JP4424284B2 - Exhaust gas sensor failure detection device - Google Patents

Description

  The present invention relates to an exhaust gas sensor failure detection device, and more particularly, to an exhaust gas sensor failure detection device suitable as a device for detecting cracks in an exhaust gas sensor.

  2. Description of the Related Art Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-55861, an apparatus that detects an abnormality of an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine is known. More specifically, the conventional apparatus is an apparatus for detecting an abnormality of an air-fuel ratio sensor that generates an output corresponding to an exhaust air-fuel ratio.

  The responsiveness of the air-fuel ratio sensor gradually decreases due to deterioration with time. For this reason, if the responsiveness of an air-fuel ratio sensor is seen, the degree of deterioration of the sensor can be detected. The air-fuel ratio sensor includes a diffusion resistance layer for suppressing the amount of exhaust gas reaching the electrode. If the diffusion resistance layer is cracked, the amount of exhaust gas reaching the electrode cannot be suppressed, and normal air-fuel ratio detection becomes impossible. Under a situation where the diffusion resistance layer is cracked, the output of the air-fuel ratio sensor reacts sensitively to changes in the exhaust air-fuel ratio. Therefore, it is possible to determine whether or not the diffusion resistance layer is cracked by looking at the responsiveness of the air-fuel ratio sensor.

  The air-fuel ratio sensor emits an output corresponding to the air-fuel ratio of the gas flowing through the exhaust passage. The air-fuel ratio of the gas flowing through the exhaust passage changes abruptly before and after the fuel cut is performed. For this reason, it is possible to detect what responsiveness the air-fuel ratio sensor has by looking at the behavior of the output of the air-fuel ratio sensor immediately after the start of fuel cut.

  Therefore, the conventional apparatus detects the responsiveness of the air-fuel ratio sensor based on the sensor current immediately after the start of the fuel cut and the sensor current when a certain amount of time has passed thereafter. Then, based on whether or not the responsiveness is normal, it is determined whether or not an abnormality has occurred in the air-fuel ratio sensor. According to such an abnormality detection method, it is possible to accurately detect anomalies such as a decrease in responsiveness due to deterioration with time and cracks in the diffusion resistance layer.

JP 2000-55861 A JP-A-8-327586

  An exhaust gas sensor such as an air-fuel ratio sensor or an oxygen sensor has an exhaust side electrode that is exposed to the exhaust gas through a diffusion resistance layer and an atmosphere side electrode that is exposed to the atmospheric layer. The atmospheric layer is isolated from the internal space of the exhaust passage by an atmospheric layer forming member made of alumina or the like. In other words, when a crack is generated in the air layer forming member, the air layer is in a state of conducting with the internal space of the exhaust passage.

  In a situation where the atmospheric layer is connected to the internal space of the exhaust passage and exhaust gas is mixed into the atmospheric layer, the air-fuel ratio sensor cannot generate a correct output corresponding to the exhaust air-fuel ratio. For this reason, it is desirable to detect a failure such as cracking of the atmospheric layer forming member that mixes exhaust gas into the atmospheric layer as an abnormality.

  However, the conventional apparatus performs abnormality detection by paying attention to the behavior of the sensor current after the start of fuel cut. After the start of the fuel cut, the air-fuel ratio inside the exhaust passage changes greatly, and the influence is greatly reflected in the sensor current. On the other hand, the influence of the exhaust gas mixed in the atmosphere layer does not appear so much in the sensor current. For this reason, it is not possible to detect a failure that causes exhaust gas to be mixed into the atmospheric layer with the above-described conventional apparatus.

  The present invention has been made to solve the above-described problems, and provides a failure detection device for an exhaust gas sensor capable of detecting a failure in which exhaust gas is mixed into the atmospheric layer of the exhaust gas sensor. With the goal.

In order to achieve the above object, a first invention is a failure detection device for an exhaust gas sensor,
The exhaust gas sensor
An exhaust-side electrode exposed in the exhaust passage of the internal combustion engine;
An air layer forming member for forming an air layer in the exhaust passage;
An atmospheric electrode exposed to the atmospheric layer;
An electrolyte layer interposed between the exhaust-side electrode and the atmosphere-side electrode and enabling movement of oxygen ions between the two,
Reverse voltage applying means for applying a reverse voltage between the two so that the potential of the exhaust side electrode is higher than the potential of the atmosphere side electrode;
Reverse current detection means for detecting a reverse current flowing between the atmosphere side electrode and the exhaust side electrode in accordance with the application of the reverse voltage;
An environment switching means for switching between a polluted environment in which the air layer is contaminated with exhaust gas and a non-polluted environment in which the pollution is mitigated when cracks are present in the air layer forming member;
A failure detection means for detecting a failure of the exhaust gas sensor based on fluctuations in the reverse current caused by switching between the contaminated environment and the non-contaminated environment;
It is characterized by providing.

The second invention is the first invention, wherein
The failure detection means includes
First reverse current acquisition means for acquiring a reverse current detected in the contaminated environment as a first reverse current;
Second reverse current acquisition means for acquiring a reverse current detected in the non-polluted environment as a second reverse current;
Failure determination means for determining the exhaust gas sensor as a failure when the absolute value of the second reverse current is larger than the absolute value of the first reverse current;
It is characterized by providing.

In a third aspect based on the second aspect, the failure determination means has a ratio of the second reverse current to the first reverse current (second reverse current / first reverse current) from 1.0. and judging as a failure of the exhaust gas sensor when it is large determination value or more.

In a fourth aspect based on the second aspect, the failure determination means has a ratio of the second reverse current to the first reverse current (second reverse current / first reverse current) from 1.0. and judging as a failure of the exhaust gas sensor when it is large determination value or more.

According to a fifth invention, in any one of the first to fourth inventions,
The environment switching means includes fuel cut means for stopping fuel injection to the internal combustion engine,
The contaminated environment is an environment immediately after the fuel injection is stopped,
The non-polluting environment is an environment at a time when fuel injection is continuously stopped for a predetermined time.

The sixth invention is the fifth invention, wherein
Exhaust pressure determination means for determining whether or not the exhaust pressure exceeds a pressure determination value;
If the period in which the exhaust gas pressure exceeds the pressure determination value exceeds the determination period, and determines the fill condition determining means and the exhaust gas-filled condition is satisfied,
Filling condition maintaining means for maintaining the establishment of the exhaust gas filling condition only until the filling maintenance time elapses after the exhaust pressure falls below the pressure determination value;
An execution condition determination unit that permits detection of the failure only when the exhaust gas filling condition is recognized at the start of fuel cut .
The exhaust gas-filled condition, when the sensor crack occurs, the air layer, a sufficient amount of exhaust gas to the detection of the sensor crack is characterized in terms der Rukoto which can determine that mixed.

The seventh invention is an exhaust gas sensor failure detection apparatus,
The exhaust gas sensor
An exhaust-side electrode exposed in the exhaust passage of the internal combustion engine;
An air layer forming member for forming an air layer in the exhaust passage;
An atmospheric electrode exposed to the atmospheric layer;
An electrolyte layer interposed between the exhaust-side electrode and the atmosphere-side electrode and enabling movement of oxygen ions between the two,
Reverse voltage applying means for applying a reverse voltage between the two so that the potential of the exhaust side electrode is higher than the potential of the atmosphere side electrode;
Reverse current detection means for detecting a reverse current flowing between the atmosphere side electrode and the exhaust side electrode in accordance with the application of the reverse voltage;
A contaminated environment forming means for creating a contaminated environment in which the air layer is contaminated with exhaust gas when cracks are present in the air layer forming member;
If the contaminated environment under reverse current detected by is a value between the judged value and 0 positioned between the reverse current generated in the reverse current and abnormal occurring normal, as a failure of the exhaust gas sensor Failure determination means for determining;
It is characterized by providing.

