JP2006057461A - Irregularity detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an irregularity detection device capable of determining irregularity of an internal combustion engine without an error. <P>SOLUTION: Accumulation of oxygen occlusion quantity Cmax is performed (step 106) when output of an oxygen sensor is rich or lean. In a step 108, it is determined whether a condition where time during which state of high intake air quantity under which intake air quantity Ga is high continues is X sec or longer and reduction quantity of intake air quantity is Y g or more is satisfied or not. In this embodiment, temperature of a catalyst is regarded as high if high intake air quantity state continues X sec or longer. Also, irregularity determination is prohibited to prevent wrong determination if temperature of the catalyst is high and reduction quantity of intake air quantity is Y g or more. Consequently, simultaneous satisfaction of two conditions means necessity of prohibition of irregularity determination in this step, oxygen occlusion quantity is cleared and irregularity determination is prohibited in a step 114. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an abnormality detection device for a vehicle, and more particularly to a technique suitable for detecting an abnormality of an internal combustion engine.

Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-19542, a system is known that includes an air-fuel ratio sensor upstream of a catalyst disposed in an exhaust passage of an internal combustion engine and an oxygen sensor downstream of the catalyst. ing. This system calculates the oxygen storage capacity of the catalyst by integrating the amount of oxygen flowing into the catalyst during a period in which the oxygen sensor generates a rich output and the air-fuel ratio sensor generates a lean output. Thereafter, when the calculated oxygen storage capacity exceeds the maximum oxygen storage capacity of the catalyst, it has a function of determining abnormality of the oxygen sensor.
JP 2004-19542 A JP-A-11-218045

  By the way, the oxygen storage capacity of the catalyst tends to be higher as the catalyst temperature is higher. Here, the catalyst temperature becomes high when the internal combustion engine is operating at a high load. At this time, the temperature of the exhaust gas discharged from the internal combustion engine is high. Therefore, in this case, the catalyst temperature tends to be high. The oxygen storage capacity increases as the temperature of the catalyst increases. For this reason, when the amount of intake air is large, the oxygen storage capacity tends to be large. On the other hand, when the intake air amount is large, a so-called “blow-through” state is likely to occur in the exhaust gas passing through the catalyst. In the above-described system for calculating the oxygen storage capacity based on the output of the oxygen sensor downstream of the catalyst, a value smaller than the actual oxygen storage capacity of the catalyst is calculated under conditions where blow-through occurs. Therefore, according to the above-described conventional apparatus, in a region where the intake air amount is large, the oxygen storage capacity calculated by the increase in the oxygen storage capacity due to the temperature and the decrease in the oxygen storage capacity due to the blow-through. Is decided.

  Here, when the operating state of the internal combustion engine shifts to a low load after the intake air amount is large, the intake air amount is reduced and the effect of “blow-through” is reduced. Since the catalyst temperature does not drop rapidly, the oxygen storage capacity of the catalyst is calculated to be the largest immediately after the operating state shifts to a low load. At this time, the above-described system detects that the calculated oxygen storage capacity exceeds the maximum oxygen storage capacity, and therefore, even if there is no abnormality in the oxygen sensor, the abnormality is determined. .

  On the other hand, there is also a system for determining deterioration of the catalyst using the calculated oxygen storage capacity. This system has a function of determining that the purification capacity of the catalyst is lowered when the calculated oxygen storage capacity is abnormally smaller than the maximum oxygen storage capacity of the catalyst. In such a system, when the catalyst temperature is high and a low-load operation state occurs, the catalyst that should be determined as abnormal is overlooked.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an abnormality detection device that can determine an abnormality of an internal combustion engine without making an error.

