JPH0357862A - Catalyst deterioration discriminator for internal combustion engine - Google Patents

Abstract

PURPOSE:To accurately discriminate deterioration of a three-way catalyst in response to a compared result by comparing reverse cycle ratios of respective air-fuel ratio sensors with a standard value at the up and down sides of the three-way catalyst arranged at an exhaust passage of an internal combustion engine. CONSTITUTION:A three-way catalyst B is set at an exhaust passage A of an internal combustion engine, and air-fuel ratio sensors C, D are provided respectively at the up and down sides thereof. In this case, the reverse cycle of output at the air-fuel ratio sensors C, D is calculated by means E, F, respectively. The reverse cycle ratio is calculated respectively by a means G. A standard value is calculated by a means H based on an operation parameter of the engine. The calculated ratio is compared with the standard value by a means I, and deterioration of a three-way catalyst B is discriminated in response to the compared result. Consequently, the deterioration of the three-way catalyst B is discriminated accurately.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an air-fuel ratio sensor (herein, an oxygen concentration sensor (02 Senna)) on the upstream and downstream sides of a catalytic converter.
The present invention relates to a catalyst deterioration determination device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream Q2 sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single O2 sensor system), the O2 sensor that detects oxygen concentration is installed at a checkpoint in the exhaust system as close to the combustion chamber as possible, that is, at the gathering point of the exhaust manifold upstream from the catalytic converter. Improving the accuracy of air-fuel ratio control is hindered by variations in sensor output characteristics. Gagaru02
In order to compensate for variations in sensor output characteristics, variations in parts such as fuel injection valves, and changes over time or aging, a second 02 sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control by the upstream 02 sensor is performed. In addition, a double O2 sensor system that performs air-fuel ratio feedback control using the downstream O2 sensor has already been proposed (
Reference: Japanese Patent Application Laid-Open No. 61-286550). In this double 02 sensor system, the O2 sensor installed downstream of the catalytic converter has a
Although it has a low response speed, it has the advantage of small variations in output characteristics for the following reason. ? 1) Downstream of the catalytic converter, the temperature of the exhaust gas is low, so there is little thermal influence.

(2) Downstream of the catalytic converter, various poisons are introduced into the catalyst.
・Since the downstream 02 sensor is wrapped, the amount of poisoning is small.

(3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the 1 NO 1 gas is close to an equilibrium state.

Therefore, as described above, by air-fuel ratio feedback control (double 02 sensor system) based on the outputs of the two 02 sensors, variations in the output characteristics of the upstream O2 sensor can be absorbed by the downstream 02 sensor. In fact, as shown in Figure 2, in the single 02 sensor system 14, if the 0■ sensor output characteristics deteriorate, it directly affects the exhaust emission characteristics, whereas in the double 02 sensor system, the upstream 02 Even if the output characteristics of the sensor deteriorate, the exhaust emission characteristics do not deteriorate. In other words, in the double 02 sensor system, as long as the downstream 02 sensor maintains stable output characteristics, good exhaust emissions are guaranteed.

In the double 02 sensor system described above, when the catalyst deteriorates, HC, Co. Under the influence of unburned gas such as H2, the output characteristics of the downstream 02 sensor deteriorate. That is, the width of the output of the downstream 02 sensor becomes large and the cycle becomes short, which causes disturbances in the air-fuel ratio feedback control by the downstream 02 sensor, making it impossible to obtain a good air-fuel ratio. This leads to deterioration of fuel efficiency, deterioration of drivability, deterioration of HC, Co, NOx emissions, etc.

For this reason, the applicant has already proposed a method for determining catalyst deterioration by comparing the ratio of the output period of the upstream 02 sensor and the output period of the upstream 02 sensor with a fixed value as a catalyst deterioration determination means. (Reference: JP-A-61
-286550 Publication>. In other words, before catalyst deterioration,
The output cycle of the downstream 02 sensor is as shown in Figure 3.
Although it is larger than the output cycle of the upstream 02 sensor, when the catalyst deteriorates, the catalytic action disappears, and the output cycle of the downstream 02 sensor corresponds to the output cycle of the upstream 02 sensor, as shown in Figure 4. This is because it changes.

