JP3161249B2 - 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 detecting an oxygen concentration at each of an upstream side and a downstream side of an exhaust purification catalyst, and performing air-fuel ratio feedback control based on the detected values. The present invention relates to a device for diagnosing catalyst deterioration based on the total amount of exhaust heat from the start of the engine and the output fluctuation ratio of the oxygen sensor upstream of the catalyst and the oxygen sensor downstream of the catalyst in the internal combustion engine configured to execute the following.

[0002]

2. Description of the Related Art Conventionally, oxygen sensors are provided upstream and downstream of a three-way catalyst provided in an exhaust system for purifying exhaust gas, and the air-fuel ratio is fed back using detection values of these two oxygen sensors. Various types of control have been proposed (see Japanese Patent Application Laid-Open No. 2-33408).

Further, when the air-fuel ratio feedback control is performed using the oxygen sensors provided on the upstream and downstream sides of the catalyst as described above, that is, the rich state and the lean state with respect to the target air-fuel ratio are determined. In the repeated state, the output fluctuation frequency of the downstream oxygen sensor tends to be smaller than the output fluctuation frequency of the oxygen sensor on the upstream side due to the oxygen storage effect of the catalyst. When it decreases, the output fluctuation frequency of the downstream oxygen sensor approaches the value on the upstream side. Therefore, the deterioration of the catalyst is diagnosed by comparing the output fluctuation frequency of the oxygen sensor during the air-fuel ratio feedback control between upstream and downstream.

[0004] When the deterioration of the catalyst is diagnosed, fail-safe operation such as changing the control constant in the air-fuel ratio feedback control is performed.

[0005]

By the way, harmful exhaust gas is largely discharged when the catalyst is not sufficiently activated, that is, when the engine is operated in a cold state. Diagnosis is made only in the fully activated state. Therefore, even if the catalyst is deteriorated, the deterioration of the catalyst in a state where the catalyst is not sufficiently activated is not determined sufficiently accurately, and harmful exhaust gas discharged in a state where the catalyst is not sufficiently activated. Could be released without proper fail-safe action.

For example, in a system as shown in FIG. 11, the temperature of the upstream-side catalyst 71 starts to gradually increase at the time of engine cold start, and is activated first. Then downstream catalyst
72 is activated with a delay. That is, the exhaust emission at the time of engine cold is greatly affected by whether or not the upstream catalyst 71 is activated, and the exhaust emission after warm-up is how much the upstream catalyst 71 and the downstream catalyst 72 are. It is greatly affected by whether it is activated or not.

On the other hand, the deterioration of the catalyst progresses as it is exposed to a higher exhaust gas temperature. Therefore, the upstream catalyst 71 exposed to a higher exhaust gas temperature is more likely to deteriorate than the downstream catalyst 72. Here, conventionally, the activation performance at the time of cooling is indirectly determined based on the diagnosis after the activation of the upstream side catalyst 71, but the accuracy is not sufficient. That is, based on the catalyst deterioration diagnosis after the catalyst is activated, the deterioration diagnosis of the catalyst before the activation such as at the time of cooling is performed, so the accuracy is not sufficient, and the appropriate fail-safe is not performed. Harmful exhaust may be emitted.

[0008] The present invention has been made in view of the above circumstances, and it is possible to determine the deterioration of the catalyst before the catalyst is sufficiently activated, and to perform a more accurate catalyst deterioration diagnosis. The purpose is to enable appropriate fail-safe operation.

[0009]

