterioration state of the entire area air-fuel ratio sensor from the activation time,
Deterioration state detection device for the full range air-fuel ratio sensor comprising:

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