JPH0916253A - Diagnostic device for exhaust gas purifying device - Google Patents

Abstract

PURPOSE: To prevent the deterioration of a catalyst from being misdecided owing to the leak to a by-pass passage side. CONSTITUTION: A control means 37 performs feedback control over an air fuel ratio on the basis of the output of an upstream-side oxygen sensor when exhaust gas is made to flow to a main passage 31a through a valve switching means 36 and the output of a downstream-side oxygen sensor when the exhaust gas is made to flow to a by-pass passage 31b. A decision means 39 decides whether or not the leak to the side of the by pass passage 31b is caused in a by-pass valve 33 only under the conditions where the deterioration of the catalyst 32 is not advanced on the basis of at least the downstream-side oxygen sensor output according to the decision result of a decision means 38, and a decision means 40 decides whether or not the deterioration of the catalyst 32 is caused on the basis of at least the downstream-side oxygen sensor unless there is the leak in the by-pass valve 33 to the by-pass passage 31b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diagnostic device for an engine exhaust purification system.

[0002]

2. Description of the Related Art Oxygen sensors are provided upstream and downstream of a three-way catalyst, the inversion frequency (or inversion period) of each oxygen sensor output is calculated, and the frequency ratio of the two is calculated according to the operating condition. It has been proposed to determine whether or not the catalyst has deteriorated by comparing it with a value (see Japanese Patent Laid-Open No. 3-57862).

Here, the principle of diagnosis is that the inversion frequency ratio of two oxygen sensor outputs changes according to the oxygen storage capacity of the catalyst, and that the oxygen storage capacity of the catalyst changes according to the degree of deterioration of the catalyst. Is used. By performing air-fuel ratio feedback control based on the output of the upstream oxygen sensor, the exhaust air-fuel ratio is reversed when the exhaust air-fuel ratio changes periodically, such as becoming rich or lean at a specified frequency. The frequency matches the reversal frequency of the upstream oxygen sensor output.
In this case, if the catalyst is fresh, the oxygen storage capacity is large, so the fluctuation of the exhaust air-fuel ratio is suppressed downstream of the catalyst, and the reversal frequency of the downstream oxygen sensor output becomes extremely small. On the other hand, when the catalyst deteriorates, the oxygen storage capacity of the catalyst decreases,
The inversion frequency of the downstream oxygen sensor output becomes large, and the inversion frequency of the downstream oxygen sensor output becomes substantially the same as the inversion frequency of the upstream oxygen sensor output when the oxygen storage capacity is completely absent. That is, the inversion frequency ratio HZRA
TE, HZRATE = inversion frequency of downstream oxygen sensor output /
Assuming the reversal frequency of the upstream oxygen sensor output, HZRATE is close to 0 when the catalyst is fresh, and approaches 1 as the catalyst deteriorates. By comparison, when HZRATE becomes equal to or higher than the determination reference value, it can be determined that the catalyst has deteriorated.

The reference value for determining the catalyst deterioration can be changed according to the operating condition which is determined by the load and the engine speed of the engine.

[0005]

By the way, an exhaust pipe is branched into a main passage and a bypass passage to install a catalyst in the main passage, and a bypass valve for switching the flow of exhaust gas between the main passage and the bypass passage is provided. , The bypass valve is controlled to switch so that the entire amount of the exhaust gas of the catalyst flows in the low exhaust temperature range and the entire amount of the exhaust gas flows in the bypass passage to prevent the deterioration of the catalyst due to the high exhaust temperature in the high exhaust temperature range. There are some (see Figure 1).

Even in such a configuration, in order to make the above deterioration determination, a downstream oxygen sensor is provided downstream of the confluence of the main passage and the bypass passage so that the catalyst is not deteriorated when the bypass passage is fully closed. Although it is determined whether or not it has occurred, in such a configuration, there is a possibility that a malfunction of the bypass valve may cause a misdiagnosis in the determination of catalyst deterioration.