[Problem to be solved by the invention]

However, in the above catalyst deterioration determination method, since the comparison reference value is constant, there is a problem that even relatively small catalyst deterioration can be determined as abnormal deterioration, or conversely, abnormal deterioration cannot be determined.

In other words, the reversal period of the upstream 02 sensor is strongly influenced by the exhaust gas flow rate (rotational speed Ne) as an operating condition parameter, while the reversal period of the downstream 02 sensor is influenced by the exhaust gas flow rate, which is related to the 02 storage amount of the catalyst and the air-fuel ratio. This is because the influence of the flow M (the intake air amount Q in terms of operating state parameters) is strong, and in this case, the exhaust gas flow rate and the exhaust gas flow rate do not correspond accurately. For example, when the rotational speed Ne is large, the exhaust gas flow rate becomes large rather than the exhaust gas flow rate, and as a result, compared to the reversal period of the downstream 02 sensor, the upstream 02
The reversal period of the sensor increases. Furthermore, when the intake air amount Q is large, the exhaust gas flow rate becomes large rather than the exhaust gas flow rate, and as a result, the reversal period of the flow fil O 2 sensor becomes larger than the reversal period of the L flow side 02 sensor. In this way, the above-mentioned comparison base 2F! value varies.9 Particularly, when the rotational speed Ne is large and the intake air fiQ is small, or when the rotational speed Ne is small and the intake air fllQ is large, the above Comparison standard values vary widely.

Therefore, an object of the present invention is to provide a double air-fuel ratio sensor (02 sensor) system that can accurately measure catalyst deterioration.

“Means for solving problems” A means for solving the problems mentioned above is shown in FIG.

That is, a three-way catalyst C installed in the exhaust passage of an internal combustion engine
C.C. is installed in the exhaust passages on the upstream and downstream sides of CRo. :l. An L-stream air-fuel ratio sensor 13 and a downstream air-fuel ratio sensor 15 are provided to detect the air-fuel ratio of the engine.

The first period calculation means calculates the reversal period CM of the output V of the upstream air-fuel ratio sensor, and the second period calculation means calculates the reversal period Cs of the output V2 of the downstream air-fuel ratio sensor, and calculates the reversal period Cs of the output V2 of the downstream air-fuel ratio sensor, The calculation means is the output of the first-stream side air-fuel ratio sensor ■1
The reference value calculation means calculates the ratio CS/CM of the reversal period CM of the output v2 of the downstream side air-fuel ratio sensor and the reversal period Cs of the output v2 of the downstream side air-fuel ratio sensor. Calculate the value k. As a result,
The comparison means compares the ratio c:s/cM with a reference value k. In this way, the deterioration of the three-way catalyst CCRo is determined based on the comparison result of the comparison means.

[For production]

According to the above-mentioned means, catalyst deterioration is determined by comparing the ratio of the output reversal period of the upstream side air-fuel ratio sensor and the output reversal period of the downstream side air-fuel ratio sensor with a predetermined value, but this predetermined value is determined depending on the operating state. It is variable depending on the parameter.

〔Example〕

FIG. 5 is an overall schematic diagram showing an embodiment of an air-fuel ratio control system for an internal combustion engine according to the present invention. In the fifth factor, an air flow meter 3 is provided in the intake vent Ii'82 of the engine body 1. The air flow meter 3 directly measures the amount of intake air, and has a built-in potentiometer, for example, to generate an analog voltage output signal proportional to the amount of intake air. This output signal is provided to the RA/0 converter 101 in the multiplexer of the control circuit 10! are doing. The distributor 4 has a crank angle sensor 5 that generates a quasi-position detection pulse signal every 720 degrees by subtracting 1 from the crank angle, and a crank angle sensor 5 that generates a quasi-position detection pulse signal every 720 degrees by subtracting 1 from the crank angle. A crank angle sensor 6 that generates a pulse signal for detecting a reference position is provided. The pulse signals of these crank angle sensors 5 and 6 are supplied to the input/output interface 102 of the control circuit 10, of which the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPII 103.

Furthermore, the intake passage 2 is supplied with electricity from the fuel supply system for each cylinder.
Fuel F1 injection J for supplying fuel ↑゛1 to the intake ball l.
``7 is set 1).

