JPH0230915A - Catalyst degradation judging device for internal combustion engine - Google Patents

Abstract

PURPOSE:To accurately judge the degradation of catalytic converter rhodium when an instrumentation time is less than a predetermined time by measuring a time from when an internal combustion engine is shifted to rich operation condition to when the output of an air/fuel ratio sensor at the down stream side of the catalytic converter is reversed to rich condition. CONSTITUTION:Respective air/fuel ratio sensors c, d are provided at the upper and down stream sides of catalytic converter rhodium b provided at the exhaust passage a of an internal combustion engine and the air/fuel ratio of the internal combustion engine is adjusted by a means e according to those respective detected results. At this time, reverse between the lean and rich condition of the output of the down stream side air/fuel ratio sensor d is judged by a means (f). The operation condition of the internal combustion engine is judged by a means g that theoretical air/fuel ratio operation condition is shifted to rich operation condition. Further, a time from the shift to when the output of the down stream side air/fuel ratio sensor d is reversed from lean condition to rich condition is measured by a means h. When the measured time is less than a predetermined time, the degradation of the catalytic inverter rhodium b is judged by a means t.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a double air-fuel ratio system in which air-fuel ratio sensors (in this specification, oxygen concentration sensors (02 sensors)) are provided on the upstream and downstream sides of a catalytic converter. The present invention relates to a catalyst deterioration determination device in a sensor system.

[Conventional technology]

In simple air-fuel ratio feedback control (single 02 sensor system), the 02 sensor that detects oxygen concentration is installed in the exhaust system as close to the combustion chamber as possible, that is, in the gathering part of the exhaust manifold upstream of the catalytic converter. Improving the accuracy of air-fuel ratio control has been hindered by variations in the output characteristics of the air-fuel ratio. It takes 02
In order to compensate for variations in sensor output characteristics, variations in components such as fuel injection valves, and changes over time or aging, a second 0□ sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control is performed by the upstream 02 sensor. In addition to this, a double 02 sensor system has already been proposed that performs air-fuel ratio feedback control using a downstream 02 sensor (
Reference: Japanese Unexamined Patent Publication No. 58-72647). This double 0
In the two-sensor system, the 02 sensor installed downstream of the catalytic converter has a lower response speed than the upstream 02 sensor, but has the advantage of less variation in output characteristics for the following reasons. There is.

(1) Downstream of the catalytic converter, the exhaust temperature is low, so there is little thermal influence.

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream 02 sensor is small.

(3) The exhaust gases are sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gases is close to an equilibrium state.

Therefore, as described above, by performing 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 02 sensor can be absorbed by the downstream 02 sensor. In fact, the second
As shown in the figure, in a single 02 sensor system, 0
If the output characteristics of the 02 sensor deteriorate, this will directly affect the exhaust emission characteristics, whereas in the double 02 sensor system, even if the output characteristics of the upstream 02 sensor deteriorate, the exhaust emission characteristics will not deteriorate. In other words, in the double 02 sensor system, good exhaust emissions are guaranteed as long as the downstream 0□ sensor maintains stable output characteristics.

The catalyst of a catalytic converter is designed so that its functionality does not deteriorate significantly as long as the vehicle is used within the range of normal usage conditions. However, if the user mistakenly adds leaded gasoline to the fuel, or if the high tension cord is disconnected or a misfire occurs for some reason during use, the catalyst's function may deteriorate significantly. In the former case, the user will not notice it at all, and in the latter case, the catalyst will rarely need to be replaced because all that is required is to reinsert the high tension cord. As a result, the vehicle may be driven without the catalytic converter sufficiently purifying the exhaust gas.

However, in the double 02 sensor system described above, if the catalyst function deteriorates as described above, IIc
, Co, 82, etc., the output characteristics of the downstream 02 sensor deteriorate. In other words, the number of reversals of the output of the downstream sensor 02 increases, and as a result,
This causes disturbance in the air-fuel ratio feedback control by the downstream 02 sensor, making it impossible to obtain a good air-fuel ratio, resulting in poor fuel efficiency, poor drivability, IIC, and C.
There is a problem in that it causes deterioration of O, NOx emissions, etc.

