JP2009250690A - Abnormality detecting device and abnormality detection method of oxygen sensor - Google Patents

Abstract

The present invention relates to an abnormality detection apparatus and an abnormality detection method for an oxygen sensor, which is intended to detect the abnormality of the sensor without affecting the normal use of the oxygen sensor.
An abnormality of an oxygen sensor that outputs a signal corresponding to the amount of oxygen ions moving between an exhaust-side electrode exposed to an exhaust space in which oxygen concentration is to be detected and an atmospheric-side electrode exposed to the atmosphere is detected. In the apparatus, when a voltage is applied between the exhaust side electrode and the atmosphere side electrode so that oxygen ions move from the exhaust side electrode toward the atmosphere side electrode, the amount of oxygen ions in that direction is detected. Conversely, when a voltage is applied between the exhaust side electrode and the atmosphere side electrode so that oxygen ions move from the atmosphere side electrode toward the exhaust side electrode, the amount of oxygen ions in that direction is detected. And abnormality of an oxygen sensor is detected based on the comparison result of the quantity of both detected oxygen ions.
[Selection] Figure 2

Description

  The present invention relates to an abnormality detection device and an abnormality detection method for an oxygen sensor, and in particular, has an exhaust side electrode exposed to an exhaust space in which an oxygen concentration is to be detected, and an atmosphere side electrode exposed to the atmosphere. The present invention relates to an abnormality detection apparatus and an abnormality detection method for an oxygen sensor that outputs a signal corresponding to the amount of oxygen ions moving between an electrode and an atmosphere-side electrode.

2. Description of the Related Art Conventionally, an apparatus that detects an abnormality of an oxygen sensor that outputs a signal corresponding to an oxygen concentration in an exhaust space such as an exhaust passage of an internal combustion engine is known (see, for example, Patent Document 1). This oxygen sensor has an exhaust-side electrode exposed to the exhaust space and an atmosphere-side electrode exposed to the atmosphere, and a signal corresponding to the amount of oxygen ions flowing between the electrodes when a voltage is applied to both electrodes. Is output. Moreover, the above-described abnormality detection device applies a reverse voltage so that oxygen ions move from the atmosphere-side electrode to the exhaust-side electrode between both electrodes, and flows between the two electrodes as the reverse voltage is applied. Based on the reverse current, an abnormality of the oxygen sensor (specifically, a sensor defect) is detected.
JP 2006-300829 A

  However, when the reverse voltage as described above is applied between the exhaust side electrode and the atmosphere side electrode when the oxygen sensor is in a normal state, oxygen ions move from the atmosphere side electrode toward the exhaust side electrode. To detect the oxygen concentration in the exhaust space after the movement, when a positive voltage opposite to the reverse voltage is applied so that oxygen ions move from the exhaust side electrode to the atmosphere side electrode, immediately after that, The oxygen ions that have moved to the exhaust side electrode will return to the atmosphere side electrode side. Therefore, in the above method, when detecting the oxygen concentration in the exhaust space, the oxygen ion content originally present on the atmosphere side electrode side is superimposed on the amount of oxygen ions corresponding to the oxygen concentration in the exhaust space, and the sensor An error may occur in the output, and a situation may occur in which the oxygen concentration in the exhaust space cannot be accurately detected.

  The present invention has been made in view of the above points, and provides an abnormality detection device and abnormality detection method for an oxygen sensor capable of detecting the abnormality of the sensor without affecting the normal use of the oxygen sensor. For the purpose.

  The above object has an exhaust-side electrode exposed to an exhaust space in which oxygen concentration is to be detected and an atmosphere-side electrode exposed to the atmosphere, and oxygen that moves between the exhaust-side electrode and the atmosphere-side electrode An apparatus for detecting an abnormality of an oxygen sensor that outputs a signal corresponding to the amount of ions, wherein oxygen ions are provided between the exhaust side electrode and the atmosphere side electrode from the exhaust side electrode toward the atmosphere side electrode. A positive voltage applying means for applying a voltage so as to move, and a first oxygen ion amount for detecting the amount of oxygen ions moving from the exhaust side electrode to the atmosphere side electrode when a voltage is applied by the positive voltage applying means A negative voltage applying means for applying a voltage so that oxygen ions move from the atmosphere side electrode to the exhaust side electrode between the detection means, the exhaust side electrode and the atmosphere side electrode; and the negative voltage Voltage application by applying means And a second oxygen ion amount detecting means for detecting the amount of oxygen ions moving from the atmosphere side electrode to the exhaust side electrode, a detection result of the first oxygen ion amount detecting means, and the second oxygen ion. This is accomplished by an oxygen sensor abnormality detection device comprising: a sensor abnormality detection unit that detects an abnormality of the oxygen sensor based on a comparison result with a detection result of the amount detection unit.

