JP3958755B2 - Deterioration state detection method and apparatus for all-range air-fuel ratio sensor - Google Patents

Description

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

  In order to control the air-fuel ratio of the air-fuel mixture supplied to the engine to the target value and reduce CO, NOx, and HC in the exhaust gas, an oxygen sensor is provided in the exhaust system, and oxygen in the exhaust gas having a correlation with the air-fuel ratio It is known to feedback control the fuel supply amount according to the concentration. The oxygen sensor used for this feedback control includes a λ sensor whose output changes stepwise at a specific oxygen concentration (especially the stoichiometric air-fuel ratio atmosphere), and an all-area empty whose output changes continuously from the lean region to the 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 feedback control. Therefore, it is used when higher speed and higher accuracy control is required. It has been.

  The full-range air-fuel ratio sensor is used as a pump cell in which two cells of an oxygen ion conductive solid electrolyte body are arranged to face each other with a gap therebetween, and one cell is pumped into the surroundings or oxygen is incorporated from the surroundings. In addition, 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 interval, and the pump cell is operated so that the output of the electromotive force cell becomes constant, and the current that flows to the pump cell at that time Is measured as a measured oxygen concentration proportional value. The operating principle of this full-range air-fuel ratio sensor is described in detail in Japanese Patent Application Laid-Open No. 62-148849, filed by the present applicant.

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

  Here, before starting the feedback control by the all-range air-fuel ratio sensor, the air-fuel ratio is often controlled to a slightly rich side so as not to stop the engine. It has been discharged. In order to complete the discharge of this high concentration of harmful exhaust gas in a short time, whether or not the full-range air-fuel ratio sensor is activated so that the full-range air-fuel ratio sensor can operate from the earliest possible time is indicated in the electromotive force cell. 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, when the electromotive force cell is heated by the heater, the resistance value gradually decreases. That is, the temperature of the electromotive force cell is estimated based on the resistance value, and based on the fact that the temperature at which the electromotive force cell is activated is reached, it is determined that the full-range air-fuel ratio sensor can start measurement.
JP-A-62-148849

  Here, the oxygen ion conductive solid electrolyte body constituting the electromotive force cell of the full range air-fuel ratio sensor does not deteriorate, but the porous electrode and the solid electrolyte body made of platinum or the like attached to the electromotive force cell Degradation occurs at the interface with the electrode. That is, when the porous electrode is used, it peels 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.

  And when deterioration progresses more than a certain amount, there is a problem that an accurate air-fuel ratio cannot be detected. However, there is currently no known method for accurately detecting sensor degradation.

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

In order to achieve the above-mentioned object, claim 1 comprises two cells each having a porous electrode provided on both sides of an oxygen ion conductive solid electrolyte heated by a heater for heating. One cell is used as a pump cell that pumps oxygen in the gap to the surroundings or pumps oxygen, 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 detects the concentration of oxygen contained in the exhaust gas of
Applying a current or voltage to the electromotive force cell;
A Vs0 voltage detection step of detecting a voltage Vs0 between the electrodes on both sides of the electromotive force cell;
An application stop step of stopping application of current or voltage applied to the electromotive force cell;
A Vs2 voltage detection step of detecting a voltage Vs2 between the electrodes on both sides of the electromotive force cell after a lapse of 10 ms to 50 ms after the application stop step;
An active state detecting step of detecting an active state of the full-range air-fuel ratio sensor from the Vs0 and Vs2,
An activation time detecting step of detecting a time Ts from when energization of the heater for heating is started after the engine is started to when it is detected in the active state detecting step that the all-range air-fuel ratio sensor is active; ,
A deterioration state detection step of detecting a deterioration state of the all-region air-fuel ratio sensor from the time Ts detected in the activation time detection step;
It consists of the technical features.

  According to a second aspect of the present invention, there is provided a method for detecting a deterioration state of an entire-range air-fuel ratio sensor, wherein the third step is executed after a predetermined time has elapsed since the energization of the heater was started. Features.

  According to a third aspect of the method for detecting the deterioration state of the air-fuel ratio sensor of claim 3, in claim 1, the third step is started after Vs0 detected in the second step becomes equal to or smaller than a predetermined magnitude. This is a technical feature.