For this reason, the applicant has already compared the output cycles of the upper and downstream 0° sensors, the output cycle of the downstream 02 sensor, and the number of inversions of the downstream 02 sensor → no output per unit time. proposed to detect catalyst deterioration (
Reference: Japanese Unexamined Patent Publication No. 61-286550, Japanese Patent Application No. 1983-
No. 241489).

[Problem to be solved by the invention]

However, in the above-mentioned catalyst deterioration determination system, since it is performed during air-fuel ratio feedback control by the upstream 0° sensor and the downstream 02 sensor,
The change in the output characteristics of the 2 sensors is also included in the output of the 0□ sensor, so there is a problem in that it is difficult to determine only catalyst deterioration. In addition, in the case of comparing the output cycles of the upstream and downstream 0° sensors, the output cycle of the upstream 02 sensor is on the order of 18, and the output cycle of the downstream 0° is on the order of l min. There was a problem in that only close conditions could be determined.

Note that in the single 02 sensor system, it is impossible to determine the deterioration of the catalyst itself.

Therefore, an object of the present invention is to provide a catalyst deterioration determination system that prevents erroneous determination in the double 02 sensor system.

[Means to solve the problem]

The means for solving the above-mentioned problems are shown in Figures 1A and 1B.
1C.

In FIG. 1A, an upstream air-fuel ratio sensor for detecting the air-fuel ratio of the engine is provided in the exhaust passage upstream of the three-way catalyst CC1o provided in the exhaust passage of the internal combustion engine, and a three-way catalyst CCR6 A downstream air-fuel ratio sensor for detecting the air-fuel ratio of the engine is provided in the exhaust passage on the downstream side of the engine. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the output VI of the upstream air-fuel ratio sensor and the output V2 of the downstream air-fuel ratio sensor. The reversal determining means determines whether the output of the downstream air-fuel ratio sensor is reversed from rich to lean or from lean to rich. On the other hand, the stoichiometric air-fuel ratio/lean operating state transition determining means determines whether the operating state of the engine is transitioning from the stoichiometric air-fuel ratio operating state to the rich operating state. As a result, the time measuring means detects the output V2 of the downstream air-fuel ratio sensor from the time when the engine operating state transitions from the stoichiometric air-fuel ratio operating state to the rich operating state.
The catalyst deterioration determining means determines that the three-way catalyst has deteriorated when the measured time TΔ is less than a predetermined time.

In FIG. 1B, °C is used instead of the stoichiometric air-fuel ratio/rich operating state transition determination means of FIG. A lean operating state transition determination means is provided, and the time measuring means measures the time from when the engine operating state transitions from the stoichiometric air-fuel ratio operating state to the lean operating state until the output v2 of the downstream air-fuel ratio sensor is reversed from Rig to Lean. Measure the time TB. In this case, the catalyst deterioration determining means uses the time T
When B is less than a predetermined time, it is determined that the three-way catalyst has deteriorated. .

In FIG. 1C, the constituent elements of FIG. 1Δ and FIG. 1B are combined. Zunawaji, the first time measuring means measures the output V of the downstream air-twist ratio sensor from the time when the operating state of the engine transitions from the stoichiometric air-fuel ratio operating state to the rich operating state.
The first time TΔ until 2 is reversed from lean to rich
The second time measuring means measures the period from when the operating state of the engine changes from the stoichiometric air-fuel ratio operating state to the lean operating state until the output v2 of the downstream air-fuel ratio sensor is reversed from rich to lean. Measure a second time TB. and,
The catalyst deterioration determining means calculates the sum of the measured first and second times as 1.
” It is determined that the three-way catalyst has deteriorated when A + T B is less than a predetermined time.

[For production]

According to the means shown in FIG.
The maximum 0□ storage amount of the three-way catalyst can be determined by measuring the 02 sweep time TΔ from the three-way catalyst when the engine is in a rich state, such as an output increase state or an OT increase state. is measured indirectly.

According to the means shown in FIG. 1B, after the engine confirms a certain degree of 02 storage state of the three-way catalyst in the stoichiometric air-fuel ratio operating state, the three-way catalyst is forced into a lean state, for example, a fuel cut state. 02 storage time to catalyst 1
' By measuring B, the maximum 02 storage amount of the three-way catalyst is indirectly measured.

