JP3149714B2 - Catalyst deterioration diagnosis device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for diagnosing catalyst deterioration of an internal combustion engine, and more particularly, to a method for diagnosing catalyst deterioration using air-fuel ratio sensors disposed upstream and downstream of a catalytic converter, respectively. About technology.

[0002]

2. Description of the Related Art An oxygen sensor (an air-fuel ratio sensor for detecting an air-fuel ratio based on the oxygen concentration in exhaust gas) is disposed upstream and downstream of a catalytic converter provided in an exhaust passage of an internal combustion engine. Mainly on the output signal of the upstream oxygen sensor, air-fuel ratio feedback control for matching the air-fuel ratio of the engine intake air-fuel mixture to the target air-fuel ratio is performed, and based on the cycle comparison of the output signals of both oxygen sensors. An apparatus configured to diagnose the deterioration of the catalyst by using
It is disclosed in Japanese Patent Application Laid-Open No. 3-205441.

In the air-fuel ratio feedback control, the fuel supply amount is controlled by pseudo proportional integral control based on rich / lean discrimination with respect to the target air-fuel ratio based on the output signal of the upstream oxygen sensor. As shown in FIG. 3A, the output signal of the sensor periodically repeats rich and lean with respect to the target air-fuel ratio. On the other hand, on the downstream side of the catalytic converter, the fluctuation of the residual oxygen concentration becomes very gentle due to the oxygen storage capacity of the catalyst, so that the output signal of the downstream oxygen sensor is as shown in FIG. In addition, the amplitude is smaller and the period is longer than the output signal of the upstream oxygen sensor.

However, when the catalyst deteriorates, the oxygen storage capacity decreases, so that the oxygen concentration does not change significantly between the upstream side and the downstream side of the catalytic converter. As a result, the output signal of the downstream oxygen sensor becomes low. As shown in FIG. 3 (d), the inversion is repeated at a cycle approximating the output signal of the oxygen sensor on the upstream side, and its amplitude also increases.

Therefore, during the air-fuel ratio feedback control, the rich / lean inversion period T of the upstream oxygen sensor is controlled.
1 and rich / lean inversion period T2 of the downstream oxygen sensor
(T1 / T2) is determined, and when this ratio becomes a predetermined value or more, that is, when the cycle T2 is shortened, it is determined that the catalyst has deteriorated. In addition, Japanese Unexamined Patent Publication
Japanese Patent No. -30915 discloses a predetermined time (response time) from the forcible transition of the air-fuel ratio from the stoichiometric air-fuel ratio to the rich state to the detection of such a rich change in the air-fuel ratio by the downstream oxygen sensor. In the following, there is disclosed a configuration in which it is considered that the response time is shortened due to the decrease in the oxygen storage capacity, and a catalyst deterioration diagnosis is performed.

[0006]

However, in the diagnostic method based on the period ratio described above, there is a large variation between the period ratio and the conversion efficiency (deterioration level). It is necessary to set the slice level used for the comparison to a relatively large value so that the deterioration determination is performed only when the deterioration is extremely advanced, and it is difficult to widen the range of the deterioration diagnosis while avoiding erroneous diagnosis. There was a problem.

On the other hand, in the diagnosis method based on the response time, only a relatively small variation occurs between the response time and the conversion efficiency (deterioration level). It is possible to make a diagnosis. However, in the diagnosis based on the response time, it is necessary to forcibly shift the air-fuel ratio from the target air-fuel ratio, so that drivability and exhaust properties may be deteriorated. Also,
Since it is necessary to make a diagnosis under limited operating conditions in order to avoid the adverse effect on the drivability as much as possible, the deterioration has been extremely advanced such that an accurate deterioration determination can be made based on the cycle ratio. Even with a catalyst, there is a problem that it takes a longer time to actually make a deterioration determination than a diagnosis based on a cycle ratio.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems. Particularly, it is possible to accurately diagnose a deteriorated state over a wide range while ensuring responsiveness of deterioration determination for a catalyst that has been extremely deteriorated. It is an object of the present invention to provide a catalyst deterioration diagnosis device capable of minimizing the influence on the operability of the catalyst.

[0009]

Therefore, an apparatus for diagnosing catalyst deterioration of an internal combustion engine according to the first aspect of the present invention is configured as shown in FIG. In FIG. 1, air-fuel ratio sensors are provided on the upstream and downstream sides of a catalytic converter interposed in an exhaust passage of an engine, respectively. The air-fuel ratio feedback control means feedback-controls the fuel supply amount to the engine based on the detection result of the upstream air-fuel ratio sensor so that the air-fuel ratio of the engine intake air-fuel mixture matches the target air-fuel ratio.

On the other hand, the first deterioration diagnosis means performs a deterioration diagnosis of the catalyst based on a comparison between the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor. Further, the second deterioration diagnosis means detects the forced change of the air-fuel ratio only when the first deterioration diagnosis means is in a state in which diagnosis cannot be made as either normal or deteriorated. The deterioration diagnosis of the catalyst is performed based on the response time until the detection by the downstream air-fuel ratio sensor.