[0007] For example, when the deterioration of the bypass valve is judged to be normal, it is assumed that the reverse frequency ratio HZRATE is slightly smaller than the judgment reference value (that is, the catalyst is not judged to be deteriorated), and the entire bypass passage is judged. When a part of the exhaust gas flows through the bypass passage due to a failure of the bypass valve when closed, the storage capacity of the catalyst is apparently reduced and the reversal frequency of the downstream oxygen sensor output increases, and the reversal frequency is correspondingly increased. Ratio HZRAT
Since E increases, if the judgment reference value is exceeded due to the increase in HZRATE, it will be erroneously diagnosed that the catalyst has deteriorated.

Therefore, the present invention is based on the downstream oxygen sensor output only under the condition that the deterioration of the catalyst does not proceed,
It is determined whether or not there is a failure in which exhaust gas leaks to the bypass passage side.The result of this judgment indicates that the catalyst will not deteriorate if and only if the condition for catalyst deterioration to proceed in the absence of a leakage failure to the bypass passage side. An object of the present invention is to prevent misdiagnosis due to a leakage failure to the bypass passage side when determining the deterioration of the catalyst by determining whether or not it has occurred.

[0009]

In the first invention, as shown in FIG. 9, the main passage 31a and the bypass passage 31b are branched upstream of the exhaust pipe 31, and the catalyst 32 is installed in the main passage 31a. A bypass valve 33 for switching the flow of the air between the main passage 31a and the bypass passage 31b is provided, while the upstream of the catalyst 32 and the main passage 31 and the bypass passage 31 are provided.
The oxygen sensors 34 and 35 are arranged on the downstream side of the confluence part of b, and the exhaust gas flows into the main passage 31a in a low exhaust temperature region, and the exhaust gas flows into the bypass passage 31b in a high exhaust temperature region. A means 36 for switching the valve 33, and based on the output of the oxygen sensor 34 on the upstream side when flowing the exhaust gas to the main passage 31a by the switching means 36, and a flow of the oxygen on the downstream side when flowing the exhaust gas to the bypass passage 31b. Means 37 for performing feedback control of the air-fuel ratio based on the sensor output, means 38 for determining whether the deterioration of the catalyst 32 does not progress or a condition for the deterioration progresses, and the catalyst based on the determination result. Whether the bypass valve 33 has a leakage failure toward the bypass passage 31b only under the condition that the deterioration of 32 does not proceed. And determining means 39 based at least on the downstream side oxygen sensor output out if the catalyst 32 when the leak failure has not occurred in the bypass valve 33 from the determination result to the bypass passage 31b side
And a means 40 for determining whether or not the catalyst 32 is deteriorated under the condition that the deterioration of (3) progresses at least based on the output of the downstream side oxygen sensor.

In a second aspect of the present invention, in the first aspect of the present invention, when the condition of deterioration of the catalyst 32 progresses, the catalyst 3 changes according to the history (for example, elapsed time) of the condition.
2 means for predicting the maximum deterioration state, at least means for calculating the current deterioration state of the catalyst 32 based on the output of the downstream oxygen sensor, and a comparison between the current deterioration state and the maximum deterioration state. Means for determining that the bypass valve 33 has a leakage failure to the bypass passage side when the deterioration state is larger than the maximum deterioration state.

According to a third aspect of the present invention, in the first or second aspect, the upstream oxygen sensor 34 is provided downstream of the bypass valve 33.

In a fourth aspect of the invention, in any one of the first to third aspects of the invention, the condition for determining a leakage failure to the bypass passage side is a steady state.

[0013]

[Operation] While a catalyst is installed in the main passage by branching into the main passage and the bypass passage upstream of the exhaust pipe, and a bypass valve for switching the exhaust flow between the main passage and the bypass passage is provided, the upstream side of the catalyst and the main passage are provided. An oxygen sensor is arranged downstream of the confluence part of the bypass passage, and the bypass valve is switched so that the exhaust gas flows to the main passage in the low exhaust temperature range and the exhaust gas flows to the bypass passage in the high exhaust temperature range. Therefore, in the case of the configuration in which the feedback control of the air-fuel ratio is performed based on the oxygen sensor output on the upstream side when flowing the exhaust gas to the main passage, and based on the oxygen sensor output on the downstream side when flowing the exhaust gas to the bypass passage, To determine whether the catalyst has deteriorated, the deterioration is determined when the bypass passage is fully closed. There is a possibility that misdiagnosis may occur the deterioration determination of the catalyst due to the failure of Subarubu. When part of the exhaust gas flows through the bypass passage due to a failure of the bypass valve when the bypass passage is fully closed, the storage capacity of the catalyst is apparently reduced and the output of the downstream oxygen sensor changes (inversion frequency increases). Therefore, an error will occur in the output of the downstream oxygen sensor by this change.