  In addition, the above object has an exhaust side electrode that is exposed to an exhaust space in which oxygen concentration is to be detected and an atmosphere side electrode that is exposed to the atmosphere, and moves between the exhaust side electrode and the atmosphere side electrode. A method for detecting an abnormality of an oxygen sensor that outputs a signal corresponding to the amount of oxygen ions to be performed, from the exhaust side electrode to the atmosphere side electrode between the exhaust side electrode and the atmosphere side electrode. A positive voltage applying step for applying a voltage so that oxygen ions move; and a first oxygen for detecting an amount of oxygen ions moving from the exhaust side electrode to the atmosphere side electrode when a voltage is applied in the positive voltage applying step An ion amount detection step, and a negative voltage application step of applying a voltage so that oxygen ions move from the atmosphere side electrode to the exhaust side electrode between the exhaust side electrode and the atmosphere side electrode; Negative electricity A second oxygen ion amount detection step for detecting the amount of oxygen ions moving from the atmosphere side electrode to the exhaust side electrode at the time of voltage application in the application step; a detection result of the first oxygen ion amount detection step; This is accomplished by an oxygen sensor abnormality detection method comprising: a sensor abnormality detection step that detects an abnormality of the oxygen sensor based on a comparison result with a detection result of the second oxygen ion amount detection step.

  In the inventions of these aspects, the oxygen ions detected when a voltage is applied between the exhaust side electrode and the atmosphere side electrode so that the oxygen ions move from the exhaust side electrode toward the atmosphere side electrode. An oxygen sensor based on a comparison result between the amount of oxygen ions detected when a voltage is applied so that oxygen ions move from the atmosphere-side electrode toward the exhaust-side electrode between the electrodes. An abnormality is detected. When the oxygen sensor is in a normal state, there is not much difference between the amounts of both oxygen ions, whereas when the oxygen sensor is in an abnormal state, there is a large difference between the amounts of both oxygen ions. Therefore, the abnormality of the oxygen sensor can be detected based on the comparison result. In addition, according to such a configuration, when the oxygen sensor is in a normal state, the amount of oxygen ions that move between the exhaust side electrode side and the atmosphere side electrode side in the process of detecting the abnormality of the oxygen sensor is determined between the forward time and the return time. Therefore, it is possible to avoid affecting the normal use of the oxygen sensor thereafter.

  In the oxygen sensor abnormality detection device described above, both the positive voltage applying means and the negative voltage applying means apply voltage at a timing when the exhaust space is in an atmospheric state or a state close to the atmospheric state. Is good.

  In the oxygen sensor abnormality detection method described above, both the positive voltage application step and the negative voltage application step apply voltage at a timing when the exhaust space is in an atmospheric state or a state close to the atmospheric state. Is good.

  In these aspects of the invention, the abnormality detection of the oxygen sensor is performed at a timing when the exhaust space is in an atmospheric state or a state close to the atmospheric state. Therefore, when the oxygen sensor is in a normal state, there is a difference between the amount of oxygen ions moving from the exhaust side electrode to the atmosphere side electrode and the amount of oxygen ions moving from the atmosphere side electrode to the exhaust side electrode. It can be suppressed from occurring.

  In the oxygen sensor abnormality detection device described above, the negative voltage application means may apply voltage after voltage application by the positive voltage application means.

  In the above-described oxygen sensor abnormality detection method, the negative voltage application step may be performed after the voltage application in the positive voltage application step.

  In the inventions of these aspects, in performing abnormality detection of the oxygen sensor, first, oxygen ions are moved from the exhaust side electrode toward the atmosphere side electrode, and thereafter, oxygen is moved from the atmosphere side electrode toward the exhaust side electrode. Ions will be moved. For this reason, a situation in which oxygen ions that are sufficiently present on the atmosphere side electrode side move to the exhaust side electrode side and then return to the atmosphere side electrode side is avoided, so that the oxygen sensor is in a normal state despite being in an abnormal state. Can be prevented from being erroneously detected.