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jackets 1 and 8 of the cylinder block of the engine body 1. Cooling water temperature T of water temperature sensor 2
Generates an analog voltage electrical signal according to IIW. This output is also supplied to the A/D converter 101. A catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three toxic components HC, Co, and NOx in exhaust gas is provided in the exhaust system downstream of the exhaust manifold l1.

A first 02 sensor 13 is installed in the exhaust manifold 11, that is, on the upstream side of the catalytic converter 12,
The 4JF trachea 14 on the downstream side of the catalytic converter 12 has a second
02 sensor 15 is provided. o2 sensor 13
, 15 generate an electric signal according to the concentration of oxygen components in the exhaust gas. That is, 02 Senna 13. 15 is an A/D converter 1 of a control circuit io which outputs a different output voltage depending on whether the air-fuel ratio is on the ≧ side or the rich side with respect to the stoichiometric air-fuel ratio.
Occurs on 01.

The control circuit 10 is configured, for example, as a microphone 1v=1 monitor, and an A/D converter 101. In addition to the human output interface 102 and the CPU 103, there is a RAM 104,
A ROM 105, a backup RAM 106, an evening lock generation time b1δ107, etc. are provided.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 that generates a signal LL indicating whether the throttle valve 16 is fully open or not. This idle state output signal LL is the input/output interface 1 of the control circuit 10.
02.

Furthermore, 18 is an alarm, and the catalytic converter 12
It is activated when the catalyst deteriorates.

Further, in the control circuit 10, a down counter 108,
A flip-flop 109 and a drive circuit 1101 are used to control the fuel injection valve 7. That is, in the routine described later, when the fuel injection amount TAU is calculated, the fuel injection MATU is reset to the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and the borrow out terminal finally reaches the "1" level, the flip flop!
09 is set, and the drive circuit 110 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is energized by the above-mentioned fuel f4 injection amount TAU, and therefore, an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Note that the interrupt of CPtll03 occurs after the A/D conversion of the A/D converter 1* device 101 is completed,
When 02 receives the pulse signal of the crank angle sensor 6,
For example, when an interrupt signal from the clock generation circuit 107 is received.

The intake air amount data Q and the cooling water temperature data THW of the air flow sensor 3 are fetched by an A/zD conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 105. In other words, data Q in RAM 105
and THW are updated at predetermined intervals. Further, the rotational speed data Ne is calculated by the crank angle sensor 6 by an interrupt every 30 degrees C^, and is stored in a predetermined area of the RAM 105.

Figure 6 is based on the output of the upstream 02 sensor 13? The first air-fuel ratio feedback control routine calculates the air-fuel ratio correction coefficient FAF, and is executed every predetermined period of time, for example, 4 ms. In step 601, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 02 sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, the output signal of the upstream 02 sensor 13 is When not inverted, the closed loop condition does not hold true when there is a fuel cut, etc., and the closed loop condition holds true in other cases. If the closed loop condition does not hold, proceed directly to step 625. Note that the air-fuel ratio correction 1 series number FAF may be set to 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 602.

In step 602, upstream side 0 ■ Output of sensor 13 ■ 1
is A/D converted and imported, and in step 603 ■, is the ratio'! 12 Determine whether the voltage vR+ is, for example, 0.45 V or less or 100, that is, determine whether the air-fuel ratio is lean or rich. Determine whether the counter CDLY is positive or not, and if CDLY>O, set CDfJ to O in step 605 and proceed to step 606Step 6
In step 06, the delay counter CDLY is incremented by 1 ibj2, and in steps 607 and 608, the delay counter CDLY is guarded at the minimum value TDL. In this case, when the delay counter CDLY reaches the minimum value TDL, the first air-fuel ratio flag F1 is set to ``0'' in step 609.
(lean). Note that the minimum value TDL is a lean delay time for maintaining the determination that the engine is in a rich state even if there is a change from rich to lean in the output of the upstream 02 sensor 13, and is defined as a negative value. . On the other hand, if it is rich (v+ > VRI), it is determined in step 610 whether the delay counter CDLY is 11 or not, and the CD
If LY<0, CDLY is set to O in step 611 and the process proceeds to step 612. In step 612, the delay counter CDLY is incremented by 1, and in steps 613 and 6
14, the delay counter CDI. Guard Y with the maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the first
Set the air-fuel ratio flag F1 to ``1'' (rich).The maximum value TDλ maintains #IIUr, which indicates that the state is in a lean state even if there is a change from lean to rich in the output of the upstream 02 sensor 13. It is defined as a positive value.