In the catalyst deterioration diagnosis apparatus for an internal combustion engine according to the present invention, the first deterioration diagnosis means may determine a ratio between an output cycle of the upstream air-fuel ratio sensor and an output cycle of the downstream air-fuel ratio sensor. is configured to perform the deterioration diagnosis of the catalyst based on, determine for the catalyst is determined to be normal
And a constant level for determining that the catalyst has deteriorated.
When the ratio exists with the judgment level, the diagnosis is performed.
The configuration is such that it is determined that the state cannot be determined .

In the catalyst deterioration diagnosis apparatus for an internal combustion engine according to the third aspect of the present invention, the second deterioration diagnosis means sets the air-fuel ratio in a lean state with respect to the target air-fuel ratio in preference to the air-fuel ratio feedback control means. The air-fuel ratio is forcibly switched to a rich state with respect to the target air-fuel ratio from the state in which the lean state is detected by the upstream and downstream air-fuel ratio sensors, and the lean state is controlled. The response time from when the switching control from the state to the rich state is detected by the upstream air-fuel ratio sensor to when the switching control is detected by the downstream air-fuel ratio sensor is measured, and the response time is compared with the determination level. Based on the above, it is configured to determine whether the catalyst is deteriorated or normal.

According to a fourth aspect of the present invention, in the catalyst deterioration diagnosis apparatus for an internal combustion engine, the second deterioration diagnosis means executes the diagnosis based on the response time a plurality of times, and deteriorates by a predetermined ratio or more in the plurality of times. When the diagnosis is made, the final deterioration judgment is performed, and when the rate of the deterioration diagnosis is less than a predetermined value, the normal judgment is made. In the catalyst deterioration diagnosis device for an internal combustion engine according to the invention of claim 5, after the second deterioration diagnosis means determines deterioration or normality, the second deterioration diagnosis means is provided until the engine is stopped. A deterioration diagnosis prohibiting means for prohibiting deterioration diagnosis due to the above is provided.

[0014]

According to the catalyst deterioration diagnostic apparatus for an internal combustion engine according to the first aspect of the present invention, the first deterioration diagnosis means detects the catalyst of the catalyst based on a comparison between the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor. When normal or deterioration can be diagnosed,
The diagnosis is not performed by the second deterioration diagnosis unit, and the deterioration diagnosis by the second deterioration diagnosis unit is performed only when the first deterioration diagnosis unit is in a state where the diagnosis cannot be performed as either deterioration or normal.

That is, in the deterioration diagnosis performed by comparing the output signals of the two air-fuel ratio sensors, a judgment is made when it is clearly determined that the air condition is normal or deteriorated. In addition, the deterioration diagnosis is performed by a second deterioration diagnosis means capable of performing a more clear deterioration diagnosis. Therefore, when the deterioration is extremely advanced or when it is clearly recognized as normal, the first deterioration diagnosis means provides the diagnosis result with good response, and the first deterioration diagnosis means may misdiagnose. , The diagnosis is performed by the second deterioration diagnosis means to provide a highly reliable diagnosis result.

According to the catalyst deterioration diagnosis apparatus for an internal combustion engine of the present invention, the oxygen storage of the catalyst is determined based on the ratio between the output cycle of the upstream air-fuel ratio sensor and the output cycle of the downstream air-fuel ratio sensor. to determine the reduction of the output cycle of the downstream air-fuel ratio sensor due to reduced capacity, but touch here
The determination level for determining that the medium is normal and the catalyst are inferior.
Between the judgment level for judging that
When the rate exists, it is determined that the diagnosis is not possible.

According to the catalyst deterioration diagnosing device for an internal combustion engine according to the third aspect of the present invention, the second deterioration diagnosing means includes:
First, the air-fuel ratio is made lean and then inverted to the rich side, and the response time from when the air-fuel ratio inversion is detected by the upstream air-fuel ratio sensor to when it is detected by the downstream air-fuel ratio sensor is measured. If the air-fuel ratio is lean, a large amount of oxygen will be stored in the catalyst by the oxygen storage capacity, so even if the air-fuel ratio reverses richly, the oxygen concentration downstream of the catalyst will change with a large response delay. When the response time falls within a certain period of time, it is determined that the oxygen storage capacity has dropped below an allowable level, and catalyst deterioration is determined.

According to the apparatus for diagnosing catalyst deterioration of an internal combustion engine according to the fourth aspect of the present invention, when the diagnosis is performed by the second deterioration diagnosing means without being able to be diagnosed by the first deterioration diagnosing means, one response time is required. Rather than immediately making a judgment in the measurement, the air-fuel ratio fluctuations and the response time are measured several times, and the deterioration judgment is made only when the response time indicating the deterioration state is measured with a probability of a predetermined ratio or more. In this case, the accuracy of diagnosis by the second deterioration diagnosis unit is ensured.