  In the oxygen sensor abnormality detection device described above, the sensor abnormality detection means is configured such that the amount of oxygen ions by the first oxygen ion amount detection means is greater than the amount of oxygen ions by the second oxygen ion amount detection means. Then, when there is a predetermined number or less, it may be detected that an abnormality has occurred in the oxygen sensor.

  In the oxygen sensor abnormality detection method, the sensor abnormality detection step may be configured such that the amount of oxygen ions in the first oxygen ion amount detection step is greater than the amount of oxygen ions in the second oxygen ion amount detection step. Then, when there is a predetermined number or less, it may be detected that an abnormality has occurred in the oxygen sensor.

  In the inventions of these aspects, the amount of oxygen ions moving from the exhaust side electrode toward the atmosphere side electrode is less than a predetermined amount compared to the amount of oxygen ions moving from the atmosphere side electrode toward the exhaust side electrode In addition, it is determined that an abnormality has occurred in the oxygen sensor. That is, if the amount of oxygen ions from the exhaust side electrode to the atmosphere side electrode is small compared to the amount of oxygen ions from the atmosphere side electrode to the exhaust side electrode, It is not determined that an abnormality has occurred in the sensor. Therefore, even when the oxygen concentration in the exhaust space is relatively low compared to the oxygen concentration in the atmosphere, the oxygen sensor abnormality detection process can be executed.

  According to the present invention, it is possible to detect a sensor abnormality without affecting the normal use of the oxygen sensor.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration diagram of an oxygen sensor 10 according to an embodiment of the present invention. FIG. 1 shows a cross-sectional view of the oxygen sensor 10. FIG. 2 shows a configuration diagram of an apparatus (abnormality detection apparatus) 12 that detects an abnormality of the oxygen sensor 10 of the present embodiment.

  The oxygen sensor 10 is a sensor provided to detect an oxygen concentration in an exhaust passage 14 of an internal combustion engine mounted on a vehicle, for example. The oxygen sensor 10 includes a sensor main body 16, a cover (not shown) that covers the sensor main body 16, and a heater 18. The oxygen sensor 10 is assembled in the exhaust passage 14 so that the sensor body 16 is covered with a cover and exposed to the exhaust passage 14. The cover is provided with a plurality of vent holes so that the gas flowing through the exhaust passage 14 reaches the oxygen sensor 10.

  As shown in FIG. 1, the sensor main body 16 includes an air layer 20, an electrolyte layer 22, and a coating layer 24. The atmospheric layer 20 is provided in a recess 26a formed in an atmospheric layer forming member 26 made of ceramic such as alumina. The electrolyte layer 22 is made of an oxygen ion conductive oxide ceramic such as zirconia, and is disposed adjacent to the air layer forming member 26 so as to close the recess 26a. The air layer 20 is surrounded by the air layer forming member 26 and the electrolyte layer 22. The atmospheric layer 20 is isolated from the internal space of the exhaust passage 14 and communicates with the atmosphere through atmospheric holes (not shown).

  An atmosphere-side electrode 30 is attached to the surface of the electrolyte layer 22 on the atmosphere layer 20 side. The atmosphere side electrode 30 is exposed to the atmosphere layer 20, that is, the atmosphere. Further, an exhaust-side electrode 32 is attached to the surface of the electrolyte layer 22 opposite to the air layer 20. The exhaust side electrode 32 is exposed to the exhaust passage 14. Specifically, since the exhaust side electrode 32 is covered with the coating layer 24, the exhaust side electrode 32 is exposed to the exhaust passage 14 through the coating layer 24. The coating layer 24 is a porous material having heat resistance, and has a function of removing substances other than oxygen molecules in the process in which the gas flowing through the exhaust passage 14 reaches the exhaust side electrode 32.

  Between the atmosphere-side electrode 30 and the exhaust-side electrode 32 of the oxygen sensor 10, a voltage (hereinafter referred to as a positive voltage) that causes the atmosphere-side electrode 30 to have a high potential with respect to the exhaust-side electrode 32, and exhaust Any voltage (hereinafter referred to as a negative voltage) that causes the side electrode 32 to have a high potential with respect to the atmosphere-side electrode 30 is selectively applied.

  That is, as shown in FIG. 2, an electronic control unit (hereinafter referred to as ECU) 34 mainly composed of a microcomputer is connected to the atmosphere side electrode 30 and the exhaust side electrode 32 of the oxygen sensor 10. Based on the signal supplied from the oxygen sensor 10, the ECU 34 detects the oxygen concentration in the exhaust passage 14 and detects an abnormality in the oxygen sensor 10, as will be described in detail later. That is, the ECU 34 also functions as the abnormality detection device 12 that detects an abnormality of the oxygen sensor 10.