  According to the first aspect of the invention, the behavior of the reverse current caused by switching between a polluted environment in which the inside of the atmospheric layer may be polluted by exhaust gas and a non-polluted environment in which the pollution is mitigated. It is possible to detect a failure of the exhaust gas sensor depending on whether or not. When there is no failure in which exhaust gas is mixed into the atmospheric layer, the reverse current is a value representing the concentration of oxygen contained in normal air regardless of the environmental switching. On the other hand, when there is a failure that causes exhaust gas to enter the atmosphere layer, the oxygen concentration in the atmosphere layer changes as a result of switching between the contaminated environment and the non-contaminated environment, and as a result, the reverse current also changes. Will occur. Therefore, according to the present invention, it is possible to accurately detect the occurrence of a failure that causes exhaust gas to be mixed into the atmospheric layer.

  According to the second invention, it is possible to compare the first reverse current detected in a contaminated environment with the second reverse current detected in a non-contaminated environment. When a failure that causes exhaust gas to enter the atmosphere layer has occurred, the absolute value of the first reverse current is smaller than the absolute value of the second current. According to the present invention, it is possible to accurately detect the occurrence of the above failure by checking whether such a situation has occurred.

  According to the third invention, by looking at whether or not the ratio of the second reverse current to the first reverse current (second reverse current / first reverse current) is not less than a determination value greater than 1.0, It is possible to accurately determine whether or not a failure has occurred in the exhaust gas sensor.

  According to the fourth invention, the exhaust gas sensor is obtained by checking whether or not the difference between the second reverse current and the first reverse current (| second reverse current−first reverse current |) is equal to or greater than a determination value. It is possible to accurately determine whether or not a failure has occurred.

  According to the fifth aspect, by stopping the fuel injection, it is possible to continuously create a polluted environment and a non-polluted environment in a short time. If a polluted environment and a non-polluted environment can be created continuously in a short time, the influence of various disturbances superimposed on the reverse current can be reduced. Therefore, according to the present invention, whether or not the state of the atmospheric layer has changed by looking at the change in the reverse current, that is, whether or not a failure that mixed exhaust gas into the atmospheric layer has occurred, It can be determined very accurately.

  According to the sixth aspect of the invention, failure detection is performed based on a comparison between the reverse current immediately after stopping fuel injection and the reverse current when a predetermined time has elapsed after the start of fuel injection. When sensor cracking occurs, the exhaust gas enters the atmosphere before the start of fuel cut. When the fuel cut is started and air begins to flow through the exhaust passage, the inside of the atmosphere layer is scavenged and the exhaust gas therein is discharged. Since the reverse current has a correlation with the oxygen concentration in the atmospheric layer, its value increases as the exhaust gas in the atmospheric layer is scavenged. For this reason, if the exhaust gas has sufficiently penetrated into the atmosphere layer at the start of the fuel cut, the presence or absence of cracks can be determined based on the behavior of the subsequent reverse current. While the exhaust gas filling condition is established and maintained, it can be ensured that the exhaust gas has sufficiently entered the atmospheric layer. In the present invention, execution of failure detection can be permitted only when the guarantee is obtained. For this reason, according to the present invention, failure diagnosis of the exhaust gas sensor can be performed accurately.

  According to the seventh aspect of the present invention, the exhaust gas is exhausted based on whether the reverse current becomes a value between the negative judgment value and 0 in a polluted environment where the inside of the atmospheric layer may be polluted by the exhaust gas. A failure of the gas sensor can be detected. If there is no failure that mixes exhaust gas into the atmosphere, pure atmosphere is introduced to the atmosphere even in a polluted environment. In this case, a sufficiently large reverse current, that is, a reverse current biased further to the negative side than the negative determination value flows. On the other hand, when there is a failure in which exhaust gas is mixed into the atmospheric layer, the oxygen concentration in the atmospheric layer in a polluted environment becomes low. In this case, the reverse current has a small absolute value and is a value located between the negative determination value and 0. For this reason, according to the present invention, it is possible to accurately detect a failure of the exhaust gas sensor only by looking at the reverse current in a contaminated environment.

Embodiment 1 FIG.
[Configuration of air-fuel ratio sensor]
FIG. 1 is a diagram for explaining the configuration of an air-fuel ratio sensor 10 used in Embodiment 1 of the present invention. More specifically, FIG. 1 shows a cross-sectional view of the sensor element portion of the air-fuel ratio sensor 10. The air-fuel ratio sensor 10 includes a sensor element having the cross-sectional structure shown in FIG. 1 and a cover for protecting the sensor element. The air-fuel ratio sensor 10 is assembled in the exhaust passage of the internal combustion engine so that the sensor element covered by the cover is exposed to the exhaust gas.

  The cover of the air-fuel ratio sensor 10 is provided with a plurality of vent holes so that the gas flowing through the exhaust passage reaches the sensor element. Therefore, the air-fuel ratio sensor 10 (sensor element) shown in FIG. 1 is placed in a state where the surroundings are exposed to the exhaust gas.

  The air-fuel ratio sensor 10 has a heater layer 12. A heater 14 for heating the sensor element to the activation temperature is embedded in the heater layer 12. In FIG. 1, an air layer forming member 16 is disposed on the heater layer 12. The air layer forming member 16 is made of ceramics such as alumina.

  An electrolyte layer 20 made of zirconia or the like is disposed on the air layer forming member 16. A recess for forming the air layer 18 is provided at the upper center of the air layer forming member 16. The atmospheric layer 18 is isolated from the internal space of the exhaust passage by the atmospheric layer forming member 16 and the electrolyte layer 20, and is opened to the atmosphere by an atmospheric hole (not shown).

  An atmosphere side electrode 22 is disposed on the lower surface of the electrolyte layer 20 so as to be exposed to the atmosphere layer 18. On the other hand, an exhaust side electrode 24 is disposed on the upper surface of the electrolyte layer 20. The exhaust side electrode 24 is covered with a diffusion resistance layer 26. The diffusion resistance layer 26 is a porous substance and has a function of appropriately regulating the speed at which the gas flowing through the exhaust passage reaches the exhaust side electrode 24.

  The air-fuel ratio sensor 10 is selectively applied with a positive voltage indicated by a symbol (i) in FIG. 1 and a reverse voltage indicated by a symbol (ii). Specifically, the positive voltage is applied so that the atmosphere-side electrode 22 has a higher potential than the exhaust-side electrode 24. In this case, a sensor current corresponding to the oxygen excess / deficiency in the exhaust gas, that is, a sensor current corresponding to the air-fuel ratio of the exhaust gas flows between the atmosphere side electrode 22 and the exhaust side electrode 24. Therefore, the exhaust air / fuel ratio can be detected by detecting the sensor current.

