JP2846552B2 - Catalyst 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 a catalyst diagnostic device for diagnosing whether a catalyst of an internal combustion engine has deteriorated.

[0002]

2. Description of the Related Art A device for purifying exhaust gas of an internal combustion engine mainly comprises a catalytic converter and an air-fuel ratio feedback control unit. The catalytic converter includes HC, N contained in exhaust gas.
It is arranged in the exhaust pipe to remove Ox and CO. In the air-fuel ratio feedback control unit, an O ₂ sensor (oxygen sensor) is disposed upstream of the catalytic converter, and the air-fuel ratio is detected. Then, the fuel injection amount to the internal combustion engine is controlled such that the air-fuel ratio becomes a predetermined value (stoichiometric). This is because the catalytic converter functions effectively when the air-fuel ratio upstream of the catalytic converter is stoichiometric.

[0003]

In the ordinary three-way catalyst system, if the performance of the catalytic converter itself deteriorates, even if the air-fuel ratio is accurately controlled by the above-mentioned air-fuel ratio feedback control unit, harmful components are not affected. Conversion efficiency decreases. Therefore, it is necessary to determine the state of deterioration of the catalytic converter, and to warn the user if the state has deteriorated.

[0004] As an apparatus for judging the deterioration state of a catalytic converter, for example, there is an "catalyst deterioration judging apparatus for an internal combustion engine" described in JP-A-2-3091. this is,
Oxygen sensors upstream and downstream of the catalytic converter (Note:
In this case, the oxygen sensor is a binary sensor), and a time difference from when the output value of the upstream oxygen sensor is inverted to when the output value of the downstream sensor is inverted is measured. Then, the deterioration state of the catalyst is determined based on the magnitude of the measured time difference. Specifically, if the time difference is small, it is determined that the catalyst is in a deteriorated state. However, in the conventional catalyst deterioration determination device, the deterioration diagnosis cannot be executed unless the catalyst is in a stable state, that is, for example, when the catalyst temperature does not exceed 400 ° C. (when the catalyst temperature is 400 In order to reach ゜ C or more, the vehicle must run at a speed higher than a certain speed (for example, 80 km / h). Therefore, conventionally, although the catalytic converter is deteriorated, the catalyst diagnosis condition is not satisfied, so that diagnosis cannot be performed, and deteriorated exhaust gas is exhausted from the deteriorated catalytic converter for a long time. There was a possibility.

[0005] The object of the present invention is not only when traveling at high speed,
It is an object of the present invention to provide a catalyst diagnosis device for an internal combustion engine that can execute a catalyst deterioration diagnosis even during a middle-speed running, a low-speed running, an idling, and the like.

[0006]

The present invention is configured as follows to achieve the above object. In a catalyst diagnosis device for an internal combustion engine, a front air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas on the upstream side of a catalyst, a rear air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas on a downstream side of the catalyst, a front air-fuel ratio sensor, and a rear air-fuel ratio sensor Conversion efficiency of catalyst based on output signal from air-fuel ratio sensor
A catalyst deterioration degree calculating unit that calculates the degree of deterioration of the catalyst corresponding to, a catalyst temperature estimating unit that estimates the temperature of the catalyst, an operating state estimating unit that estimates the operating state of the vehicle, and for each operating state,
Conversion efficiency above a specified value above the temperature at which conversion efficiency is stable
A deterioration determination criterion storage unit that stores a deterioration determination criterion based on a change characteristic of a normal catalyst with respect to temperature, and a catalyst deterioration degree calculated by a catalyst deterioration degree calculation unit and estimated by a catalyst temperature estimation unit. It was based on the catalyst temperature, and calculates the change characteristic of the degradation degree against <br/> the temperature of the catalyst, reading the deterioration determination reference in the operating state indicated by the driving state estimation unit from deterioration determination reference storage unit, the deterioration determination Reference and change in the calculated degree of deterioration
By comparing the characteristics and determining degradation determining unit deterioration of the catalyst
Equipped with a.