In step 616, it is determined whether the sign of the first air-fuel ratio flag Fl has been reversed, that is, it is determined whether the air-fuel ratio after the delay processing has been reversed. If the air-fuel ratio is reversed, in step 617, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the first air-fuel ratio flag F1. If it is a reversal from rich to lean, in step 618 FAF 4-1? AF +
If you want to increase RSR and skip, and conversely change from lean to rich, use Step 619Nite FAF + FA.
F-RsL Toskiff-like decrease. In other words, skip processing is performed. Next, in step 623, the inversion number counter C, is counted up by +1, and the process proceeds to step 624. Note that the reversal number counter CM is used in the catalyst deterioration determination routine shown in FIG. 10, which will be described later.If the sign of the first air-fuel ratio flux Fl is not reversed in step 616, steps 620, 621, and 6 are used.
Integration processing is performed at 22. That is, in step 620, it is determined whether F'l="O" or not, and if F1="0" (lean), step 621 sets FAF-FAF1KTR, and on the other hand, F1="0" (lean). If it is 1゛゜ (rich), it is set as F8F4-FAF-KIL in step 622. Here, the integral constants KIn and KIL are set sufficiently small compared to the skip amounts RSR and RSL.
In other words, KIR(K[L)<RSR(RSL).
Therefore, step 621 is a lean-like R(F 1 = ”
The fuel injection amount is gradually increased at step 62.
2 is rich IQ! (Fl-"1°')" gradually decreases the fuel injection amount.

Steps 618, 619, 621, 622
The air-fuel ratio correction coefficient FAF calculated in step 62
4, guarded at a minimum value of 0.8, and
It is guarded at a maximum value of 1 or 2, for example. This results in
When the air-fuel ratio correction coefficient FAF becomes too large or too small due to some kind of problem, the air-fuel ratio of the engine is controlled using that value to prevent over-rich or over-lean conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends at step 625.

FIG. 7 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 6. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream 02 sensor l3 as shown in FIG. 7(A), the delay counter CD
As shown in FIG. 7(B), LY is counted up in a rich state and counted down in a lean state.

As a result, a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed as shown in FIG. 7(C). For example, even if the air-fuel ratio signal A/F changes from lean to rich at time L, the delayed air-fuel ratio signal A/F changes from lean to rich.
F' is maintained lean for the rich delay time TDR and then changes to rich at time t2.

Even if the air-fuel ratio signal A/F changes from rich to lean at time t, the delayed air-fuel ratio signal A/F' is held rich for an amount equivalent to the lean delay time (-TDL) and then changes to lean at time t. Changes to lean at L and F.

However, the air-fuel ratio signal A/F at time ts. When the rich delay time TDR is inverted in a short period like ts and tt, it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, at time t8, the air-fuel ratio signal A/F after the delay processing ' is inverted, that is, the air-fuel ratio signal A/F' after the delay process is more stable than the air-fuel ratio signal A/F before the delay process.

In this way, stable air-fuel ratio signals A, /F' after delay processing are obtained.
Based on the air-fuel ratio correction coefficient FAF shown in Figure 7 (D>
is obtained.

Next, the second air-fuel ratio feedback control by the downstream 02 sensor 15 will be explained. As the second air-fuel ratio feedback control, the step -IRsR, RSL. integral constant K
IR, KIL, delay time TDR, TDL, or comparison voltage VR of output V1 of upstream 02 sensor 13
A system that makes I variable and a second air-fuel ratio correction coefficient F
There is a system that introduces AF2.

For example, if you increase Rich Skip JLRSR,
The control air-fuel ratio can be shifted to the rich side, and even if the lean skip iRsL is made small, the controlled +Xa air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip 1iRsL is increased, the control air-fuel ratio can be shifted to the lean side Furthermore, even if the rich skip amount RSR is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, by correcting the rich skip amount RSR and the lean skip amount RSL according to the output of the downstream 02 sensor l5, the air-fuel ratio can be adjusted. Can be controlled.