Accordingly, an apparatus for diagnosing catalyst deterioration of an internal combustion engine according to the present invention, as shown in FIG. 1, includes an exhaust purification catalyst provided in an exhaust passage of the engine and an upstream side of the exhaust purification catalyst. An upstream oxygen sensor whose output value changes in response to the oxygen concentration in the exhaust gas, a downstream oxygen sensor whose output value changes in response to the oxygen concentration in the exhaust gas downstream of the exhaust purification catalyst, Air-fuel ratio feedback control means for feedback-controlling the amount of fuel supplied to the engine in a direction to bring the air-fuel ratio of the engine intake air-fuel mixture closer to the target air-fuel ratio based on the outputs of the upstream oxygen sensor and the downstream oxygen sensor,
In an internal combustion engine comprising: a total calorie calculating means for calculating the total calorific value of exhaust gas from the time of engine start; an upstream elapsed time from when lean rich in the upstream oxygen sensor is inverted to when it is inverted; Lean and oxygen sensor
And the elapsed time ratio calculation means for calculating a ratio between the downstream elapse before inversion from rich is inverted, the exhaust total heat from the time of the calculated engine start that the total amount of heat calculation means Tokoro
When reaching a constant target exhaust total heat, the ratio of the upstream side elapsed time and downstream elapsed time until the computed lean-rich by the elapsed time ratio calculation means for inverting the inverted
And a catalyst deterioration diagnosing means for diagnosing deterioration of the exhaust gas purification catalyst based on the rate . The catalyst deterioration diagnosis
The means is configured to reduce the target total heat amount of the exhaust gas at the time of starting the engine.
It is preferable to set variably according to the temperature of the recirculating water.

[0010] The catalyst deterioration of the internal combustion engine according to the present invention.
In the diagnostic apparatus, the catalyst deterioration diagnosis means may execute the elapsed time ratio operation.
After the lean rich calculated by the arithmetic means is inverted
Ratio of upstream elapsed time and downstream elapsed time until reversal
The total heat when the rate reaches a predetermined target elapsed time ratio
To the total calorific value of exhaust gas from the start of the engine calculated by the
And diagnosing deterioration of the exhaust purification catalyst based on the
May be implemented. Here, the catalyst deterioration diagnosing means includes
The ratio of the elapsed time of the target to the
It is good to set it variably. Further, the exhaust gas purifying catalyst includes exhaust temperature detecting means for detecting the temperature of exhaust gas on the upstream side of the exhaust gas purifying catalyst, and intake air flow rate detecting means for detecting a flow rate of intake air taken into the engine. The total heat quantity of the exhaust gas from the start of the engine may be calculated based on the intake air flow rate and the intake air flow rate.

[0011]

In FIG. 1, an upstream oxygen sensor and a downstream oxygen sensor are respectively provided upstream and downstream of an exhaust purification catalyst provided in an exhaust passage of an engine, and output in response to oxygen concentration in exhaust gas. A sensor whose value changes. The air-fuel ratio feedback control means feedback-controls the amount of fuel supplied to the engine in a direction in which the air-fuel ratio of the engine intake air-fuel mixture approaches the target air-fuel ratio based on the output values of the upstream oxygen sensor and the downstream oxygen sensor.

On the other hand, the elapsed time ratio calculating means reverses the upstream elapsed time from when the lean rich in the upstream oxygen sensor is inverted to when it is inverted, and after the lean rich in the downstream oxygen sensor is inverted. Calculate the ratio with the elapsed time on the downstream side. Here, due to the oxygen storage effect of the catalyst, the time required for inversion of the downstream oxygen sensor tends to be longer than the time required for inversion of the upstream oxygen sensor.

Here, if the catalyst has not deteriorated,
Since the oxygen storage effect is gradually exerted, the time required for inversion of the downstream oxygen sensor becomes gradually longer than the time required for inversion of the upstream side, and thus the elapsed time ratio (= upstream elapsed time / downstream) Side elapsed time) quickly approaches a value close to zero. On the other hand, when the catalyst is deteriorated and the oxygen storage effect is reduced, the time related to the inversion of the downstream oxygen sensor is not so different from the time related to the inversion of the upstream, so that the elapsed time ratio is a value close to 1. Some time is longer.

The total calorie computing means computes the total calorific value of the exhaust gas from the start of the engine. According to the fifth aspect of the invention, the exhaust gas temperature detecting means detects the temperature of the exhaust gas on the upstream side of the exhaust gas purification catalyst, and the intake air flow rate detecting means detects the flow rate of the intake air taken into the engine to obtain the total heat quantity. The total heat quantity of the exhaust gas from the start of the engine is calculated by the calculating means based on the exhaust gas temperature and the flow rate of the intake air taken into the engine.

