JPH03249320A - Deterioration detecting device for catalyst - Google Patents

Abstract

PURPOSE:To detect deterioration of a catalyst with good accuracy by calculating a correlation coefficient on the basis of output values of first and second oxygen sensors arranged respectively on upper and lower stream from a catalyst. CONSTITUTION:A catalyst 15 for cleaning exhaust gas is arranged in the exhaust system of an engine 1, while oxygen sensors 16, 18 are respectively provided on upper and lower stream from the catalyst 15 so as to detect whether an air fuel ratio is rich or lean condition in comparison with a theoretical air fuel ratio. in an ECU 20, correlation coefficients of respective output values are calculated on the basis of the output values of the oxygen sensors 16, 16, so that deterioration of the catalyst 15 is detected in response to the correlation coefficients. In this state, the characteristics of the correlation coefficient and the cleaning rate of the catalyst 15, include enough resolution capacity even in a low cleaning ratio. It is thus possible to detect deterioration of the catalyst with good accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalyst deterioration detection device that is installed in an engine exhaust system and detects deterioration of a catalyst for purifying exhaust gas.

[Prior Art] Conventionally, in the above-mentioned device, for example, oxygen sensors are placed upstream and downstream of the catalyst, and deterioration of the catalyst is detected by comparing the output values (reversal frequency) from these oxygen sensors. (For example, Utility Model Application No. 63-12822
Publication No. 1, etc.).

[Problems to be Solved by the Invention] However, the above-mentioned apparatus has poor decomposition ability at low purification rates. Therefore, there is a problem in that the accuracy of deterioration detection is poor and the purification rate at which it is determined that the catalyst has deteriorated cannot be arbitrarily set.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a device that can accurately detect deterioration of a catalyst.

[Means for Solving the Problems] As shown in FIG. 1, the present invention includes a catalyst disposed in the exhaust system of an engine for purifying exhaust gas, and a
The first one is arranged downstream and detects whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio. a second oxygen sensor; and the first oxygen sensor. Correlation coefficient calculation means for calculating a correlation coefficient between these output values based on the output value of the second oxygen sensor; Deterioration detection means for detecting deterioration of the catalyst according to the correlation coefficient. The main subject is a catalyst deterioration detection device.

[Effect]

With the above configuration, in the correlation coefficient calculating means, the first and second
Based on the output values of the oxygen sensors, a correlation coefficient between these output values is calculated. The deterioration detection means detects deterioration of the catalyst according to the above-mentioned correlation coefficient.

[Embodiment] Hereinafter, an embodiment in which the present invention is applied to a vehicle engine will be described based on the drawings.

FIG. 2 is a schematic configuration diagram of one embodiment. An air flow meter 3 is provided in an intake passage 2 of the engine 1. The air flow meter 3 directly measures the amount of intake air guided through the air cleaner 4.

Further, the intake passage 2 is provided with a throttle valve 6 that opens and closes according to the amount of operation of the accelerator 5 by the driver to adjust the amount of intake air supplied to the engine 1.

Furthermore, a fuel injection valve 8 is provided for each cylinder to supply pressurized fuel from the fuel supply system 7 to the intake port.

The distributor 9 is also provided with a reference position sensor 10 that generates a reference position detection signal every 720° CA and a crank angle sensor 11 that generates a crank angle detection signal every 30° CA.

Furthermore, the water jacket 12 of the cylinder block of the engine 1 is provided with a water temperature sensor 13 for detecting the temperature of cooling water.

On the other hand, in the exhaust system, three harmful components HC and Co in the exhaust gas are located downstream of the exhaust manifold 14.

A three-way catalyst 15 is provided to purify NOx at the same time. A first oxygen sensor (Oz sensor) 16 is provided upstream of the three-way catalyst 15, that is, in the exhaust manifold, and a second oxygen sensor (Oz sensor) 16 is provided in the exhaust pipe 17 downstream of the three-way catalyst 15.
A sensor 18 is provided. As is well known, the first. The second 02 sensor 16.1B generates different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.