  Specifically, the reverse voltage is applied so that the exhaust side electrode 24 has a higher potential than the atmosphere side electrode 22. In this case, oxygen in contact with the surface of the atmosphere side electrode 22 is ionized and pumped toward the exhaust side electrode 24. As a result, a negative current having a correlation with the oxygen concentration in the atmosphere layer, that is, a reverse current flows between the exhaust side electrode 24 and the atmosphere side electrode 22. Here, the direction of current from the atmosphere side electrode 22 to the exhaust side electrode 24 is defined as a positive direction, and the opposite direction is defined as a negative direction.

[Air-fuel ratio sensor drive circuit]
FIG. 2 is a circuit diagram for explaining the configuration of the engine computer 30 for driving the air-fuel ratio sensor 10. The circuit shown in FIG. 2 includes a positive terminal 32 connected to the atmosphere-side electrode 22 of the air-fuel ratio sensor 10 and a negative terminal 34 connected to the exhaust-side electrode 24 of the air-fuel ratio sensor 10.

  The potential of the positive terminal 32 is always controlled to the positive reference voltage (3.3 V) by feedback from the operational amplifier 36. A feedback circuit using an operational amplifier 38 and a switch circuit using a transistor 40 are connected to the negative terminal 34. The transistor 40 switches between an ON state and an OFF state according to the state of the port 3. The potential of the negative terminal 34 is controlled to the negative reference voltage (2.9 V) by the function of the operational amplifier 38 when the transistor 40 is in the OFF state. On the other hand, when the transistor 40 is turned on, the input potential to the operational amplifier 38 increases, and the potential of the negative terminal 34 rises to a reverse voltage potential (about 3.7 V) higher than the positive reference voltage.

  Since the engine computer 30 is configured as described above, a positive voltage of about 0.4 V can be applied to the air-fuel ratio sensor 10 by setting the port 3 to the OFF state. Further, by setting the port 3 to the ON state, a reverse voltage of about 0.4 V can be applied to the air-fuel ratio sensor 10.

  The engine computer 30 further has an ADC2 port and an ADC4 port. A potential corresponding to the sensor current flowing through the air-fuel ratio sensor 10 appears at the ADC2 port. Further, the potential of the negative terminal 34 is led to the ADC4 port. Therefore, the engine computer 30 can detect the sensor current by taking in the potential of the ADC2 port. Further, by taking in the potential of the ADC4 port, it is possible to detect what potential is being supplied to the exhaust-side terminal 24 of the air-fuel ratio sensor 10.

[Sensor crack judgment principle]
The engine computer 30 shown in FIG. 2 can detect the sensor current while applying a positive voltage of about 0.4 V to the air-fuel ratio sensor 10. In this case, the exhaust air / fuel ratio can be detected based on the sensor current. Further, the engine computer 30 can detect the sensor current (reverse current) while applying a reverse voltage of about 0.4 V to the air-fuel ratio sensor 10. In this case, the reverse current is a value having a correlation with the oxygen concentration inside the atmospheric layer 18.

  When the air-fuel ratio sensor 10 is normal, the atmosphere layer 18 is maintained in a state isolated from the internal space of the exhaust passage. However, the air-fuel ratio sensor 10 may be cracked to the atmosphere layer 18 or the like. FIG. 1 shows a state in which the crack is generated in the heater layer 12 and the atmospheric layer forming member 16.

  During operation of the internal combustion engine, the internal pressure of the exhaust passage becomes higher than the pressure of the atmospheric layer 18 due to the pressure of the exhaust gas. For this reason, if the above-mentioned crack is generated in the air-fuel ratio sensor 10, a situation occurs in which the gas flowing in the exhaust passage enters the atmosphere layer 18 through the crack. In this case, the oxygen concentration in the atmosphere layer 18 is reduced by mixing exhaust gas as compared with the case where the above-described crack does not exist.

  As described above, the reverse current flowing through the air-fuel ratio sensor 10 has a value corresponding to the oxygen concentration inside the atmospheric layer 18. For this reason, when the crack exists in the atmospheric layer 18, the reverse current becomes a small value compared with the normal time. Therefore, the engine computer 30 applies a reverse voltage to the air-fuel ratio sensor 10 in an environment where exhaust gas including burned gas is flowing through the exhaust passage, and as a result, whether or not the reverse current is normally generated. By looking at the above, it can be determined whether or not the air-fuel ratio sensor 10 is cracked.

[Reverse current variation factors]
Incidentally, the value of the reverse current flowing through the air-fuel ratio sensor 10 varies under the influence of various factors. Hereinafter, some factors affecting the value of the reverse current will be described.

1. Variation of diffusion resistance layer When a reverse voltage is applied, oxygen is ionized on the surface of the atmosphere-side electrode 22, and the ionized oxygen is returned to oxygen on the surface of the exhaust-side electrode 24 and released into the exhaust passage. At this time, since the surface of the atmosphere side electrode 22 is directly exposed to the atmosphere layer 18, oxygen ionization can be rapidly advanced. However, the surface of the exhaust side electrode 24 is covered with the diffusion resistance layer 26. For this reason, the reaction at the exhaust side electrode 24 is limited by the speed at which oxygen passes through the diffusion resistance layer 26. Eventually, the value of the reverse current is governed by the latter speed and is affected by the dispersion of the diffusion resistance layer (however, the effect is not so great).

2. Variation in internal resistance of air-fuel ratio sensor When a positive voltage is applied to the air-fuel ratio sensor 10, the number of oxygen reaching the exhaust-side electrode 24 is increased by the diffusion resistance layer 26 even if the positive voltage is increased. Be ruled. For this reason, if an appropriate positive voltage is applied, the sensor current is maintained at a limit current corresponding to the exhaust air-fuel ratio regardless of fluctuations in the applied voltage. That is, in this case, a situation is created in which the internal resistance of the air-fuel ratio sensor 10 hardly affects the sensor current value.

  On the other hand, when a reverse voltage is applied, oxygen is successively supplied to the surface of the atmosphere-side electrode 22, so that the sensor current has a value corresponding to the applied voltage. In this case, more specifically, the sensor current has a value inversely proportional to the internal resistance of the sensor. For this reason, the value of the reverse current flowing through the air-fuel ratio sensor 10 is affected by variations in the internal resistance of the sensor.

3. Variation in applied voltage The value of the reverse voltage applied to the air-fuel ratio sensor 10 varies to some extent due to tolerances of circuit components. As described above, the value of the reverse current is a value corresponding to the value of the applied reverse voltage due to the absence of the diffusion resistance layer. For this reason, variations due to variations in applied voltage are superimposed on the reverse current.

4). Variation in atmospheric pressure The atmospheric pressure surrounding an internal combustion engine is not necessarily constant. Further, when the atmospheric pressure is different, the oxygen concentration in the atmosphere varies (for example, the oxygen concentration at an altitude of 2400 m is about 75% of the oxygen concentration at an altitude of 0 m). If the oxygen concentration in the atmosphere fluctuates, the influence is inevitably reflected in the value of the reverse current. Therefore, as shown in FIG. 3, the value of the reverse current flowing through the air-fuel ratio sensor 10 has a proportional relationship with the atmospheric pressure. Therefore, the value of the reverse current is affected by variations in atmospheric pressure.