Therefore, according to the first aspect of the present invention,
As shown in FIG. 2, if the elapsed time ratio HzRATE at the time when the total exhaust heat amount ΔQ from the start of the engine reaches the target total exhaust heat amount ΔQ _T is equal to or less than the predetermined elapsed time ratio HzRATE ₀ , the catalyst has not deteriorated. If the elapsed time ratio HzRATE when the total exhaust heat amount ΔQ from the start of the engine reaches the target total exhaust heat amount ΔQ _T is larger than the predetermined elapsed time ratio HzRATE ₀ , it can be determined that the catalyst has deteriorated.

According to the third aspect of the present invention, as shown in FIG. 3, the elapsed time ratio HzRATE becomes lower than 1 and reaches the target elapsed time ratio HzRATE _T from the time of starting the engine. The exhaust total heat quantity ΣQ of the specified exhaust total heat quantity ΣQ
If it is ₀ or less, it can be determined that the catalyst has not deteriorated, and when the elapsed time ratio HzRATE falls below 1 and reaches the target elapsed time ratio HzRATE _T , the total exhaust heat quantity ΣQ from the start of the engine at the time when the target elapsed time ratio HzRATE _T has reached the predetermined value If the total calorific _{value of} exhaust gas is larger than 0Q ₀ ,
It can be determined that the catalyst has deteriorated.

That is, the catalyst deterioration diagnosing means diagnoses the deterioration of the exhaust gas purifying catalyst based on the total heat quantity of the exhaust gas from the start of the engine and the ratio of the elapsed time on the upstream side to the elapsed time on the downstream side.

[0018]

Embodiments of the present invention will be described below. In FIG. 4 showing one embodiment, an internal combustion engine 1 includes an air cleaner 2.
Air is sucked from the air through the intake duct 3, the throttle valve 4 and the intake manifold 5. A fuel injection valve 6 is provided in each branch of the intake manifold 5 for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that is energized by a solenoid and opens, and is deenergized and closed, and is energized and opened by an injection pulse signal from a control unit 12 described below. Fuel which is pressure-fed from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator is injected and supplied into the intake manifold 5.

Each of the combustion chambers of the engine 1 is provided with an ignition plug 7, which ignites a spark to ignite and burn an air-fuel mixture. Then, exhaust gas is exhausted from the engine 1 via an exhaust manifold 8, an exhaust duct 9, a three-way catalyst 10 for exhaust gas purification (an exhaust gas purification catalyst), and a muffler 11. The three-way catalyst 10 has an oxygen storage effect and is a catalyst that oxidizes CO and HC in exhaust components and reduces NOx to convert it to other harmless substances. When the mixture is burned at the stoichiometric air-fuel ratio, the two conversion efficiencies are the best.

The control unit 12 includes a CPU, an RO,
A microcomputer including an M, a RAM, an A / D converter, and an input / output interface is provided. The microcomputer receives detection signals from various sensors, performs arithmetic processing as described later, Control the operation. As the various sensors, a hot wire type or flap type air flow meter 13 is provided in the intake duct 3, and outputs a voltage signal corresponding to the intake air amount A of the engine 1. That is, the air flow meter 13 has a function of an intake air flow rate detecting unit.

A crank angle sensor 14 is provided and outputs a reference angle signal REF for each predetermined piston position and a unit angle signal POS for each unit angle. Here, the engine rotation speed Ne can be calculated by measuring the generation cycle of the reference angle signal REF or the number of generations of the unit angle signal POS within a predetermined time. Further, a water temperature sensor 15 for detecting a cooling water temperature Tw of the water jacket of the engine 1 is provided.

Further, a first oxygen sensor 16 as an upstream oxygen sensor is provided at the gathering portion of the exhaust manifold 8 upstream of the three-way catalyst 10.
A second oxygen sensor 17 as a downstream oxygen sensor is provided downstream of 10 and upstream of the muffler 11. The first
The oxygen sensor 16 and the second oxygen sensor 17 are known sensors (for example, a zirconia tube type oxygen sensor) whose output values change in response to the oxygen concentration in the exhaust gas. Is a rich / lean sensor that can detect the rich / lean ratio of the exhaust air-fuel ratio with respect to the stoichiometric air-fuel ratio by utilizing the fact that the air-fuel ratio changes suddenly.