Preferably, the catalyst diagnosis device for an internal combustion engine further includes an intake air amount sensor for detecting an intake air amount of the internal combustion engine, and the catalyst temperature estimating section includes an intake air amount detected by the intake air amount sensor. Based on the above, the catalyst temperature is estimated. Preferably, the catalyst diagnostic device for an internal combustion engine further includes a fuel injection amount control unit that calculates a fuel injection amount of the fuel injection valve and supplies a fuel injection pulse signal to the fuel injection valve. Estimates the catalyst temperature based on the pulse width of the fuel injection pulse signal.

Preferably, the catalyst diagnostic apparatus for an internal combustion engine further includes a fuel injection amount control unit for calculating a fuel injection amount of the fuel injection valve and supplying a fuel injection pulse signal to the fuel injection valve. The temperature estimating unit estimates the catalyst temperature based on the fuel injection amount calculated by the fuel injection amount control unit. Preferably, in the catalyst diagnosis device for an internal combustion engine, further comprising an exhaust gas temperature sensor for measuring an exhaust gas temperature of the internal combustion engine, the catalyst temperature estimating unit,
The catalyst temperature is estimated based on the exhaust gas temperature detected by the exhaust gas temperature sensor.

Further, in a catalyst diagnosis device for an internal combustion engine,
The output signals from the front air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas on the upstream side of the catalyst, the rear air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas on the downstream side of the catalyst, and the front air-fuel ratio sensor and the rear air-fuel ratio sensor A catalyst deterioration degree calculation unit that calculates a degree of deterioration of the catalyst corresponding to the conversion efficiency of the catalyst, a catalyst temperature measurement unit that measures the temperature of the catalyst, an operation state estimation unit that estimates an operation state of the vehicle, and a vehicle. Conversion efficiency is low for each operating condition
And deterioration determination reference storage unit for storing the deterioration determination criteria based on the change characteristics with respect to temperature of normal catalysts having a predetermined value or more conversion efficiency at a constant temperature or more, the catalyst deterioration degree calculation unit
Measured by the calculated catalyst deterioration degree and catalyst temperature
On the basis of the catalyst temperature degradation, and calculates the change characteristic of the deterioration degree against the temperature of the catalyst, reading the deterioration determination reference in the operating state indicated by the driving state estimation unit from deterioration determination reference storage unit, which the read A deterioration determination unit is provided for comparing the determination criterion with the calculated change characteristic of the degree of deterioration to determine the deterioration of the catalyst.

Preferably, in the catalyst diagnosis device for an internal combustion engine, the catalyst deterioration degree calculating section includes a cross-correlation function between an output signal of the front air-fuel ratio sensor and an output signal of the rear air-fuel ratio sensor, and a function of the front air-fuel ratio sensor. A correlation function calculator for calculating an autocorrelation function of the output signal; a sequential deterioration index calculator for calculating a sequential deterioration index which is a ratio between a maximum value of the cross-correlation function and the autocorrelation function; A final deterioration index calculating unit that calculates a final deterioration index that is an average value of the deterioration indexes and outputs the final deterioration index as a catalyst deterioration degree.

[0011]

The operating state estimating section estimates the operating state of the vehicle, and the catalyst temperature estimating section estimates the catalyst temperature. Further, the catalyst deterioration degree is calculated by the catalyst deterioration degree calculation unit based on the output signals from the front air-fuel ratio sensor and the rear air-fuel ratio sensor. If the deterioration criterion is set, the change in the degree of deterioration of the normal catalyst with respect to the change in the temperature of the catalyst is set for each operating state of the vehicle, and is stored in the deterioration criterion storage unit. When the deterioration of the catalyst is determined, the change in the degree of deterioration with respect to the change in the calculated catalyst temperature is calculated. Then, the deterioration criterion corresponding to the operating state at that time is read from the deterioration criterion storage unit. The read deterioration determination criterion is compared with a change in the calculated degree of deterioration with respect to a temperature change. If the change in the calculated degree of deterioration is larger than the deterioration determination reference, the deterioration determining unit determines that the catalyst has deteriorated.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a first embodiment of the present invention. In FIG. 1, a fuel injection control unit 7 includes an air-fuel ratio feedback calculation unit 8, a fuel injection amount calculation unit 9,
And an output unit 10 for controlling a fuel injection amount of the engine 1. A front O ₂ sensor, that is, an oxygen sensor (air-fuel ratio sensor) 3 is disposed upstream of the catalytic converter 2. The front O ₂ sensor 3 is a lambda (λ) sensor, and for example, zirconia or titania is used as a material of the detection element.