According to the means of FIG. 1C, the maximum zero of the three-way catalyst is determined by the sum of the 02 sweep time TA of the three-way catalyst in the means of FIG. 1A and the 02 storage time TB of the three-way catalyst in the means of FIG. 1B. □Measure storage amount indirectly.

The degree of deterioration of the three-way catalyst is estimated by indirectly measuring the maximum 02 storage amount of the three-way catalyst using the means shown in FIGS. 1A to 1C.

〔Example〕

First, to explain the 02 storage effect of a three-way catalyst, a three-way catalyst simultaneously purifies NO, CD, and IIc, and its purification rate η is compared to the theoretical empty space, as shown by the dashed line in Figure 3. N on the richer side than the fuel ratio (λ=1)
The purification rate of Ox is high, and the purification rate of Co and HC is high on the lean side (HC is not shown, but it has the same tendency as CO). In this case, the three-way catalyst takes in 0□ when the air-fuel ratio is lean, and when the air-fuel ratio becomes rich, it takes in CO,
It has a 0□ storage effect that takes in HC and makes it react with 02 that is taken in when it is lean, and air-fuel ratio feedback control actively utilizes this 0□ storage effect, so it adjusts the optimum frequency, The air-fuel ratio is controlled by the amplitude. In general, if a three-way catalyst is new, its 02 storage effect is large. Therefore, as shown by the solid line in Figure 3, the purification rate η improves during air-fuel ratio feedback control, and if the required purification rate η is η0, , the controllable air-fuel ratio window W is substantially wide < (W=W,)
Become. However, as the three-way catalyst deteriorates, its 0□ storage effect becomes smaller, and the air-fuel ratio window W becomes very narrow (w=
W2), therefore, air-fuel ratio feedback control for the stoichiometric air-fuel ratio must also be performed within this range (W2). As a result, HC.

Causes an increase in Co, NOX emisidine.

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device between internal combustion stages according to the present invention. In FIG. 4, an air flow meter 3 is provided in an intake passage 2 of an engine main body l. The air flow meter 3 directly measures the amount of intake air, has a built-in potentiometer, and generates an analog voltage output signal proportional to the amount of intake air in °C. This output signal is supplied to the MA/D converter 101 in the multiplexer of the control circuit 10. distributor 4
For example, the axis is 720° in terms of crank angle.
A crank angle sensor 5 that generates a reference position detection pulse signal every 30° in terms of crank angle and a crank angle sensor 6 that generates a reference position detection pulse signal every 30° in terms of crank angle are provided. The pulse signals of these crank angle sensors 5 and 6 are transmitted to the human output interface 102 of the control circuit 10.
The output of the crank angle sensor 6 is C.
It is supplied to the interrupt terminal of PU103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to the intake port for each cylinder.

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body 1. The water temperature sensor 9 indicates the temperature of the cooling water 'I
” Generates an analog voltage electrical signal according to the HW.

This output is also supplied to the A/D converter 101.

A catalytic converter 12 is provided in the exhaust system downstream of the exhaust manifold 11 and houses a three-way catalyst that simultaneously purifies three harmful components 11C, Co, and NOX in the exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
A first 02 sensor 13 is provided on the upstream side of the catalytic converter 12, and a second 02 sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12.

The 02 sensor 13.15 generates an electrical signal according to the concentration of oxygen components in the exhaust gas. That is, 0□ sensor 13,
15 is a control port IL'810 that outputs a different output voltage depending on whether the air-fuel ratio is on the °C')-rich side or on the rich side with respect to the stoichiometric air-fuel ratio.
This occurs in the A/D converter 101.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for detecting whether or not the throttle valve 16 is fully open.
0 human output interface 102. Further, the throttle valve 16 of the intake passage 2 is provided with a full switch 18 that is turned on when the throttle valve 16 is opened at a certain degree, for example, 70 degrees or more, and this output signal VL
is also supplied to the input/output interface 102 of the control circuit 10.