According to the catalyst deterioration diagnosing device for an internal combustion engine according to the fifth aspect of the present invention, after the second deterioration diagnosing means makes a final judgment of deterioration or normality, the engine is stopped until the engine is stopped. The deterioration diagnosis by the second deterioration diagnosis unit is prohibited, and the frequency of the deterioration diagnosis by the second deterioration diagnosis unit accompanying the air-fuel ratio fluctuation is reduced.

[0020]

Embodiments of the present invention will be described below. FIG. 2 is a system configuration diagram of the embodiment. In FIG. 2, a fuel injection valve 3 for injecting fuel toward an intake port of each cylinder is provided for each cylinder in an intake passage 2 of the internal combustion engine 1 and adjusts an intake air amount. A throttle valve 4 is interposed, and an air flow meter 5 such as a hot wire type for detecting an intake air flow rate Q is disposed upstream of the throttle valve 4.

On the other hand, a catalytic converter 7 using, for example, a three-way catalyst is interposed in the exhaust passage 6. An upstream side and a downstream side of the catalytic converter 7 have an air-fuel ratio of an engine intake air-fuel mixture. First and second oxygen sensors 8 and 9 for detecting oxygen concentrations in exhaust gas which are closely related to each other are provided.
The first and second oxygen sensors 8 and 9 generate an electromotive force according to the oxygen concentration in the exhaust gas. In particular, the electromotive force changes suddenly at the stoichiometric air-fuel ratio, and is richer than the stoichiometric air-fuel ratio ( A high level (about 1 V) electromotive force is generated on the rich side, and a low level (about 100 mV) electromotive force is generated on the lean side (lean side). The first oxygen sensor 8 corresponds to an upstream air-fuel ratio sensor, and the second oxygen sensor 9 corresponds to a downstream air-fuel ratio sensor.

A muffler 10 is provided downstream of the second oxygen sensor 9 on the downstream side, and engine exhaust is discharged through the catalytic converter 7 and the muffler 10. Further, a water temperature sensor 11 for detecting a cooling water temperature Tw of the engine 1 and a crank angle sensor 12 for emitting a pulse signal at every predetermined crank angle are provided. Based on the pulse signal from the crank angle sensor 12, the engine rotation speed is determined. N is calculated.

A control unit 13 containing a microcomputer has a basic pulse width based on an intake air flow rate Q detected by the air flow meter 5 and an engine speed N calculated based on a pulse signal from the crank angle sensor 12. (Basic fuel injection amount) Tp = T × K × Q / N
(K is a constant), and the basic pulse width is subjected to various increase corrections and air-fuel ratio feedback corrections to determine the final injection pulse width (fuel injection amount) TI.

Specifically, the pulse width TI is calculated according to the following equation. TI = Tp × COEF × α + Ts Here, COEF is various increase correction coefficients, and includes, for example, a water temperature increase correction according to the water temperature Tw, and an air-fuel ratio correction at high speed and high load. Ts is a voltage correction amount added according to the battery voltage so as to compensate for the invalid injection time of the fuel injection valve.

Α is an air-fuel ratio feedback correction coefficient calculated mainly based on the output signal of the first oxygen sensor 8 on the upstream side. That is, the output signal of the first oxygen sensor 8 is compared with a slice level corresponding to the target air-fuel ratio (the stoichiometric air-fuel ratio) to determine whether the actual air-fuel ratio is rich or lean with respect to the target air-fuel ratio. The air-fuel ratio is controlled by the proportional integral control. When the air-fuel ratio is controlled to be 1.0 or more of the initial value, the air-fuel ratio is controlled to the rich side.

FIG. 3A shows an example of an output signal of the first oxygen sensor 8 during the air-fuel ratio feedback control.
(B) shows the air-fuel ratio feedback correction coefficient α corresponding to the output signal. As described above, the air-fuel ratio feedback correction coefficient α is obtained by pseudo proportional integral control. When the output of the first oxygen sensor 8 crosses a predetermined slice level and reverses from the rich side to the lean side, A constant proportional amount P _L is added to the correction coefficient α,
And, integral amount in inclination by a predetermined integral constant I _L is gradually being added gradually. Similarly, when inverted from the lean side to the rich side, certain proportional portion P _R from the correction coefficient α is subtracted,
And it is gradually decreased by the integral component with a slope by a predetermined integral constant I _R. By repeating such an operation, the actual air-fuel ratio is maintained at approximately the stoichiometric air-fuel ratio while changing at a cycle of about 1 to 2 Hz.

The function of the proportional integral control of the air-fuel ratio feedback correction coefficient α by the control unit 13 corresponds to the air-fuel ratio feedback control means in this embodiment. Note that the air-fuel ratio feedback correction coefficient α is clamped to 1 at the time of low water temperature, high-speed high load, or fuel cut during deceleration where it is necessary to perform the fuel increase correction.
The state is substantially in the open control state.