  In order to achieve the above object, according to a first aspect of the present invention, in the abnormality detection device, catalyst temperature determination means for determining whether or not a temperature of a catalyst disposed in an exhaust passage of the internal combustion engine is higher than a reference temperature, and the internal combustion engine Intake air amount detection means for detecting the amount of air sucked into the engine, and oxygen storage capacity calculation means for calculating the oxygen storage capacity of the catalyst by integrating the excess and deficiency of oxygen in the exhaust gas flowing into the catalyst An anomaly detection means for detecting an anomaly based on the oxygen storage capacity; an anomaly detection for prohibiting the operation of the anomaly detection means when the catalyst temperature is higher than a reference temperature and the air amount is less than a determination flow rate; And a prohibiting means.

  In a second aspect based on the first aspect, the catalyst temperature determination means is configured such that the catalyst temperature is higher than the reference temperature when the air amount detected by the intake air amount detection means continues to be higher than a predetermined value. It includes a high intake air amount duration determination unit that determines that the intake air amount is high.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the exhaust air / fuel ratio upstream of the catalyst is leaned in response to the output of the oxygen sensor located downstream of the catalyst changing from a rich output to a lean output. In addition, the active air-fuel ratio is changed from the rich air-fuel ratio to the lean air-fuel ratio by changing the air-fuel ratio from the rich air-fuel ratio to the rich air-fuel ratio. Active oxygen ratio control means for executing fuel ratio control, wherein the oxygen storage capacity calculating means is configured to maintain the output of the oxygen sensor at a rich output or a lean output during the execution of the active air fuel ratio control. A means for calculating an oxygen storage capacity of the catalyst by accumulating oxygen excess / deficiency in the exhaust gas flowing into the catalyst; Means for detecting an abnormality when the storage capacity exceeds the maximum oxygen storage amount of the catalyst, and the abnormality detection prohibiting means is configured such that the catalyst temperature is higher than a reference temperature and the air amount is higher than a determination flow rate. In the case where the amount is small, the oxygen storage capacity calculating means includes means for setting the value of the oxygen storage capacity calculated to zero.

  According to the first aspect of the present invention, it is possible to prohibit abnormality detection of the internal combustion engine when the catalyst temperature is high and the amount of air taken into the internal combustion engine is small. Under the above condition, the oxygen storage capacity becomes larger than the normal value. According to the present invention, it is possible to prevent erroneous determination of the abnormality detection device by prohibiting determination in that state.

  According to the second invention, it is possible to accurately determine whether or not the temperature of the catalyst exceeds the determination value based on whether or not the state where the intake air amount is high continues.

  According to the third aspect of the invention, by executing active air-fuel ratio control, the actual oxygen storage amount is increased or decreased, and the oxygen storage amount can be calculated momentarily by integrating the excess and deficiency amounts of oxygen. . Under the situation where the output of the oxygen sensor does not reverse, the oxygen storage amount becomes excessive, and an abnormality can be determined when the value exceeds the determination value. When the catalyst temperature and the intake air amount satisfy the conditions for prohibiting abnormality determination, the value of the oxygen storage capacity is set to zero at that time. In this case, the oxygen storage capacity can be prevented from exceeding the determination value, and as a result, abnormality detection can be prohibited.

Embodiment 1 FIG.
[Hardware Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining the configuration of an air-fuel ratio control apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, the apparatus of this embodiment includes an upstream catalyst (S / C) 12 and a downstream catalyst (U / F) 14 disposed in an exhaust passage 10 of the internal combustion engine. The upstream catalyst 12 and the downstream catalyst 14 are all three-way catalysts that can simultaneously purify CO, HC, and NOx.

  An air-fuel ratio sensor 16 and an oxygen sensor 18 are disposed upstream and downstream of the upstream catalyst 12, respectively. The air-fuel ratio sensor 16 is a sensor that emits a substantially linear output with respect to the air-fuel ratio A / F of the exhaust gas flowing into the upstream catalyst 12. On the other hand, the oxygen sensor 18 is a sensor that suddenly changes the output depending on whether the exhaust gas flowing out from the upstream catalyst 12 is rich or lean with respect to the stoichiometric air-fuel ratio.