This alarm is activated when it is determined that the three-way catalyst of the 19-piece catalytic converter 12 has deteriorated.

The J11 circuit IO is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102, and an RO controller (104) outside the CPU 103.
, a RAM 105, a backup RAM 106, a clock generation circuit 107, and the like.

Further, at the control port 11810, the down counter 10
8, a flip-flop 109, and a drive circuit 110 are for controlling the fuel injection valve 7. That is,
In the routine described below, when the fuel injection LITAU is calculated, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110
starts energizing. On the other hand, when the down counter 108 counts the clock signal (not shown) and the carrier terminal reaches the "1" level, the flip-flop 109 is reset and the drive circuit 110 controls the fuel injection valve 7. Stop biasing. In other words, the above fuel injection ff1T
The fuel injection valve 7 is energized by AU, and therefore, an amount of fuel corresponding to the fuel injection amount TΔU is sent into the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 10.
When the Δ/D conversion of 1 is completed, the human output interface 102
When the controller receives a pulse signal from the crank angle sensor 6, when it receives an interrupt signal from the clock generation circuit 107, etc.

The intake air m data Q and cooling water temperature data 'l'-HW of the air flow meter 3 are obtained by A/D executed at predetermined time intervals.
The data is fetched by the conversion routine and stored in a predetermined area of the RAM 105. That is, data Q and 'f'HW in RAM 105 are updated at predetermined time intervals. In addition, the rotational speed data Ne is 30° of the crank angle sensor 6.
It is calculated by an interrupt for each CA and stored in a predetermined area of the RAM 105.

Figure 5 is based on the output of the downstream 02 sensor 13.
A first air-fuel ratio feedback control routine that calculates the air-fuel ratio correction number FAF, and for a predetermined period of time, e.g.
Executed every s.

In step 501, 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 never reversed while the engine is starting, increasing after engine startup, increasing warm-up, increasing power, or increasing OTP to prevent catalyst overheating. The closed-loop condition is not satisfied when the fuel is not being used, when the fuel is being cut (XFC-"1°), etc., and the closed-loop condition is satisfied in other cases.

If the closed loop condition is not satisfied, the process proceeds to step 527 and the FAF is set to the value immediately before the end of the closed loop control.

Note that it may be set to a constant value, for example, 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 502.

Note that the fuel cut flag xFC in step 501
is executed by the routine shown in FIG. This routine is executed for a predetermined period of time, for example, 4 ms@, and is for setting the fuel cut flag XFC as shown in FIG. 8107. In FIG. 7, No indicates the fuel cut rotation speed, and N indicates the fuel cut return rotation speed, both of which are updated according to the engine cooling water temperature THW. Step 6
01, the output signal LL of the idle switch 17 is “1”.
”, that is, whether it is in an idle state or not.

If it is in the non-idle state, proceed to step 604; on the other hand,
If it is in the idle state, the process advances to step 602. In step 602, the rotation speed N is obtained from RAMIQ5. Read out the fuel cut rotation speed N. Step 603
Now, compare it with the fuel cut return rotational speed N. As a result, when N8≦N, the fuel cut flag
I I 11. NR<N.

<Nc, the flag X 1''C is held at the previous state. Then, the process ends at step 606.

Returning to FIG. 5, in step 502, the output v1 of the upstream 02 sensor 13 is A/D converted and taken in, and in step 5
03, it is determined whether Cvl is less than the comparison voltage VR+for example 0.45V, that is, it is determined whether the air-fuel ratio is rich or lean, that is, the air-fuel ratio is lean (Vl ≦VR
I), the delay counter C is set in step 504.
It is determined whether DLY is negative or not, and if CDLY > (], CDLY is set to 0 in step 505, and step 50
Proceed to step 6. In step 506, the delay counter CD
LY is subtracted by 1, and the delay counter CDLY is guarded at the minimum value TDL in steps 507 and 508. In this case, when the delay counter (1:DLY) reaches the minimum value TDL, the first air-fuel ratio flag Fl is set to 0'' (lean) in step 509.