On the other hand, the rich lean determination result based on the output signal of the second oxygen sensor 9 on the downstream side, proportional portion P _L used in the proportional integral control, is P _R, the second oxygen sensor 9
Is corrected in a direction approaching the target air-fuel ratio (the stoichiometric air-fuel ratio). Note that the air-fuel ratio feedback control based on the output signals of the first and second oxygen sensors 8 and 9 is not limited to the example described above, and in particular, the correction control based on the output of the second oxygen sensor 9 on the downstream side. Is a configuration for correcting a slice level used for making a rich / lean determination based on an output signal of the first oxygen sensor 8 and a delay time from the rich / lean inversion to performing the proportional control. A configuration for controlling based on the output may be used.

In the present embodiment, the control unit 13 diagnoses the deterioration of the catalyst of the catalytic converter 7 as described later, and turns on the warning lamp 14 when it is determined that the deterioration exceeds a predetermined level. , To warn the driver. Here, FIGS. 4 and 5
An embodiment of the catalyst deterioration diagnosis will be described in detail according to the flowchart of FIG. In this embodiment, the functions as the first deterioration diagnosis means and the second deterioration diagnosis means are as shown in FIG.
As shown in the flowchart of FIG. 5, the control unit 13 is provided as software.

The routines shown in the flow charts of FIGS. 4 and 5 are repeatedly executed at predetermined time intervals. First, step 1 (S1 in the drawings; the same applies hereinafter).
Then, it is determined whether or not the catalyst deterioration diagnosis condition is satisfied. The diagnostic conditions include that the water temperature at the time of engine start is equal to or higher than a predetermined value, that a predetermined time has elapsed after completion of engine warm-up, and that the second oxygen sensor 9 on the downstream side is activated (active state). Is determined based on the output signal level), and the process proceeds to step 2 only when all the conditions are satisfied.

In step 2, the current engine operating conditions are:
It is determined whether or not the air-fuel ratio is within the region where the feedback control is performed. Specifically, the condition of the feedback control is that the vehicle speed is within a predetermined range, the engine speed N is within a predetermined range, and the engine load represented by the basic pulse width Tp is within a predetermined range. If all of these conditions are satisfied, it is determined that the air-fuel ratio feedback control is being performed, and it is determined that the catalyst can be diagnosed, and the process proceeds to step 4, where the air-fuel ratio feedback control is not performed. In some cases, it is determined that catalyst diagnosis is also impossible, and the process proceeds to step 3 to clear various parameters (FO2CT, RO2CT, D20K, D2STB described later).

That is, in the present embodiment, as will be described later, based on the output fluctuation period of the first and second oxygen sensors 8 and 9 when the rich / lean operation with respect to the target air-fuel ratio is repeated with the air-fuel ratio feedback control. Since the catalyst deterioration diagnosis is performed, the condition for performing the air-fuel ratio feedback control is a necessary condition for the deterioration diagnosis. In step 4, it is determined whether or not the flag D20K indicating the shift to the second diagnosis is set to 0 and the condition for performing the first diagnosis is satisfied. The first diagnosis (first deterioration diagnosis means) indicates a deterioration diagnosis based on the cycle ratio of the output signals of the first and second oxygen sensors 8 and 9 as described later, and the second diagnosis (second deterioration diagnosis means). Means of deterioration diagnosis means deterioration diagnosis based on a response delay time on the downstream side of the catalyst with respect to the air-fuel ratio fluctuation.

When the flag D20K is 0, the routine proceeds to step 5, where it is determined whether or not the counter FO2CT for counting the number of rich / lean inversions of the upstream first oxygen sensor 8 is equal to or greater than a predetermined value CMSW. . The number of times of rich / lean inversion indicates that the output signals of the first and second oxygen sensors 8 and 9 cross over a slice level corresponding to the stoichiometric air-fuel ratio and the air-fuel ratio is changed from rich to lean or from lean to rich. It shows the number of times the device is in the closed state.

Here, the rich / lean inversion number FO2C
When T is less than the predetermined value CMSW, the process proceeds to step 6 and counts the number of rich / lean inversions FO2CT of the first oxygen sensor 8 on the upstream side and the number of rich / lean inversions RO2CT of the second oxygen sensor 9 on the downstream side. Is performed. On the other hand, if it is determined in step 5 that the rich / lean inversion number FO2CT of the upstream first oxygen sensor 8 has become equal to or greater than the predetermined value CMSW, the process proceeds to step 7, and the inversion times RO2CT and FO2CT are determined.
Is calculated (HZR = RO2CT / FO2CT).

When the catalyst has not deteriorated and has the expected oxygen storage capacity, the number of inversions RO2CT on the downstream side is smaller than the predetermined number of inversions FO2CT on the upstream side. When the oxygen storage capacity decreases with the progress, the number of reversals RO2CT on the downstream side gradually approaches the number of reversals FO2CT on the upstream side as the deterioration progresses, and as a result, the ratio HZR increases as the deterioration progresses. Value (see FIG. 3).