In this embodiment, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the first and second oxygen sensors 16 and 17 output a high voltage (rich output) near 1 V, and output the air-fuel ratio. Is lower than the stoichiometric air-fuel ratio, a low voltage (lean output) near 0 V is output. Further, a temperature sensor 19 as exhaust temperature detecting means for detecting the temperature of the exhaust gas on the upstream side of the three-way catalyst 10 is provided at the gathering portion of the exhaust manifold 8 on the upstream side of the three-way catalyst 10.

Further, an ignition switch 20 for determining ON / OFF of the engine 1 is provided. Here, the CPU of the microcomputer built in the control unit 12 calculates the basic fuel injection amount Tp based on the intake air flow rate A and the engine speed Ne detected by the sensors, while the cooling water temperature Tw Various correction coefficients COEF for correcting the basic fuel injection amount Tp are calculated and set based on the above.

When the predetermined feedback control condition is satisfied, the control unit 12 having the function as the air-fuel ratio feedback control means calculates an air-fuel ratio feedback correction coefficient LMD for correcting the basic injection amount Tp. The calculation is performed as follows based on the outputs of the first oxygen sensor 16 and the second oxygen sensor 17. That is, as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-72438, the air-fuel ratio is controlled by proportional / integral control in accordance with the rich / lean relative to the target air-fuel ratio determined based on the output of the upstream first oxygen sensor 16. Feedback correction coefficient LMD
On the other hand, the proportional operation amount (proportional amount P) in the proportional / integral control is corrected based on the rich / lean relative to the target air-fuel ratio detected by the second oxygen sensor 17 on the downstream side.

However, the air-fuel ratio feedback control using the first oxygen sensor 16 and the second oxygen sensor 17 is not limited to the above-described correction of the proportional operation amount, and the timing of performing the proportional control is determined by the second oxygen sensor. A configuration that corrects based on the detection result of 17 or a configuration that corrects the reference level used for rich / lean determination based on the output of the first oxygen sensor 16 based on the output of the second oxygen sensor 17 may be used. good.

Then, the basic fuel injection amount Tp is changed by the various correction coefficients COEF and the air-fuel ratio feedback correction coefficient L.
The final fuel injection amount Ti is obtained by correcting with the MD and the correction amount Ts based on the battery voltage, and an injection pulse signal having a pulse width corresponding to the fuel injection amount Ti is output to the fuel injection valve 6 at a predetermined timing. I do. On the other hand, the control unit 12 is provided with a self-diagnosis function for diagnosing the deterioration of the three-way catalyst 10, as shown in the flowcharts of FIGS.

Incidentally, in this embodiment, the total calorie calculating means,
The functions as the elapsed time ratio calculating means and the catalyst deterioration diagnosing means are provided in the control unit 12 by software as shown in the flowcharts of FIGS. 5 to 7 and FIG. First, a first embodiment of the self-diagnosis is shown in FIGS.
This will be described according to the flowchart of FIG.

In the flow chart of FIG. 5, in step 1 (S1 in the figure, the same applies hereinafter), an ON / OF signal from the ignition switch 20 is read, and when the power is turned on, the flow proceeds to the following steps. In step 2, the cooling water temperature Tw _ST of the engine 1 at the time of starting is read by the water temperature sensor 15.

In step 3, when the engine 1 is started at the cooling water temperature Tw _ST read in step 2, the three-way catalyst 10
The target total exhaust heat quantity ΣQ _T required for activation is read. Here, the target total exhaust heat quantity ΣQ _T is an amount obtained in advance by an experiment or the like. As shown in FIG. 8, the lower the cooling water temperature Tw _ST of the engine 1 at the time of starting, the more the three-way catalyst 10 is cooled. Since a large amount of total exhaust heat is required, and the higher the cooling water temperature Tw _ST of the engine 1 at the time of starting, the higher the temperature of the three-way catalyst 10 becomes, the smaller the total exhaust heat amount ΔQ _T becomes.