Note that the minimum value '1' D L is a one-step delay state to maintain the judgment that the rich state is present even if there is a change from rich to lean in the output of the upstream 0□ sensor 13, and the negative Defined by the value of On the other hand, Rich (Vl
> VILI), it is determined in step 510 whether the delay counter CDLY is positive or not, and if CDLY<0, in step 511 C[lLY is set to 0, and the process proceeds to step 512. In step 512, the delay counter ll'DLY is incremented by 1, and in steps 513 and 514, the delay counter CDLY is guarded with the maximum value TDR. In this case, the delay counter C0LY reaches the maximum value TDR.
When reaching , the first air-fuel ratio flag F1 is set to "1" (IJ petit) in step 515.

Note that the maximum value TDR is a rich delay time for maintaining the determination that the engine is in a lean state even if there is a change from lean to rich in the output of the upstream 02 sensor 13.
C1 is defined as a positive value.

In step 51G, it is determined whether the sign of the first air-fuel ratio flag F1 has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, in step 517, the air-fuel ratio flag F1 of 'L51 is set.
The value of determines whether the reversal is from rich to lean or from lean to rich. If reversing from rich to lean, step 15181 1”PAF-FA
F +R3R toss + 7't' white (increase this, conversely, if it is a reversal from lean to rich, step 51
91 trowel FAF--FAF-R3L. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 516, step 520.521.5
Integration processing is performed at 22. That is, in step 520, I? 1="0" or not, and if F1="0" (lean), in step 521 FAF (-FA
I' +KIR, and on the other hand, if F1="1" (rich), step 5221 goes to F r' 4-PAF
-KIL and 74-ro. Here, the integral constants KIR, KI
L is the skip amount R3R.

It is set sufficiently small compared to flsL, that is, K
IR(KIL)<ItSR(R3L). Therefore, step 521 is in a lean state (F 1 = “O”
), the fuel injection amount is gradually increased, and step 522 is a rich state (F1="1"), and the fuel injection amount is gradually decreased.

The air-fuel ratio correction coefficient FAF calculated in steps 51B and 51.9.521.522 is calculated in step 523.524.
In step 525 = 526, the air-fuel ratio correction coefficient FAF becomes too large, or If it becomes too small, the air-fuel ratio between stages is controlled using that value to prevent over-rich or over-lean conditions.

The PAF calculated as described above is stored in R in M105, and the routine ends in step 527.

FIG. 8 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 5. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream 02 sensor 13 as shown in FIG. 8(A), the delay counter CD
LY is counted up in the rich state and counted down in the lean state, as shown in FIG. 8(,B). As a result, as shown in FIG. 8(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, at time t, the air-fuel ratio signal A/'F
Even if ' changes from lean to rich, the delayed air-fuel ratio signal A/F' changes to rich at time t2 after being held lean for the rich delay time TDR. Even if the air-fuel ratio signal A/F changes from rich to lean at time t3, the delayed air-fuel ratio signal Δ/F' is kept rich for the lean delay time (-TDL) and then changes to lean at time t. It changes to IJ-n at . However, air-fuel ratio signal A
/F' is time ts, t6. When the rich delay time TDR is reversed in a short period such as t, 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
be reversed. In other words, the air-fuel ratio signal Δ/F after the delay processing
' is more stable than the air-fuel ratio signal A/F before the delay processing. In this way, the stable air-fuel ratio signal A/F' after the delay processing
Based on the air-fuel ratio correction coefficient FAF not shown in Fig. 8(D)
is obtained.

Next, the second air-fuel ratio feedback control by the downstream 02 sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts ll5R, R3L, integral constants KIR, KIL, and delay time TDR as first air-fuel ratio feedback control constants.

There is a system in which TO+1 or the comparison voltage V Rl of the output V1 of the upstream 02 sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAF2 is introduced.

For example, if you increase the rich skip amount RS R,
The control air-fuel ratio can be shifted to the rich side, and the control air-fuel ratio can also be shifted to the rich side even if the lean skip bond R3L is made small.On the other hand, the lean skip ff1RS 1. If , is increased, the controlled air-fuel ratio can be shifted to the lean side, and even if rich skip 1R3R is decreased, the controlled air-fuel ratio can be shifted to the lean side.