In order to achieve the above-mentioned object, claim 4 is provided such that two cells each provided with a porous electrode on both sides of an oxygen ion conductive solid electrolyte heated by a heater for heating are arranged to face each other through a gap. , one of the cell Kumikomu the pumping or oxygen oxygen in the gap around the pump cell, respectively used as an electromotive force cell generates a voltage of the other cell by the oxygen concentration difference of the oxygen reference chamber and the gap, the engine A full-range air-fuel ratio sensor for detecting the concentration of oxygen contained in the exhaust gas of
Applying means for applying current or voltage to the electromotive force cell;
Vs0 voltage detecting means for detecting a voltage Vs0 between the electrodes on both sides of the electromotive force cell;
Application stopping means for stopping application of current or voltage applied to the electromotive force cell after elapse of a predetermined time after starting energization of the heater for heating after starting the engine ;
Vs2 voltage detecting means for detecting a voltage Vs2 between the electrodes on both surfaces of the electromotive force cell after elapse of 10 ms to 50 ms after the application of the current or voltage is stopped;
Active state detecting means for detecting an active state of the full-range air-fuel ratio sensor from the Vs0 and Vs2,
An activation time detection means for detecting an activation time from when the energization of the heating heater is started after the engine is started until the full-range air-fuel ratio sensor is activated;
The present invention is characterized by comprising deterioration state detecting means for detecting a deterioration state of the full-range air-fuel ratio sensor from the activation time.

In claim 1, a current or voltage is applied to the electromotive force cell, and the voltage Vs0 between the electrodes on both sides of the electromotive force cell is detected. Further, the application of the current or 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 time of 10 ms to 50 ms has elapsed since the stop. Then, the active state of the full-range air-fuel ratio sensor is detected from Vs0 and Vs2. A time Ts from when energization to the heater is started after the engine is started to when it is detected that the full-range air-fuel ratio sensor is active is detected. Here, when the full-range air-fuel ratio sensor deteriorates, the temperature reaching the activity increases. That is, the heating time required for activation becomes longer. For this reason, the deterioration state of the full-range air-fuel ratio sensor is detected from the time Ts until activation.

  According to a second aspect of the present invention, the application of the current or voltage applied to the electromotive force cell is stopped after a predetermined time has elapsed since the energization of the heater was started. That is, until the possibility of reaching the activation occurs, a current is passed through the electromotive force cell (or voltage is applied) without interruption.

  According to the third aspect of the present invention, the application of the current or voltage applied to the electromotive force cell is stopped after the detected Vs0 becomes equal to or less than a predetermined magnitude. That is, until the possibility of reaching the activation occurs, the current is continued to flow (or voltage is applied) to the electromotive force cell without interruption.

According to a fourth aspect of the present invention, the applying means applies a current or voltage to the electromotive force cell, and the Vs0 voltage detecting means detects the voltage Vs0 between the electrodes on both sides of the electromotive force cell. Then, after the application stopping means starts energizing the heater after the engine is started , the application of the current or voltage applied to the electromotive force cell is stopped after a predetermined time has elapsed, and the Vs2 voltage detecting means The voltage Vs2 between the electrodes on both sides of the electromotive force cell after the elapse of 10 ms to 50 ms after the application of the voltage is stopped is detected. Thereafter, the active state detection means detects the active state of the full-range air-fuel ratio sensor from Vs0 and Vs2, and the activation time detection means starts energizing the heater for heating after starting the engine, and then the full-range air-fuel ratio. The activation time until the sensor becomes active is detected. Here, when the full-range air-fuel ratio sensor deteriorates, the temperature reaching the activity 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 full-range air-fuel ratio sensor based on the activation time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings.
FIG. 1 shows a full range oxygen sensor according to one embodiment of the present invention. A 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 measures the temperature of the sensor element 10. A heater 70 controlled by the heater control circuit 60 is attached to the sensor element 10 via a ceramic bonding agent (not shown). The heater 70 is made of a ceramic such as alumina as an insulating material, and a heater wire 72 is disposed therein. The heater control circuit 60 functions to apply electric power to the heater 70 so as to keep the temperature of the sensor element 10 measured by the controller 50 at a 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 formed 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 formed of platinum on the front and back surfaces thereof. Yes. The porous electrode 12 on the surface side exposed to the measurement gas is referred to as an Ip + electrode because an Ip + voltage is applied to pass an Ip current. The porous electrode 16 on the back surface side is referred to as an Ip-electrode because an Ip-voltage is applied in order to pass an Ip current.