Moreover, 19 is an alarm for issuing a warning to the driver when it is determined that the catalyst has deteriorated when the purification rate α of the three-way catalyst 15 becomes less than a predetermined value (50% in this embodiment).

The electronic control unit (ECU) 20 is configured as a microcomputer, for example, and includes an A/D converter 101 as is well known.
．． 110 boats 102. CPtJ103, ROM104
．． RAM105. Backup RAM106. A clock generation circuit 107 and the like are provided.

The ECU 20 controls the intake air amount Q detected by the air flow meter 3.
The basic fuel injection amount is set according to the cooling water temperature THW detected by the water temperature sensor 13, the rotation speed NE calculated based on the crank angle detection signal output from the crank angle sensor 11, etc. And the first. Second 0□ sensor 1
The basic fuel injection amount is corrected according to the signal of 6, 1B so that the purification rate α of the three-way catalyst 15 is maximized, and the fuel injection amount T
AU is set (air-fuel ratio feedback system).

Then, a control signal corresponding to the fuel injection amount TAU is output from the I10 port 102 to the fuel injection valve 8.

Next, a method for detecting the purification rate α of the three-way catalyst 15 will be explained.

As the purification rate α of the three-way catalyst 15 decreases, that is, as the three-way catalyst 15 deteriorates, the daily output of the second 0□ sensor becomes the first 0!
The behavior of the output of the sensor 16 approaches, and the first. The correlation between the output values of the second oxygen sensor 16 and 1B increases. Here, the first. Consider the correlation coefficient r for the output values of the second 0□ sensors 16 and 18.

The correlation coefficient r is generally calculated by the following formula.

Here, xi, yi are the output values, x, y are the average values of the output values xi, yi (i is the number of sampling times of the output value)
It is.

As shown in FIG. 3, the characteristics of the correlation coefficient r and the purification rate α of the three-way catalyst 15 are such that the correlation coefficient r approaches 1 as the purification rate α decreases. Using this characteristic, three-way catalyst 15
A correlation coefficient (reference value) ro corresponding to the purification rate α of the deterioration determination standard is determined in advance, and if the calculated correlation coefficient r is equal to or greater than the reference value r0, it is determined that the three-way catalyst 5 has deteriorated. judge.

The operation of this embodiment will be explained below based on the flowchart shown in FIG. The following routine is executed at predetermined intervals (for example, every 4m5ec). First, in step 100, the output value VO of the first 0□ sensor 16
, F is taken in. Similarly, in step 101, the output values VO and R of the second 02 sensor 18 are taken in. In step 102, it is determined whether the conditions for detecting deterioration of the three-way catalyst 15 are satisfied. Here, the deterioration detection conditions include "feedback control of the air-fuel ratio by the first 02 sensor 16 is being executed" and "the engine 1 is in a predetermined stable operating state (for example, the rotation speed and engine load are set in advance. (within the specified range).” As a result of the determination in step 102, if the deterioration detection condition is satisfied, the process proceeds to step 103, where the output value vO□F of the first 02 sensor 16 is set as a variable xi, and the output value vO□F of the first 02 sensor 16 is Assign the output values VO and R to the variable yi.

Next, in step 104, it is determined whether flag F2 is set. Here, the flag F2 is set when detection of deterioration of the three-way catalyst 15 is completed. and,
As a result of the determination, flag F2 is set. That is, if the deterioration detection has already been completed, this routine is ended.

Further, in step 104, if the flag F2 is not set, that is, if the deterioration detection is not completed, the process proceeds to step 105, where it is determined whether the flag F1 is set. Here, the flag F1 is set when the calculation of the average values x and y of the variables xi and yi (i=1..., 100) is completed.

As a result of the determination, flag F1 is not set.
That is, if the calculation of the average values x and y has not been completed, the process advances to step 106 and average value calculation processing is performed.