In addition, by increasing the rich integral constant KIn, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIL
The controlled air-fuel ratio can be shifted to a rich measurement even if KIL is made small, and on the other hand, the controlled air-fuel ratio can be shifted to a lean side by increasing the lean integral constant KIL.
The control air-fuel ratio can be shifted to lean measurement even if the value is reduced. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KIR-3 and the lean integral constant KIL according to the output of the downstream 02 sensor l5. If the rich delay time TDR is set large or the lean delay time (-.TDL) is set small, the control air-fuel ratio can be shifted to the rich side, and conversely,
By setting the lean delay time (-TDL) to be large or the rich delay time (TDR) to be small, the controlled air-fuel ratio can be shifted to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of the downstream side 02 sensor 15. Furthermore, the comparison voltage V
By increasing IN, the control air-fuel ratio can be shifted to rich measurement,
Further, by decreasing the comparison voltage V R l, the control air-fuel ratio can be shifted to the lean side. U (that is, downstream side 02 sensor 1
The air-fuel ratio can be controlled by correcting the comparison voltage V91 in accordance with the output of No.5.

Making these skip amount, integral constant, delay time, and comparison voltage variable by the downstream 02 sensor has its own advantages. For example, the delay time allows for very delicate air-fuel ratio adjustment, and the skip amount can be controlled with good response without lengthening the air-fuel ratio feedback period unlike the delay time. Therefore, naturally, two or more of these variable amounts can be used in combination.

Next, a double O2 sensor system in which the skip amount as an air-fuel ratio feedback control constant is variable will be explained. FIG. 8 shows a second air-fuel ratio feedback control routine based on the output of the downstream lo2 sensor 15, which is executed every predetermined period of time, for example, 512 ms. Step 801~
In 805, it is determined whether the downstream rho2 sensor 15 is in a closed loop condition. For example, upstream side 02 sensor 13
In addition to the failure of the closed loop condition (step 801), the cooling water temperature THW is lower than a predetermined value (for example, 70°C) (step 8o2), and the throttle valve 16 is fully closed (L
When L = "1") (step 803), when the load is light (Q / N e < X + 'H step 804)
, when the downstream side 02 sensor l5 is not activated (
The closed-loop condition is not satisfied in step 805), and the closed-loop condition is satisfied in other cases.

If the condition is not a closed loop condition, the process proceeds to step 817, and if the condition is a closed loop condition, the process proceeds to step 806.

In step 806, the output V2 of the downstream side 02 sensor 15 is
In step 809, is V2 equal to or lower than the comparison voltage VR, for example 0.55V? In other words, it determines whether the air-fuel ratio is rich or lean. Note that the comparison voltage V R 2 is upstream of the catalytic converter l2,
The upstream (II! IO2
Although it is set higher than the comparison voltage ■3 of the output of the sensor 13, this setting may be arbitrary. As a result, V2≦V
If it is R2 (lean), proceed to step 808 and set the second air-fuel ratio flag F2 to "On, L, Sarani, St."
7' 8094: TERSR"RSR+ΔRS. On the other hand, if V2>VR■ (rich>), step 81
0, the second air-fuel ratio flag F2 is set to "1°", and further, in step 811, RSR-RSR-ΔRS is set. Therefore, step 80.9 is a lean state!!! (
The rich skip amount RSR is gradually increased with F2="O゜゛), and step 811 is a rich skip amount RSR (F2="1
゜゜) gradually decreases the rich skip amount RSR.

In step 812, it is determined whether the sign of the second air-fuel ratio flag F2 has been inverted, that is, it is determined whether the air-fuel ratio downstream of the catalyst has been inverted. Note that F20 is the previous value of F2. If the air-fuel ratio is inverted, step 813
The inversion number counter Cs is incremented by 1 at . The reversal number counter C3 is used in a catalyst deterioration determination routine shown in FIG. 10, which will be described later.

In step 815, rich skip firtsR is guarded at a maximum value, for example, 7.5%, and at a minimum value, for example, 2.5%. Note that the minimum value of 2.5% is a value at a level that does not impair transient followability, and the maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

In step 816, lean skip jiR. sL,
Let RSL←10%-1'lSR. The routine then ends at step 817.

FIG. 9 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, at 360°C. Step 901
Then, the intake air amount data Q and the rotational speed data Ne are read out from the RAM 105 to calculate the basic injection amount TAUP.

For example, TAUP←α·Q/Ne (α is a constant).