The fuel injection amount calculation section 9 is based on the intake air amount Qa detected by the intake air amount sensor 5 and the rotation speed Ne detected by the rotation speed detection sensor 6, and basically calculates the following equation (1). The injection amount F0 is calculated. F0 = k0Qa / Ne (1) where k0 is a predetermined coefficient. On the other hand, the air-fuel ratio feedback calculation unit 8 samples the output signal of the front O2 sensor 3 disposed upstream of the catalytic converter 2 at a predetermined timing, and, based on the detected value, sets the air-fuel ratio to a desired value. Then, the correction coefficient α is calculated and supplied to the fuel injection amount calculation unit 9.

The fuel injection amount calculator 9 calculates the injection amount F by adding the correction coefficient α to the basic injection amount F0 according to the following equation (2). F = k0Qa / Ne (1 + α) (2) Then, the fuel injection amount calculator 9 supplies a signal indicating the calculated injection amount F to the output unit 10. Then, the output unit 10
Applies a voltage duty signal corresponding to the injection amount F to the fuel injection valve 26. Due to the air-fuel ratio control described above, the air-fuel ratio is perturbed upstream and downstream of the catalytic converter 2 at values before and after stoichiometry.

In the present invention, the perturbation of the air-fuel ratio by the air-fuel ratio feedback control is used as a test signal for diagnosing deterioration of the catalytic converter. That is, if the catalytic converter 2 is not deteriorated, the perturbation of the air-fuel ratio is reduced in the downstream of the catalytic converter 2 due to the oxidation / reduction action of the catalyst. On the other hand, when the catalytic converter 2 deteriorates, the downstream air-fuel ratio perturbation approaches the upstream one. Thus, the deterioration is diagnosed by focusing on the similarity of the air-fuel ratio perturbation before and after the catalytic converter.

The catalyst deterioration diagnosing means 11 includes a load estimating unit 15
And a catalyst deterioration index calculating unit 18 and a catalyst temperature estimating unit 19
And an operating state estimating unit 20. Further, the catalyst deterioration diagnosing means diagnosis 11 includes a comparing unit 21, a judgment index setting unit 22, a judgment index storage unit 23, and a deterioration judgment unit 24.
And FIG. 2 is a detailed block diagram of the catalyst deterioration index calculator 18. In FIG. 2, the front O ₂ sensor 3
Is supplied to the sampling unit 12A.
Sampling is performed at regular intervals or at regular angles, and is temporarily stored in the memory 13A. Further, a rear O ₂ sensor (air-fuel ratio sensor) disposed downstream of the catalytic converter 2
4 is supplied to the sampling unit 12B. Then, it is sampled at regular intervals or at regular angles, and is temporarily stored in the memory 13B.