However, under the condition that the deterioration of the catalyst does not proceed, the output of the oxygen sensor on the downstream side changes only when the exhaust passage leaks into the bypass passage. Therefore, according to the first aspect of the present invention, it is possible to determine whether or not the leakage failure to the bypass passage side occurs based on the output of the downstream oxygen sensor only under the condition that the deterioration of the catalyst does not proceed. Further, from the result of the determination, when the condition for catalyst deterioration to proceed in the case where no leakage failure to the bypass passage side occurs, it is determined whether or not the catalyst has deteriorated. There will be no misdiagnosis due to leakage failure.

In the second aspect of the invention, the maximum deterioration state of the catalyst is predicted according to the history of the conditions under which the deterioration of the catalyst progresses, and is calculated based on this maximum deterioration state and the output of the downstream oxygen sensor. Comparing the current deterioration state with the current deterioration state, the current deterioration state does not become larger than the maximum deterioration state. Conversely, when the current deterioration state is larger than the maximum deterioration state, it can be determined that there is a leak failure to the bypass passage side, and in the second aspect, the catalyst deterioration progresses. However, it becomes possible to diagnose the leakage failure to the bypass passage side.

In the third invention, the upstream oxygen sensor 34
Is provided on the downstream side of the bypass valve 33, it is possible to prevent deterioration of the oxygen sensor 34 due to exposure to high temperature exhaust gas.

According to the fourth aspect of the invention, since the condition for determining the leakage failure to the bypass passage side is the steady state, the downstream oxygen sensor is compared with the case where the leakage failure to the bypass passage side is determined even during the transition. The output is stable and the judgment accuracy is improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, an exhaust pipe 3 connected to an exhaust manifold 2 is branched into a main passage 3a and a bypass passage 3b, and a front catalyst 4 made of a three-way catalyst is provided in the main passage. The rear catalyst 5, which is a three-way catalyst, is also installed downstream.

Immediately downstream of the branch point of the bypass passage 3b,
A bypass valve 6 for switching the flow of exhaust gas between the main passage 3a and the bypass passage 3b is provided, and this bypass valve 6 is driven by a drive device 7 (for example, a step motor or the like). In the bypass valve 6, the butterfly valve 6a on the main passage side and the butterfly valve 6b on the bypass passage side are substantially orthogonal to each other.
The bypass passage side valve 6b is fully closed when the main passage side valve 6a is fully opened, and conversely, the bypass passage side valve 6b is fully opened when the main passage side valve 6a is fully closed. . The bypass exchange valve 6 can also be provided at the branch portion or the merging portion of the bypass passage 3b and the main passage 3a.

In the control unit 21 composed of a microcomputer, a basic injection pulse width T described later
p, engine speed NRPM, cooling water temperature Tw
According to the above, the exhaust temperature Texh is predicted, and the front catalyst 4 is prevented from deteriorating when the total amount of exhaust of the front catalyst 4 is in the low exhaust temperature range such as low speed and low load, and when the high exhaust temperature range is in the high speed and high load. Therefore, the bypass valve 6 is switched and controlled so that the entire amount of exhaust gas flows through the bypass passage 3b.

Immediately upstream of the front catalyst 4, an upstream oxygen sensor 11 is provided downstream of the valve 6a, and a downstream oxygen sensor 12 is provided near the confluence of the main passage 3a and the bypass passage 3b.
Are respectively provided. The upstream oxygen sensor 11 is provided downstream of the valve 6a in order to prevent the sensor 11 from deteriorating due to the high exhaust temperature.