  The ECU 34 has a first external terminal 36 to which the atmosphere side electrode 30 is connected and a second external terminal 38 to which the exhaust side electrode 32 is connected. The second external terminal 38 is connected to a predetermined potential (2.5 volts in FIG. 2) V0 offset from the GND potential. Therefore, a constant predetermined potential V0 is supplied to the exhaust side electrode 32 (or the atmosphere side electrode 30). The first external terminal 36 is connected to a switch element Tr1 via a resistor Rs and a resistor R1 (resistance value = Rx), and a resistor Rs and a resistor R2 (resistance value equal to the resistor R1 = Rx). The switch element Tr2 is connected via

  The switch element Tr1 is a pnp bipolar transistor, for example, and has a collector connected to the resistor R1. The emitter of the switch element Tr1 is connected to a potential (V0 + C) obtained by adding a predetermined potential C (for example, 0.5 volts) to the predetermined potential V0, and the base thereof has a first potential. Input port 40 is connected. The switch element Tr2 is an npn bipolar transistor, for example, and has a collector connected to the resistor R2. The emitter of the switch element Tr2 is connected to a potential (V0-C) obtained by subtracting a predetermined potential C (for example, 0.5 volts) from the above-described predetermined potential V0. A second input port 42 is connected.

  Signals for selectively turning on / off the switch elements Tr1, Tr2 are input to the first and second input ports 40, 42 from the CPU of the ECU 34. For this reason, one of the potentials (V0 + C) and (V0−C) is selectively input to the atmosphere-side electrode 30 (or the exhaust-side electrode 32).

  A current detection circuit 44 is connected to both terminals of the resistor Rs (that is, the terminals 36 and 37). The current detection circuit 44 has a role of detecting a current flowing between the electrodes 30 and 32 of the oxygen sensor 10. In the following, the direction of the current from the atmosphere side electrode 30 to the exhaust side electrode 32 is a positive direction, and the opposite direction is a negative direction. The ECU 34 detects the oxygen concentration in the exhaust passage 14 based on the current value flowing through the oxygen sensor 10 detected by the current detection circuit 44 when a predetermined voltage is applied between the electrodes 30 and 32 of the oxygen sensor 10. Further, the abnormality of the oxygen sensor 10 is detected.

  The heater 18 is a device that heats the sensor body 16 to an activation temperature. The heater 18 is embedded in a heater layer 50 disposed adjacent to the air layer forming member 26 that forms the air layer 20 of the sensor body 16.

  Hereinafter, a processing method using the oxygen sensor 10 in the present embodiment will be described.

  First, a method for detecting the oxygen concentration in the normal exhaust passage 14 will be described. The ECU 34 applies a positive voltage between the atmosphere side electrode 30 and the exhaust side electrode 32 of the oxygen sensor 10 when the oxygen concentration in the exhaust passage 14 is to be detected. Specifically, a signal for turning on the switching element Tr1 is input to the first input port 40, and a signal for turning off the switching element Tr2 is input to the second input port. In this case, the potential of the first external terminal 36 is higher than the potential of the second external terminal 38, and the atmosphere-side electrode 30 of the oxygen sensor 10 is at a higher potential than the exhaust-side electrode 32.

  For this reason, when a positive voltage is applied between the atmosphere-side electrode 30 and the exhaust-side electrode 32, oxygen adhering to the surface of the exhaust-side electrode 32 is ionized and moves toward the atmosphere-side electrode 30. At this time, the amount of the moving oxygen ions depends on the oxygen concentration in the exhaust gas in the exhaust passage 14. The direction in which oxygen ions move and the direction in which current flows are in the opposite directions. Accordingly, when a positive voltage is applied between the exhaust side electrode 32 and the atmosphere side electrode 30, a sensor current corresponding to the oxygen concentration in the exhaust passage 14 flows from the atmosphere side electrode 30 to the exhaust side electrode 32.

  The ECU 34 uses a current detection circuit 44 to output a sensor output (voltage) generated between both ends of the resistor Rs when a positive voltage is applied between the atmosphere-side electrode 30 and the exhaust-side electrode 32 of the oxygen sensor 10. Is converted to AD to detect a sensor current flowing between the electrodes 30 and 32 of the oxygen sensor 10, and the oxygen concentration in the exhaust passage 14 is detected based on the sensor current value. Then, the internal combustion engine is controlled based on the detected oxygen concentration.