Next, the output signal x from the memory 13A and the output signal y from the memory 13B are calculated by the cross-correlation calculator 1
4B. The cross-correlation calculator 14B calculates the following equation (3
The calculations shown in -1) to (3-n) are executed. Σx _n y ₀ = x ₀ y ₀ + ... x _{od n} y ₀ --- (3-1) Σx _n1 y ₀₁ = x ₀₁ y ₀₁ + ... x _odn1 y _{01 -----} (3-2) _{~ Σx nn y 0n = x 0n} y 0n + ··· x odnn y 0n --- (3-n) that is, the sensor 4 at the time t2 shown in FIG. 3 (B)
A signal y ₀ of the signal from the signal x _ODN sensor 3 at the time t0 shown in FIG. 3 (A) to x _0, each of the product is calculated. Subsequently, a signal y ₀₁ at time t3,
The product of each of the signals x _odn1 to x ₀₁ is calculated. In this way, calculations are performed until the respective products of the signal y _0n and the signals x _odnn to x _0n are obtained. Note that in FIG. 3, from time t0 to t1
Is a delay time (phase) of the output signal S4 of the sensor 4 with respect to the output signal S3 of the sensor 3. Signal x
The product of the signal x and the signal x delayed by τ with respect to the signal x takes the maximum value. Then, the calculation results obtained by the above equations (3-1) to (3-n) are supplied to the cross-correlation function calculation unit 14D, and the cross-correlation function Y shown in the following equation (4) is calculated.

[0018]

(Equation 1)

The output signal x from the memory 13A is
It is supplied to the autocorrelation calculator 14A. Autocorrelation calculator 1
4A executes the calculation shown in the following equation (5).

[0020]

(Equation 2)

Then, the calculated auto-correlation function X and cross-correlation function Y are supplied to the calculation unit 16A. Calculation unit 1
6A calculates the sequential deterioration index Φi according to the following equation (6). .PHI.i = YM / X (6) where YM is the maximum value of the term constituting the cross-correlation function Y. When the catalytic converter 2 deteriorates, the similarity of the air-fuel ratio perturbation before and after the catalytic converter 2 increases,
The successive deterioration index Φi increases (approaches 1). This is shown in FIG. That is, the deterioration index Φia when the deterioration of the catalytic converter 2 is large is the deterioration index Φi when the deterioration is small.
It is larger than b.

As described above, the deterioration index Φi is sequentially calculated and supplied to the final deterioration index I calculating unit 16B. The calculation unit 16B calculates an average value of the calculated n deterioration indexes Φi as shown in the following equation (7). Then, the calculated average value is used as the final deterioration index I of the catalytic converter 2. I = (ΣΦi) / n --- (7) Here, instead of using the sequential deterioration index Φi as it is, using the average value, that is, the final deterioration index I, during normal driving, the engine speed and load are This is because if it fluctuates, the sequential deterioration index Φi also fluctuates under the influence. That is, the sequential deterioration index Φi is obtained and accumulated for a certain period of time, a certain number of rotations, or a certain load zone, and the average value is used as the final deterioration index I.
By doing so, it is possible to determine the deterioration in the entire operation range. However, when the operating state is limited to some extent, the determination may be performed using the sequential deterioration index Φi as it is. Note that the average value of the deterioration indexes Φi may be the average value of the nth to the nth deterioration indexes. The calculated final deterioration index I is supplied to the comparison unit 21 and the judgment index setting unit 22.

In FIG. 1, the catalyst temperature estimating unit 19 includes:
An intake air amount signal Qa from the intake air amount sensor 5 is supplied, and the catalyst temperature is estimated based on the supplied signal Qa. That is, as shown in FIG. 5, a line CQ indicating the relationship between the intake air amount Qa and the catalyst temperature is obtained in advance, and the obtained line CQ
(For example, when the air amount is Q1, the catalyst temperature is estimated as CT1, and when the air amount is Q2, the catalyst temperature is estimated as CT2). The signal T indicating the estimated catalyst temperature is supplied to the comparison unit 21 and the determination index setting unit 2
2 is supplied.

The load estimating section 15 is supplied with a shift signal SL from a shift lever (not shown) and a switch signal SA for auxiliary equipment such as an air conditioner, and estimates the current load state. Then, the signal L indicating the estimated load is supplied to the operating state estimating unit 20. The driving state estimating unit 20 is also supplied with a signal Ne from the rotation speed detection sensor 6, and based on the supplied signals L and Ne, the driving state such as a normal driving state, an idling state, and an auxiliary equipment use state is determined. Presumed. The signal C indicating the estimated operation state is supplied to the comparison unit 21 and the determination index setting unit 22.