First, in step 106, it is determined whether the counter C1 indicating the number of sampling times of the data xi, yi is equal to or greater than a predetermined value (for example, 100 in this embodiment).

Then, if the counter C1 is less than 00, step 1
At 07 and 108, the current xiyi is added to the integrated values x and y, respectively, to obtain new integrated values x and y. In the following step 109, the counter C1 is incremented (C1+1
→C1). After steps 107 to 109 are repeated 100 times, the counter C1 becomes 100 in step 106, and the process proceeds from step 106 to step 110. In steps 110 and 111, the above-mentioned step 10
The integrated values x and y of the 100 variables xi and yi obtained in step 7108 are divided by 100 to obtain average values x and y.

Then, in step 112, a flag F1 is set to indicate that the calculation of the average values x and y has been completed.

Further, if the flag Fl is set in step 105, the process advances to step 113. In step 113, the sum of squares
Counter C2 indicating the number of times of integration of i, Yl and sum of products XY
It is determined whether or not is greater than or equal to a predetermined value (for example, 100 in this embodiment). Here, the sum of squares Xi, Yl and the sum of products XY represent the following equation.

X1=Σ (xi-x)2 Yl=Σ (yi-y)2 XY=Σ (xi-χ)χ (yi-y) Then, counter C2 is less than 100, that is, the sum of squares XI, Yl and the sum of products If the calculation of XY has not been completed, proceed to step 1.
14 to 116, sum of squares X1. Yl and the sum of products χY are calculated. Then, in step 117, the counter C2 is incremented (C2+1→C2), and this routine ends.

Further, as a result of the determination in step 113, the counter C2 is 1.
00 or more, that is, if the calculation of the sums of squares XI, Yl and the sum of products XY has been completed, the process advances to step 118. Then, in step 118, the sum of squares XI calculated as described above
, Yl and the sum of products XY, the correlation coefficient r of the output values VO2F and VO□R of the first and second 02 sensors 16 and 18 is calculated. Then, in the following step 119, a flag F2 is set to indicate that the calculation of the correlation coefficient r has been completed.

Next, it is detected from the correlation coefficient r calculated in step 120 whether the three-way catalyst 15 has deteriorated. Specifically, the detection is performed based on whether the correlation coefficient r is equal to or greater than the reference 1r (for example, 0.7 in this embodiment). Here, the reference value r0 of 0.7, which is a criterion for determining the deterioration of the three-way catalyst 15, corresponds to a purification rate of 50%, as shown in FIG. That is, in this embodiment, when the purification rate becomes 50% or less, it is determined that the three-way catalyst 15 has deteriorated. That is, when the correlation coefficient r is less than 0.7, it is determined that the three-way catalyst 15 has not deteriorated,
This routine ends.

When the correlation coefficient r is 0.7 or more in step 120,
It is determined that the three-way catalyst 15 has deteriorated, and the process proceeds to step 121. In step 121, a diagnostic process for the three-way catalyst 15 is performed. Diagnostic processing includes, for example, storing a code indicating that the three-way catalyst 15 has deteriorated in the backup RAM 106, and warning the driver of an abnormality using the alarm 19.

On the other hand, if the deterioration detection condition for the three-way catalyst 15 is not satisfied in step 102, the process proceeds to step 122. Then, in steps 122 to 129, each parameter (counter C1, C2° flag Fl, F2. sum of squares XI, Yl, sum of products xy).

The correlation coefficient r) is initialized, and this routine ends.

In this embodiment, data x for calculating average values x and y
i, yi are different from data xi, yi for calculating the sum of squares XI, Yl and the sum of products XY. However, in the steady operating state, which is the deterioration detection condition, the first. Second 0□
Since the output values VO, F, and VOzR of the sensors 16 and 18 hardly change, there is no problem even if the correlation coefficient r is calculated by the method described above. Further, by using the method described above, the RAM 105 for storing the data xi and yi is not required, so that the storage area does not increase significantly compared to the conventional method.

Through the above processing, the first. Second Ot sensor 16.18
The correlation coefficient r is determined from the output value of .