As signals from these two oxygen sensors 11 and 12, a sensor 13 for detecting the engine coolant temperature Tw, an air flow meter 14, a signal for each unit angle of the crank angle and a reference position signal (Ref signal) are output. Is input to the control unit 21 together with a signal from the crank angle sensor 15, which controls the intake air amount Qa and the engine speed NRPM.
The basic injection pulse width Tp is calculated from the fuel injection pulse width Tp, and the fuel injector 22 installed in the intake port is opened in synchronization with the engine rotation to inject fuel for a time corresponding to the basic injection pulse width Tp. The air-fuel ratio feedback correction coefficient α is calculated so that is within a narrow range centered on the stoichiometric air-fuel ratio.
By multiplying p, feedback control of the air-fuel ratio is performed.

In this case, when the exhaust gas is passed through the main passage 3a, the air-fuel ratio feedback correction coefficient α is calculated based on the output of the upstream oxygen sensor, and when the exhaust gas is passed through the bypass passage 3b, it is based on the downstream oxygen sensor output. To calculate α.

As described above, the bypass valve 6 is switched according to the temperature range, and when the exhaust gas is made to flow to the main passage 3a by this switching, the exhaust gas is made to flow to the bypass passage 3b based on the upstream oxygen sensor output. Even when the feedback control of the air-fuel ratio is performed based on the output of the oxygen sensor on the downstream side, if it is attempted to determine whether the front catalyst 4 has deteriorated, the deterioration occurs when the bypass passage 3b is fully closed. Although the determination is made, in this configuration, there is a possibility that the deterioration of the front catalyst 4 may be misdiagnosed due to the failure of the bypass valve 6. When the bypass passage 3b is fully closed, for example, when foreign matter is caught between the bypass passage side valve 6b and the intake passage wall and a part of the exhaust gas flows through the bypass passage 3b, the storage capacity of the front catalyst 4 apparently decreases. This is because the inversion frequency of the downstream oxygen sensor output increases in this state, and an error occurs in the downstream oxygen sensor output by this increase. It should be noted that in the following, deterioration is determined only for the front catalyst, so the front catalyst is simply referred to as the catalyst.

In order to deal with this, the present invention determines whether or not a leak failure to the bypass passage side occurs by using the output of the downstream oxygen sensor only under the condition that the deterioration of the catalyst 4 does not proceed. As a result, it is determined whether or not the catalyst 4 has deteriorated only when the condition for the deterioration of the catalyst 4 to proceed in the case where no leakage failure to the bypass passage side occurs.

The contents of this control executed by the control unit 21 will be described with reference to the following flow chart.

The flowcharts of FIGS. 2 and 3 are executed, for example, every 10 seconds.

Steps 1 to 4 in FIG. 2 are a part for checking whether the condition is a diagnostic condition. First, in step 1, it is checked whether the catalyst 4 and the two oxygen sensors 11 and 12 are activated. For example, when the cooling water temperature is 60 ° C. or higher, or when 100 seconds or more has elapsed after the start, it is determined that the cooling water has been activated, and the process proceeds to step 2. Otherwise, the flow of FIG. 2 ends.

At step 2, it is determined whether the air-fuel ratio feedback control is being performed (abbreviated in the figure as air-fuel ratio F / B). If the air-fuel ratio feedback control is being performed, the routine proceeds to step 3, otherwise, the flow of FIG. To finish.

In step 3, it is checked from the output signal to the drive device 7 whether the main passage side valve 6a is in the fully opened state,
If it is in the fully open state, the process proceeds to step 4, and if not, the flow of FIG. 2 ends.

In step 4, it is checked whether or not it is in a steady operation state. For example, the basic injection pulse width Tp and the rotation speed NRPM
If each change width per 10 seconds is within a predetermined value,
When it is determined that the vehicle is in the steady operation state, the process proceeds to step 11 of FIG. 3, and if not, the flow of FIG. Here, the steady state is one of the requirements for the diagnostic condition. The inversion frequency ratio HZRATE is not stable in the non-steady state, and an error may occur when the HZRATE is determined. Is.

In step 11 of FIG. 3, it is judged from the high exhaust temperature flag fhitem whether or not the high exhaust temperature range is entered after the previous diagnosis. High exhaust temperature flag f
hitem is a flag which is initialized to "0" at the time of starting and is set to "1" if it is in the high exhaust temperature range in steps 18, 19 and 20 described later. Now, assuming that the temperature is not in the high exhaust gas temperature range, proceed to step 12.