The determination index setting unit 22 calculates the change of the catalyst deterioration index with respect to the change of the operating state and the catalyst temperature when the determination index is set, and calculates 50% to 50% of the calculated catalyst deterioration index.
70% is stored in the determination index storage unit 23 as a determination index. At the time of setting the determination index, an unused healthy catalyst or a healthy catalyst after traveling 4000 miles (characteristics are stabilized) is used. FIG. 6 is a schematic diagram of the determination index stored in the determination index storage unit 23, and a deterioration index curve with respect to the catalyst temperature is stored for each operating state. For example, the normal running state catalyst determination index 23-1
Includes a catalyst deterioration index curve BC1 in a normal running state.
Are set, and the deterioration index curves BC2 and BC3 in the respective states are set in the high load state catalyst determination index 23-2 and the low load state catalyst determination index 23-3. In addition, for example, the auxiliary equipment use state catalyst inferiority determination index 23-n includes:
A deterioration index curve BCn in the auxiliary equipment use state is set.

In FIG. 1, the comparison unit 21 determines the relationship between the catalyst deterioration index and the catalyst temperature based on the supplied catalyst estimated temperature signal T, operating state estimation signal C, and catalyst deterioration index signal I. A deterioration index curve shown is created. Then, the judgment index curve in the operating state of the created deterioration index curve is read from the deterioration index storage unit 23. The comparison unit 21
The read determination index curve is compared with the created deterioration index curve, and a signal J indicating the comparison result is supplied to the deterioration determination unit 24. The deterioration determination unit 24 determines whether the supplied signal J
Then, it is determined whether or not the catalyst 2 has deteriorated, and if it has, the in-vehicle display means (not shown) indicates that the catalyst has deteriorated.

FIG. 7 is an operation flowchart of the catalyst deterioration diagnosing means 11. In step 100 of FIG. 7, the driving state is estimated by the driving state estimation unit 20.
Next, in step 101, the catalyst temperature is estimated by the catalyst temperature estimation unit 19. Then, in step 102, the catalyst deterioration index calculating unit 18 calculates the catalyst deterioration index.

Next, in step 103, the comparison unit 21 and the determination index setting unit 22 determine whether or not the determination index is set. If the judgment index is set, step 1
In step 05, a judgment index curve is set by the judgment index setting unit 22 and stored in the storage unit 23. Then, the process returns to step 100.

If it is determined in step 103 that the judgment index is not set, the process proceeds to step 104. Then, in step 104, the comparing section 21 calculates a deterioration index curve. Subsequently, in step 106, the comparison unit 21 reads the determination index curve stored in the storage unit 23, and compares the read determination index curve with the calculated deterioration index curve.
Next, the process proceeds to step 107, where the deterioration determination unit 24
It is determined whether or not the deterioration index is smaller than the determination index.
If the deterioration index is smaller than the judgment index, step 100
Return to If it is determined in step 107 that the deterioration index is larger than the determination index, the process proceeds to step 108, and the appropriate display means displays that the catalyst has deteriorated.

As described above, according to the first embodiment of the present invention, a curve indicating the relationship between a healthy catalyst deterioration index and temperature, and an actual catalyst deterioration index and temperature in each operating state. Is compared with the curve indicating the relationship, and it is configured to determine whether or not the catalyst is degraded, so that not only at the time of high-speed running, but also at the time of medium-speed running, low-speed running, idling, etc. Even in the case of a low temperature state, it is possible to execute a catalyst deterioration diagnosis, and it is possible to realize a catalyst diagnosis device for an internal combustion engine in which emission of deteriorated exhaust gas for a long time is suppressed.

In the above example, the intake air amount Q
When estimating the catalyst temperature from a, the intake air amount is measured at several points, and a value obtained by dividing the sum of the air amounts Qa per unit time by the total for a predetermined time is used. That is, as shown in FIG. 8, the intake air amounts Qa0 to Qan corresponding to the times t0 to tn are measured, and Q _{AVEa is calculated} according to the following equation (8).
_Is calculated, and the catalyst temperature is estimated based on the calculated intake air amount Q _AVEa .