The ratio HZR indicates the ratio of the rich / lean inversion cycle of the second oxygen sensor 9 on the downstream side to the rich / lean inversion cycle of the first oxygen sensor 8 on the upstream side. Therefore, instead of counting the number of reversals,
A configuration for detecting an inversion cycle or an inversion frequency may be used. In step 8, the inversion times RO2CT and FO2CT are cleared, respectively, to prepare for the measurement of the next inversion number.

In step 9, the ratio HZR is compared with a predetermined value COKHZ (judgment level) used for normality judgment (see FIG. 6). If the ratio HZR is less than the predetermined value COKHZ and is sufficiently small, the catalyst is activated. Judge that the intended oxygen storage capacity is being demonstrated (see Fig. 3), and
Proceeding to 10, a "normal" determination is made, and the warning light 14 indicating catalyst deterioration is turned off.

On the other hand, when it is determined in step 9 that the ratio HZR exceeds the predetermined value COKHZ, and at least when the state cannot be determined to be normal, the process proceeds to step 11, where a predetermined value CNGHZ ( FIG.
And the ratio HZR. Here, when the ratio HZR is equal to or higher than the predetermined value CNGHZ, the output signal of the downstream second oxygen sensor 9 is inverted because the oxygen storage capacity of the catalyst is reduced to such an extent that the catalyst is clearly degraded. Assuming that the cycle is approaching the reversal cycle of the first oxygen sensor 8 on the upstream side (see FIG. 3), the process proceeds to step 12 to determine “deterioration”, and the warning indicating catalyst deterioration is made. The light 14 is turned on to warn the driver.

When it is determined in step 11 that the ratio HZR is less than the predetermined value CNGHZ, the diagnosis based on the ratio HZR is in a state in which it cannot be determined that the ratio is normal or deteriorated (diagnosis disabled state). In this case, the process proceeds to step 13 to execute the second diagnosis for performing the deterioration diagnosis using a different method as described later, and the flag D2
Set 1 to 0K.

That is, a large variation is expected in the relationship between the ratio HZR and the actual oxygen storage capacity (deterioration level or conversion efficiency of the catalyst). If it is configured to discriminate each other, erroneous diagnosis may be caused. Therefore, a region that can be clearly judged to be deteriorated or normal is defined by two predetermined values COKHZ and CN.
GHZ (judgment level) for the area where there is a possibility of erroneous diagnosis (the area between two predetermined values COKHZ and CNGHZ: FIG. 3)
), The diagnosis is not possible, and the deterioration diagnosis is performed by the second diagnosis using a different diagnosis method described later.

When the flag D20K is set to 1 at step 13, the process proceeds to step 14 to execute the second diagnosis. still,
When it is determined in step 4 that the flag D20K is set to 1, the process jumps from step 4 to step 14 and proceeds. In step 14, the flag D2STB indicating whether or not the second diagnosis is ready is determined. Here, the preparation for performing the second diagnosis means that the air-fuel ratio of the engine intake air-fuel mixture is forcibly made lean and the lean state becomes the first or the first state.
It is assumed that the states are detected by the second oxygen sensors 8 and 9, respectively.

If the flag D2STB is set to 0 and the second diagnosis is not ready, the step
Proceeding to 15, the air-fuel ratio feedback correction coefficient α is forcibly clamped to a predetermined value αL set in advance to make the air-fuel ratio lean. Then, in the next step 16, the output signal FO2 of the upstream first oxygen sensor 8 is compared with the slice level SLL of the lean determination, and the output signal FO2 becomes lower than the slice level SLL. When the first oxygen sensor 8 detects that the air-fuel ratio is lean, the process proceeds to step S17.

In step 17, similarly, the downstream second
The output signal RO2 of the oxygen sensor 9 is compared with the slice level SLL of the lean determination, and the output signal RO2 becomes lower than the slice level SLL.
If it is detected that the air-fuel ratio is lean, the routine proceeds to step 18, where 1 is set to the flag D2STB. In step 19, the air-fuel ratio feedback correction coefficient α is forcibly clamped to a predetermined value αR set in advance to reverse the air-fuel ratio to a rich state. As a result, a change in the air-fuel ratio from the lean state to the rich state with respect to the stoichiometric air-fuel ratio is forcibly generated.

In the next step 20, the output signal FO2 of the second oxygen sensor 8 on the upstream side and the slice level for rich determination are determined.
SLR is compared with the output signal FO2 until the output signal FO2 exceeds the slice level SLR and a rich inversion is detected. The process proceeds to step 21 and a timer for measuring the response time of the second oxygen sensor 9 on the downstream side. Reset TIMER to zero. That is, the air-fuel ratio feedback correction coefficient α is switched from αL to αR, and the timer TIMER is maintained until the lean-to-rich inversion of the air-fuel ratio is actually detected by the first oxygen sensor 8 on the upstream side. Is kept at zero.