  The output of the air-fuel ratio sensor 16 and the output of the oxygen sensor 18 are respectively supplied to an ECU (Electronic Control Unit) 20. The ECU 20 is further connected to an air flow meter 22, a rotation speed sensor 24, a fuel injection valve 26, and the like. The air flow meter 22 is a sensor that detects an intake air amount Ga of the internal combustion engine. The rotational speed sensor 24 is a sensor that generates an output corresponding to the engine rotational speed Ne. The fuel injection valve 26 is an electromagnetic valve for injecting fuel into the intake port of the internal combustion engine.

[Control in Embodiment 1]
(Active control)
FIG. 2 is a timing chart for explaining active control in the first embodiment of the present invention. Specifically, FIG. 2 (A) is a waveform showing the vehicle speed, FIG. 2 (B) shows the change in the intake air amount, and FIG. 2 (C) and FIG. 2 (D) are the air-fuel ratio sensors. 16 and the output change of the oxygen sensor 18 are shown. FIG. 2 (E) shows the change in the amount of oxygen stored in the upstream catalyst 12, and FIG. 2 (F) shows the value of the oxygen storage capacity Cmax integrated by the ECU 20 based on the value in FIG. 2 (E). ing.

  During execution of active control, first, the pre-catalyst air-fuel ratio is maintained at a predetermined rich air-fuel ratio or lean air-fuel ratio. In FIG. 2C, the portion where the output of the air-fuel ratio sensor 16 is a rich air-fuel ratio indicates a state where the pre-catalyst air-fuel ratio is maintained at the rich air-fuel ratio. When the pre-catalyst air-fuel ratio is maintained at the rich air-fuel ratio, the upstream catalyst 12 releases the stored oxygen to oxidize unburned components (HC, CO) in the exhaust gas. During the period in which the stored oxygen remains in the upstream catalyst 12, the exhaust gas purified to the stoichiometric air-fuel ratio flows downstream. Accordingly, the post-catalyst air-fuel ratio is maintained substantially at the stoichiometric air-fuel ratio during that time.

  As a result of maintaining the pre-catalyst air-fuel ratio rich, when all of the stored oxygen in the upstream catalyst 12 is consumed, thereafter, rich exhaust gas containing unburned components begins to flow downstream of the upstream catalyst 12. When rich exhaust gas starts to flow out downstream of the upstream catalyst 12, the sensor output of the oxygen sensor 18 changes from lean output to rich output. In FIG. 2D, in the portion where the sensor output of the oxygen sensor 18 is suddenly changing from the lean output to the rich output, all the stored oxygen in the upstream catalyst 12 is consumed, and then the output of the oxygen sensor 18 is lean. It shows a state in which the output is inverted to the rich output.

  When the ECU 20 determines that the output of the oxygen sensor 18 has changed to a rich output, it determines that the stored oxygen of the upstream catalyst 12 has been used up at that time. Then, the ECU 20 changes the ratio of the fuel injection amount to the intake air amount Ga so that the pre-catalyst air-fuel ratio reverses lean. As a result, as shown in FIG. 2C, the pre-catalyst air-fuel ratio is reversed from rich to lean.

  Thereafter, the pre-catalyst air-fuel ratio is maintained lean while the active control is being executed. During the period in which the pre-catalyst air-fuel ratio is maintained lean, the upstream catalyst 12 continues to store oxygen until the oxygen storage capacity is fully stored. Then, while the upstream catalyst 12 is storing excess oxygen in the exhaust gas, the purified exhaust gas is discharged downstream of the upstream catalyst 12, and thereafter, the oxygen having the full oxygen storage capacity is stored in the upstream catalyst 12. Lean exhaust gas containing oxygen begins to flow downstream.