The characteristics of this correlation coefficient r and the purification rate of the three-way catalyst 15 are
As shown in the figure, sufficient decomposition capacity (
slope of the characteristic diagram). Therefore, the three-way catalyst 1
5 can be detected with high accuracy.

Further, the purification rate α, which is a criterion for determining the deterioration of the three-way catalyst 15, can be arbitrarily set.

In the embodiment described above, the exhaust gas delay time TL from when the exhaust gas discharged from the engine 1 reaches the first 02 sensor 16 to when it crawls through the three-way catalyst 15 and reaches the second 02 sensor 18 is negligible. Since it is the time of 1st. Second
The timings at which the output values ■0□F and VO□R of the 02 sensor 16°18 are taken in are the same (step 1°O, 101 in FIG. 4). Therefore, by taking in the output value vO□F of the first 02 sensor 16 and then delaying it by the exhaust gas delay time T to take in the output value ■OtR of the second 0□ sensor 18, this exhaust gas Errors associated with the delay time TL can be absorbed.

The process will be explained below using the flowchart shown in FIG.

First, in step 200, it is determined whether the counter C3 is O or not. Here, the counter C3 measures the time since the output value ■0□F of the first 0□ sensor 16 is taken in. In addition, this counter C3 is the second 0□ sensor 1
The output value of 8 is reset when 0 and R are taken in. If the counter C3 is not 0, the process advances to step 201. Further, if the counter C3 is 0, that is, the output [VO, R of the second Ox sensor 18 was taken in at the previous control timing, the process proceeds to step 100. In this step 100, as in the previous embodiment, the output value of the first 02 sensor 16 is
The process advances to step 201. At step 201, the counter C3 is incremented (C3→C3+1).

In the following step 202, it is determined whether the counter C3 is at a predetermined value. Here, the predetermined value corresponds to the exhaust gas delay time TL. If the counter C3 is not at the predetermined value, that is, if the exhaust gas delay time TL has not yet elapsed since the output value VO□F of the first Ox sensor was taken in, this routine is ended. Further, in step 202, the counter C3
If the exhaust gas delay time TL has elapsed since the output value ■0□F of the first 02 sensor is taken in a predetermined value, that is, the output value Take in the output value ■0□R. In step 203, reset the counter C3 as described above (C3→C3+1
)do. The following control is the same as step 102 and subsequent steps in FIG. 4 of the embodiment described above, so a description thereof will be omitted.

〔Effect of the invention〕

As detailed above, according to the present invention, first. Deterioration of the catalyst is detected according to a correlation coefficient calculated based on the output value of the second oxygen sensor. The characteristics of the correlation coefficient and the purification rate of the catalyst indicate that the catalyst has sufficient decomposition ability even at a low purification rate. Therefore, there is an excellent effect that deterioration of the catalyst can be detected with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a diagram corresponding to the claims of the present invention, Fig. 2 is a configuration diagram of an embodiment to which the present invention is applied, Fig. 3 is a characteristic diagram of purification rate, and Fig. 4 is a flowchart for explaining the operation of the embodiment. ,
FIG. 5 is a flowchart for explaining the operation of another embodiment. 15... Three-way catalyst, 16... First 0□ sensor, 1
8... Second Ox sensor, 19... Alarm, 20
...ECU.

Claims (2)

[Claims] (1) A catalyst installed in the engine exhaust system to purify exhaust gas; A catalyst installed upstream and downstream of this catalyst to detect whether the air-fuel ratio is rich or lean relative to the stoichiometric air-fuel ratio. 1. 2nd
an oxygen sensor; a correlation coefficient calculating means for calculating a correlation coefficient between the output values of the first and second oxygen sensors; A deterioration detection device for a catalyst, comprising: deterioration detection means for detecting. (2) The correlation coefficient calculation means calculates the correlation coefficient r according to the output values xi and yi of the first and second oxygen sensors, ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (@x@ , @y@ is the average value of the output values xi and yi).