  Similarly, the electromotive force cell 24 is formed of stabilized or partially stabilized zirconia (ZrO 2), and has porous electrodes 22 and 28 mainly formed of platinum on the front surface and the back surface, respectively. A gap 20 surrounded by the porous diffusion layer 18 is formed between the pump cell 14 and the electromotive force cell 24. In other words, the gap 20 communicates with the measurement gas atmosphere via the porous diffusion layer 18. In this embodiment, the porous diffusion layer 18 filled with a porous material is used, but small holes can 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. Since the positive voltage of the electromotive force of the electromotive force cell 24 is generated, the porous electrode 28 is referred to as a Vs + electrode. 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 to the gap 20 side through the porous diffusion layer 18. Here, when the atmosphere in the gap 20 is maintained at the stoichiometric air-fuel ratio, the difference between the Vs + electrode 28 of the electromotive force cell 24 and the reference oxygen chamber 26 where the oxygen concentration is kept substantially constant, A potential of about 0.45 v is generated between the Vs-electrode 22. For this reason, 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 is 0.45 v. Based on the pump cell current amount Ip for maintaining the theoretical air-fuel ratio, the oxygen concentration in the measurement gas is measured.

Next, the operation of activity detection by the controller 50 will be described with reference to FIGS.
After starting the engine, the controller 50 supplies current to the heater 70 via the heater control circuit 60 to heat and activate the sensor element 10. Then, the current Icp is supplied to the electromotive force cell 24, and it is detected whether the temperature of the electromotive force cell 24 is increased and activated based on the voltage Vs of the electromotive force cell 24, and the measurement of the oxygen concentration is started. At the same time, the deterioration of the full-range 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 current to the heater 70 via the heater control circuit 60, and also causes a constant current Icp to flow through the electromotive force cell 24 and both sides of 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 is equal to or lower than the potential Vss (see FIG. 3A) at which the possibility of reaching the activation occurs (S12). That is, until the possibility of reaching the activation occurs, the current continues to flow through the electromotive force cell 24 without being interrupted as described later.

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

  At time t3 immediately after current interruption (after 10 μs to 10 ms elapses) (Yes in S18), the controller 50 measures the electric potential Vs1 of the electromotive force cell 24 at the time t3, so that the electric potential Vs0 immediately before voltage interruption and the electric potential Vs0 A difference from the potential Vs1 at time t3, that is, a 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 map prepared in advance (S22). After that, when 10 to 50 ms elapses from time t2 when the current Icp is cut off and time t4 is reached (S24 is Yes), the potential Vs2 of the electromotive force cell 24 at the time t4 is measured, so that the potential immediately before the voltage cut-off is obtained. A difference between Vs0 and the potential Vs2 at time t4, that is, a voltage drop Vsd2 is calculated (S26). Thereafter, the internal resistance Rvs2 including the degradation component of the electromotive force cell 24 is calculated or retrieved from a map prepared in advance (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 interrupted will be described with reference to FIG. First, the voltage Vs of the electromotive force cell 24 is expressed 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 rapidly decreases 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 varies 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 above). 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 deterioration of the electromotive force cell 24 as described later.

  As described above, after rapidly decreasing, the voltage Vs of the electromotive force cell 24 further gradually decreases. This gradual decrease in potential mainly depends on the deterioration of the electromotive force cell 24, that is, the sensor element 10. As described above, the electromotive force cell 24 of the sensor element 10 has platinum porous electrodes 22 and 28 attached to the front and back surfaces of the partially stabilized zirconia plate. While peeling occurs between the porous electrodes 22 and 28, 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 appear directly immediately after the current interruption described above. Therefore, in this embodiment, the current Icp interruption time is 10 to 10 At time t4 when ˜50 ms elapses, the voltage drop Vsd2 is measured, and the internal resistance Rvs2 including the deterioration is calculated.

  In the next step (S30), it is determined whether or not Rvs2 is equal to or smaller than a predetermined value. If Rvs2 is equal to or smaller than the predetermined value, it is determined that the element is activated, and the process proceeds to the next step. If it 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 it has been activated, a map stored in advance is searched in S32, and element degradation is determined using Rvs1 and Rvs2 obtained in the above step (S32). FIG. 7 shows an example of the map.