  In FIG. 2D, the portion where the output of the oxygen sensor 18 begins to change from the rich output to the lean output indicates that lean exhaust gas has started to flow out downstream of the upstream catalyst 12. During the execution of the active control, the ECU 20 receives the output reversal of the oxygen sensor 18 and reverses the pre-catalyst air-fuel ratio to a rich state again. Thereafter, as long as the execution of the active control is continued, the above-described process, that is, the process of forcibly reversing the pre-catalyst air-fuel ratio in response to the output reversal of the oxygen sensor 18 is repeatedly performed.

  During the execution of the active control, the sensor output of the oxygen sensor 18 is inverted from the lean output to the rich output when all the oxygen in the upstream catalyst 12 is consumed, as described above. The sensor output is inverted from the rich output to the lean output when the upstream catalyst 12 occludes oxygen to the full oxygen storage capacity Cmax. Therefore, after the sensor output of the oxygen sensor 18 is inverted from the lean output to the rich output (the pre-catalyst air-fuel ratio is changed to the lean air-fuel ratio after receiving this inversion), the sensor output is inverted from the rich output to the lean output. Until then, if the oxygen excess in the exhaust gas flowing into the upstream catalyst 12 is integrated, the oxygen storage capacity Cmax of the upstream catalyst 12 can be obtained. Similarly, after the sensor output of the oxygen sensor 18 is inverted from the rich output to the lean output (after this inversion, the pre-catalyst air-fuel ratio is changed to the rich air-fuel ratio thereafter), the sensor output is inverted from the lean output to the rich output. In the meantime, the oxygen storage capacity Cmax of the upstream catalyst 12 can be obtained by integrating the oxygen deficiency in the exhaust gas flowing into the upstream catalyst 12.

(Calculation method of oxygen storage capacity Cmax)
Hereinafter, a method for calculating the oxygen storage capacity Cmax of the upstream catalyst 12 will be described.

When the pre-catalyst air-fuel ratio A / F is lean, the oxygen excess amount ΔOSA in the exhaust gas flowing into the upstream catalyst 12 can be obtained by the following equation.
ΔOSA = (A / F−A / Fstoichi) × fuel injection amount × α (1)
(However, A / Fstoichi is the stoichiometric air-fuel ratio, and α is the ratio of oxygen in the air.)
On the other hand, when the pre-catalyst air-fuel ratio A / F is rich, the oxygen deficiency ΔOSA in the exhaust gas flowing into the upstream catalyst 12 can be obtained by the following equation.
ΔOSA = (A / Fstoichi−A / F) × fuel injection amount × α (2)
Therefore, if | A / F−A / Fstoichi | = ΔA / F, the exhaust gas flowing into the upstream catalyst 12 is distinguished without distinguishing when the pre-catalyst air-fuel ratio A / F is rich or lean. The excess / deficiency amount ΔOSA of oxygen in the gas can be expressed by the following equation.
ΔOSA = ΔA / F × fuel injection amount × α (3)
The ECU 20 clears the oxygen storage amount OSA every time the output of the oxygen sensor 18 is inverted, and thereafter calculates the integrated value of the oxygen excess / deficiency ΔOSA as the oxygen storage amount OSA as shown in the following equation.
OSA = ΣΔOSA
= Σ (ΔA / F × fuel injection amount × α) (4)
The waveform of OSA shown in FIG. 2 (E) shows a change in the oxygen storage amount OSA calculated by the ECU 20 in this way.