Here, when the output signal FO2 exceeds the slice level SLR and rich inversion is detected, the process proceeds to step 22, where the timer TIMER is incremented.
In step 23, the output signal of the downstream second oxygen sensor 9 is output.
Compare RO2 with slice level SLR of rich judgment,
Until the output signal RO2 exceeds the slice level SLR and rich inversion is detected, the timer TIMER in the step 22 is kept incremented. Therefore, the timer TIMER measures the delay time from when the lean-rich inversion is detected by the upstream first oxygen sensor 8 to when the air-fuel ratio inversion is detected by the downstream second oxygen sensor 9. Will be.

When it is determined in step 23 that the second-side oxygen sensor 9 on the downstream side has detected rich inversion of the air-fuel ratio, the process proceeds to step 24. In step 24, the value of the timer TIMER, that is, the upstream first oxygen sensor 8
Then, the response time required from when the lean-rich inversion is detected to when the inversion is detected by the second oxygen sensor 9 on the downstream side with a delay is compared with a predetermined value TMOK (see FIG. 7).

Here, the value of the timer TIMER is a predetermined value TM.
When it is OK or more, it is determined that the air-fuel ratio inversion on the downstream side of the catalyst has been delayed by a predetermined amount due to the oxygen storage capacity of the catalyst, and the process proceeds to step 25. That is, in the lean state of the air-fuel ratio, a large amount of oxygen is stored in the catalyst by the oxygen storage capacity. Therefore, even if the oxygen concentration on the upstream side of the catalyst decreases (even if the exhaust air-fuel ratio is reversed to rich), In this case, a decrease in the oxygen concentration (enrichment of the exhaust air-fuel ratio) is delayed by the stored oxygen.

In step 25, "normal" is determined,
The warning light 14 indicating catalyst deterioration is turned off. On the other hand, when it is determined in step 24 that the value of the timer TIMER is less than the predetermined value TMOK, the exhaust air-fuel ratio on the downstream side of the catalyst fluctuates relatively without delay due to the decrease in the oxygen storage capacity due to the deterioration of the catalyst. It proceeds to step 26.

In step 26, a judgment of "deterioration" is made,
The warning light 14 indicating catalyst deterioration is turned on to warn the driver. When the forced air-fuel ratio fluctuation is generated as described above, in the deterioration diagnosis based on the response delay time when the exhaust air-fuel ratio downstream of the catalyst fluctuates with a delay, the leanness of the upstream first oxygen sensor 8 is determined. The diagnosis is performed based on the time from the rich inversion to the leaning of the second oxygen sensor 9 on the downstream side → the rich inversion. Therefore, the correlation between the time and the oxygen storage capacity has relatively little variation, and the predetermined reference The deterioration or normality can be clearly diagnosed on the basis of (see FIG. 7). On the other hand, in the diagnosis based on the cycle ratio in the above-described first diagnosis, the fluctuation variation of the cycle ratio is relatively large.
In an intermediate deterioration state, the possibility of erroneous diagnosis is high (see FIG. 6).

However, in the second diagnosis, it is necessary to forcibly generate a change in the air-fuel ratio for the diagnosis, which may adversely affect the drivability and the exhaust characteristics. Since the output of the oxygen sensor is monitored during the air-fuel ratio feedback control, there is no effect on the drivability. Therefore, by performing the second diagnosis only when a clear diagnosis result cannot be output in the first diagnosis, when the first diagnosis can clearly determine normal or deteriorated, the second diagnosis that affects drivability is performed. While the first diagnosis can provide a diagnosis result with good response without executing the first diagnosis,
In a state where there is a possibility of erroneous diagnosis in the first diagnosis, the second diagnosis with higher accuracy is executed to provide a highly reliable diagnosis result.

The flowcharts of FIGS. 8 and 9 show the diagnostic control of the second embodiment, and flow from the flowchart of FIG. 4 to the flowchart of FIG. Therefore, the description of the parts shown in the flowchart of FIG. 4 is omitted, and the parts shown in the flowcharts of FIGS. 8 and 9 relating to the second diagnosis having a feature in the second embodiment will be described.

In the second embodiment, when the diagnosis cannot be made by the first diagnosis, the routine proceeds to step 31, where the permission flag D2GO for the second diagnosis is determined. The permission flag D2GO is set to 1 indicating a diagnosis permission state at the time of starting. If it is determined in step 31 that the permission flag D2GO is set to 1, the process proceeds to step 32.

In the processing of steps 32 to 41, the air-fuel ratio is once controlled to be lean and then richly inverted, and after such inversion is detected by the first oxygen sensor 8 on the upstream side, the second oxygen sensor on the downstream side is detected. 9 is to measure the time until it is detected, and is exactly the same as the processing of steps 14 to 23 shown in the flowchart of FIG.

If the second oxygen sensor 9 on the downstream side detects a rich reversal of the air-fuel ratio in step 41, the process proceeds to step 42, where a counter D2COUNT for counting the number of executions of the second diagnosis is incremented. Note that the second diagnostic execution count D2CO
UNT is reset to zero at startup. In step 43, the second diagnostic execution number D2COUNT
Is compared with a predetermined value D2MAX indicating the maximum value of the number of times of execution of the second diagnosis. If the number of times of execution of the second diagnosis has not reached the maximum value, the routine proceeds to step 44.