In step 4, the ignition switch
From 20, it is determined whether the engine 1 has been started. Note that whether or not the engine 1 has been started may be determined based on whether or not the engine rotation speed Ne detected by the crank angle sensor 14 has reached a predetermined rotation speed. In step 5, the total heat quantity of exhaust ΣQ exhausted from the engine 1 from the time of starting the engine is calculated according to the flowchart shown in FIG.

That is, in step 21, it is determined whether or not the engine 1 has been started. In step 22, the intake air amount A of the engine 1 is read from the air flow meter 13. In step 23, the temperature _TEXT of the exhaust gas upstream of the three-way catalyst 10 is read by the temperature sensor 19 as the temperature of the exhaust gas flowing into the three-way catalyst 10. In step 24, the heat quantity Q of the exhaust gas flowing into the three-way catalyst 10 is calculated according to the following equation.

Q = T _EXT × A × K1 where K1 is a calorific value conversion coefficient. In step 25, the total heat quantity ΔQ of the exhaust gas flowing into the three-way catalyst 10 since the start of the engine 1 is calculated by integrating the exhaust heat quantity Q calculated in step 24.

ΣQ = ∫Qdt Returning to the description of FIG. In step 6, it is determined whether or not the operating condition is such that the air-fuel ratio feedback control is performed. For example, when the coolant temperature Tw is equal to or lower than a predetermined value, when the fuel is being increased at the time of starting or warming up, when the output signal of the first oxygen sensor 16 has never been inverted, or when the fuel is being cut, It is assumed that none of the conditions is an operating condition for performing feedback control of the air-fuel ratio.

If it is determined that the operating condition is such that the air-fuel ratio feedback control is performed, the process proceeds to step S7. Here, when the feedback control of the air-fuel ratio is performed, as shown in FIG. 9, the output of the oxygen sensor periodically changes according to the change of the exhaust air-fuel ratio, and the air-fuel ratio feedback correction coefficient αn periodically changes. fluctuate.

In step 7, the elapsed time ratio HzRATE when the feedback control is being performed is calculated according to the flowchart shown in FIG. That is, step 41
Then, the period _TF of the output waveform of the first oxygen sensor 16 is read. In step 42, it reads the period T _R of the output waveform of the second oxygen sensor 17. In step 43, the ratio of the period T _F obtained in step 41 to the period T _R obtained in step 42 is calculated as an elapsed time ratio HzRATE.

HzRATE = T _F / T _R Return to the description of FIG. 5 again. In step 8, step 5
In total heat [sum] Q of exhaust gas flowing into the three-way catalyst 10 from the calculated engine 1 is started, it is determined whether the became read elaborate target exhaust total heat [sum] Q _T or more in Step 3, [sum] Q ≧ sigma
If determined to be Q _T , go to step 9
Read the determination elapsed time ratio HzRATE ₀ .

[0038] At step 10, a comparison between the elapsed time ratio HZRATE the determination elapsed time ratio HZRATE ₀ calculated in step 7. Here, the determination elapsed time ratio HzRATE ₀ is, as shown in FIG. 2, the elapsed time ratio Hz when the total exhaust heat quantity ΔQ from the start of the engine reaches the target total exhaust heat quantity ΔQ _T.
If the RATE is equal to or less than the determination elapsed time ratio HzRATE _0, it can be determined that the catalyst has not deteriorated, and the elapsed time ratio HzRATE when the total exhaust heat quantity ΣQ from the engine start reaches the target total exhaust heat quantity ΣQ _T is determined. If the elapsed time ratio is larger than ₀ , it can be determined that the catalyst has deteriorated.

Therefore, in step 10, HzRATE ≦ Hz
When RATE ₀ is determined, it indicates that the three-way catalyst 10 has a sufficient function as a catalyst, that is, the three-way catalyst 10
Is normal, it is determined that the three-way catalyst 10 is normal. If it is determined in step 10 that HzRATE ≦ HzRATE ₀ (HzRATE> HzRATE ₀ ), the three-way catalyst 10 does not have a sufficient function as a catalyst, and
Flowed through without reaction of the exhaust gas is performed at 10, with the rate of change of the air-fuel ratio detected by the second oxygen sensor 17 is also decreased, the period T _R of the output waveform also does not become large, when the engine is started with Total exhaust heat from the engine ΣQ is the target total exhaust heat ΣQ
Despite reaching _T , it can be considered that the HzRATE does not decrease. Accordingly, the process proceeds to step 12, where it is determined that the three-way catalyst 10 has deteriorated, and the process proceeds to step 13, for example, a pilot lamp or the like is turned on to display the deterioration of the three-way catalyst 10.