  Next, a method for detecting an abnormality of the oxygen sensor 10 will be described with reference to FIGS. 3 and 4. FIG. 3 shows a time chart of processing for detecting an abnormality of the oxygen sensor 10 of the present embodiment. 3A shows a change in voltage applied between the electrodes 30 and 32 of the oxygen sensor 10, and FIG. 3B shows a sensor current flowing between the electrodes 30 and 32 of the oxygen sensor 10. The change of each is shown. FIG. 4 shows a flowchart of an example of a control routine executed by the ECU 34 in the abnormality detection device 12 of the present embodiment.

  The ECU 34 performs timing when the exhaust passage 14 is in an atmospheric state or a state close to the atmospheric state (for example, when the sensor current detected using the current detection circuit 44 when a positive voltage is applied to the oxygen sensor 10 is substantially zero, that is, When the sensor output (voltage) generated between both ends of the resistor Rs is substantially zero, or when a predetermined time has elapsed after the fuel cut to the internal combustion engine), the oxygen sensor 10 is abnormal (specifically, The presence or absence of an abnormal clogging of the coating layer 24 facing the exhaust passage 14 is detected.

  The ECU 34 alternately applies a positive voltage and a negative voltage between the atmosphere-side electrode 30 and the exhaust-side electrode 32 of the oxygen sensor 10 when it is necessary to detect the presence or absence of such an abnormality (when an affirmative determination is made in step 100). . Specifically, first, a positive voltage is applied between the atmosphere side electrode 30 and the exhaust side electrode 32 of the oxygen sensor 10 (step 102).

  When such a positive voltage is applied in a situation where no abnormality has occurred in the oxygen sensor 10, oxygen ions on the exhaust passage 14 side move from the exhaust side electrode 32 toward the atmosphere side electrode 30 as usual. A positive sensor current corresponding to the oxygen concentration of 14 flows. On the other hand, when such a positive voltage is applied in a situation where the oxygen sensor 10 is abnormal, oxygen that has already adhered to the surface of the exhaust side electrode 32 is ionized and moves toward the atmosphere side electrode 30. After that, oxygen in the exhaust passage 14 is difficult to be drawn to the exhaust side electrode 32 through the coating layer 24, and oxygen ions are difficult to move from the exhaust side electrode 32 toward the atmosphere side electrode 30. As much as normal sensor current does not flow, the sensor current is smaller than normal.

  The ECU 34 starts applying the positive voltage in a situation in which a positive voltage is applied between the atmosphere-side electrode 30 and the exhaust-side electrode 32 of the oxygen sensor 10 in order to detect whether or not the oxygen sensor 10 is abnormal. When time T1 has elapsed (specifically, a time required for at least oxygen already attached to the surface of the exhaust-side electrode 32 to be ionized and move toward the atmosphere-side electrode 30), the current detection circuit 44, the sensor output generated between both ends of the resistor Rs is AD converted to detect the sensor current I flowing between the electrodes 30 and 32 of the oxygen sensor 10. The detected sensor current I is defined as a sensor current I + when a positive voltage is applied (step 104).

  Thereafter, the ECU 34 switches the direction of the voltage applied between the atmosphere side electrode 30 and the exhaust side electrode 32 of the oxygen sensor 10 and applies a negative voltage between the electrodes 30 and 32 (step 106). The application of the negative voltage is performed at the same potential level and for the same time as the application of the positive voltage. When such a negative voltage is applied, oxygen ions on the atmosphere layer 20 side move from the atmosphere side electrode 30 toward the exhaust side electrode 32 regardless of whether or not the oxygen sensor 10 has an abnormality. A negative sensor current corresponding to the oxygen concentration of the layer 20 flows. Even if the oxygen sensor 10 has an abnormality, the sensor current has the same magnitude as that in the normal state.

  The ECU 34 starts application of the negative voltage in a situation where a negative voltage is applied between the atmosphere-side electrode 30 and the exhaust-side electrode 32 of the oxygen sensor 10 in order to detect whether or not the oxygen sensor 10 is abnormal. When the same time as the predetermined time T1 elapses, the sensor current I flowing between the electrodes 30 and 32 of the oxygen sensor 10 is converted from the sensor output generated between both ends of the resistor Rs by using the current detection circuit 44. To detect. The detected sensor current I is defined as a sensor current I− when a negative voltage is applied (step 108).

  When the ECU 34 detects the sensor current I + when the positive voltage is applied and the sensor current I− when the negative voltage is applied, the absolute value (= | I− | / | I + |) of the ratio is equal to or greater than the predetermined value X0. It is determined whether or not (step 110). The predetermined value X0 is the absolute value of the minimum ratio that can be determined that the coating layer 24 of the oxygen sensor 10 is clogged, and exceeds “1.0”, for example, “1.5”. Or “2.0”. As a result, when a negative determination is made, it is determined that no abnormality has occurred in the oxygen sensor 10 (step 112). On the other hand, when a positive determination is made, it is determined that an abnormality has occurred in the oxygen sensor 10 (step 114).

  Thus, in the abnormality detection device 12 of the present embodiment, a positive voltage is applied between the atmosphere side electrode 30 and the exhaust side electrode 32 of the oxygen sensor 10 in a situation where the exhaust passage 14 is in an atmospheric state or a state close to the atmospheric state. By alternately applying negative and negative voltages and comparing the sensor currents obtained at the time of applying the respective voltages, it is possible to detect the presence or absence of abnormality of the oxygen sensor 10.

  In a situation where the exhaust passage 14 is in an atmospheric state or a state close to the atmospheric state, the oxygen concentration in the exhaust passage 14 does not become so large with respect to the oxygen concentration in the atmospheric layer 20, so that a positive voltage is applied to the oxygen sensor 10. Sometimes the amount of oxygen ions that move between the electrodes 30 and 32 and the amount of oxygen ions that move between the electrodes 30 and 32 when a negative voltage is applied do not deviate so much, and the absolute value of the sensor current at both timings is too large. There is no difference. However, when an abnormality occurs in the oxygen sensor 10 in spite of such a situation, oxygen ions are difficult to move from the exhaust side electrode 32 toward the atmosphere side electrode 30, so that a positive voltage is applied to the oxygen sensor 10. The amount of oxygen ions is less than the amount of oxygen ions when a negative voltage is applied, and the absolute value of the sensor current when a positive voltage is applied is predetermined compared to the absolute value of the sensor current when a negative voltage is applied. It gets smaller.

  In this embodiment, the absolute value of the sensor current when a positive voltage is applied is compared with the absolute value of the sensor current when a negative voltage is applied, and as a result of the comparison, the absolute value of the sensor current when a positive voltage is applied is a negative voltage. It is determined whether or not an abnormality has occurred in the oxygen sensor 10 based on whether or not the absolute value of the sensor current at the time of application is smaller than a predetermined value. Therefore, according to the abnormality detection device 10 for the oxygen sensor 10 of the present embodiment, it is possible to accurately determine whether or not an abnormality has occurred in the oxygen sensor 10.

  In this configuration, abnormality detection of the oxygen sensor 10 is performed in a situation where the exhaust passage 14 is in an atmospheric state or a state close to the atmospheric state. In such a situation, when the oxygen sensor 10 is in a normal state, the amount of oxygen ions moving from the exhaust side electrode 32 toward the atmosphere side electrode 30 when a positive voltage is applied and the exhaust side from the atmosphere side electrode 30 when a negative voltage is applied. It is possible to suppress a difference between the amount of oxygen ions moving toward the electrode 32. Therefore, according to the present embodiment, it is possible to improve the determination accuracy of whether or not an abnormality has occurred in the oxygen sensor 10.

  Further, in such a configuration, the amount of oxygen ions from the exhaust side electrode 32 to the atmosphere side electrode 30 when the positive voltage is applied to the oxygen sensor 10 is the oxygen from the atmosphere side electrode 30 to the exhaust side electrode 32 when the negative voltage is applied. It is determined that an abnormality has occurred in the oxygen sensor 10 when it is less than a predetermined amount compared to the amount of ions. That is, even if the amount of oxygen ions at the time of applying a positive voltage to the oxygen sensor 10 is small compared to the amount of oxygen ions at the time of applying a negative voltage, if the difference does not reach a predetermined value or more, the oxygen sensor 10 is abnormal. Is not determined to have occurred. Therefore, according to the present embodiment, it is possible to detect the presence or absence of abnormality of the oxygen sensor 10 even in a situation where the oxygen concentration in the exhaust passage 14 is relatively low as compared with the oxygen concentration in the atmospheric layer 20. ing.

  In the present embodiment, a positive voltage and a negative voltage are alternately applied between the exhaust side electrode 32 and the atmosphere side electrode 30 in order to detect whether the oxygen sensor 10 is abnormal. The positive voltage is applied first and the negative voltage is applied later.

  In the configuration in which the negative voltage is applied first and the positive voltage is applied later, the oxygen in the atmosphere layer 20 is ionized and moved from the atmosphere side electrode 30 toward the exhaust side electrode 32 by the application of the negative voltage. If a positive voltage is applied immediately thereafter, the oxygen ions that have moved to the exhaust side electrode 32 will return to the atmosphere side electrode 30, so that the oxygen concentration in the exhaust passage 14 is detected when a positive voltage is applied to the oxygen sensor 10. For this reason, the oxygen ion content originally present on the atmosphere layer 20 side is superimposed on the amount of oxygen ions corresponding to the oxygen concentration in the exhaust passage 14, and an error occurs in the sensor output, so that the oxygen concentration in the exhaust passage 14 is increased. There may be a situation in which it is impossible to accurately detect.

  In contrast, in the configuration of the present embodiment, as described above, the positive voltage is applied to the oxygen sensor 10 first, and the negative voltage is applied later. In this case, a situation in which oxygen ions sufficiently present on the atmosphere layer 20 side (atmosphere side electrode 30 side) move to the exhaust passage 14 side (exhaust side electrode 32 side) and then return to the atmosphere layer 20 side is avoided. . For this reason, according to the present embodiment, when the oxygen sensor 10 is in an abnormal state, it is possible to prevent the amount of oxygen ions moving from the exhaust passage 14 side to the atmosphere layer 20 side from being unduly increased. It is possible to prevent erroneous detection that the sensor 10 is in a normal state despite the occurrence of an abnormality in the sensor 10.

  Further, in the configuration of the present embodiment, the application of the positive voltage and the application of the negative voltage to the oxygen sensor 10 are performed at the same potential level and for the same time. In this case, when the oxygen sensor 10 is in a normal state, the amount of oxygen ions that move from the exhaust-side electrode 32 toward the atmosphere-side electrode 30 by applying a positive voltage in the course of abnormality detection processing of the oxygen sensor 10, The amount of oxygen ions moving from the atmosphere-side electrode 30 toward the exhaust-side electrode 32 by applying a negative voltage becomes substantially uniform, and the charge once accumulated in the atmosphere-side electrode 30 by applying a positive voltage is exhausted by the negative-voltage application. It will be discharged to the 32 side. For this reason, according to the present embodiment, after performing the abnormality detection process of the oxygen sensor 10, when the oxygen concentration of the exhaust passage 14 is detected using the oxygen sensor 10 to control the internal combustion engine, for example, It is possible to avoid the charge accumulated in the atmosphere-side electrode 30 due to the application of a positive voltage from affecting the oxygen concentration detection that is the normal use of the oxygen sensor 10.

  Therefore, according to the abnormality detection device 12 of the oxygen sensor 10 of the present embodiment, it is possible to accurately determine the presence or absence of the sensor abnormality without affecting the normal use of the oxygen sensor 10.

  In the above-described embodiment, the ECU 34 executes the processing of step 102 in the routine shown in FIG. 4, whereby the “positive voltage applying means” and the “positive voltage applying step” described in the claims are performed as steps. The “first oxygen ion amount detection means” and the “first oxygen ion amount detection step” described in the claims by executing the processing of 104 perform the processing of step 106. The “negative voltage applying means” and the “negative voltage applying step” described in the range execute the processing of step 108 to perform the “second oxygen ion amount detecting means” and the “second oxygen ion detecting means” described in the claims. The “oxygen ion amount detection step” executes the processing of steps 110 to 114 to thereby execute “sensor abnormality detection means” and “sensor abnormality detection” described in the claims. Detection step "are realized respectively.

  By the way, in the above embodiment, in order to detect the presence / absence of abnormality of the oxygen sensor 10, the ratio of the absolute value of the sensor current when the positive voltage is applied to the oxygen sensor 10 and the sensor current when the negative voltage is applied is calculated. Thus, it is determined whether or not the ratio is equal to or greater than the predetermined value X0 exceeding “1.0”, but the present invention is not limited to this, and the difference between the absolute values is calculated. Then, it may be determined whether or not the difference is greater than or equal to a predetermined difference.