In step 44, the oxygen storage capacity of the catalyst from when the upstream first oxygen sensor 8 detects a lean to rich inversion of the air-fuel ratio to when the downstream second oxygen sensor 9 detects such inversion. Timer TI indicating delay time due to
The value of MER is compared with a predetermined value TMOK. Where the timer TI
When the value of MER is equal to or more than the predetermined value TMOK and the catalyst is expected to be normal (see FIG. 7), the second diagnosis is performed again, but the value of the timer TIMER is less than the predetermined value TMOK. If catalyst deterioration is expected (see FIG. 7), the routine proceeds to step 45, where the number of deterioration determinations by the second diagnosis is performed.
Count up D2NG. In addition, the deterioration judgment number D2
NG shall be cleared at the time of starting.

Then, in the next step 46, the number of times of deterioration determination D2NG counted up is compared with a predetermined value D2NGSL, and when the number of times of deterioration determination D2NG is less than the predetermined value D2NGSL, the second diagnosis is performed again. However, if the deterioration determination count D2NG is equal to or greater than the predetermined value D2NGSL, the step
Proceeding to 47, the catalyst is judged to be "deteriorated", the warning light 14 is lit, and in the next step 48, the permission flag
Until the engine is stopped after the D2GO is reset to zero, the execution of the second diagnosis is prohibited (deterioration diagnosis prohibiting means). Since the permission flag D2GO is set to 1 at the time of starting, the second diagnosis can be performed at the time of restart.

On the other hand, when it is determined in step 43 that the number of executions of the second diagnosis has reached the maximum value, that is, the maximum value D2MA
If the number of times of deterioration determination does not reach the predetermined value D2NGSL during the execution of the second diagnosis only for X, the routine proceeds to step 49, where it is determined that the catalyst is "normal", and the warning lamp 14 is turned off. Further, the process proceeds to step 50, where the second diagnosis permission flag D2 is set.
Until GO is reset to zero and then the engine is stopped, the execution of the second diagnosis is prohibited (deterioration diagnosis prohibiting means).

That is, if the first diagnosis based on the ratio HZR cannot determine that the engine is normal or deteriorated, the second diagnosis based on the response delay time of the downstream air-fuel ratio with respect to the forced air-fuel ratio fluctuation is performed. It is executed a plurality of times, and when the deterioration is determined a predetermined number of times or more (predetermined ratio or more) in the plurality of diagnoses, the final deterioration determination is first performed, and otherwise the normal determination is made. After the deterioration diagnosis is performed a plurality of times, the execution of the second diagnosis is prohibited until the engine is stopped thereafter.

According to this configuration, the accuracy of the determination is improved by performing the second diagnosis a plurality of times, and the subsequent second diagnosis is prohibited, and the execution frequency of the second diagnosis that affects the drivability is reduced. It is possible to further reduce. That is, according to the second embodiment, similarly to the first embodiment, the execution of the second diagnosis is limited to the case where the diagnosis cannot be performed by the first diagnosis, and the number of times of execution is the maximum during one trip. Since the value is limited to the value D2MAX, the influence on the operability due to the execution of the second diagnosis can be minimized while ensuring the accuracy of the diagnosis.

[0060]

As described above, according to the apparatus for diagnosing catalyst deterioration of an internal combustion engine according to the first aspect of the present invention, when the deterioration is extremely advanced or when the air-fuel ratio is clearly recognized to be normal, the air-fuel ratio between the upstream and downstream air-fuel ratios is determined. While it is possible to provide a diagnosis result with good response by the deterioration diagnosis based on the comparison of the output signals between the sensors, only when the diagnosis is not possible due to the possibility of erroneous diagnosis by the deterioration diagnosis based on the comparison of the output signals, Since the deterioration diagnosis based on the response time to the air-fuel ratio fluctuation with higher reliability is performed, there is an effect that the influence on the drivability due to the deterioration diagnosis can be suppressed while providing a highly reliable diagnosis result.

According to the apparatus for diagnosing catalyst deterioration of an internal combustion engine according to the second aspect of the present invention, in the deterioration diagnosis based on the comparison of the output signals between the upstream and downstream air-fuel ratio sensors, the normal judgment level is determined.
By comparing the deterioration determination level with the cycle ratio of the output signal, it is possible to determine whether the catalyst is in one of three states: normal, deteriorated, and undiagnosable. According to the catalyst deterioration diagnostic apparatus for an internal combustion engine according to the third aspect of the present invention, the air-fuel ratio is forcibly made lean and then richly inverted, and the response delay of the air-fuel ratio change on the downstream side of the catalyst with respect to the air-fuel ratio inversion is delayed. From the time, there is an effect that it is possible to accurately diagnose catalyst deterioration accompanied by a decrease in oxygen storage capacity. According to the catalyst deterioration diagnosis apparatus for an internal combustion engine according to the invention of claim 4, the deterioration diagnosis based on the response time is performed a plurality of times, and the deterioration time is measured only when the response time indicating the deterioration state is measured with a probability equal to or more than a predetermined value. Since the judgment is made, there is an effect that a more accurate diagnosis result can be provided.