  The output of the oxygen sensor 18 is inverted either when all the oxygen in the upstream catalyst 12 is released or when the oxygen is fully stored in the upstream catalyst 12. In the former case, thereafter, the oxygen storage capacity Cmax of the upstream catalyst 12 is obtained by accumulating the excess oxygen amount ΔOSA until oxygen is fully stored in the upstream catalyst 12 and the output of the oxygen sensor 18 is reversed again. it can. In the latter case, the oxygen storage capacity Cmax of the upstream catalyst 12 is obtained by integrating the oxygen deficiency ΔOSA until all the oxygen in the upstream catalyst 12 is released and the output of the downstream oxygen sensor 34 is reversed again. be able to. That is, in any case, when the output of the oxygen sensor 18 is reversed, the oxygen storage amount OSA calculated at that time can be recognized as the oxygen storage capacity Cmax of the upstream catalyst 12. Therefore, the ECU 20 calculates the oxygen storage amount OSA by the above method, and when the output of the oxygen sensor 18 is reversed, prior to clearing the oxygen storage amount OSA at that time, the ECU 20 calculates the value of the oxygen storage amount OSA. It is assumed that the storage capacity is Cmax. The waveform shown in FIG. 2F shows the change in the oxygen storage capacity Cmax calculated by the ECU 20 in this way.

(Abnormality judgment)
When the oxygen storage capacity Cmax is calculated by the method as described above, the abnormality of the oxygen sensor 18 or the upstream catalyst 12 can be determined using this value. Hereinafter, the abnormality determination method will be described.

  During the execution of the active control, the target air-fuel ratio inversion command is issued in response to the inversion of the output of the oxygen sensor 18. Therefore, when the output of the oxygen sensor 18 is not reversed, the target air-fuel ratio is also maintained at the rich target value. The ECU 20 tries to obtain the oxygen storage capacity Cmax of the upstream catalyst 12 by calculating the oxygen excess / deficiency in the exhaust gas flowing into the upstream catalyst 12, but in this case, the above integration is unreasonably long. Therefore, the calculated oxygen storage capacity Cmax is an unreasonably large value. Therefore, in the present embodiment, when the calculated value of the oxygen storage capacity Cmax becomes unreasonably large as the active control is executed, the ECU 20 determines that the oxygen sensor 18 is abnormal at that time. Yes.

(Phenomenon caused by change in intake air volume)
In this embodiment, abnormality determination of the oxygen sensor 18 and the upstream catalyst 12 is performed using the method described above. However, when abnormality determination is performed by such a method, there is a situation in which an erroneous determination occurs. is there. A situation where an erroneous determination occurs will be described with reference to FIG. As shown in FIG. 2, the vehicle equipped with the abnormality detection device of the present embodiment travels while maintaining the speed shown in FIG. 2A while performing active control. At this time, the value of the intake air amount Ga sucked into the internal combustion engine is 40 (FIG. 2B).

Triggered by the deceleration of the vehicle speed at time _{t 1,} the value of the intake air amount Ga is reduced to 8 (FIG. 2 (A), (B) ). Immediately after this, the outputs of the air-fuel ratio sensor 16 and the oxygen sensor 18 change as shown in FIGS. 2C and 2D, respectively, and the amplitude of the oxygen storage amount OSA also increases (FIG. 2E). . Further, as the oxygen storage amount OSA changes, the value of the oxygen storage capacity Cmax also increases (FIG. 2 (F)).

  In such a situation, it is determined that the value of the oxygen storage capacity Cmax is unreasonably large, so that the abnormality determination is performed even if the oxygen sensor 18 is not abnormal. Even when the upstream catalyst 12 has an abnormality, the value of the oxygen storage capacity Cmax is not unduly reduced, so that the abnormality determination is neglected. Details of the reason why such erroneous determination occurs will be described below.

  When the vehicle is traveling at a high speed as shown in FIG. 2A, the value of the intake air amount Ga is large and the exhaust gas is also hot. In general, the temperature characteristics of the catalyst tend to activate the purification capacity as the temperature increases. Accordingly, if the value of the intake air amount Ga is large, it can be said that the oxygen storage capacity Cmax of the upstream catalyst 12 becomes a large value.