[0032]

(Equation 3)

FIG. 9 is a schematic block diagram of a second embodiment of the present invention. In the second embodiment, the voltage duty signal TP supplied from the output unit 10 to the fuel injection valve 26 is used.
The catalyst temperature is estimated based on the pulse width of. That is, the voltage duty signal TP output from the output unit 10
Is supplied to the catalyst temperature estimating unit 25, and the catalyst temperature is estimated from the pulse width. In the estimation of the catalyst temperature, for example, as shown in FIG. 10, when the engine speed is low, the estimated straight line CP1 is used, and when the engine speed is medium, the estimated straight line CP2 is used. . When the engine speed is high, the estimated straight line CP3 is used. Then, a signal T indicating the estimated catalyst temperature is supplied to the comparison unit 21 and the determination index setting unit 22. Other configurations are the same as those of the above-described first embodiment, and a description thereof will not be repeated.
In the second embodiment of the present invention, the same effect as in the first embodiment can be obtained.

In the second embodiment, when estimating the catalyst temperature from the voltage duty signal TP as in the first embodiment, the sum of the pulse widths of the voltage duty signal TP per unit time is determined by a predetermined value. Use the value divided by the total time. That is, the pulse width TP1 to TPn of the signal TP corresponding to each of the times t0 to tn is measured, T _AVEP is calculated according to the following equation (9), and the calculated pulse width T
_The catalyst temperature is estimated based on _AVEP .

[0035]

(Equation 4)

FIG. 11 is a schematic configuration diagram of a third embodiment of the present invention. In the third embodiment, a catalyst temperature measuring section 27 is disposed near the catalytic converter 2, and the temperature of the catalytic converter 2 is directly measured by the catalyst temperature measuring section 27. Then, the signal T indicating the catalyst temperature is output from the catalyst temperature measurement unit 27 to the comparison unit 21 and the determination index setting unit 22.
Supplied to The other configuration is the same as that of the first embodiment, and the description is omitted. In the third embodiment described above, the same effect as in the first embodiment can be obtained.

In the example described above, from the intake air amount Qa or the pulse width of the signal supplied to the fuel injection valve,
Although the catalyst temperature is estimated, the exhaust gas temperature of the catalytic converter 2 may be measured, and the catalyst temperature may be estimated from the measured exhaust gas temperature. Further, the catalyst temperature may be estimated from the fuel injection amount calculated by the fuel injection amount calculation unit 9 instead of the signal pulse width to the fuel injection valve.

Further, in the above-described embodiment, the deterioration of the catalyst is determined based on the similarity of the air-fuel ratio perturbation before and after the catalytic converter. However, the present invention is not limited to this. A configuration for determining deterioration may be used. For example, a configuration may be adopted in which the deterioration state of the catalyst is determined based on a time difference from when the output value of the air-fuel ratio sensor on the upstream side of the catalyst is inverted to when the output value of the air-fuel ratio sensor on the downstream side is inverted.

[0039]

Since the present invention is configured as described above, it has the following effects. In a catalyst diagnosis device for an internal combustion engine, a front air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas on the upstream side of a catalyst, a rear air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas on a downstream side of the catalyst, a front air-fuel ratio sensor, and a rear air-fuel ratio sensor Based on an output signal from the air-fuel ratio sensor, a catalyst deterioration degree calculation unit that calculates the degree of deterioration of the catalyst, a catalyst temperature estimation unit that estimates the temperature of the catalyst, and an operation state estimation unit that estimates the operation state of the vehicle, For each operating state, a deterioration criterion storage unit that stores a deterioration criterion that is a change in the degree of deterioration with respect to a normal catalyst temperature change, and a catalyst deterioration degree signal from the catalyst deterioration degree calculation unit and a catalyst deterioration degree Based on the catalyst temperature signal,
A change in the degree of deterioration with respect to a change in the temperature of the catalyst is calculated, a deterioration determination criterion in the operating state indicated by the operating state estimating unit is read out from the deterioration determination reference storage unit, and the deterioration determination criterion is compared with the calculated change in the degree of deterioration. And a deterioration determining unit that determines deterioration of the catalyst. Therefore, a catalyst diagnosis device for an internal combustion engine that can execute the catalyst deterioration diagnosis not only at the time of high-speed running but also at the time of middle-speed running, low-speed running, idling, and the like when the catalyst temperature is low. Can be realized, and the emission of the deteriorated exhaust gas over a long period of time can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of the present invention.