As described above, in the first embodiment,
The total exhaust heat quantity ΣQ from the start of the engine is the target total exhaust heat quantity ΣQ
_{If T} is reached, if the three-way catalyst 10 is normal, HzRATE
When the three-way catalyst 10 is deteriorated and the HzRATE does not decrease when the three-way catalyst 10 is deteriorated, the first oxygen sensor 16 and the second oxygen sensor 17 are provided with the three-way catalyst 10 interposed therebetween. A temperature sensor 19 for detecting the temperature of the exhaust gas flowing into the three-way catalyst 10 is provided, and the deterioration of the three-way catalyst 10 is diagnosed based on the total exhaust heat quantity ΔQ and the elapsed time ratio HzRATE.

Accordingly, the deterioration diagnosis of the three-way catalyst 10 can be performed without waiting for the three-way catalyst 10 to be completely activated, and the deterioration of the three-way catalyst 10 can be detected quickly and more accurately. Thus, when the three-way catalyst 10 is deteriorated, there is an effect that it is possible to appropriately perform fail-safe such as changing a control constant in the air-fuel ratio feedback control.

Next, a second embodiment of the self-diagnosis will be described with reference to the flow charts of FIGS. Note that steps having the same functions as those in the flowchart of FIG. 7 described above are denoted by the same step numbers, and description thereof will be omitted. In step 23, a target elapsed time ratio HzRATE _T required to activate the three-way catalyst 10 when the engine 1 is started at the cooling water temperature Tw _ST read in step 2 is set. Here, if the target elapsed time ratio HZRATE _T is the elapsed time ratio HZRATE reaches the target elapsed time ratio HZRATE _T is be regarded when sufficient exhaust total heat is supplied to the three-way catalyst 10 This is a possible ratio, and is set, for example, as shown in FIG.

In step 28, the process calculated in step 7 is executed.
The overtime ratio HzRATE starts to decrease and set in step 23.
Target elapsed time ratio HzRATE_TDetermine if
HzRATE ≦ HzRATE_TIf it is determined that
Proceed to step 29 to determine the total exhaust heat quantity ΣQ₀Read. Stay
In Step 30, the total exhaust calorific value ΣQ calculated in Step 5 is determined.
Constant exhaust total heat ΣQ ₀Compare with.

Here, if the total exhaust heat quantity ΔQ from the start of the engine at the time when the elapsed time ratio HzRATE falls below 1 and reaches the target elapsed time rate HzRATE _T is equal to or less than the determination total exhaust heat quantity ΔQ _0. , So much heat is three way catalyst 10
Even if it is not supplied, the elapsed time ratio HzRATE is sufficiently reduced, and it can be determined that the catalyst has not deteriorated.
Further, if the exhaust total heat [sum] Q from when the engine is started at the time when the elapsed time ratio HZRATE is come lower than 1 reaches the target elapsed time ratio HZRATE _T is greater than the determination exhaust total heat [sum] Q _0, a sufficient amount of exhaust Is supplied to the three-way catalyst 10, the elapsed time ratio HzRATE is not sufficiently reduced, and it can be determined that the catalyst has deteriorated.

Therefore, in step 30, ΣQ ≦ ΣQ
When it is determined to be ₀ , it indicates that the three-way catalyst 10 has a sufficient function as a catalyst, that is, when it is possible to determine that the three-way catalyst 10 is normal, and Proceeding to 11, it is determined that the three-way catalyst 10 is normal. In addition step 10 is not a ΣQ ≦ ΣQ ₀ (ΣQ>
When it is determined to be ΣQ ₀ ), the three-way catalyst 10 does not have a sufficient function as a catalyst, and the three-way catalyst 10 passes without causing a reaction of exhaust gas.
Since the fallen rate of change of the air-fuel ratio detected by the period T _R of the output waveform takes time becomes large, with and elapsed time ratio HzRATE is come lower than first target elapsed time ratio It can be considered that a large amount of the total exhaust heat ΣQ from the start of the engine is required before reaching HzRATE _T. Therefore, proceed to step 12, and the three-way catalyst
It is determined that the three-way catalyst 10 has deteriorated, and the process proceeds to step 13, where, for example, a pilot lamp or the like is turned on to display the deterioration of the three-way catalyst 10.