[Difficulty in detecting abnormalities based on reverse current]
As described above, the value of the reverse current that flows when a reverse voltage is applied to the air-fuel ratio sensor 10 varies due to various factors other than the degree of mixing of burned gas into the atmospheric layer 18.
FIG. 4 shows that a reverse current flowing through a normal sensor and a reverse current flowing through a cracked sensor fluctuate due to the internal resistance of the sensor, that is, fluctuate due to a temperature change of the sensor. It is the figure which expressed the situation contrasted (refer the said factor 2).

More specifically, FIG. 4 clearly shows the following two points.
1. The reverse current flowing through the sensor that has cracks leading to the atmospheric layer has a smaller absolute value than the reverse current that occurs during normal operation due to the presence of burned gas in the atmospheric layer 18.
2. Both the reverse current flowing through a normal sensor and the reverse current flowing through a cracked sensor show a significant correlation with the internal resistance of the sensor, that is, with the temperature of the sensor.

  How much the reverse current decreases due to the effect of sensor cracking is determined by how much burned gas is mixed into the atmosphere layer 18 due to the effect of sensor cracking. For this reason, when the crack which generate | occur | produced is very small and the burned gas mixed in the atmospheric layer 18 is a trace amount, it is between the reverse current which flows through the sensor which the crack generate | occur | produced, and the reverse current which flows through a normal sensor. There is no big difference. In such a case, an overlap occurs between a reverse current flowing through a normal sensor at a low temperature and a reverse current flowing through an abnormal sensor at a high temperature.

  Furthermore, as described above, variations due to various factors are superimposed on the reverse current. For this reason, it is not always easy to determine the presence or absence of sensor cracks based on the reverse current itself. That is, it is not always easy to determine the presence or absence of a sensor crack by setting a determination value that distinguishes between a normal value and an abnormal value of a reverse current and comparing the absolute value of the reverse current with the determination value. .

[Optimization of abnormality detection using reverse current]
By the way, when the crack which leads to the atmospheric layer 18 has arisen, the concentration of the burned gas in the atmospheric layer 18 changes according to the burned gas concentration in the gas flowing through the exhaust passage. Specifically, when the exhaust air-fuel ratio is rich, the burned gas concentration in the atmosphere layer 18 is higher than when the exhaust air-fuel ratio is lean. On the other hand, if such sensor cracking does not occur, the burned gas concentration in the atmospheric layer 18 remains zero, regardless of the exhaust air / fuel ratio. For this reason, it is possible to accurately determine whether or not the air-fuel ratio sensor 10 has cracks leading to the atmospheric layer 18 by checking whether or not the reverse current changes with the fluctuation of the exhaust air-fuel ratio. It is.

  In an internal combustion engine, processing for stopping fuel injection at the time of deceleration, that is, fuel cut, is executed in order to improve fuel consumption characteristics. The exhaust air-fuel ratio changes significantly before and after the start of fuel cut. For this reason, in the present embodiment, a reverse current is detected after the start of fuel cut, and it is determined whether or not a crack leading to the atmospheric layer 18 has occurred based on the behavior of the detected value. It was.

  FIG. 5 is a timing chart for explaining the contents of processing executed by the apparatus of the present embodiment to detect a failure of the air-fuel ratio sensor 10. More specifically, FIG. 5A shows a waveform indicating the execution state of fuel cut. FIG. 5B is a waveform showing a change in applied voltage to the air-fuel ratio sensor 10. FIG. 5C shows a waveform of the sensor current flowing through the air-fuel ratio sensor 10.

  The apparatus of the present embodiment applies a positive voltage to the air-fuel ratio sensor 10 before the fuel cut is started (see FIG. 5B). Therefore, during this period, the engine computer 30 can detect the exhaust air-fuel ratio based on the sensor current.

  When the fuel cut is started, the applied voltage is changed to the reverse voltage at that time (see FIG. 5B), and the reverse current generated by the application of the reverse voltage is acquired as the first reverse current i1. (See FIG. 5C).

  Before the fuel cut is started, the air-fuel ratio of the exhaust passage is maintained near the stoichiometric air-fuel ratio. For this reason, when the crack which leads to the atmospheric layer 18 has arisen, the burned gas is mixed in the atmospheric layer 18 at the time of a fuel cut start. In this case, the first reverse current i1 has a small absolute value as indicated by a solid line in FIG.

  On the other hand, when there is no crack leading to the air layer 18, the inside of the air layer 18 is maintained in a pure air atmosphere at the start of fuel cut. In this case, since the oxygen concentration in the atmospheric layer 18 has a sufficiently high value, the first reverse current i1 has a large absolute value as indicated by a broken line in FIG.

  When a predetermined reverse voltage application time t (for example, 50 to 100 msec) elapses after the start of fuel cut, the applied voltage is returned to a positive voltage at that time. Thereafter, when the elapsed time from the fuel cut start time reaches a reverse voltage application period T (for example, 1 sec), the applied voltage is again set to the reverse voltage for the reverse voltage application time t. The engine computer 30 acquires the reverse current generated at that time as the second reverse current i2 (see FIG. 5C).

  During the fuel cut, air that does not contain fuel flows around the air-fuel ratio sensor 10. For this reason, even when the crack which leads to the atmospheric layer 18 has arisen, when the reverse voltage application period T has passed, a state in which almost no burned gas is contained in the atmospheric layer 18 is formed. Therefore, the second reverse current i2 has a value corresponding to a substantially pure oxygen concentration in the atmosphere, regardless of whether or not the above-described cracking occurs.

  Thereafter, the engine computer 30 determines whether or not the absolute value of the second reverse current i2 is significantly larger than the absolute value of the first reverse current i1. As a result, when it is determined that both do not change so much, it is determined that the air-fuel ratio sensor 10 is normal. On the other hand, if it is determined that the absolute value of the second reverse current i2 is sufficiently larger than the absolute value of the first reverse current i1, the air-fuel ratio sensor 10 is cracked leading to the atmospheric layer 18. to decide.

  According to the above processing, the atmosphere layer 18 may be contaminated by burned gas (contaminated environment) and the environment in which the contamination is mitigated (non-contaminated) in a short period after the start of fuel cut. Pollution environment), and the first reverse current and the second reverse current can be obtained in each environment. During such a short period, it is difficult for a large change to occur in various factors affecting the reverse current. Therefore, the difference between the first reverse current and the second reverse current accurately represents the concentration change of the burned gas in the atmospheric layer 18. For this reason, according to the apparatus of the present embodiment, it is accurately determined whether the burned gas concentration in the atmospheric layer 18 has changed with the execution of the fuel cut, that is, whether a crack leading to the atmospheric layer 18 has occurred. It is possible.

[Specific Processing in Embodiment 1]
FIG. 6 is a flowchart of a routine executed by the engine computer 30 to realize the above function. According to the routine shown in FIG. 6, it is first determined whether or not a fuel cut is being executed (step 100).

  As a result, if it is determined that the fuel cut is not being executed, this routine is immediately terminated, and other arithmetic processing (processing such as air-fuel ratio control based on sensor current) is started. On the other hand, if the execution of the fuel cut is confirmed, it is next determined whether or not the elapsed time from the fuel cut start time is equal to or less than the reverse voltage application time t (step 102).

  Immediately after the start of the fuel cut, the condition of step 102 is satisfied. In this case, next, a process for applying a reverse voltage to the air-fuel ratio sensor 10, specifically, a process for supplying an ON signal to the port 3 in the circuit shown in FIG. 2 is executed (step 104). Next, a process of acquiring the detected reverse current peak value as the first reverse current is executed (step 106).