In step 902, the final injection J31TAU is
Calculate by 4-TAUP-FAF・β+γ. In addition, β. γ is t determined by other operating state parameters
+I] Positive amount. Next, in step 903, the injection ffiTAU is set in the down counter 108 and the flip-flop 109 is set to open the fuel injection. Then, in step 904, this process ends. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the borrow-out signal from the down counter 108, and the fuel injection ends.

FIG. 10 shows a catalyst deterioration determination routine, which is executed every predetermined period of time, for example, 16 ms. In step 1001, it is determined whether the closed loop conditions (steps 801 to 805 in FIG. 8) by the downstream side 02 sensor 15 are satisfied. In other words, upstream side 02 sensor 13 and downstream ra
Air-fuel ratio feedback control by the O2 sensor l5 is executed to determine whether or not the values of the above-mentioned reversal number counters CM and CS are valid. If the values of the reversal number counters CM and Cs are valid, the process proceeds to step 1002; otherwise, the process directly proceeds to step 1013.

In step 1002, the time measurement counter CN is counted up by +1, and in step 1003, the RAM 105
In step 1004, the intake air amount Q is read out and the cumulative intake air amount Qro is updated.In step 1004, the rotational speed Ne is read out from the RAM 105 and the cumulative rotational speed NeTOT is updated. In step 1005, a predetermined time has elapsed (CM
>CNA), and only if a predetermined period of time has elapsed, proceed to steps 1006 to 1012. Note that the predetermined time is 1-2 minutes, and for example, CN^=5
It is 000.

Steps 1006 to 10l2 will be explained. In step 1006, the average intake air fi Q Av is defined as Q
AV” Q TOT/C N , and in step 1007, the average rotational speed N
cAv is calculated by Ne^v4-Nevoy/CN, and in step 1008, in preparation for the next execution, the values CM,
Clear QTOT and NeTov.

In step 1009, the output of the upstream sensor 02 sensor 13 is
, and the output of the downstream side 02 sensor 15 (1/CM). For example, as shown in FIG. 11A, the average intake stored in the ROM 104 Air amount QAV and average rotational speed N eAV
It is obtained by interpolation calculation using a two-dimensional map of .

In this case, ka+>kam. k+b＞knb
, k ++ > krv. In other words, the parameter N eAV corresponding to the exhaust gas flow velocity is 0 on the upstream side.
It greatly affects the reversal period of the output V, of the two sensors 13, and N
The larger the eAV, the higher the output of the upstream sensor 02 sensor 13.
, the inversion period 1/CM becomes larger, and therefore, the larger NeAV becomes, the larger k is set.

On the other hand, the parameter QAV corresponding to the exhaust gas flow rate greatly influences the reversal period of the output V2 of the downstream sensor 15, and the larger QAυ becomes, the larger the reversal period 1/Cs of the output V2 of the downstream sensor 15. Therefore, the larger QAv is, the smaller k is set. Note that, instead of the two-dimensional map shown in FIG. 11A, the comparison reference value k may be obtained using a {dimensional map of the ratio Q AV/N eAV shown in FIG. 11B.

In step 1010, the ratio CS/CM (reversal period and (which is inversely proportional to the number). That is, it is determined whether Cs/CM>k. As a result, if Cs/CM>k, there is no catalyst deterioration, and in step 1011, the alarm 18 is activated to notify the driver. Cs/CI,I≦
If k is found, the process directly advances to step 1012.

In step 1012, the inversion number counters C, , Cs are cleared in preparation for the next execution.

This routine ends at step 1013. In addition,
In FIG. 10, the intake air amount Q is used as the exhaust gas flow rate parameter, but other load parameters such as the intake air pressure PM may be used. Also, step 1008. 1
In 007, the average intake air JLQAV and the average rotational speed NeAv are calculated, but rounded values may also be used. In addition, the first air-fuel ratio feedback control is performed every 4 ms.
Also, the second air-fuel ratio feedback control is 512+os
The reason why the air-fuel ratio feedback control is performed every time is that the air-fuel ratio feedback control is mainly performed by the upstream 02 sensor, which has good responsiveness, and the downstream 02 sensor, which has poor responsiveness, is used as a secondary control.