  However, when the value of the intake air amount Ga is large, a so-called “blow-through” phenomenon occurs in the upstream catalyst 12. “Blow-through” is a phenomenon in which exhaust gas that should be purified by the upstream catalyst 12 flows into the downstream catalyst 14 without being purified. This is a phenomenon that generally occurs when the value of the intake air amount Ga is large. The timing chart shown in FIG. 3 is a diagram for explaining the effect of blow-by on the calculated value of the oxygen storage capacity Cmax. More specifically, FIGS. 3A and 3C show changes in the output values of the air-fuel ratio sensor 16 and the oxygen sensor 18, respectively, and FIG. 3B shows the oxygen storage amount.

  In FIG. 3, the ECU 20 performs active control based on the output value of the oxygen sensor 18. Further, it is in a high-load operation state in which the value of the intake air amount Ga is large. The waveforms shown by the solid lines in FIGS. 3A and 3C show the output values of the air-fuel ratio sensor 16 and the oxygen sensor 18 without considering the effect of “blow-through”. On the other hand, the waveforms shown by the broken lines in FIGS. 3A and 3C show the output values of the air-fuel ratio sensor 16 and the oxygen sensor 18 in consideration of the effect of “blow-through”. First, the value of Cmax when “blow-through” is not considered will be described.

The ECU 20 starts control when the air-fuel ratio sensor 16 is rich and the oxygen sensor 18 is lean (FIGS. 3A and 3C). Oxygen sensor 18 at time t ₁ is accompanied to the inverted output to the rich (Fig. 3 (C)), the output of the air-fuel ratio sensor 16 is controlled to be lean (Figure 3 (A)). The output of the oxygen sensor 18 at time t ₂ is in association with the inverted in lean (Figure 3 (C)), the output of the air-fuel ratio sensor 16 is controlled to be rich (Figure 3 (A)). The change in the oxygen storage amount of the upstream catalyst 12 when performing the above control has the waveform shown in FIG. Further, when the oxygen storage capacity Cmax of the upstream catalyst 12 at this time is expressed by Cmax1, the height corresponding to the value of Cmax1 is the height shown in FIG.

On the other hand, when “blow-through” is considered, even if the ECU 20 controls the air-fuel ratio sensor 16 to maintain a rich output, the exhaust gas that has blown off the upstream catalyst 12 passes through the oxygen sensor 18. Therefore, the output value of the oxygen sensor 18 has a waveform in which the output is richly inverted at time t ₁ ′ earlier than time t ₁ , as indicated by a broken line in FIG. Further, it occurs similar phenomenon when controlling to keep the air-fuel ratio sensor 16 in the lean output, such as output of the oxygen sensor 18, an output at an earlier time t _{2 'from} the time t ₂ is reversed to the lean It becomes a waveform. In the upstream catalyst 12, oxygen necessary for purification of exhaust gas remains in the catalyst by the amount of exhaust gas blown through the downstream catalyst 14. Therefore, the change in the oxygen storage amount is shown in FIG. It becomes a waveform. When the oxygen storage capacity Cmax of the upstream catalyst 12 at this time is expressed by Cmax2, the value corresponding to the value of Cmax2 is the height shown in FIG.

  From the above, the oxygen storage capacity Cmax when the intake air amount Ga is large is offset by the effect of blow-through by the oxygen storage capacity Cmax of the catalyst activated by high temperature (corresponding to Cmax1 shown in FIG. 3B). Thus, it can be seen that it is almost equal to Cmax during normal operation (see Cmax2 shown in FIG. 3B). On the other hand, when there is no effect of blow-through, that is, when the temperature is high and the intake air amount Ga is small, the oxygen storage capacity Cmax of the catalyst (corresponding to Cmax1 shown in FIG. 3B) is the value during normal operation. It can be seen that a larger value is measured compared to Cmax.

  Here, as previously shown in FIG. 2, when the intake air amount Ga suddenly decreases from a high state by an operation such as suddenly reducing the vehicle speed, the catalyst is a high temperature catalyst and the intake air amount Ga. The above condition that is small is established. In such a situation, as shown in FIG. 3, the oxygen storage capacity Cmax becomes a larger value than usual. At this time, the above-described erroneous detection of abnormality detection occurs. Therefore, in the present embodiment, the abnormality determination is prohibited under the condition that the catalyst temperature is high and the intake air amount Ga is small. The method will be described below.