On the other hand, it is possible to determine deterioration from calculation using Rvs1 and Rvs2. In a simple model, the difference between Rvs2 and Rvs1 is considered to be a resistance component at the interface between the porous electrode and the solid electrolyte body. Then, although it is determined that the resistance component is deteriorated when the resistance component is larger than a certain size, the resistance component at the interface also basically has temperature dependence. Therefore, a method is used in which the temperature is compensated using the following equation and the deterioration is determined based on whether the magnitude is larger than a predetermined value Rr.

When it is determined that the sensor has deteriorated based on the map or the mathematical expression, the result is recorded in the memory, and the air-fuel ratio detection operation of the full-range air-fuel ratio sensor is not started (S34). On the other hand, if the sensor is not deteriorated, measurement of the oxygen concentration is started (S36), and the activity determination program is terminated.
In the first embodiment, in addition to being able to detect the activity of the full-range air-fuel ratio sensor, it is possible to accurately determine deterioration of the electromotive force cell 24 due to secular change.

  Next, the operation of the activation and deterioration detection 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 of the second embodiment and the method for interrupting the current are the same as those of the first embodiment described above with reference to FIGS. And the description thereof is omitted.

  After starting the engine, the controller 50 according to the second embodiment applies a current to the heater 70 via the heater control circuit 60 to heat and activate the sensor element 10. Then, a current Icp is supplied to the electromotive force cell 24 to detect whether 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. Determine deterioration. This operation is illustrated 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 is expanded. This will be described in detail with reference to FIG.

  First, the controller 50 starts applying current to the heater 70 via the heater control circuit 60 after the engine is started. At the same time, a constant current Icp is supplied to the electromotive force cell 24, and the voltage between the porous electrodes 22 and 28 on both sides of the electromotive force cell 24 is measured (S50). Then, after starting a timer for measuring the time until activation (S52), the time when the voltage Vs of the electromotive force cell 24 may reach the activation, that is, the time when the activation can be reached in the shortest time (FIG. 3 ( See A)) It is determined whether T5 has elapsed (S54). That is, until the possibility of reaching the activation occurs, the current continues to flow through the electromotive force cell 24 without being interrupted as described later.

  Then, when it is time that there is a possibility of reaching the activity (Yes in S54), it is determined whether the predetermined interval has passed (S56), and the time t2 that becomes the predetermined interval shown in FIGS. 3 (A) and 3 (B). (S56 is Yes), after measuring the potential Vs0 of the electromotive force cell 24 (S57), the current Icp to the electromotive force cell 24 is cut off (S58). FIG. 6 shows an enlarged waveform diagram at the time of current interruption shown in FIG.

  When 10-50 ms elapses after the current is cut off and time t4 is reached (Yes in S60), by measuring the potential Vs2 of the electromotive force cell 24 at the time t4, the potential Vs0 immediately before the voltage cut-off and the time t4 are measured. The difference between the voltage Vs2 and the voltage drop Vsd2 is calculated (S62). Then, the internal resistance (resistance value Rvs3 including the degradation component) of the electromotive force cell 24 is calculated or retrieved from a map prepared in advance (S64). Thereafter, the activation of the element is determined based on whether or not the calculated internal resistance Rvs3 of the electromotive force cell 24 has reached a predetermined value (S66).

  Here, when the activation 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 interval has passed (S56 is Yes). Icp is cut off (S58), and the above-described processing is resumed.

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

  Here, when the time Ts does not exceed the longest time (S70 is No), application of current to the pump cell 14 is started, and measurement of the oxygen concentration in the exhaust gas by the entire region air-fuel ratio sensor is started (S74). ). On the other hand, when the time Ts exceeds the longest time (S70 is Yes), the deterioration of the whole area air-fuel ratio sensor is recorded in the memory for storing the state of the vehicle provided in the engine control unit or the like ( S72) Thereafter, the detection of the oxygen concentration by the full-range air-fuel ratio sensor is not started. Based on the record in the memory, the entire area air-fuel ratio sensor 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 detecting the presence / absence of activity of the full-range air-fuel ratio sensor, it is possible to accurately determine the deterioration of the electromotive force cell 24 due to secular change.

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

  Furthermore, in the first and second embodiments, a constant current is applied to the electromotive force cell 24, but instead, a constant voltage may be applied and cut off at a predetermined interval. In the above embodiment, the deterioration is detected when the full-range air-fuel ratio sensor is warmed up. However, the deterioration state is similarly detected by cutting off the current flowing to the electromotive force cell even during normal operation. I can do it.