In step 12, it is judged from the value of the valve check flag fvalchk whether or not the failure diagnosis of the bypass valve has already been executed after the present start. fv
When “archk = 0”, it is determined that the valve failure diagnosis is not yet executed, and the process proceeds to step 13 and the subsequent steps.

Steps 13, 14, and 15 are parts for determining whether or not the bypass valve 6 has a leakage failure to the bypass passage side. The determination of the leak failure here is a failure in which the exhaust passage leaks into the bypass passage 3b due to foreign matter or the like even though the valve 6b on the bypass passage side is in the fully closed state. It is a thing. Since the leaked exhaust gas is not purified by the catalyst 4 and causes deterioration of exhaust emission, it is necessary to determine a leak failure to the bypass passage side occurring in the valve 6. If the valve 6b has a leak, the reversal frequency of the downstream oxygen sensor output becomes the same as the reversal frequency of the upstream oxygen sensor output. Frequency ratio HZR
It can be determined from ATE.

In steps 13, 14, and 15, the reverse frequency ratio H is set in the same manner as steps 21, 22, and 23 described later.
Monitors ZRATE, basic injection Tp, rotation speed NRP
By searching M for a map containing FIG. 4,
The failure judgment value HZVAL is calculated, and HZRATE and HZVA
Compare L.

As a result of this comparison, HZRATE is HZVA.
If it is L or more, it is judged that the valve 6b has a leakage failure,
Proceeding to step 16, the alarm for warning the leak failure of the valve 6b is turned on (or the warning buzzer is sounded).

On the other hand, if HZRATE is smaller than HZVAL, it is determined that no leak failure has occurred in the valve 6b, and the valve check flag fvalchk is set to "1" in step 17. By setting the flag fvalchk to "1", the flow from step 12 to step 21 onward is started from the next control cycle. This is valve 6
The determination of the leak failure in b is made only once in one travel. However, for example, at an interval of 10 minutes, the flag fvalc
If hk is initialized to "0", it becomes possible to periodically diagnose a leak failure of the valve 6b during traveling.

At step 18, the exhaust temperature Texh is obtained by searching the map having the contents of FIG. 6 from Tp and NRPM, and this is compared with the predetermined value T0 at step 19 so that the exhaust temperature Texh is not less than the predetermined value T0. If so, it is determined that the exhaust gas is in the high exhaust temperature range, and the flag fhitem is set to "1" in step 20. The predetermined value T0 is generally a lower limit value (for example, 600 ° C.) of the temperature at which the deterioration of the catalyst 4 progresses.

By setting the flag fitem to "1", the process advances from step 11 to step 21 onward from the next control cycle. That is, if the high exhaust temperature range is entered after the completion of the determination of the leakage failure of the valve 6b (a condition under which the deterioration of the catalyst 4 progresses), the determination of the leakage failure of the valve 6b is not performed thereafter. In other words, the previous valve 6
Only when the high exhaust temperature range is not entered (the deterioration of the catalyst 4 is not progressing) after the completion of the leak failure determination of b, the valve 6
That is, the leakage failure determination of b is performed.

In steps 11 and 12, the flag fh is set.
When the high exhaust temperature is experienced because the item is "1" and when the valve failure diagnosis is completed because the flag fvalchk is "1", the process proceeds to step 21 and subsequent steps.

Steps 21, 22, and 23 are parts for determining whether or not the catalyst 4 has deteriorated. In the same manner as in the conventional case, HZRATE is monitored and Tp and NRPM are searched for a map having the contents of FIG. By determining the deterioration determination value HZCAT of the catalyst, HZRATE and HZCA
Compare T. As a result of the comparison, HZRATE is HZCAT
If it is smaller, it is determined that the catalyst 4 has not deteriorated and the flow of FIG. 3 is terminated. If HZRATE is HZCAT or more, it is determined that the catalyst 4 has deteriorated, and in step 24, the catalyst 4 has deteriorated. Turn on the alarm to warn that.