As described above, in the second embodiment,
When the elapsed time ratio HzRATE reaches the target elapsed time ratio HzRATE _T , if the three-way catalyst 10 is normal, the total exhaust heat quantity ΣQ
Less than the determination exhaust total heat [sum] Q _0, that is less elapsed time, heat ratio HzRATE decreases, the three-way catalyst 10 has deteriorated determined exhaust total heat [sum] Q ₀ more exhaust total heat [sum] Q
Paying attention to the fact that the elapsed time ratio HzRATE does not decrease unless the oxygen is supplied, the first oxygen sensor 16 and the second oxygen sensor 17 are provided with the three-way catalyst 10 interposed therebetween, and the temperature of the exhaust gas flowing into the three-way catalyst 10 is further reduced. A temperature sensor 19 for detection is provided, and the deterioration of the three-way catalyst 10 is diagnosed based on the exhaust total heat quantity ΔQ and the elapsed time ratio HzRATE.

Therefore, the second embodiment has the same effects as the first embodiment.

[0048]

As described above, according to the present invention, an oxygen sensor is provided on each of the upstream and downstream sides of the exhaust purification catalyst, and exhaust temperature detecting means for detecting the temperature of exhaust gas on the upstream side of the exhaust purification catalyst is provided. Calculating the total heat quantity of the exhaust gas from the start of the engine based on the outputs of these oxygen sensors and the exhaust gas temperature and the intake air flow rate, and when the total heat quantity of the exhaust gas from the start of the engine reaches a predetermined total heat quantity of the exhaust gas. When the three-way catalyst is deteriorated, the upstream elapsed time from when the lean rich in the upstream oxygen sensor is inverted to when it is inverted, and the time when the lean rich in the downstream oxygen sensor is inverted and then inverted. Focusing on the fact that the ratio of the three-way catalyst to the downstream elapsed time does not decrease, the deterioration diagnosis of the catalyst is performed, so that the deterioration diagnosis of the three-way catalyst can be performed without waiting for the three-way catalyst to be completely activated. Is possible Doo ing. Calculate elapsed time ratio
If the three-way catalyst has not deteriorated, a large amount of heat
If the elapsed time ratio is sufficiently reduced even if
Focusing on the above, the catalyst degradation diagnosis was performed,
Without waiting for the three-way catalyst to fully activate,
Deterioration diagnosis of the three-way catalyst becomes possible. Therefore, according to the present invention,
Then, it is possible to detect the deterioration of the three-way catalyst quickly and more accurately, and it is possible to secure the opportunity of the catalyst deterioration diagnosis promptly and improve the reliability of the diagnosis, and to deteriorate the three-way catalyst. In this case, there is an effect that it is possible to appropriately perform fail-safe such as changing a control constant in the air-fuel ratio feedback control.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a characteristic diagram illustrating the operation of the present invention.

FIG. 3 is a characteristic diagram illustrating the operation of the present invention.

FIG. 4 is a system schematic diagram showing an embodiment of the present invention.

FIG. 5 is a flowchart showing catalyst deterioration diagnosis control according to the first embodiment of the present invention.

FIG. 6 is a flowchart showing a routine for calculating the total heat quantity of exhaust gas / Q according to the present invention;

FIG. 7 is a flowchart showing an elapsed time rate HzRATE calculation routine according to the present invention;

FIG. 8 shows the target exhaust total heat quantity ΔQ _T and cooling water temperature T according to the present invention.
w Characteristic diagram showing the relationship with _ST

FIG. 9 is a time chart showing characteristics of feedback control in the embodiment of the present invention.

FIG. 10 is a flowchart illustrating catalyst deterioration diagnosis control according to a second embodiment of the present invention.