  As described above, in the deterioration detection device for the full-range air-fuel ratio sensor according to claims 1 and 4, the electromotive force 10 ms to 50 ms after the application of the current or voltage to the electromotive force cell is stopped. Whether or not the electromotive force cell is activated is detected from the voltage of the cell, and the presence or absence of degradation is determined based on the time required for the activation, so that the degradation state of the entire region air-fuel ratio sensor can be accurately detected.

  In the deterioration detection method for the full-range air-fuel ratio sensor according to claim 2 or 3, since the current is continuously supplied to the electromotive force cell without interruption until the possibility of reaching the activation occurs, the activation and deterioration states are detected. The activation and the degradation can be detected with a slight operation without unnecessarily executing the operation for detecting the error.

It is explanatory drawing which shows the structure of the full range air-fuel ratio sensor which concerns on 1st embodiment of this invention, a heater control circuit, and a controller. It is a flowchart which shows the process by the controller shown in FIG. FIG. 3A is a waveform diagram showing 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 a 2nd embodiment. FIG. 6 is an enlarged waveform diagram showing the waveform at the time of current interruption shown in FIG. It is a map used for the map determination of process S32 in the flowchart of FIG. It is a flowchart which shows the modification of the process by the controller which concerns on 1st Embodiment. It is a flowchart which shows the modification of the process by the controller which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sensor element 14 Pump cell 20 Space | interval 22, 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 for heating are opposed to each other through a gap, and one cell is surrounded by oxygen in the gap. The pump cell that pumps out or pumps oxygen, 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 detects the concentration of oxygen contained in the engine exhaust gas. In the full range air-fuel ratio sensor,
Applying a current or voltage to the electromotive force cell;
A Vs0 voltage detection step of detecting a voltage Vs0 between the electrodes on both sides of the electromotive force cell;
An application stop step of stopping application of current or voltage applied to the electromotive force cell;
A Vs2 voltage detection step of detecting a voltage Vs2 between the electrodes on both sides of the electromotive force cell after elapse of 10 ms to 50 ms after the application stop step;
An active state detecting step of detecting an active state of the full-range air-fuel ratio sensor from the Vs0 and Vs2,
An activation time detecting step for detecting a time Ts from when energization of the heater for heating is started after the engine is started until it is detected in the active state detecting step that the all-range air-fuel ratio sensor is active; ,
A deterioration state detection step of detecting a deterioration state of the all-region air-fuel ratio sensor from the time Ts detected in the activation time detection step;
A method for detecting a deterioration state of an entire-range air-fuel ratio sensor comprising 2. The method for detecting a deterioration state of an entire-range air-fuel ratio sensor according to claim 1, wherein the application stopping step is executed after a predetermined time has elapsed since energization of the heater was started. 2. The deterioration detection method for a full-range air-fuel ratio sensor according to claim 1, wherein the application stop step is started after Vs0 detected in the Vs0 voltage detection step becomes equal to or less than a predetermined magnitude. Two cells having porous electrodes provided on both sides of an oxygen ion conductive solid electrolyte body heated by a heater for heating are opposed to each other through a gap, and one cell is surrounded by oxygen in the gap. A pump cell that pumps out or pumps oxygen, and 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 detects the concentration of oxygen contained in the engine exhaust gas. A full-range air-fuel ratio sensor,
Applying means for applying current or voltage to the electromotive force cell;
Vs0 voltage detecting means for detecting a voltage Vs0 between the electrodes on both sides of the electromotive force cell;
Application stopping means for stopping application of current or voltage applied to the electromotive force cell after elapse of a predetermined time after starting energization of the heater for heating after starting the engine;
Vs2 voltage detecting means for detecting a voltage Vs2 between the electrodes on both surfaces of the electromotive force cell after elapse of 10 ms to 50 ms after the application of the current or voltage is stopped;
Active state detecting means for detecting an active state of the full-range air-fuel ratio sensor from the Vs0 and Vs2,
An activation time detection means for detecting an activation time from when the energization of the heating heater is started after the engine is started until the full-range air-fuel ratio sensor is activated;
A degradation state detection device for a full-range air-fuel ratio sensor, comprising: a degradation state detection means for detecting a degradation state of the full-range air-fuel ratio sensor from the activation time.

Images