The above two judgment values HZVAL and HZCA
As shown in FIGS. 4 and 5, T is a characteristic that the value basically increases as the basic injection pulse width Tp increases and the rotational speed NRPM increases. Since it is actually affected by the mounting position of the downstream side oxygen sensor 12, etc., it is necessary to obtain it experimentally.

As described above, in the first embodiment, the history of the exhaust temperature before the diagnosis is checked to determine whether or not the deterioration of the catalyst 4 has progressed, and the condition of the deterioration of the catalyst 4 has not progressed. It is judged whether or not the bypass valve 6 has a leak failure to the bypass passage side only by the above, and if there is no leak failure to the bypass passage side from the judgment result, the catalyst 4
Since it is determined whether or not the catalyst 4 is deteriorated under the condition that the deterioration of the catalyst 4 progresses, the leakage diagnosis to the bypass passage side can be performed, and the bypass passage side can be determined when the deterioration of the catalyst 4 is determined. There will be no misdiagnosis due to leakage failure.

FIG. 7 is a second embodiment and corresponds to FIG. FIG.
The difference from is that step 31 to step 37 are added, and these differences will be mainly described.

When it is determined in step 11 that the high exhaust temperature range has been entered after the previous failure determination of the valve 6b, the reversal frequency ratio H at the time of the previous failure determination is determined in step 31.
Read ZPRE. This HZPRE is the inversion frequency ratio HZRA in step 37 before the end of the flow of FIG.
It can be obtained by storing TE in memory as HZPRE.

At step 32, the time elapsed in the high exhaust temperature range (history of the condition under which the deterioration of the catalyst 4 progresses) is read, and at step 33, the table having the contents of FIG. Change rate (increase rate) DHZ of inversion frequency ratio HZRATE due to catalyst deterioration
Ask for. Here, DHZ is a table in which a change (increase) in HZRATE due to catalyst deterioration in a high exhaust temperature range is experimentally obtained in advance and is stored in a memory as a table for elapsed time. It is a value.

At step 34, the HZRATE of this time is monitored, and at step 35, it is sent to HTPRE.
Compare with the value with HZ added. That is, the previous valve 6b
HZPRE + DHZ is the catalyst maximum deterioration state equivalent amount when predicting the deterioration of the catalyst 4 due to the subsequent high exhaust temperature with respect to the timing of the leak failure determination of HZRATE, which is the catalyst deterioration state equivalent amount measured this time. By comparison, if HZRATE <HZPRE + DHZ,
This means that the deterioration of the catalyst 4 is within the expected range. Conversely, when HZRATE ≧ HZPRE + DHZ, it is determined that the inversion frequency ratio is not increased due to the deterioration of the catalyst 4 (that is, the leakage failure of the valve 6b), and the leakage failure occurs in the valve 6b in step 36. Turn on the alarm to warn that.

On the other hand, HZRATE <HTPRE + DHZ
If it is, there is no leakage failure in the valve 6b, and therefore it is judged whether or not the catalyst 4 is deteriorated. Then, the process proceeds to step 22 and subsequent steps, and the deterioration judgment of the catalyst 4 is carried out similarly to the first embodiment.

As described above, in the second embodiment, it is possible to determine the leakage failure of the valve 6b even when the high exhaust temperature range where the deterioration of the catalyst 4 progresses is experienced.

In the two embodiments, the case where each of the leak failure of the valve 6b and the deterioration of the catalyst 4 is determined based on the inversion frequency ratio HZRATE of the outputs of the two oxygen sensors has been described, but the present invention is not limited to this and, for example, upstream. It can also be applied to the judgment by the method of judgment based on the response delay from the time of reversing the output of the side oxygen sensor to the reversal of the output of the downstream oxygen sensor, or the method of judging by the reversal frequency (or amplitude) of the output of the downstream oxygen sensor is there.

Further, although the description has been given of the normal three-way catalyst as the front catalyst, the present invention is not limited to this, and it is applicable as long as it has an oxygen storage capacity and there is a correlation between the oxygen storage capacity and the conversion performance. Is. That is, it is needless to say that the NOx occlusion reduction type three-way catalyst and the oxidation catalyst may be applied, although there are differences in degree.