FIG. 2 is a partial schematic configuration diagram of the example of FIG. 1;

FIG. 3 is an explanatory diagram of a correlation calculation executed by a correlation calculation unit.

FIG. 4 is a graph showing a relationship between deterioration of a catalytic converter and a deterioration index Φi.

FIG. 5 is a graph for explaining an example of estimating a catalyst temperature from an intake air amount.

FIG. 6 is a schematic configuration diagram of the inside of a judgment index storage unit.

FIG. 7 is an operation flowchart of the example of FIG. 1;

FIG. 8 is a graph for explaining calculation of an intake air amount used for estimating a catalyst temperature in the example of FIG. 1;

FIG. 9 is a schematic configuration diagram of a second embodiment of the present invention.

FIG. 10 is a graph for explaining an example of estimating a catalyst temperature from a pulse width.

FIG. 11 is a schematic configuration diagram of a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 2 Catalytic converter 3 Front O ₂ sensor 4 Rear O ₂ sensor 5 Intake air amount sensor 6 Revolution detection sensor 7 Fuel injection control means 8 Air-fuel ratio feedback calculation unit 9 Fuel injection amount calculation unit 10 Output unit 11 Catalyst deterioration diagnosis means 12A, 12B Data sampling unit 13A, 13B memory 14A Autocorrelation calculation unit 14B Cross-correlation calculation unit 14D Cross-correlation function calculation unit 15 Load estimation unit 16A Successive deterioration index Φi calculation unit 16B Final deterioration index I calculation unit 18 Catalyst deterioration index calculation Units 19 and 25 Catalyst temperature estimation unit 20 Operating state estimation unit 21 Comparison unit 22 Determination index setting unit 23 Determination index storage unit 24 Deterioration determination unit 25 Interpolation map 26 Fuel injector 27 Catalyst temperature measurement unit

Continued on the front page (72) Inventor Toshio Ishii 2520 Oji Takaba, Katsuta City, Ibaraki Prefecture Inside the Automotive Equipment Division, Hitachi, Ltd. 3 Hitachi Automotive Engineering Co., Ltd. (72) Inventor Agustin Rogerio 2477 Kashima-Yatsu, Kata-shi, Ibaraki Pref. Hitachi Automotive Engineering Co., Ltd. Examiner Makoto Watanabe (56) Reference JP Hei 5-248227 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) F01N 3/20 F01N 3/24

Claims (7)