In addition, a double 02 sensor system that corrects other control constants such as delay time, integral constant, etc. in the air-fuel ratio feedback control by the upstream 02 sensor, using the output of the downstream 02 sensor, also includes a second air-fuel ratio sensor. The present invention can also be applied to a double 02 sensor system that introduces a fuel ratio correction coefficient. Furthermore, controllability can be improved by simultaneously controlling two of the skip amount, delay time, and integral constant.

Furthermore, it is also possible to fix one of the skip amounts RSR and RSL and make only the other variable, and the delay times TDR and RSL may be fixed.
It is also possible for children to have one TDL fixed and only the other variable, or to have one of the rich integral constant KIR and lean integral constant KIL fixed and the other variable. Further, as an intake air amount sensor, an Elman vortex sensor, a heat 1 wire sensor, etc. can be used instead of an air flow meter. Furthermore, in the above embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed, but the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio.
Electric bleed air conditioner l ~ Controls the air-fuel ratio by adjusting the amount of air bleed from the carburetor using a roll valve and introducing atmospheric air into the main system passage and slow system passage; the secondary air is sent to the engine's exhaust system. ? The present invention can be applied to things that adjust air volume, etc.

In this case, the basic injection IJt in step 901
The basic fuel injection amount corresponding to iTAUP is determined by the carburetor itself, that is, it is determined according to the intake air amount, the intake pipe negative pressure and the engine rotation speed, and in step 902
The supplied air amount corresponding to the final fuel injection JtTAU is calculated.

Furthermore, in the above embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a CO sensor, lean mixture sensor, etc. may also be used. In particular, when a TiO sensor is used as the upstream air-fuel ratio sensor, control responsiveness improves.
Overcorrection due to the output of the downstream air-fuel ratio sensor can be prevented.

Further, although the above-described embodiment is constructed using a microcomputer, that is, a digital circuit, it may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent erroneous determination of catalyst deterioration in a catalytic converter. ．．

[Brief explanation of drawings]

Figure 1 is an overall block diagram for explaining the printing process of the present invention, Figure 2 is a single O2 sensor system l1 and a double O2 sensor system.
■Exhaust emission characteristics diagram to explain the sensor system. Figure 3 is a timing diagram showing the 02 sensor waveform before catalyst deterioration. Figure 4 is a timing diagram showing the 02 sensor type after catalyst deterioration. An overall schematic diagram showing an embodiment of the air-fuel ratio control (31) device for an internal combustion engine according to the present invention. FIGS. 6, 8, 9, and 10 explain the operation of the control circuit shown in FIG. Figure 7 is a timing diagram for supplementary explanation of the flowchart in Figure 6, and Figures 11A and 11B are flowchart 1 in Figure 10.
FIG. 3 is a diagram showing comparison reference values used in FIG. ■... Engine body, 2... Air flow meter, 1... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, l3... Upstream side 02 sensor, 15... Downstream side 02 sensor, 17... Idle switch.

Claims (1)

[Claims] 1. Three-way catalyst (12) provided in the exhaust passage of an internal combustion engine
an upstream air-fuel ratio sensor (13) provided in the exhaust passage upstream of the three-way catalyst to detect the air-fuel ratio of the engine; and an upstream air-fuel ratio sensor (13) provided in the exhaust passage downstream of the three-way catalyst to detect the air-fuel ratio of the engine. a downstream air-fuel ratio sensor (15) that detects the air-fuel ratio of the air-fuel ratio, and an inversion period (
C_M), a second period calculation means for calculating the reversal period (C_S) of the output (V_2) of the downstream air-fuel ratio sensor, and Ratio calculation means for calculating the ratio between the reversal period and the reversal period of the output of the downstream air-fuel ratio sensor; Reference value calculation means for calculating a reference value (k) according to operating state parameters of the engine; 1. A catalyst deterioration determination device for an internal combustion engine, comprising: comparison means for comparing the calculated ratio with the reference value, and deterioration of the three-way catalyst is determined based on the comparison result of the comparison means. 2. The catalyst deterioration determination device for an internal combustion engine according to claim 1, wherein the reference value is made smaller as the load of the engine becomes smaller and as the rotational speed of the engine becomes larger. 3. The catalyst deterioration determination device for an internal combustion engine according to claim 1, wherein the reference value is increased as the ratio between the load of the engine and the rotational speed of the engine increases.