  After the fuel cut is started, the processes of steps 100 to 106 are repeatedly executed until the reverse voltage application time t elapses. As a result, finally, the peak value of the reverse current generated before the reverse voltage application time t elapses after the start of the fuel cut is stored as the first reverse current i1.

  If the routine shown in FIG. 6 is started after the reverse voltage application time t has elapsed, it is determined that the condition of step 102 is not satisfied. In this case, it is next determined whether the elapsed time after the start of the fuel cut is longer than the reverse voltage application period T and equal to or shorter than T + t (step 108).

  The above determination is denied until the elapsed time after the start of the fuel cut reaches the reverse voltage application period T. In this case, next, a process for applying a positive voltage to the air-fuel ratio sensor 10, that is, a process for setting the supply potential to the port 3 (see FIG. 2) to the OFF potential is executed (step 110).

  On the other hand, after the elapsed time after the start of the fuel cut reaches the reverse voltage application cycle T, until the elapsed time exceeds T + t, it is determined in step 108 that the condition is satisfied. In this case, first, processing for applying a reverse voltage is executed (step 112), and then processing for acquiring the peak value of the reverse current as the second reverse current is executed (step 114).

  Until the elapsed time after the start of the fuel cut exceeds T + t, the processes of steps 112 and 114 are repeatedly executed every time the routine shown in FIG. 6 is started. As a result, finally, the peak value of the reverse current generated until the elapsed time reaches T + t is stored as the second reverse current i2.

  In the routine shown in FIG. 6, following the process of step 114, it is determined whether the ratio (i2 / i1) of the second reverse current i2 to the first reverse current i1 is greater than or equal to the determination value R (step 116). . The determination value R is a value larger than 1.0 set to determine whether the absolute value of i2 is significantly larger than the absolute value of i1. Therefore, when the above condition is satisfied, it can be determined that the absolute value of the second reverse current i2 is significantly larger than the absolute value of the first reverse current i1. In this case, the engine computer 30 recognizes the presence of cracks leading to the atmospheric layer 18 and makes an abnormality determination (step 118).

  On the other hand, if it is determined in step 116 that i2 / i1 ≧ R is not established, it can be determined that the second reverse current i2 and the first reverse current i1 are not significantly different. In this case, the presence of cracks leading to the atmospheric layer 18 is denied, and a normal determination is made (step 120).

  After the elapsed time after the start of the fuel cut exceeds T + t, it is determined in step 108 that the condition is not satisfied each time the routine shown in FIG. 6 is started, and the processing of step 110, that is, the positive voltage is applied to the air-fuel ratio sensor 10. Is repeatedly executed.

  According to the processing described above, the operation described with reference to FIG. 5 can be realized. Therefore, according to the apparatus of the present embodiment, it is possible to determine very accurately whether or not the air-fuel ratio sensor 10 is cracked leading to the atmospheric layer 18 without being affected by various disturbances. .

  By the way, in the first embodiment described above, in order to eliminate the influence of various factors that cause variations in the reverse current flowing through the air-fuel ratio sensor 10, the first reverse current i1 is measured in a contaminated environment, and non-polluted. The second reverse current i2 is measured under the environment, and the presence / absence of a failure is determined based on the ratio (i2 / i1). However, the determination method is not limited to this. In other words, when the reverse current variation can be suppressed to a sufficiently small level and the overlap between the reverse current that occurs during normal operation and the reverse current that occurs during a failure can be avoided, it is based on the value of the single reverse current itself. Thus, the presence or absence of a failure may be determined.

  Specifically, this modification can be realized by the following method. That is, here, first, a determination value (negative determination value) positioned between the reverse current generated in the normal state and the reverse current generated in the abnormal state is set by the adaptation operation. A reverse current is detected in a contaminated environment, and it is determined whether the reverse current is located between the determination value and 0. As a result, when the reverse current is located between the determination value and 0, it can be determined that the oxygen concentration in the atmospheric layer 18 is low, that is, that a crack leading to the atmospheric layer 18 has occurred. On the other hand, when the reverse current is not positioned between the determination value and 0, that is, when the reverse current is more negative than the determination value, it can be determined that the air-fuel ratio sensor 10 is normal.

  When the above modification is used, various factors that affect the reverse current may be normalized. Specifically, as a reverse current detection condition, it may be requested that the sensor temperature, the atmospheric pressure, the applied voltage, and the like each match a predetermined value. When such a condition is imposed, although the frequency of failure detection decreases, it is possible to improve the accuracy of failure detection based on a single reverse current.

  In the first embodiment described above, the “contaminated environment” is defined immediately after the start of the fuel cut, that is, the environment in which the first reverse current is measured. However, the environment in which the first reverse current is measured is limited to this. Is not to be done. That is, the first reverse current may be measured in an environment in which the atmosphere layer 18 may be contaminated with burned gas. For example, the normal operating environment is changed to a polluted environment regardless of the execution of fuel cut. And the first reverse current may be measured under a normal driving environment.

  In the first embodiment described above, after the fuel cut is started, the first reverse current i1 and the second reverse current i2 are measured at a predetermined interval, and the behavior of the reverse current is determined by comparing them. However, the method for determining the behavior is not limited to this. For example, after the start of the fuel cut, the change in the reverse current may be continuously monitored, and the presence or absence of a sensor crack may be determined based on the monitoring result.

  In the first embodiment described above, in order to determine whether or not the absolute value of the second reverse current i2 is significantly larger than the absolute value of the first reverse current i1, the ratio (i2 / It is determined whether i1) is equal to or greater than the determination value R, but the determination method is not limited to this. For example, the same determination may be realized by checking whether or not the difference (| i2−i1 |) between the second reverse current i2 and the first reverse current i1 is larger than the determination value.

  In the first embodiment described above, the target of failure detection is the air-fuel ratio sensor, but the target is not limited to this. That is, the failure detection method of the first embodiment can also be applied to an oxygen sensor.

  In the first embodiment described above, the engine computer 30 executes the processes of steps 104 and 112 to increase the potential of the negative terminal 34, whereby the “reverse voltage applying means” in the first invention is provided. By reading the potential of the ADC2 port in the processing of steps 106 and 114, the “reverse current detecting means” in the first invention performs the fuel cut, and the “environment switching means” in the first invention and The “failure detection means” according to the first aspect of the present invention is realized by the “fuel cut means” according to the fifth aspect of the invention executing the processes of steps 116 to 120 described above.

  In the first embodiment described above, the engine computer 30 executes the process of step 106, so that the “first reverse current acquisition means” in the second invention executes the process of step 114. As a result, the “second reverse current acquisition means” in the second invention realizes the “failure determination means” in the second invention by executing the processing of steps 116 and 118 described above.

  Further, according to the configuration of the first embodiment described above, the engine computer 30 causes the port 3 to be set to the ON potential, whereby the “reverse voltage applying means” according to the seventh aspect of the present invention is supplied to the port 3. The "reverse current detecting means" in the seventh invention is caused by reading the potential of the ADC2 port under the circumstances, and the "contaminated environment forming means" in the seventh invention is caused by operating the internal combustion engine normally. By determining whether the reverse current detected from the potential of the ADC2 port is a value between a negative determination value and 0, the “failure determination means in the seventh invention can be realized respectively. .

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. The system of the present embodiment can be realized by causing the engine computer 30 to execute a routine shown in FIG. 10 described later in the hardware configuration of the first embodiment.

  As in the system of the first embodiment, the system of the present embodiment includes a first reverse current i1 detected immediately after the start of fuel cut and a second reverse current i2 detected after the reverse voltage application period T. Based on the comparison, the presence or absence of a sensor crack is determined. If the exhaust gas is sufficiently mixed in the atmospheric layer 18 at the start of the fuel cut, the oxygen concentration in the atmospheric layer 18 increases significantly after the start of the fuel cut. be able to.

  However, the assumption that sufficient exhaust gas is mixed in the atmosphere layer 18 at the start of fuel cut does not always hold when a sensor crack occurs. And in the situation where this premise is not materialized, it is difficult to detect a sensor crack correctly by the above-mentioned method.

  FIG. 7 is a timing chart in the case where the above assumption is established. On the other hand, FIG. 8 is a timing chart when the premise is not satisfied. In these drawings, FIGS. 7A and 8A show changes in the intake air amount Ga. Further, G shown in these drawings is a determination value for determining whether or not sufficient exhaust pressure is generated.

  Even if sensor cracking occurs in the air-fuel ratio sensor 10, the exhaust gas does not enter the atmosphere layer 18 if the exhaust pressure is a value close to atmospheric pressure. In other words, in order for the exhaust gas to enter the atmosphere layer 18 when the sensor crack occurs, the exhaust pressure needs to be increased to such an extent that the exhaust gas enters. The determination value G is a value for guaranteeing the generation of the necessary exhaust pressure. Therefore, when the condition of Ga> G is satisfied, it can be determined that the condition for the exhaust gas to enter the atmosphere layer 18 is satisfied.

  FIGS. 7B and 8B show changes in the integrated air amount GVOL. The integrated air amount GVOL is an integrated value of the intake air amount Ga generated under the condition that Ga> G is established. Therefore, the value is reset to 0 when the intake air amount Ga falls below the determination value G (see time t3).

  As described above, a certain amount of exhaust pressure is required for the exhaust gas to enter the atmosphere layer 18 from the location of the sensor crack. In particular, when the sensor crack is small, a sufficient amount of exhaust gas does not enter unless the exhaust pressure is maintained for a certain period of time. The integrated air amount GVOL is a characteristic value representing a period in which sufficient exhaust pressure is continuously generated, that is, a period in which the relationship of Ga> G is established. Further, V shown in FIGS. 7B and 8B is a determination amount for determining whether or not the period is sufficient. Therefore, when the establishment of GVOL> V is recognized, it can be ensured that a sufficient amount of exhaust gas is mixed in the atmospheric layer 18 on the condition that a sensor crack has occurred.

  FIG. 7C and FIG. 8C show a fuel cut state. In the example shown in FIG. 7, the intake air amount Ga exceeds the determination value G at time t1, and the integrated air amount GVOL exceeds the determination amount V at time t2. Thereafter, the throttle valve is suddenly closed, and GVOL is reset to zero at time t3 because Ga falls below G. Then, after a short delay time Tf, fuel cut is started at time t4.

  According to the example shown in FIG. 7, a sufficiently high exhaust pressure is secured until time t3. In other words, in this example, until time t3, an environment in which exhaust gas enters the atmosphere layer 18 from the location of the sensor crack is prepared. When Ga falls below G after time t3, the exhaust pressure drops rapidly, and this time, an environment in which the gas in the atmospheric layer 18 is scavenged is established. However, if the delay time Tf from time t3 to time t4 when fuel cut is started is sufficiently short, a significant amount of exhaust gas remains in the atmosphere layer 18 at time t4. For this reason, in the case shown in FIG. 7, if the application of the reverse voltage is started simultaneously with the start of the fuel cut, the above assumption is established and the sensor crack can be detected.

  FIG. 8 shows an example in which the throttle valve is gently closed after the time t2. In this example, the fuel cut is started when a long delay time Tf has elapsed (time t4) after the intake air amount Ga falls below the determination value G at time t3. In the case shown in FIG. 8, the scavenging environment of the atmosphere layer 18 is established over a long period of time after the time t3 and before the start of the fuel cut, and the scavenging of the atmosphere layer 18 is sufficiently advanced. In this case, since the above assumption is broken at the start of fuel cut, a situation in which sensor cracks cannot be detected properly may occur.

  Further, even if GVOL> V is not satisfied in the first place prior to the fuel cut, the above assumption is not satisfied at the start of the fuel cut. Accordingly, in this case as well, the occurrence of sensor cracks cannot be accurately detected based on the comparison between the first reverse current i1 and the second reverse current i2.

  Therefore, in the present embodiment, prior to the fuel cut, the fuel cut is performed after a sufficiently short time after the cumulative air amount GVOL exceeds the determination amount G, and after the intake air amount Ga falls below the determination value G. The sensor crack detection is permitted only when both of the above are established.

  FIG. 9 is a timing chart for explaining the operation in the case where sensor crack detection is performed according to the above rules. Specifically, FIG. 9A shows changes in the intake air amount Ga. FIG. 9B shows a change in the integrated air amount GVOL. FIG. 9C shows a state of a gas replacement flag described later. FIG. 9D shows a change in the delay time Tf. FIG. 9E shows a fuel cut state.

  FIG. 9 shows an example in which the intake air amount Ga changes in the same manner as in the case shown in FIG. When the sensor crack has occurred, it can be determined that the exhaust gas has sufficiently entered the atmosphere layer 18 when the integrated air amount GVOL exceeds the determination amount V (time t2). As shown in FIG. 9C, the gas replacement flag is a flag that is turned ON at that time. Therefore, in the system of the present embodiment, if the gas replacement flag is ON, it can be recognized that there is a history of exhaust gas sufficiently entering the atmosphere layer 18.

  The delay time Tf is an elapsed time from when the exhaust pressure is lowered and the environment in which the atmosphere layer 18 is scavenged is prepared until the fuel cut is started. For this reason, as shown in FIG. 9D, the delay time Tf is incremented from time t3 when the intake air amount Ga falls below the determination value G to time t4 when the fuel cut is started.

  In this embodiment, the engine computer 30 has the gas replacement flag ON at the start of fuel cut, and the delay time Tf is equal to or shorter than the determination permission waiting time (hereinafter simply referred to as “determination time”) Ts. Determine whether. The determination time Ts is a time during which a significant amount of exhaust gas stays in the atmosphere layer 18 in a situation where the scavenging environment is in place. Therefore, when both of the above two conditions are satisfied, it can be determined that the exhaust gas is sufficiently mixed in the atmospheric layer 18.

  FIG. 9 shows an example in which these conditions are both established at the start of fuel cut. The system of the present embodiment permits detection of sensor cracks only in such a case. For this reason, according to the system of the present embodiment, it is possible to effectively prevent erroneous determination in an environment where exhaust gas is not sufficiently present in the atmospheric layer 18.

[Specific Processing in Second Embodiment]
FIG. 10 is a flowchart of a routine executed by the engine computer 30 in the present embodiment. In FIG. 10, steps 220 to 238 are substantially the same as steps 102 to 120 shown in FIG.

  In the routine shown in FIG. 10, first, it is determined whether or not the intake air amount Ga exceeds the determination value G (step 190). It is determined that this condition is not satisfied under a situation where Ga is maintained at a small value after the internal combustion engine is started.

  If it is recognized that Ga> G is not established, the integrated air amount GVOL is set to 0 (step 192). Next, it is determined whether or not the condition satisfaction flag is ON (step 194). The condition satisfaction flag is a flag that is set when a sensor crack detection condition is satisfied at the start of fuel cut. Immediately after starting the internal combustion engine, this flag is turned OFF by the initial process. In this case, it is determined in step 194 that the condition is not satisfied, and then it is determined whether the gas replacement flag is ON (step 196).

  The gas replacement flag is also turned off by the initial process immediately after starting the internal combustion engine. Therefore, in this case, it is determined in step 196 that the condition is not satisfied. When the above determination is made, the delay time Tf is then set to the maximum value (step 198). Thereafter, the current processing cycle is promptly terminated.

  If the intake air amount Ga has a sufficiently large value, it is determined in step 190 that Ga> G is satisfied. In this case, next, the integrated air amount GVOL is incremented (step 200). According to the processing described above, the integrated air amount GVOL can store the integrated amount of the intake air amount Ga generated while Ga> G is continuously established.

  Next, it is determined whether or not the integrated air amount GVOL exceeds the determination amount V (step 202). Immediately after Ga> G is established, the relationship of GVOL> V is not established, and it is determined in step 202 that the condition is not established. In this case, after the gas replacement flag is turned off, the current processing cycle is terminated.

  While the establishment of Ga> G is maintained, the process of step 202 is executed every time the routine shown in FIG. 10 is started. If Ga falls below G before GVOL> V is established, steps 192 to 198 are executed, whereby all settings are returned to the initial state again. On the other hand, if the relationship of Ga> G is maintained until GVOL> V is satisfied, it is determined in step 202 that the condition is satisfied. In this case, the gas replacement flag is turned on (step 206), and the delay time Tf is further set to 0 (step 208).

  If the intake air amount Ga falls below the determination value G after the above processing, it is determined in step 196 that the gas replacement flag is ON, following the processing in steps 192 and 194. In this case, the delay time Tf is incremented (step 210), and then it is determined whether the delay time Tf is shorter than the determination time Ts (step 212).

  The delay time Tf is set to 0 at the same time when the gas replacement flag is turned ON (see step 208 above). For this reason, Tf <Ts is satisfied when the process of step 212 is executed for the first time. In this case, it is next determined whether or not a fuel cut has been started (step 214).

  Until the start of the fuel cut is recognized, it is determined in step 214 that the fuel cut is OFF. In this case, after this, the condition satisfaction flag is turned off (step 216), and the current processing cycle is terminated.

  As long as the intake air amount Ga does not exceed the determination value G, the process of step 214 is repeated each time the routine shown in FIG. 10 is started until the delay time Tf reaches the determination time Ts. If the fuel cut is started before the delay time Tf reaches the determination time Ts, the condition of step 214 is satisfied, and the condition satisfaction flag is turned ON (step 218).

  Thereafter, substantially the same processing as steps 102 to 120 shown in FIG. 6 is executed. That is, individually, it is first determined whether the elapsed time from the fuel cut start time is equal to or less than the reverse voltage application time t (step 220).

  Immediately after the start of the fuel cut, the condition of step 220 is satisfied. In that case, next, a process is executed to apply a reverse voltage to the air-fuel ratio sensor 10 (step 222). Next, a process for acquiring the peak value of the reverse current as the first reverse current i1 is executed (step 224).

  When the routine shown in FIG. 10 is started again while the intake air amount Ga is below the determination value G, it is determined in step 194 that the condition satisfaction flag is ON. As a result, the processing after step 214 is executed unconditionally. Then, after the fuel cut is started, the processes of steps 220 to 224 are repeated until the reverse voltage application time t elapses.

  If the reverse voltage application time t elapses with the fuel cut being executed, the condition of step 220 is not satisfied. In this case, it is next determined whether the elapsed time after the start of the fuel cut is longer than the reverse voltage application period T and equal to or shorter than T + t (step 226).

  The above determination is denied until the elapsed time after the start of the fuel cut reaches the reverse voltage application period T. In this case, next, a process for applying a positive voltage to the air-fuel ratio sensor 10 is executed (step 228).

  On the other hand, after the elapsed time reaches the reverse voltage application period T and until T + t is exceeded, in step 226, the satisfaction of the condition is determined. In this case, first, a process for applying a reverse voltage is executed (step 230), and then a process for acquiring the peak value of the reverse current as the second reverse current i2 is executed (step 232).

  Until the elapsed time after the start of fuel cut exceeds T + t, the processing of steps 230 and 232 is repeated each time the routine shown in FIG. 10 is started. As a result, finally, the peak value of the reverse current generated until the elapsed time reaches T + t is stored as the second reverse current i2.

  In the routine shown in FIG. 10, following the process of step 232, it is determined whether the ratio (i2 / i1) of the second reverse current i2 to the first reverse current i1 is greater than or equal to the determination value R (step 234). . The determination value R is a value larger than 1.0 set to determine whether the absolute value of i2 is significantly larger than the absolute value of i1. Therefore, when the above condition is satisfied, it can be determined that the absolute value of the second reverse current i2 is significantly larger than the absolute value of the first reverse current i1. In this case, the engine computer 30 recognizes the presence of a sensor crack and makes an abnormality determination (step 236).

  On the other hand, if it is determined in step 234 that i2 / i1 ≧ R is not established, it can be determined that the second reverse current i2 and the first reverse current i1 are not significantly different. In this case, the presence of a sensor crack is denied and a normal determination is made (step 238).

  After the fuel cut starts, after the elapsed time exceeds T + t, every time the routine shown in FIG. Is applied. Thereafter, when the fuel cut is completed, the condition in step 214 is not satisfied, and in step 216, the condition satisfaction flag is reset to OFF.

  Thereafter, if the relationship of Ga> G is maintained, the process of step 210 (increment of Tf) is repeated every time the routine shown in FIG. 10 is started. As a result, when the delay time Tf reaches the determination time Ts, the condition of step 212 is not satisfied and the gas replacement flag is turned OFF (step 240). The initial state is restored by the above processing.

  According to the routine shown in FIG. 10, as described above, after the gas replacement flag is turned ON (see step 206), if the intake air amount Ga falls below the determination amount G, step 194 → until fuel cut is started. The process from 196 to 210 to 216 is repeated. If the fuel cut is started before the delay time Tf reaches the determination time Ts, sensor crack detection processing is performed by the processing from step 218 onward.

  On the other hand, if the fuel cut is not started before the delay time Tf reaches the determination time Ts, the process of step 240 is executed without executing the sensor crack detection process. Is restored. That is, according to the process shown in FIG. 10, the detection of the sensor crack is permitted only when the environment where exhaust gas should sufficiently remain in the atmospheric layer 18 is prepared at the start of the fuel cut. The detection can be prohibited. For this reason, according to the system of the present embodiment, it is possible to reliably avoid the inconvenience that the sensor crack is overlooked when the throttle valve is gently closed.

  In the above description, the determination time Ts is handled as a fixed value, but the time may be changed according to the operating state of the internal combustion engine. That is, after the intake air amount Ga falls below the determination value G (after the throttle valve is closed), scavenging in the atmospheric layer 18 progresses more rapidly as the exhaust pressure is lower. In a situation where the throttle valve is closed, the exhaust pressure is likely to be lowered (negative pressure) as the engine speed NE is higher. For this reason, the time during which sufficient exhaust gas remains in the atmospheric layer 18 becomes shorter as the engine speed NE is higher.

  FIG. 11 is an example of a map in which the determination time Ts is determined in relation to the engine speed NE based on the above tendency. When this map is used, the engine computer 30 is caused to set the determination time Ts when, for example, the condition of step 190 is not satisfied for the first time after the gas replacement flag is turned ON. In this case, the higher the engine speed NE, the shorter the delay time Tf in which detection of sensor cracks is allowed, and the determination accuracy regarding the presence or absence of sensor cracks can be further increased.

  In the second embodiment described above, it is determined based on the intake air amount Ga whether the environment in which the exhaust gas enters the atmosphere layer 18 is prepared and whether the atmosphere layer 18 is in an environment in which the atmosphere layer 18 is scavenged. However, the determination method is not limited to this. That is, these determinations may be made based on the exhaust pressure.

  Furthermore, in Embodiment 2 described above, the period during which sufficient exhaust pressure is generated is determined based on GVOL, but the determination method is not limited to this. That is, the determination may be made based on whether or not the environment in which the exhaust pressure is equal to or higher than a predetermined value has continued for a predetermined time.

  In the second embodiment described above, the engine computer 30 executes the processing of steps 218 to 238, so that the “failure detection means” in the first invention executes the processing of step 190. The “exhaust pressure determining means” in the sixth invention executes the process of step 202, and the “filling condition determining means” in the sixth invention executes the process of step 212, whereby the sixth invention. The “filling condition maintaining means” and the “execution condition determining means” in FIG.

It is sectional drawing for demonstrating the structure of the air fuel ratio sensor used in Embodiment 1 of this invention. It is a circuit diagram for demonstrating the structure of the engine computer 30 for driving the air fuel ratio sensor shown in FIG. It is a figure which shows the correlation with atmospheric pressure and a reverse current (absolute value). It is a figure which shows the correlation of the internal resistance (or sensor temperature) and reverse current of an air fuel ratio sensor. It is a timing chart for demonstrating the technique of the failure detection in Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. FIG. 5 is a timing chart for explaining an operation in which exhaust gas remains in the atmosphere when a sensor crack occurs, at the start of fuel cut. 6 is a timing chart for explaining an operation in which exhaust gas does not remain in the atmosphere layer at the start of fuel cut even when sensor cracking occurs. In Embodiment 2 of this invention, it is a timing chart for demonstrating operation | movement when the detection of a sensor crack is permitted. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a map of determination time Ts used in the modification of Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Air-fuel ratio sensor 16 Atmosphere layer formation member 18 Atmosphere layer 20 Electrolyte layer 22 Atmosphere side electrode 24 Exhaust side electrode 26 Diffusion resistance layer 30 Engine computer 32 Positive electrode terminal 34 Negative electrode terminal
i1 1st reverse current
i2 Second reverse current
t Reverse voltage application time
T Reverse voltage application cycle
R judgment value
Ga intake air volume
G judgment value
GVOL Integrated air volume
V judgment amount
Tf waiting time
Ts judgment waiting time (judgment time)

Claims (7)

A failure detection device for an exhaust gas sensor,
The exhaust gas sensor
An exhaust-side electrode exposed in the exhaust passage of the internal combustion engine;
An air layer forming member for forming an air layer in the exhaust passage;
An atmospheric electrode exposed to the atmospheric layer;
An electrolyte layer interposed between the exhaust-side electrode and the atmosphere-side electrode and enabling movement of oxygen ions between the two,
Reverse voltage applying means for applying a reverse voltage between the two so that the potential of the exhaust side electrode is higher than the potential of the atmosphere side electrode;
Reverse current detection means for detecting a reverse current flowing between the atmosphere side electrode and the exhaust side electrode in accordance with the application of the reverse voltage;
An environment switching means for switching between a polluted environment in which the air layer is contaminated with exhaust gas and a non-polluted environment in which the pollution is mitigated when cracks are present in the air layer forming member;
A failure detection means for detecting a failure of the exhaust gas sensor based on fluctuations in the reverse current caused by switching between the contaminated environment and the non-contaminated environment;
An exhaust gas sensor failure detection apparatus comprising: The failure detection means includes
First reverse current acquisition means for acquiring a reverse current detected in the contaminated environment as a first reverse current;
Second reverse current acquisition means for acquiring a reverse current detected in the non-polluted environment as a second reverse current;
Failure determination means for determining the exhaust gas sensor as a failure when the absolute value of the second reverse current is larger than the absolute value of the first reverse current;
The failure detection device for an exhaust gas sensor according to claim 1, comprising: Said failure determining means, the ratio of the second reverse current to the first reverse current (second reverse current / first reverse current), as a failure of the exhaust gas sensor when it is large determination value or more than 1.0 3. The exhaust gas sensor failure detection apparatus according to claim 2, wherein the determination is performed. Said failure determining means, the difference between the second reverse current and the first reverse current, according to claim 2, wherein the determining as a failure of the exhaust gas sensor if the determination value or more exhaust gas sensors Fault detection device. The environment switching means includes fuel cut means for stopping fuel injection to the internal combustion engine,
The contaminated environment is an environment immediately after the fuel injection is stopped,
The exhaust gas sensor failure detection device according to any one of claims 1 to 4, wherein the non-polluting environment is an environment when fuel injection is stopped for a predetermined time. Exhaust pressure determination means for determining whether or not the exhaust pressure exceeds a pressure determination value;
If the period in which the exhaust gas pressure exceeds the pressure determination value exceeds the determination period, and determines the fill condition determining means and the exhaust gas-filled condition is satisfied,
Filling condition maintaining means for maintaining the establishment of the exhaust gas filling condition only until the filling maintenance time elapses after the exhaust pressure falls below the pressure determination value;
An execution condition determination unit that permits detection of the failure only when the exhaust gas filling condition is recognized at the start of fuel cut .
The exhaust gas-filled condition, when the sensor crack has occurred, the atmospheric layer, claim exhaust gas in an amount sufficient for detection of the sensor crack is characterized in terms der Rukoto it can be determined that the mixed 5 The failure detection device for an exhaust gas sensor as described. A failure detection device for an exhaust gas sensor,
The exhaust gas sensor
An exhaust-side electrode exposed in the exhaust passage of the internal combustion engine;
An air layer forming member for forming an air layer in the exhaust passage;
An atmospheric electrode exposed to the atmospheric layer;
An electrolyte layer interposed between the exhaust-side electrode and the atmosphere-side electrode and enabling movement of oxygen ions between the two,
Reverse voltage applying means for applying a reverse voltage between the two so that the potential of the exhaust side electrode is higher than the potential of the atmosphere side electrode;
Reverse current detection means for detecting a reverse current flowing between the atmosphere side electrode and the exhaust side electrode in accordance with the application of the reverse voltage;
A contaminated environment forming means for creating a contaminated environment in which the air layer is contaminated with exhaust gas when cracks are present in the air layer forming member;
If the contaminated environment under reverse current detected by is a value between the judged value and 0 positioned between the reverse current generated in the reverse current and abnormal occurring normal, as a failure of the exhaust gas sensor Failure determination means for determining;
An exhaust gas sensor failure detection apparatus comprising:

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