(Abnormality judgment control)
FIG. 4 shows a flowchart of a control routine executed by the ECU 20 in order to realize the above function. In the present embodiment, a description will be given of a mode in which the abnormality determination of the oxygen sensor 18 is prohibited by assuming that the catalyst is at a high temperature because the state where the intake air amount Ga is large continues for a long time.

  In the routine shown in FIG. 4, it is first determined whether or not active control is being performed (step 100). If it is determined that the active control is not performed, the process of step 100 is repeated again. On the other hand, if it is determined that the active control is being performed, then the output of the oxygen sensor is read (step 102).

  When the output of the oxygen sensor 18 is read, it is next determined whether or not the output of the oxygen sensor is 0.59 (V) or more or 0.21 (V) or less (step 104). When the output of the oxygen sensor 18 is 0.59 (V) or more, it is determined that the output is rich, and the process proceeds to step 106. On the other hand, if it is 0.21 (V) or less, it is determined that the output is lean, and the process proceeds to step 106 in the same manner. On the other hand, if the output is greater than 0.21 (V) and less than 0.59 (V), the process proceeds to step 100.

  In step 106, the oxygen storage amount OSA is integrated. Cmax can be calculated by combining step 104 and step 106. Specifically, by integrating the oxygen storage amount OSA from when the output of the oxygen sensor 18 becomes rich until it is inverted to a lean output, or from when it becomes lean to when it is inverted to a rich output, the oxygen sensor 18 is integrated. When the output of 18 is inverted, the oxygen storage capacity Cmax can be obtained. When the accumulation of the oxygen storage amount OSA is completed, the process proceeds to step 108.

  In step 108, the condition that the time of the high intake air amount state in which the intake air amount Ga is high continues for X (sec) or more and the decrease amount of the intake air amount is Y (g) or more is satisfied. It is determined whether or not. In the present embodiment, as described above, the catalyst is regarded as having a high temperature because the state of the high intake air amount continues for X (sec) or more. Further, when the catalyst is at a high temperature and the amount of decrease in the intake air amount is Y (g) or more, abnormality determination is prohibited in order to prevent erroneous determination. Therefore, seeing the two conditions at the same time in this step indicates that the abnormality determination needs to be prohibited, and the processing is shifted to step 114. On the other hand, if at least one of the two conditions is not satisfied in this step, it indicates that it is not necessary to prohibit the abnormality determination, and the process proceeds to step 110, where normal abnormality determination is performed.

  In step 114, the oxygen storage amount is cleared. The process of this step is a process for prohibiting the abnormality determination of the oxygen sensor 18 performed when the oxygen storage amount OSA calculated in the previous step 106 exceeds the normal oxygen storage amount. By clearing the oxygen storage amount in this step, OSA becomes a value smaller than the normal oxygen storage amount, so that abnormality detection is not performed. When the process of clearing the oxygen storage amount is completed, the process is transferred to step 100 again.

  On the other hand, when performing normal abnormality determination, it is determined in step 110 whether or not the oxygen storage amount OSA is 1.2 (g) or more. When the oxygen storage amount OSA is 1.2 (g) or more, it is determined that an abnormality has occurred in the oxygen sensor 18 (step 112), and this routine is terminated as it is. On the other hand, if it is less than 1.2 (g), it is determined that there is no abnormality in the oxygen sensor 18, and the process proceeds to step 100.

  By performing the processing as described above, it is possible to inhibit the abnormality detection of the oxygen sensor 18 in a state where the catalyst temperature is high and the intake air amount is small. Thereby, erroneous determination of abnormality detection can be prevented, and accurate abnormality detection can always be performed.