FIG. 11 is a schematic diagram illustrating a conventional problem.

[Explanation of symbols]

 Reference Signs List 1 engine 6 fuel injection valve 10 three-way catalyst (exhaust purification catalyst) 12 control unit 13 air flow meter 14 crank angle sensor 16 first oxygen sensor 17 second oxygen sensor 19 temperature sensor

Claims (5)

(57) [Claims] An exhaust purification catalyst provided in an exhaust passage of an engine; an upstream oxygen sensor whose output value changes in response to an oxygen concentration in exhaust gas upstream of the exhaust purification catalyst; A downstream oxygen sensor whose output value changes in response to the oxygen concentration in the exhaust gas on the downstream side, and the air-fuel ratio of the engine intake air-fuel mixture based on the output of each of the upstream oxygen sensor and the downstream oxygen sensor. Air-fuel ratio feedback control means for feedback-controlling the amount of fuel supplied to the engine in a direction approaching the fuel ratio; in an internal combustion engine comprising: a total heat quantity calculation means for calculating a total heat quantity of exhaust gas from the time of engine start; Elapsed time on the upstream side from when lean rich is inverted in the sensor to when it is inverted, and downstream elapsed time from when lean rich is inverted on the downstream oxygen sensor until it is inverted. And the elapsed time ratio calculation means for calculating a ratio, at which the exhaust total heat from the time of the calculated engine start that the total amount of heat calculating means reaches a predetermined target exhaust total heat, the after <br/> over time Catalyst deterioration diagnosing means for diagnosing the deterioration of the exhaust purification catalyst based on a ratio of the upstream elapsed time and the downstream elapsed time from when the lean / rich calculated by the ratio calculating means is inverted to when it is inverted, An apparatus for diagnosing catalyst deterioration of an internal combustion engine, comprising: 2. The method according to claim 1, wherein the catalyst deterioration diagnosis means includes a target exhaust total exhaust amount.
The amount of heat can be varied according to the coolant temperature at engine start
The internal combustion engine according to claim 1, wherein
Catalyst deterioration diagnosis device. 3. An exhaust purification catalyst provided in an exhaust passage of an engine.
In response to the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst.
In response to the upstream oxygen sensor whose output value changes, and the oxygen concentration in the exhaust gas downstream of the exhaust purification catalyst,
A downstream oxygen sensor whose output value changes , and each of the upstream oxygen sensor and the downstream oxygen sensor
Set the air-fuel ratio of the engine intake air-fuel mixture to the target air-fuel ratio based on the output
Feedback system for fuel supply to the engine in the direction of approach
Control means for controlling the air-fuel ratio feedback control means for controlling the total heat quantity of the exhaust gas from the start of the engine in the internal combustion engine comprising :
The lean-rich in the upstream oxygen sensor reverses?
Elapsed time on the upstream side until reversal and the downstream oxygen sensor
From when lean rich reverses to when it reverses
Elapsed time ratio calculator that calculates the ratio with the downstream elapsed time
And the lean / rear calculated by the elapsed time ratio calculating means.
And the elapsed time from when the switch
The ratio with the flow side elapsed time reaches the predetermined target elapsed time ratio.
At the time of engine start calculated by the total calorie calculation means
Degradation of the exhaust gas purification catalyst based on the total amount of exhaust heat from
Catalyst deterioration diagnosing means for diagnosing the deterioration of the catalyst of the internal combustion engine.
Diagnostic device. 4. The method according to claim 1, wherein the catalyst deterioration diagnosis means is configured to determine whether the target elapses.
Variable depending on the coolant temperature at engine start
The internal combustion engine according to claim 3, wherein the internal combustion engine is set to:
Catalyst deterioration diagnosis device. 5. An exhaust gas temperature detecting means for detecting a temperature of exhaust gas on an upstream side of an exhaust purification catalyst, and an intake air flow rate detecting means for detecting a flow rate of intake air to be taken into an engine. The apparatus according to any one of claims 1 to 4, wherein a total calorific value of the exhaust gas from an engine start is calculated based on the exhaust gas temperature and the intake air flow rate.