(57) [Claims] 1. A catalyst diagnostic device for an internal combustion engine, comprising: a front air-fuel ratio sensor disposed upstream of a catalyst for detecting an air-fuel ratio of exhaust gas upstream of the catalyst; A rear air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas on the side, and a catalyst deterioration calculating a catalyst deterioration degree corresponding to the conversion efficiency of the catalyst based on output signals from the front air-fuel ratio sensor and the rear air-fuel ratio sensor. Degree calculating section, a catalyst temperature estimating section for estimating the temperature of the catalyst, an operating state estimating section for estimating an operating state of a vehicle equipped with the internal combustion engine, and a conversion efficiency for each operating state of the vehicle. Below stable temperature
The temperature of a normal catalyst having a conversion efficiency above a predetermined value
And deterioration determination reference storage unit for storing the deterioration determination criteria based on the change characteristics with respect to the catalyst deterioration degree calculated by the catalyst deterioration degree calculation unit and on the basis of the catalyst temperature estimated by the catalyst temperature estimating unit, the temperature of the catalyst Deterioration change characteristics for the operating state indicated by the operating state estimator are read out from the deterioration determination reference storage unit, and the read deterioration determination criterion and the calculated deterioration degree change characteristics are calculated. And a deterioration determination unit that determines deterioration of the catalyst by comparing the above. And a catalyst diagnosis device for an internal combustion engine. 2. The catalyst diagnostic device for an internal combustion engine according to claim 1, further comprising an intake air amount sensor for detecting an intake air amount of the internal combustion engine, wherein the catalyst temperature estimating unit is detected by the intake air amount sensor. Based on the intake air volume
A catalyst diagnosis device for an internal combustion engine, which estimates a catalyst temperature. 3. The catalyst diagnosis apparatus for an internal combustion engine according to claim 1, further comprising a fuel injection amount control unit that calculates a fuel injection amount of the fuel injection valve and supplies a fuel injection pulse signal to the fuel injection valve. And a catalyst temperature estimating unit for estimating the catalyst temperature based on a pulse width of a fuel injection pulse signal. 4. The catalyst diagnosis apparatus for an internal combustion engine according to claim 1, further comprising a fuel injection amount control unit that calculates a fuel injection amount of the fuel injection valve and supplies a fuel injection pulse signal to the fuel injection valve. And a catalyst temperature estimating unit for estimating the catalyst temperature based on the fuel injection amount calculated by the fuel injection amount control unit. 5. The catalyst diagnostic device for an internal combustion engine according to claim 1, further comprising an exhaust gas temperature sensor for measuring an exhaust gas temperature of the internal combustion engine, wherein the catalyst temperature estimating unit is detected by the exhaust gas temperature sensor. A catalyst diagnosis device for an internal combustion engine, wherein the catalyst temperature is estimated based on the exhaust gas temperature. 6. A catalyst diagnostic device for an internal combustion engine, comprising: a front air-fuel ratio sensor disposed upstream of the catalyst for detecting an air-fuel ratio of exhaust gas upstream of the catalyst; A rear air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas on the side, and a catalyst deterioration calculating a catalyst deterioration degree corresponding to the conversion efficiency of the catalyst based on output signals from the front air-fuel ratio sensor and the rear air-fuel ratio sensor. Degree calculating unit, a catalyst temperature measuring unit that measures the temperature of the catalyst, an operating state estimating unit that estimates an operating state of a vehicle equipped with the internal combustion engine, and a conversion efficiency for each operating state of the vehicle. Below stable temperature
The temperature of a normal catalyst having a conversion efficiency above a predetermined value
And deterioration determination reference storage unit for storing the deterioration determination criteria based on the change characteristics with respect to the catalyst deterioration degree calculated by the catalyst deterioration degree calculation section and the sensed catalyst temperature by the catalyst temperature measuring part, the temperature of the catalyst Deterioration change characteristics for the operating state indicated by the operating state estimator are read out from the deterioration determination reference storage unit, and the read deterioration determination criterion and the calculated deterioration degree change characteristics are calculated. And a deterioration determination unit that determines deterioration of the catalyst by comparing the above. And a catalyst diagnosis device for an internal combustion engine. 7. The catalyst diagnostic device for an internal combustion engine according to claim 1, wherein the catalyst deterioration degree calculating unit includes an output signal of the front air-fuel ratio sensor and a signal of the rear air-fuel ratio sensor. A correlation function calculator for calculating a cross-correlation function with the output signal and an auto-correlation function of the output signal of the front air-fuel ratio sensor; and a ratio between the maximum value of the cross-correlation function and the auto-correlation function. A sequential deterioration index calculating unit that calculates a next deterioration index, a final deterioration index calculating unit that calculates a final deterioration index that is an average value of a predetermined number of the sequential deterioration indexes, and outputs the final deterioration index as a catalyst deterioration degree; A catalyst diagnostic device for an internal combustion engine, comprising: