JP2011095199A - Abnormality diagnostic device for gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To distinguish resettable abnormalities from unresettable abnormalities in abnormality diagnosis of gas sensors. <P>SOLUTION: An exhaust pipe 14 of an engine 10 includes a gas sensor (O2 sensor 20) provided with a sensor element 21 having a solid electrolytic layer 24 and a pair of electrodes 25 and 26 arranged in the solid electrolytic layer 24. An ECU 40 diagnoses abnormalities of the gas sensor 20 on the basis of electric signals from the pair of electrodes 25 and 26. The ECU 40 especially determines the presence of the state of continuity of at least either one of the pair of electrodes 25 and 26 with the side of the exhaust pipe 14 due to water immersion and limits the implementation of sensor abnormality diagnosis based on output values of the gas sensor 20 in the case that it is determined that the state of continuity is present. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an abnormality diagnosis device for a gas sensor, and more specifically, for a gas sensor having a sensor element having a solid electrolyte body and a pair of electrodes arranged on the solid electrolyte body, the abnormality diagnosis of the gas sensor is performed based on the sensor output value. The present invention relates to an abnormality diagnosis device for a gas sensor.

  Conventionally, in an internal combustion engine, a gas sensor such as an O2 sensor having a solid electrolyte body and a pair of electrodes is disposed in an exhaust pipe, and air-fuel ratio control is performed based on an output value of the gas sensor. In addition, various methods for performing abnormality diagnosis of gas sensors have been proposed in order to appropriately perform air-fuel ratio control of an internal combustion engine (see, for example, Patent Document 1 and Patent Document 2).

  In Patent Document 1, a bias is applied to the negative terminal of the O2 sensor, and the voltage at the positive terminal is detected in the voltage application state. If the detected voltage is equal to or higher than the bias voltage, it is determined that the detected voltage is a normal value associated with lean air-fuel ratio. On the other hand, it is disclosed that when the detected voltage is less than the bias voltage, it is determined that a short circuit abnormality or a disconnection abnormality has occurred with respect to the ground circuit at the positive terminal.

  Further, in Patent Document 2, a bias is applied to the negative terminal of the O2 sensor, and the positive terminal and the negative terminal of the O2 sensor are detected in the voltage application state to detect the positive terminal. It is disclosed that the presence or absence of a short circuit abnormality of the side terminal or the negative side terminal is determined. Among these, specifically for abnormality diagnosis of the negative side terminal, when the terminal voltage of the negative side terminal is excessive or excessive with respect to the bias voltage, the negative terminal wiring is in a power fault abnormality in contact with the power supply line, or It is determined that a ground fault has occurred where the negative terminal wiring is in contact with the ground line.

JP 2005-171898 A Japanese Patent No. 4157576

  For example, when the internal combustion engine is cold started, water vapor may be adhered to the gas sensor due to condensation or scattering of water vapor in the exhaust pipe. Here, when water adheres to the gas sensor, it is conceivable that the electrode of the sensor element and the exhaust pipe side are connected via the water, and these are in a conductive state. In such a case, it is conceivable that the sensor output shows an abnormal value, but this is a temporary abnormality until the water adhering to the gas sensor disappears. However, the above-mentioned patent document does not distinguish between such a temporary abnormality (an abnormality that can be restored spontaneously) and an abnormality that is not. In other words, it is conceivable that a sensor or the like is diagnosed as being abnormal due to a temporary abnormality even though the sensor or circuit is normal.

  The present invention has been made in order to solve the above-described problems, and a main object of the present invention is to provide a gas sensor abnormality diagnosis device capable of distinguishing between a recoverable abnormality and a non-recoverable abnormality in the abnormality diagnosis of the gas sensor. And

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

  The present invention is applied to a gas sensor which is attached to an exhaust pipe of an internal combustion engine and includes a sensor element having a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, and is based on an electric signal from the pair of electrodes. The present invention relates to an abnormality diagnosis device for a gas sensor that performs abnormality diagnosis of the gas sensor. According to the first aspect of the present invention, continuity determination means for determining that at least one of the pair of electrodes is in a state where continuity with the exhaust pipe side is caused by water, and the continuity determination means determines the continuity. Diagnosis limiting means for limiting the execution of the sensor abnormality diagnosis based on the output value of the gas sensor when it is determined that the state is generated.

  For example, in a low temperature environment such as when the internal combustion engine is cold started, water vapor in the exhaust pipe may condense and the condensed water may adhere to the gas sensor. At this time, it is conceivable that the electrode of the sensor element and the exhaust pipe side become conductive due to water adhering to the gas sensor. In such a case, the output of the gas sensor is different from that in the normal state, and it is conceivable that the abnormality of the gas sensor is diagnosed. However, the conductive state between the electrode and the exhaust pipe due to the water is temporary, and it is necessary to distinguish from abnormalities that cannot be restored naturally, such as disconnection or short circuit of the sensor terminal.

  In view of this point, the present invention limits the execution of an abnormality diagnosis of a gas sensor when it is determined that electrical connection between the electrode and the exhaust pipe occurs. Thereby, in the abnormality diagnosis of the gas sensor, it is possible to distinguish between a recoverable abnormality caused by the moisture of the gas sensor and an abnormality that is not. As a result, the abnormality diagnosis accuracy of the gas sensor can be improved.

  Here, it is estimated that the continuity between the electrode and the exhaust pipe due to the flooded water is based on, for example, the elapsed time from the start of the internal combustion engine, the accumulated air amount, the engine temperature, etc. To do. Alternatively, a sensor or the like detects that water has occurred in the exhaust pipe, and determines based on the detection result. Further, the restriction on the execution of the sensor abnormality diagnosis includes a case where a prohibition period for the abnormality diagnosis is provided and a case where the abnormality determination value of the abnormality diagnosis is changed to the abnormality range side.

  In the configuration in which one of the pair of electrodes is exposed on the exhaust side, the condensed water in the exhaust easily adheres to the electrode exposed on the exhaust side, and conduction between the electrode and the exhaust pipe side is caused by the attached condensed water. Prone to occur. Therefore, as in the second aspect of the invention, the pair of electrodes is a first electrode, one of which is exposed to the exhaust side, and the other is a second electrode, which is exposed to the reference chamber of the atmospheric atmosphere. The continuity determining means may be applied to a configuration in which it is determined that the continuity between the first electrode and the exhaust pipe is generated.

  In general, an electric heater is attached to the gas sensor, and the sensor element is activated and the activated state is maintained by the heat generated by the heater. Here, when the sensor element is rapidly heated under the condition that the gas sensor is wet, there is a risk that the element cracks due to the water at the beginning of heating. Therefore, in the heater control of the gas sensor, the heater input power is limited at the time of starting the internal combustion engine or the like as a countermeasure against element cracking due to water exposure. On the other hand, it is considered that conduction between the electrode of the sensor element and the exhaust pipe side due to moisture can occur even in a state where a small amount of water is attached to the sensor element to the extent that it is determined that the risk of element cracking has been eliminated. . In other words, even if the risk of element cracking due to flooding has been eliminated, there is a continued risk of continuity between the sensor element electrode and the exhaust pipe due to flooding. There is a risk.

  In view of this point, in the invention according to claim 3, the gas sensor is provided with a heater for heating the sensor element, and the continuity determination unit is configured to prevent the heater and the exhaust gas from being discharged after the energization restriction of the heater is released. It is determined that electrical connection with the tube side occurs. According to this configuration, after the restriction on the heating of the sensor element by the heater is released, the execution of abnormality diagnosis based on the sensor output is restricted, so that the continuity between the electrode of the sensor element and the exhaust pipe side due to moisture can occur The implementation of the abnormality diagnosis below can be suitably limited.

  By the way, it is considered that the amount of water generated in the exhaust pipe changes depending on various conditions such as the engine temperature at the time of starting the engine and the outside air temperature. In addition, once continuity between the electrode and the exhaust pipe occurs due to moisture, the time required for the continuity to be canceled (the time required until water disappears) varies depending on various conditions. Specifically, for example, it is considered to change depending on the engine operating state, the engine temperature rising speed, the outside air temperature, the heater input power, and the like. In view of this point, as in the invention described in claim 4, it is preferable to include a time setting unit that variably sets a time limit for limiting the execution of the sensor abnormality diagnosis by the diagnosis limiting unit. At this time, the time limit may be increased as the amount of water generated in the exhaust pipe increases or as the time required for water disappearance increases.

  In an O2 sensor that generates an electromotive force between both positive and negative electrodes according to the oxygen concentration of exhaust gas, an electromotive force that differs depending on whether the air-fuel ratio of the internal combustion engine is rich or lean is generated. While it is 9V, the electromotive force at the time of lean becomes about 0V. In this case, the sensor output in the lean state and the sensor output at the time of occurrence of disconnection or short-circuit show the same tendency, so that it may be impossible to accurately diagnose the normality / abnormality of the sensor. In view of this, the voltage of the negative electrode may be made higher than the ground voltage by connecting a bias power supply to the negative electrode of the O2 sensor. At this time, since the gas concentration cannot be detected properly unless the bias application to the negative electrode is properly performed, an abnormality diagnosis may be performed to determine whether the bias application is properly performed.

  Here, when the electrode of the sensor element and the exhaust pipe side are in a conductive state, current leakage from the electrode to the exhaust pipe side occurs, and as a result, the voltage of the negative electrode may be lower than the bias voltage. . However, this voltage drop is temporary, and can be recovered by increasing the temperature in the exhaust pipe.

  In view of this point, in the invention according to claim 5, the gas sensor is an O2 sensor that generates an electromotive force between both positive and negative electrodes according to the oxygen concentration of the exhaust gas, and detects the electromotive force of the O2 sensor. In the electromotive force detection circuit, a bias power source is connected to the negative electrode of the O2 sensor, and the abnormality diagnosis is performed based on the voltage of the positive electrode or the negative electrode of the O2 sensor. By doing so, it is possible to avoid diagnosing a temporary abnormality of the bias as an irreversible abnormality.

1 is an overall schematic configuration diagram of an engine control system. Sectional drawing which shows schematic structure of an O2 sensor. The electromotive force characteristic view which shows the relationship between the air fuel ratio of exhaust gas, and the electromotive force of a sensor element. The figure which shows the circuit structure of an electromotive force detection circuit part. The flowchart which shows the process sequence of a bias abnormality diagnosis. The flowchart which shows the process sequence of abnormality diagnosis of an O2 sensor. The time chart which shows the specific aspect of abnormality diagnosis of an O2 sensor.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. In this embodiment, an engine control system that uses an O2 sensor provided in an exhaust pipe of an in-vehicle engine and performs various controls of the engine based on the output of the O2 sensor will be described. In this control system, an electronic control unit (hereinafter referred to as ECU) is used as a center to control the fuel injection amount, control the ignition timing, and the like. FIG. 1 is a block diagram showing the overall outline of this system.

  In FIG. 1, an engine 10 is, for example, a gasoline engine, and includes a throttle valve 11, a fuel injection valve 12, an ignition device 13, and the like. The exhaust pipe 14 of the engine 10 is provided with a three-way catalyst 15 as a waste purification device, and an air-fuel ratio (oxygen concentration) of an air-fuel mixture is detected on the upstream side or downstream side of the three-way catalyst 15 with exhaust gas as a detection target. An O2 sensor 20 is provided to detect the above. FIG. 1 shows a case where the A / F sensor 16 is provided on the upstream side of the three-way catalyst 15 and the O2 sensor 20 is provided on the downstream side.

  FIG. 2 is a cross-sectional view showing a schematic configuration of the O2 sensor 20. The O2 sensor 20 has a sensor element 21 having a cup-type structure. The sensor element 21 has an intermediate portion inserted into a metal housing 22 and fixed to the housing 22. Note that the gap S between the housing 222 and the sensor element 21 is filled with a member made of an insulating material. The housing 22 is provided with a screw portion 22 a that is screwed into a screw hole provided in the metal exhaust pipe 14, and a flange portion 22 b that is in contact with the outer wall of the exhaust pipe 14. The screw portion 22a is screwed into the screw hole of the exhaust pipe 14, so that the O2 sensor 20 can be attached to the exhaust pipe 14.

  An element cover 23 is attached to the lower end of the housing 22, and the entire element of the sensor element 21 is accommodated in the element cover 23. The element cover 23 has a double tube structure in which an outer tube 23a and an inner tube 23b are overlapped, and a plurality of holes through which exhaust gas can pass are provided in the outer tube 23a and the inner tube 23b. By passing the exhaust gas in the exhaust pipe 14 through the hole of the element cover 23, the space 29 around the sensor element 21 in the element cover 23 is in an exhaust gas atmosphere.

  The sensor element 21 has a solid electrolyte layer 24 formed in a cup shape in cross section, an exhaust gas side electrode layer 25 as a negative electrode is provided on the outer surface thereof, and an atmosphere side electrode layer as a positive electrode on the inner surface thereof. 26 is provided. The solid electrolyte layer 24 is made of an oxygen ion conductive oxide sintered body in which CaO, MgO, Y2O3 or the like is dissolved in ZrO2, HfO2, ThO2, BiO2 or the like as a stabilizer. Each of the electrode layers 25 and 26 is made of a noble metal having high catalytic activity such as platinum, and the surface thereof is subjected to porous chemical plating. An internal space surrounded by the solid electrolyte layer 24 is an atmospheric chamber 27, and a heater 28 is accommodated in the atmospheric chamber 27. The heater 28 has a heat generation capacity sufficient to activate the sensor element 21, and the entire sensor element 21 is heated by the heat generation energy.

  In the sensor element 21, the outer side (exhaust gas side electrode layer 25 side) of the solid electrolyte layer 24 is an exhaust gas atmosphere, and the inner side (air side electrode layer 26 side) is an air atmosphere. That is, the exhaust gas side electrode layer 25 is exposed to the exhaust gas side, and the atmosphere side electrode layer 26 is exposed to the atmosphere chamber 27. An electromotive force is generated between the electrode layers 25 and 26 according to the difference in oxygen concentration between the exhaust gas side and the atmospheric chamber 27 (difference in oxygen partial pressure). The exhaust gas side electrode layer 25 corresponds to the first electrode, and the atmosphere side electrode layer 26 corresponds to the second electrode.

  FIG. 3 is an electromotive force characteristic diagram showing the relationship between the air-fuel ratio of exhaust gas and the electromotive force of the sensor element 21. As shown in FIG. 3, the sensor element 21 has characteristics that generate different electromotive forces depending on whether the air-fuel ratio is rich or lean, and the electromotive force changes suddenly near the stoichiometric air-fuel ratio (stoichiometric). Specifically, the sensor electromotive force when the fuel is rich is about 0.9V, and the sensor electromotive force when the fuel is lean is about 0V.

  Returning to the description of FIG. 1, the present system also includes a throttle opening sensor 31 that detects the opening of the throttle valve 11 and a rectangular crank angle at every predetermined crank angle of the engine (for example, at a cycle of 30 ° CA). Various sensors such as a crank angle sensor 32 that outputs a signal, a coolant temperature sensor 33 that detects the temperature of engine coolant, and various switches such as an ignition switch (IG switch) 34 are provided.

  The ECU 40 is mainly configured by a microcomputer 41 composed of a well-known CPU, ROM, RAM, and the like, and executes various control programs stored in the ROM, so that the ECU 40 according to each engine operating state. Various controls of the engine 10 are performed. That is, the microcomputer 41 of the ECU 40 inputs signals from the various sensors and the like, calculates the fuel injection amount and ignition timing based on the various signals, and controls the drive of the fuel injection valve 12 and the ignition device 13.

  The microcomputer 41 performs heater energization control of the O2 sensor 20. With this energization control, the sensor element 21 is activated by the heat generated by the heater 28 when the engine is started, and once the activation is completed, the activated state is maintained by appropriately energizing. When the sensor element 21 is activated, for example, water generated in the exhaust pipe 14 at the time of cold start of the engine 10 may adhere to the sensor element 21, and the sensor element 21 is rapidly heated in such a state, thereby There is a possibility that the element 21 is damaged (an element crack occurs). Therefore, in this control, when the risk of water generation in the exhaust pipe 14 is high when the engine 10 is started, the start of energization of the heater 28 is delayed until the risk of water generation is suppressed.

  The ECU 40 is provided with an electromotive force detection circuit unit 42 that detects an electromotive force of the O2 sensor 20. For example, in the control of the fuel injection amount, the microcomputer 41 performs air-fuel ratio control based on the electromotive force detected by the electromotive force detection circuit unit 42 so that the actual air-fuel ratio becomes the target air-fuel ratio (theoretical air-fuel ratio).

  FIG. 4 is a diagram illustrating a circuit configuration of the electromotive force detection circuit unit 42. In FIG. 4, the electromotive force detection circuit unit 42 includes a positive terminal (S + terminal) connected to the atmosphere-side electrode layer 26 of the sensor element 21 and a negative terminal (S−) connected to the exhaust gas-side electrode layer 25. Terminal). The S + terminal and the S− terminal are respectively connected to the + input terminal and the − input terminal of the microcomputer 41, and each terminal voltage of the sensor element 21 is sequentially measured in the microcomputer 41.

  The electromotive force detection circuit unit 42 is provided with a resistance voltage dividing circuit 43 including two resistors connected to a constant voltage source (constant voltage Vcc), and the divided voltage of the resistance voltage dividing circuit 43 is S−. Applied to the terminal. That is, by applying a bias to the S-terminal, the same terminal voltage is offset, so that the negative terminal voltage of the sensor element 21 is set to a predetermined bias voltage Vbi (for example, 1.5 V) higher than the ground voltage. ing. Therefore, the positive terminal voltage VO + of the sensor element 21 becomes a value equal to or higher than the bias voltage Vbi if the O2 sensor 20 is normal. Thus, in this system, when the bias voltage Vbi is applied to the S-terminal, the sensor electromotive force becomes close to 0 V due to fuel lean (normal time), and this is caused by a short circuit or disconnection of the positive terminal. Thus, it is possible to determine when the sensor electromotive force is in the vicinity of 0 V (when abnormal).

  Here, when an abnormality such as a short circuit of the negative terminal (S− terminal) of the sensor element 21 occurs, the negative terminal voltage VO− of the sensor element 21 deviates from the bias voltage Vbi, and the oxygen concentration in the exhaust gas is reduced. It is conceivable that it cannot be detected accurately. Therefore, the microcomputer 41 reads the negative terminal voltage VO− of the sensor element 21 as a process for diagnosing that the bias application of the negative terminal is properly performed (bias abnormality diagnosis process), and reads the read voltage. It is determined whether or not VO− is within an appropriate range. When the negative terminal voltage VO− is outside the proper range, it is diagnosed that the bias application is not properly performed, that is, there is an abnormality in the O2 sensor 20 (an abnormality such as a short circuit of the negative terminal).

  FIG. 5 is a flowchart showing the procedure of the bias abnormality diagnosis process as a premise. This process is executed at predetermined intervals by the microcomputer 41 of the ECU 40.

  In FIG. 5, first, in step S101, it is determined whether or not an execution condition for bias abnormality diagnosis is satisfied. This execution condition includes at least one of the IG switch 34 being in an ON state and the battery voltage being equal to or higher than a determination value.

  If the condition for executing the bias abnormality diagnosis is satisfied, the process proceeds to step S102, where the negative terminal voltage VO− of the sensor element 21 is read. In step S103, whether the read negative terminal voltage VO− is outside the proper range. Determine whether. Specifically, as an appropriate range of the negative terminal voltage VO−, for example, when the applied voltage of the S− terminal is 1.5V, the appropriate range is set to 1.3 to 1.5V. If the negative terminal voltage VO− is within the appropriate range, the process proceeds to step S104, and it is determined that the bias is properly applied (the negative terminal of the O2 sensor 20 is normal). Then, this process ends.

  On the other hand, if the negative terminal voltage VO− is outside the appropriate range, the process proceeds to step S105, and the abnormality determination counter Tf is incremented by “1”. Thereafter, in step S106, it is determined whether or not the abnormality determination counter Tf is larger than the determination value. If the abnormality determination counter Tf is larger than the determination value, the process proceeds to step S107, and the bias is appropriately applied. It is determined that there is no abnormality (the negative terminal of the sensor element 21 is abnormal), and the fact that an abnormality has occurred is notified by lighting of a warning lamp or the like.

  By the way, for example, when the engine 10 is cold-started, the inside of the exhaust pipe 14 is in a low temperature state. In such a state, it is conceivable that the water vapor in the exhaust pipe 14 is condensed, and the condensed water is applied to the O2 sensor 20 so that the exhaust gas side electrode layer 25 is wetted.

  When the exhaust gas side electrode layer 25 is exposed to water, the exhaust gas side electrode layer 25 and the exhaust pipe 14 side are in communication with each other through the water, whereby the exhaust gas side electrode layer 25 and the exhaust pipe 14 side are electrically connected. There is a risk of entering a state. More specifically, since the exhaust gas side electrode layer 25 is exposed to the exhaust gas atmosphere space 29, when the exhaust pipe 14 is in a low temperature state, such as when the engine is cold started, condensed water is present in the exhaust gas side electrode layer 25. The environment is easy to adhere. Further, when condensed water adheres to the exhaust gas side electrode layer 25, the attached condensed water enters, for example, the gap SW portion in FIG. 2, and the exhaust gas side electrode layer 25 and the metal housing 22 pass through the condensed water. It is possible to become in a state of communication. In this case, the exhaust gas side electrode layer 25 and the exhaust pipe 14 are in communication with each other through the path of the exhaust gas side electrode layer 25 → condensed water → the housing 22 → the exhaust pipe 14. Note that the water in the gap SW is generated when water enters the gap, for example, soaking the filling member.

  Thus, when the exhaust gas side electrode layer 25 and the exhaust pipe 14 side are in a conductive state, the negative terminal voltage VO− of the sensor element 21 is caused by leakage of the bias current supplied from the constant voltage source. It may be lower than the appropriate value. In this case, it is diagnosed that the bias application is not properly performed by the bias abnormality diagnosis process, that is, the O2 sensor 20 is abnormal. However, this exhaust gas side electrode layer 25 is temporarily covered with water. For example, the warm-up of the engine 10 proceeds and the inside of the exhaust pipe 14 becomes a high temperature state, or the sensor element 21 is heated by the heater 28. Thus, when the water in the gap SW evaporates, the negative terminal voltage VO− returns to a normal value. In this case, it is no longer an abnormal condition. Therefore, such a temporary abnormality that can be recovered due to water exposure is diagnosed as an abnormality as in the case of an abnormality that cannot be recovered spontaneously, such as a short circuit or disconnection, and the processing for handling the subsequent abnormality is the same. Is not appropriate.

  Therefore, in the present embodiment, it is determined whether or not the exhaust gas side electrode layer 25 and the exhaust pipe 14 are in a state in which electrical continuity occurs. Implementation of sensor abnormality diagnosis (bias abnormality diagnosis) based on the output value is limited.

  FIG. 6 is a flowchart showing a processing procedure of abnormality diagnosis processing of the O2 sensor 20 in the present embodiment. This process is executed at predetermined intervals by the microcomputer 41 of the ECU 40.

In FIG. 6, first, in step S <b> 201, it is determined whether or not an energization execution condition for the heater 28 is satisfied. The heater energization execution condition is a condition that is established in a situation where it is presumed that the possibility of element cracking due to moisture on the sensor element 21 has been eliminated.
The elapsed time from turning on the IG switch 34 is equal to or greater than the determination value TM1. The integrated air amount calculated from the engine start calculated based on the output value of the throttle opening sensor 31 is equal to or greater than the determination value Q1. It is assumed that the cooling water temperature by the cooling water temperature sensor 33 is at least one of a determination value TW1 and the temperature of the sensor element 21 is at least a determination value TS1.

  When the heater energization execution condition is not satisfied, the process proceeds to step S202, and energization of the heater 28 is limited as a measure for preventing the sensor element 21 from cracking. The energization restriction includes prohibiting heater energization and energizing the heater while performing power restriction based on all energization. On the other hand, if the heater energization execution condition is satisfied, the process proceeds to step S203, and energization of the heater 28 is permitted. That is, if the sensor element 21 is not activated, the sensor element 21 is heated by energization of the heater 28.

In the next step 204, it is determined whether or not the pseudo earth elimination condition is satisfied. The pseudo earth elimination condition is a condition that is established in a situation where it is estimated that the possibility of conduction between the exhaust gas side electrode layer 25 and the exhaust pipe 14 due to water exposure (the possibility of being in a pseudo grounded state) has been eliminated. Yes, specifically,
(1) The elapsed time from turning on the IG switch 34 has become the determination value TM2. (2) The integrated air amount calculated from the engine start calculated based on the output value of the throttle opening sensor 31 is equal to or greater than the determination value Q2. (3) The cooling water temperature by the cooling water temperature sensor 33 is not less than the determination value TW2, (4) the temperature of the sensor element 21 is not less than the determination value TS2, and (5) the sensor element 21 is in an active state. At least one of the conditions.

  Among the pseudo earth elimination conditions, (1) to (4) use the same parameters as the heater energization execution conditions, and thereby determine whether or not pseudo earth is caused by water. Here, when comparing the case where the conductive state between the exhaust gas side electrode layer 25 and the exhaust pipe 14 occurs due to water exposure (when pseudo grounding occurs) and the case where element cracking occurs due to water exposure, the pseudo earth is better. It can be caused by a smaller amount of water. That is, pseudo-earthing due to water can occur even in a state where a small amount of water to the extent that it is determined that the risk of element cracking has been eliminated adheres to the exhaust gas side electrode layer 25. Therefore, even in a state where the risk of element cracking due to water exposure has been eliminated, the possibility of false earthing due to water exposure continues, and there is a risk of erroneous diagnosis in sensor abnormality diagnosis during that period. Therefore, in the present embodiment, the determination values TM2, Q2, TW2, and TS2 of (1) to (4) are set higher than the determination values TM1, Q1, TW1, and TS1 in the heater energization execution condition. is there. Thereby, for example, after the engine 10 is cold started, even if the amount of water adhering to the sensor element 21 is small, the execution of the bias abnormality diagnosis is limited until the water adhering is eliminated. ing.

  If the pseudo earth elimination condition is satisfied, the process proceeds to step S205, and the bias abnormality diagnosis process shown in FIG. 5 is executed. On the other hand, if the pseudo earth elimination condition is not satisfied, the process proceeds to step S206 to limit the execution of the bias abnormality diagnosis process. As an implementation restriction of the bias abnormality diagnosis process, for example, the execution of the process is prohibited, or the determination value of the abnormality determination counter Tf is changed to a larger side. Alternatively, in step S103 of FIG. 5, the appropriate range of the negative terminal voltage VO− is expanded and the negative terminal voltage VO− is compared with the appropriate range.

  FIG. 7 is a time chart showing a specific mode of abnormality diagnosis of the O2 sensor 20 in this system. In the figure, the solid line indicates a case where the implementation of the bias abnormality diagnosis is limited when the exhaust gas side electrode layer 25 and the exhaust pipe 14 are in a conductive state, and the alternate long and short dash line indicates a bias when the conductive state is generated. The case where the execution of abnormality diagnosis is not limited is shown. In FIG. 7, it is assumed that the engine is cold start.

  In FIG. 7, when the IG switch 34 is turned on at timing t11, various controls relating to the operation of the engine 10 such as throttle opening control, fuel injection control, and ignition control are started. As a result, combustion of the fuel is started and the engine speed is increased. Since the engine cold start is assumed now, the inside of the exhaust pipe 14 is in a low temperature state immediately after the IG switch 34 is turned on. Therefore, there is a possibility that condensed water adheres to the exhaust pipe 14 or the sensor element 21. Therefore, in order to suppress the occurrence of sensor element cracking due to condensed water, immediately after the IG switch 34 is turned on, for example, heater energization is prohibited as a heating restriction of the sensor element 21 by the heater 28. In addition, since there is a possibility that the exhaust gas side electrode layer 25 and the exhaust pipe 14 side may be connected by the condensed water, for example, the implementation of the diagnosis is prohibited as a restriction on the bias abnormality diagnosis.

  For example, when the integrated value (integrated air amount) from the IG-ON timing t11 becomes equal to or greater than the determination value Q1 for the air amount passing through the throttle valve 11, it is determined that the heater energization execution condition is satisfied at the timing t14. The heating restriction of the sensor element 21 by the heater 28 is released (heater energization is started). After that, when the integrated air amount becomes equal to or greater than the determination value Q2 at timing t16, it is determined that the pseudo earth elimination condition is satisfied, and the restriction on the bias abnormality diagnosis is released (execution of the bias abnormality diagnosis is started). .

  Here, let us consider a case in which the condensed water in the exhaust pipe 14 is brought into conduction between the exhaust gas side electrode layer 25 and the exhaust pipe 14 immediately after the engine is started. In this case, in the configuration in which the bias abnormality diagnosis is performed regardless of the conduction state (one-dot chain line in the figure), the negative side terminal of the sensor element 21 is in a pseudo ground state at the timing t12 when the conduction state is established. The negative terminal voltage VO− of the sensor element 21 is lower than an appropriate value (1.5 V in this embodiment). When the negative terminal voltage VO− falls below the lower limit value Vbth of the appropriate range, the abnormality determination counter Tf increases after the timing t13. When the abnormality determination counter Tf exceeds the determination value Tfth, it is determined at the timing t15 that the voltage application at the negative terminal is abnormal. The abnormality determination at this time is based on a temporary abnormality due to the exhaust gas side electrode layer 25 and the exhaust pipe 14 side being in a conductive state due to water exposure.

  On the other hand, in the present embodiment, as shown by the solid line in the figure, after the IG switch 34 is turned on, the accumulated air amount becomes equal to or greater than the determination value Q2, and the period until it is determined that the pseudo earth elimination condition is satisfied, the bias Implementation of abnormality diagnosis is limited. In other words, for example, during a cold start of the engine 10, the bias abnormality diagnosis is limited during a period in which even a slight amount of water may be generated. Therefore, it is possible to avoid diagnosing that the bias voltage is abnormal based on a temporary abnormality due to conduction between the exhaust gas side electrode layer 25 and the exhaust pipe 14 side.

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

  It is determined whether or not continuity between the exhaust gas side electrode layer 25 and the exhaust pipe 14 is generated. When it is determined that the continuity is generated, sensor abnormality diagnosis based on the output value of the O2 sensor 20 is determined. Therefore, in the abnormality diagnosis of the O 2 sensor 20, it is possible to distinguish between a recoverable abnormality due to the O 2 sensor 20 being wet and an abnormality that is not. As a result, the abnormality diagnosis accuracy of the O2 sensor 20 can be improved.

  In the O2 sensor 20, since the exhaust gas side electrode layer 25 is exposed to the exhaust gas side, the condensed water in the exhaust pipe 14 is likely to adhere to the exhaust gas side electrode layer 25, and the exhaust gas side electrode layer 25 is covered with the condensed water. And the exhaust pipe 14 side are easily connected. In this regard, in this embodiment, since it is configured to limit the implementation of the bias abnormality diagnosis process when it is determined that the exhaust gas side electrode layer 25 and the exhaust pipe 14 side are in a conductive state, the bias abnormality diagnosis process is performed. It is possible to avoid diagnosing a temporary bias abnormality as an irrecoverable abnormality.

  Since the determination whether or not the exhaust gas side electrode layer 25 and the exhaust pipe 14 are in a state of conduction is performed after releasing the heater energization restriction for preventing element cracking, there is a risk of element cracking. Even in a state where a small amount of water that is judged to be eliminated remains attached to the exhaust gas side electrode layer 25, the execution of the bias abnormality diagnosis process can be restricted. Accordingly, it is possible to suitably limit the execution of the abnormality diagnosis in a situation where conduction between the exhaust gas side electrode layer 25 and the exhaust pipe 14 side due to water can occur. In addition, since the bias abnormality diagnosis can be performed promptly when the occurrence of the state in which the exhaust gas side electrode layer 25 and the exhaust pipe 14 are connected is eliminated, the abnormality can be accurately and as quickly as possible when the bias abnormality occurs. Can be detected.

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

  A time limit for limiting the execution of sensor abnormality diagnosis (bias abnormality diagnosis) is variably set, and the execution of the sensor abnormality diagnosis is limited according to the set time limit. Specifically, in view of the fact that the amount of water generated in the exhaust pipe 14 varies depending on various conditions such as the engine temperature at the time of starting the engine and the outside air temperature, the time limit is set according to the amount of water generated in the exhaust pipe 14. Is set to be variable. At this time, the time limit may be set longer as the amount of water generated increases.

  Alternatively, the time required for the water once generated in the exhaust pipe 14 to disappear (water loss required time) varies depending on, for example, the engine operating state, the engine temperature rising speed, the outside air temperature, the input power of the heater 28, and the like. In view of this, the time limit is variably set according to the time required for water loss. At this time, the time limit may be set longer as the time required for water disappearance is longer.

  In the above embodiment, the determination as to whether or not the exhaust gas side electrode layer 25 and the exhaust pipe 14 are in a conductive state is made based on the success or failure of the pseudo earth elimination condition. A water detection means is provided in the exhaust pipe 14, and based on the detection result, it is determined that at least one of the pair of electrodes and the exhaust pipe 14 side are connected to the exhaust pipe 14 due to water. May be.

  In the above-described embodiment, the case where the exhaust gas side electrode layer 25 of the sensor element 21 is connected to the exhaust pipe 14 side has been described. However, in the case where the atmosphere side electrode layer 26 is connected to the exhaust pipe 14 side, In addition, it may be configured to limit the execution of the sensor abnormality diagnosis related to the positive terminal of the sensor element 21. For example, when a crack or the like occurs in the solid electrolyte layer 24, it is conceivable that the condensed water in the exhaust pipe 14 enters from that portion, so that the atmosphere-side electrode layer 26 and the exhaust pipe 14 side become conductive. In this case, the positive side terminal of the sensor element 21 is in a pseudo-grounded state, and as a result, there is a possibility that the sensor element 21 is diagnosed as having an abnormality such as an inactive abnormality or a short circuit of the positive side terminal. Therefore, when the conduction state between the atmosphere-side electrode layer 26 and the exhaust pipe 14 is generated, that is, during the period until the pseudo earth elimination condition is satisfied, the execution of the abnormality diagnosis related to the positive terminal of the sensor element 21 may be limited. .

  In the above embodiment, the O2 sensor 20 is applied as the gas sensor. However, a wide-area detection type A / F sensor (A / F) that supplies a current according to the oxygen concentration in the exhaust gas while a voltage is applied to the pair of electrodes. : Air-fuel ratio). For example, in a so-called cup-type A / F sensor having a sensor element having a cup-shaped cross section, the sensor element includes a solid electrolyte layer, a pair of electrodes provided across the solid electrolyte layer, and an outer surface of the solid electrolyte layer ( And a porous diffusion resistance layer surrounding the exhaust side electrode. The pair of electrodes includes an exhaust gas side electrode layer that contacts exhaust gas on the outer surface of the solid electrolyte layer, and an atmosphere side electrode layer that contacts the atmosphere on the inner surface of the solid electrolyte layer. In the sensor element having this configuration, the surrounding exhaust gas passes through the diffusion resistance layer and reaches the exhaust gas side electrode. By applying a voltage to the solid electrolyte layer, an oxygen ion current corresponding to the oxygen concentration in the exhaust gas is generated when the air-fuel ratio is lean, and an oxygen ion current corresponding to the unburned gas concentration is generated when the air-fuel ratio is rich. .

  In the sensor element having this configuration, for example, when a crack or the like occurs in the diffusion resistance layer, the exhaust gas side electrode layer and the exhaust pipe 14 side may be in a conductive state due to intrusion of condensed water in the exhaust pipe from the site. Conceivable. In this case, it is conceivable that the negative terminal of the sensor element is in a pseudo-grounded state, and as a result, voltage application to the sensor element cannot be properly performed and a sensor abnormality is diagnosed. Therefore, even when the A / F sensor is applied to the present invention, it can be said that the same effect as the above effect, that is, an effect of distinguishing between a recoverable abnormality and an abnormality that cannot be recovered in the abnormality diagnosis of the gas sensor.

  In the above embodiment, the cup-type O2 sensor has been described. However, the present invention may be applied to an O2 sensor having a laminated sensor element in which a solid electrolyte layer or an insulating layer is laminated.

  In the above embodiment, the O2 sensor is applied as the gas sensor, but may be applied to a gas sensor other than the O2 sensor (for example, a CO sensor, a NOx sensor, etc.).

  DESCRIPTION OF SYMBOLS 10 ... Engine, 14 ... Exhaust pipe, 20 ... O2 sensor (gas sensor), 21 ... Sensor element, 22 ... Housing, 24 ... Solid electrolyte layer, 25 ... Exhaust gas side electrode layer (first electrode), 26 ... Air side electrode layer (Second electrode), 28... Heater, 40... ECU (conduction determination means, diagnosis limiting means, time setting means).

Claims (5)

Applied to an exhaust pipe of an internal combustion engine and applied to a gas sensor having a sensor element having a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, and based on an electric signal from the pair of electrodes, In the gas sensor abnormality diagnosis device that performs abnormality diagnosis,
Continuity determination means for determining that at least one of the pair of electrodes is in a state where continuity with the exhaust pipe side is caused by water;
Diagnosis limiting means for limiting the execution of sensor abnormality diagnosis based on the output value of the gas sensor when the continuity determination means determines that the continuity is in a state to occur; and
An abnormality diagnosis device for a gas sensor, comprising: One of the pair of electrodes is a first electrode exposed to the exhaust side, and the other is a second electrode exposed to a reference chamber in an air atmosphere,
The abnormality diagnosis device for a gas sensor according to claim 1, wherein the continuity determining means determines that the continuity between the first electrode and the exhaust pipe is generated. The gas sensor is provided with a heater for heating the sensor element,
3. The gas sensor abnormality diagnosis device according to claim 1, wherein the continuity determination unit determines that the continuity between the electrode and the exhaust pipe is generated after the restriction on energization of the heater is released.   4. The gas sensor abnormality diagnosis device according to claim 1, further comprising a time setting unit configured to variably set a time limit for limiting the execution of the sensor abnormality diagnosis by the diagnosis limiting unit. 5. The gas sensor is an O2 sensor that generates an electromotive force between both positive and negative electrodes according to the oxygen concentration of exhaust gas,
In the electromotive force detection circuit for detecting the electromotive force of the O2 sensor, a bias power source is connected to the negative electrode of the O2 sensor,
The abnormality diagnosis device for a gas sensor according to any one of claims 1 to 4, wherein the abnormality diagnosis is performed based on a voltage of a positive electrode or a negative electrode of the O2 sensor.

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