According to the catalyst deterioration diagnosing apparatus for an internal combustion engine according to the fifth aspect of the present invention, after the deterioration or normality of the catalyst is diagnosed by the deterioration diagnosis based on the response time, the response time is maintained until the engine is stopped. Since the deterioration diagnosis based on the air-fuel ratio is not re-executed, the frequency of execution of the deterioration diagnosis accompanied by the air-fuel ratio fluctuation can be reduced, and the effect of the deterioration diagnosis on the operability can be sufficiently suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a catalyst deterioration diagnosis apparatus according to the first embodiment of the present invention.

FIG. 2 is a system configuration diagram of an embodiment.

FIG. 3 is a diagram showing a correlation between air-fuel ratio feedback control and an oxygen sensor output.

FIG. 4 is a flowchart showing catalyst deterioration diagnosis control according to the first embodiment.

FIG. 5 is a flowchart illustrating catalyst deterioration diagnosis control according to the first embodiment.

FIG. 6 is a diagram showing characteristics of deterioration diagnosis based on a cycle ratio.

FIG. 7 is a diagram showing characteristics of deterioration diagnosis based on response time.

FIG. 8 is a flowchart illustrating catalyst deterioration diagnosis control according to a second embodiment.

FIG. 9 is a flowchart illustrating catalyst deterioration diagnosis control according to a second embodiment.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 2 intake passage 3 fuel injection valve 4 throttle valve 5 air flow meter 6 exhaust passage 7 catalytic converter 8 first oxygen sensor 9 second oxygen sensor 11 water temperature sensor 12 crank angle sensor 13 control unit 14 warning light

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F01N 3/20 F02D 45/00 341 F02D 45/00 368

Claims (5)

(57) [Claims] An upstream air-fuel ratio sensor disposed upstream of a catalytic converter disposed in an exhaust passage of the engine; a downstream air-fuel ratio sensor disposed downstream of the catalytic converter; Air-fuel ratio feedback control means for feedback-controlling the amount of fuel supplied to the engine to match the air-fuel ratio of the engine intake air-fuel mixture to the target air-fuel ratio based on the detection result of the upstream air-fuel ratio sensor. In the engine, a first deterioration diagnosis means for performing deterioration diagnosis of the catalyst based on a comparison between an output of the upstream air-fuel ratio sensor and an output of the downstream air-fuel ratio sensor; In a state where diagnosis cannot be performed
Only when that, the air-fuel ratio variation that gave forcibly caused is and a second deterioration diagnosis means for performing deterioration diagnosis of the catalyst based on the response time until detected by the downstream air-fuel ratio sensor Deterioration diagnostic device for internal combustion engines. 2. The apparatus according to claim 1, wherein the first deterioration diagnosis means performs deterioration diagnosis of the catalyst based on a ratio of an output cycle of the upstream air-fuel ratio sensor to an output cycle of the downstream air-fuel ratio sensor. A judgment level for judging that the catalyst is normal.
And a determination for determining that the catalyst has deteriorated.
When the ratio exists between the level and the
The apparatus for diagnosing catalyst deterioration of an internal combustion engine according to claim 1 , wherein the apparatus is determined to be in an active state . 3. The second deterioration diagnosis means forcibly controls the air-fuel ratio to a lean state with respect to a target air-fuel ratio prior to the air-fuel ratio feedback control means, and the lean state is determined on the upstream side. The air-fuel ratio is forcibly switched to a rich state with respect to the target air-fuel ratio from the state detected by the air-fuel ratio sensor on the downstream side, and the switching control from the lean state to the rich state is performed by the upstream air-fuel ratio sensor. Measuring the response time from the detection in step t to the detection of the switching control by the downstream air-fuel ratio sensor, and determining whether the catalyst is deteriorated or normal based on a comparison between the response time and the determination level. The catalyst degradation diagnosis device for an internal combustion engine according to claim 1 or 2, wherein: 4. The method according to claim 1, wherein the second deterioration diagnosis means executes the diagnosis based on the response time a plurality of times, and makes a final deterioration determination when the deterioration is diagnosed by a predetermined ratio or more in the plurality of times.
The catalyst deterioration diagnosis device for an internal combustion engine according to any one of claims 1 to 3, wherein the normality determination is performed when a rate of the deterioration diagnosis is less than a predetermined value. 5. A deterioration diagnosis prohibiting means for prohibiting the deterioration diagnosis by the second deterioration diagnosis means until the engine is stopped after the second deterioration diagnosis means determines the deterioration or normality. The device for diagnosing catalyst deterioration of an internal combustion engine according to any one of claims 1 to 4, wherein the device is provided.