It is a block diagram of the oxygen sensor which is one Example of this invention. It is a block diagram of the abnormality detection apparatus of the oxygen sensor of a present Example. It is a time chart of the process for detecting abnormality of the oxygen sensor of a present Example. It is a flowchart of an example of the control routine performed in the abnormality detection device of the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Oxygen sensor 12 Abnormality detection apparatus 14 Exhaust passage 20 Atmosphere layer 22 Electrolyte layer 30 Atmosphere side electrode 32 Exhaust side electrode 34 Electronic control unit (ECU)
44 Current detection circuit

Claims (8)

According to the amount of oxygen ions that move between the exhaust-side electrode and the atmosphere-side electrode, the exhaust-side electrode that is exposed to the exhaust space where the oxygen concentration is to be detected and the atmosphere-side electrode that is exposed to the atmosphere A device for detecting an abnormality in an oxygen sensor that outputs a signal,
Positive voltage applying means for applying a voltage so that oxygen ions move from the exhaust side electrode to the atmosphere side electrode between the exhaust side electrode and the atmosphere side electrode;
First oxygen ion amount detection means for detecting the amount of oxygen ions moving from the exhaust side electrode to the atmosphere side electrode when a voltage is applied by the positive voltage application means;
Negative voltage application means for applying a voltage so that oxygen ions move from the atmosphere side electrode toward the exhaust side electrode between the exhaust side electrode and the atmosphere side electrode;
Second oxygen ion amount detection means for detecting the amount of oxygen ions moving from the atmosphere side electrode to the exhaust side electrode when a voltage is applied by the negative voltage application means;
Sensor abnormality detection means for detecting an abnormality of the oxygen sensor based on a comparison result between a detection result of the first oxygen ion amount detection means and a detection result of the second oxygen ion amount detection means;
An oxygen sensor abnormality detection device comprising:   2. The oxygen sensor abnormality detection device according to claim 1, wherein both the positive voltage applying unit and the negative voltage applying unit apply voltage at a timing when the exhaust space is in an atmospheric state or a state close to an atmospheric state. .   3. The oxygen sensor abnormality detection device according to claim 1, wherein the negative voltage applying unit applies a voltage after voltage application by the positive voltage applying unit is performed. 4.   The sensor abnormality detection unit is configured to detect the oxygen sensor when the amount of oxygen ions by the first oxygen ion amount detection unit is less than a predetermined amount compared to the amount of oxygen ions by the second oxygen ion amount detection unit. The oxygen sensor abnormality detection device according to any one of claims 1 to 3, wherein an abnormality is detected. According to the amount of oxygen ions that move between the exhaust-side electrode and the atmosphere-side electrode, the exhaust-side electrode that is exposed to the exhaust space where the oxygen concentration is to be detected and the atmosphere-side electrode that is exposed to the atmosphere A method of detecting an abnormality of an oxygen sensor that outputs a signal,
A positive voltage application step of applying a voltage so that oxygen ions move from the exhaust side electrode toward the atmosphere side electrode between the exhaust side electrode and the atmosphere side electrode;
A first oxygen ion amount detection step for detecting an amount of oxygen ions moving from the exhaust side electrode to the atmosphere side electrode at the time of voltage application in the positive voltage application step;
A negative voltage application step of applying a voltage so that oxygen ions move from the atmosphere side electrode to the exhaust side electrode between the exhaust side electrode and the atmosphere side electrode;
A second oxygen ion amount detection step for detecting the amount of oxygen ions moving from the atmosphere side electrode to the exhaust side electrode when a voltage is applied in the negative voltage application step;
A sensor abnormality detection step for detecting abnormality of the oxygen sensor based on a comparison result between the detection result of the first oxygen ion amount detection step and the detection result of the second oxygen ion amount detection step;
An abnormality detection method for an oxygen sensor, comprising:   6. The oxygen sensor abnormality detection method according to claim 5, wherein both the positive voltage application step and the negative voltage application step perform voltage application at a timing when the exhaust space is in an atmospheric state or a state close to an atmospheric state. .   The oxygen sensor abnormality detection method according to claim 5 or 6, wherein the negative voltage application step performs voltage application after voltage application in the positive voltage application step.   In the sensor abnormality detection step, when the amount of oxygen ions in the first oxygen ion amount detection step is less than a predetermined amount as compared with the amount of oxygen ions in the second oxygen ion amount detection step, the sensor abnormality detection step The oxygen sensor abnormality detection method according to any one of claims 5 to 7, wherein an abnormality is detected.

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