[0052]

According to the first aspect of the present invention, the leakage failure to the bypass passage side can be determined, and a misdiagnosis due to the leakage failure to the bypass passage side does not occur when determining the deterioration of the catalyst.

In the second aspect of the present invention, it is possible to determine the leakage failure to the bypass passage side even under the condition that the deterioration of the catalyst progresses.

According to the third aspect of the invention, deterioration of the upstream oxygen sensor due to exposure to high temperature exhaust gas can be prevented.

In the fourth aspect of the invention, the output of the oxygen sensor is stable and the determination accuracy is improved as compared with the case where the leakage failure to the bypass passage side is determined at the time of transition.

[Brief description of the drawings]

FIG. 1 is a control system diagram of an embodiment.

FIG. 2 is a flowchart for explaining determination of diagnostic conditions.

FIG. 3 is a flowchart for explaining the determination of a leak failure of the valve 6b and deterioration of the catalyst 4.

FIG. 4 is a characteristic diagram of a determination value HZVAL.

FIG. 5 is a characteristic diagram of a determination value HZCAT.

FIG. 6 is a characteristic diagram of exhaust temperature.

FIG. 7 is a flow chart for explaining the determination of the leakage failure of the valve 6b and the deterioration of the catalyst 4 in the second embodiment.

FIG. 8: HZR versus elapsed time in high exhaust temperature range
It is a characteristic view of change DHZ of ATE.

FIG. 9 is a diagram corresponding to the claims of the first invention.

[Explanation of symbols]

 3 Exhaust Pipe 3a Main Passage 3b Bypass Passage 4 Front Catalyst 6 Bypass Valve 11 Upstream Oxygen Sensor 12 Downstream Oxygen Sensor 21 Control Unit 31a Main Passage 31b Bypass Passage 32 Catalyst 33 Bypass Valve 34 Upstream Oxygen Sensor 35 Downstream Oxygen Sensor 36 Valve switching means 37 Air-fuel ratio feedback control means 38 Determination means 39 Valve failure determination means 40 Catalyst deterioration determination means

Claims (4)

[Claims] 1. A bypass valve for branching a main passage and a bypass passage upstream of an exhaust pipe to install a catalyst in the main passage, and switching a flow of exhaust gas between the main passage and the bypass passage while the upstream of the catalyst is provided. And an oxygen sensor disposed downstream of the confluence of the main passage and the bypass passage, so that the exhaust gas flows into the main passage in the low exhaust temperature range and the exhaust passage into the bypass passage in the high exhaust temperature range. A means for switching the bypass valve, and based on the output of the oxygen sensor on the upstream side when flowing the exhaust gas to the main passage by the switching means, and based on the output of the oxygen sensor on the downstream side when flowing the exhaust gas to the bypass passage. Means for respectively performing feedback control of the air-fuel ratio, and determining whether the condition is such that the deterioration of the catalyst does not progress or the deterioration progresses And a means for judging, based on at least the output of the downstream side oxygen sensor, whether or not the bypass valve has a leakage failure to the bypass passage side only under the condition that the deterioration of the catalyst does not progress from the judgment result. Based on at least the output of the downstream oxygen sensor, it is determined whether the catalyst has deteriorated under the condition that the deterioration of the catalyst progresses in the case where the bypass valve does not have a leakage failure to the bypass passage side from the determination result. An exhaust gas purification device diagnostic device comprising: 2. A catalyst for predicting a maximum deterioration state of the catalyst according to a history of the condition when the catalyst deteriorates, and the catalyst based on at least the output of the downstream oxygen sensor. A means for calculating the current deterioration state, and if the current deterioration state is larger than the maximum deterioration state than the comparison between the current deterioration state and the maximum deterioration state, the bypass valve has a leakage failure to the bypass passage side. The exhaust gas purifying apparatus diagnostic apparatus according to claim 1, further comprising: means for determining that there is. 3. The exhaust purification system diagnostic device according to claim 1, wherein the upstream oxygen sensor is provided downstream of the bypass valve. 4. The diagnostic device for an exhaust emission control device according to claim 1, wherein the condition for determining the leakage failure to the bypass passage side is a steady state.