  In the present embodiment, the “oxygen storage capacity calculating means” is executed by executing step 106, the “catalyst temperature determining means” and the “intake air amount detecting means” are executed by executing step 108, and the step 110 is executed. Thus, the “abnormality detection means” can be realized, and the “abnormality detection prohibition means” can be realized by performing the steps 106, 108 and 114.

  In this embodiment, the time during which the high intake air amount continues is used to determine the catalyst temperature, which is a condition for prohibiting abnormality detection. For example, the temperature of the catalyst is directly determined using a temperature sensor or the like. May be.

  Further, in this embodiment, the oxygen sensor 18 is a target of abnormality determination, but it can also be used for abnormality determination of the upstream catalyst 12. Abnormality in the purification capacity of the catalyst is determined when the oxygen storage capacity Cmax is abnormally small compared to the maximum oxygen storage amount of the catalyst, but Cmax is large when the high temperature catalyst and the intake air amount Ga are small. Therefore, it is difficult to determine abnormality of the catalyst. However, if the method of prohibiting abnormality detection according to this embodiment is used, it is possible to reliably determine abnormality of the catalyst that should be determined to be abnormal.

It is a figure for demonstrating the structure of embodiment suitable for this invention. It is a timing chart explaining the contents of control performed in an embodiment suitable for the present invention. It is a timing chart explaining the contents of control performed in an embodiment suitable for the present invention. It is a flowchart explaining the control content performed in embodiment suitable for this invention.

Explanation of symbols

10 Exhaust passage 12 Upstream catalyst (S / C)
14 Downstream catalyst (U / F)
16 Air-fuel ratio sensor 18 Oxygen sensor 20 ECU (Electronic Control Unit)
22 Air flow meter 24 Rotation speed sensor 26 Fuel injection valve

Claims (3)

Catalyst temperature determining means for determining whether the temperature of the catalyst disposed in the exhaust passage of the internal combustion engine is higher than a reference temperature;
Intake air amount detection means for detecting the amount of air sucked into the internal combustion engine;
An oxygen storage capacity calculating means for calculating the oxygen storage capacity of the catalyst by integrating the oxygen excess / deficiency in the exhaust gas flowing into the catalyst;
An abnormality detecting means for detecting an abnormality based on the oxygen storage capacity;
An abnormality detection prohibiting means for prohibiting the operation of the abnormality detecting means when the catalyst temperature is higher than a reference temperature and the air amount is less than a determination flow rate;
An abnormality detection device comprising:   The catalyst temperature determination means is a high intake air amount duration determination means for determining that the catalyst temperature is higher than the reference temperature when the state in which the air amount detected by the intake air amount detection means is higher than a predetermined value continues. The abnormality detection device according to claim 1, comprising: In response to the output of the oxygen sensor located downstream of the catalyst changing from rich output to lean output, the exhaust air / fuel ratio upstream of the catalyst is changed from lean air / fuel ratio to rich air / fuel ratio, and the output of the oxygen sensor Active air-fuel ratio control means for performing active air-fuel ratio control for changing the exhaust air-fuel ratio upstream of the catalyst from the rich air-fuel ratio to the lean air-fuel ratio in response to the change from lean output to rich output,
The oxygen storage capacity calculating means calculates oxygen excess / deficiency in exhaust gas flowing into the catalyst during a period in which the output of the oxygen sensor is maintained at a rich output or a lean output during execution of the active air-fuel ratio control. Including a means for calculating the oxygen storage capacity of the catalyst by integrating,
The abnormality detecting means includes means for detecting an abnormality when the oxygen storage capacity exceeds a maximum oxygen storage amount of the catalyst; and
The abnormality detection prohibiting means is a means for setting the value of the oxygen storage capacity calculated by the oxygen storage capacity calculating means to zero when the catalyst temperature is higher than a reference temperature and the air amount is lower than the determination flow rate. The abnormality detection device according to claim 1 or 2, characterized by comprising:

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