Therefore, the air-fuel ratio can be controlled by correcting the rich skip IR3R and the lean skip habit R3L according to the output of the downstream 0□ sensor 15.

In addition, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIL
On the other hand, increasing the lean integral constant KIL allows the control air-fuel ratio to shift to the lean side, and even if the rich integral constant KIR is decreased, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KIR and the lean integral constant KIL according to the output of the downstream 02 sensor 15. Rich delay time TDR
If the lean delay time (-TDL) 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 time TDR and 'I'DL according to the output of the downstream side 02 sensor 15. Furthermore, the comparison voltage V
By increasing RI, the control air-fuel ratio can be shifted to the rich side,
Further, by reducing the comparison voltage V Rl, the control air-fuel ratio can be shifted to the lean side. Therefore, by correcting the comparison voltage VRI according to the output of the downstream 02 sensor 15, the air-fuel ratio can be controlled.

Making these skip m, 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 02 sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be described.

FIG. 9 shows a second air-fuel ratio feedback control routine that calculates skip i R3R and R3L based on the output of the downstream side 02 sensor 15.
Executed every 2+ns.

In steps 901 to 905, it is determined whether the downstream O2 sensor 15 is in a closed loop condition. For example, in addition to the failure of the closed loop condition determined by the upstream 0□ sensor 13 (step 901), when the cooling water temperature TIIW is lower than a predetermined value (for example, 70°C) (step 902), the throttle valve 16 is fully opened (LL = "1"). ) (7) (step 9o3), when downstream side 02 sensor 15 is not activated (step 904), when IFJ load (Q/
Ne≦X, > (step 905), etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. If the condition is not a closed loop condition, the process advances to step 912.

If the closed loop condition is met, proceed to step 906. In step 906, the output V2 of the downstream O2 sensor 15 is A/D converted and taken in, and in step 907, the output V2 of the downstream O2 sensor 15 is taken in.
It is determined whether or not the comparison voltage VR is, for example, 0.55V or less. In other words, it determines whether the air-fuel ratio is rich or lean.

Note that the comparison voltage VR2 is set at the upstream side 02 sensor 13 in consideration of the fact that the output characteristics are different due to the influence of raw gas and the deterioration rate is different upstream and downstream of the catalytic converter 12.
is set higher than the comparison voltage VRI of the output. As a result, if V2≦VR□ (lean), the process proceeds to step 908, and on the other hand, if V2>VR2 (rich), the process proceeds to step 909. In step 908, the rich skip poison RS R is increased by a relatively small value ΔR8, and on the other hand,
In step 909, the bridge skip amount R3R is set to the value ΔR3.
decrease only. Note that the integral amount ΔR3 at steps 908 and 909 may be different and may be variable. Step 910 performs guard processing of RSR calculated as described above, for example, the minimum value MI
Guard at N = 2.596 and maximum value MAX = 7.5%. Note that the minimum value MIN is a level at which transient followability is not impaired, and the maximum value MAX is at a level at which drivability does not deteriorate due to air-fuel ratio changes and movements.

In step 911, the -leadge skip fiR3L is set to R
Calculate with OM104-R3R. That is, R3R+R3L=10%.

After the R3R calculated as described above is stored in the I'lAM 105, this routine ends in step 912.

FIG. 10 shows the injection tT (calculation routine), which is executed at every predetermined crank angle, for example every 360° CA.

In step 1001, the fuel cut flag XFC is set to "0".
If XFC="1", the process directly proceeds to step 1008 and no fuel injection is performed.

On the other hand, if XFC="O", the process advances to step 1002. In step 1002, intake air amount data Q and rotational speed data N are obtained by RAJ, 4105. Read “C”
Calculate basic injection fiiTAIIP. For example, T.A.
IIP-α・Q/N@ (α is a constant). In step 1003, go to R. Cooling water temperature data T HW from M105.
is read out and the one-dimensional map stored in the ROM 104 is used to interpolate and calculate the warm-up increase Fhl Q'fF W I.

As shown in the figure, this warm-up increase fil (direction I"W I) is set to decrease -C as the current cooling water temperature T HW rises. Next, in step 1004, the load, for example, Intake air per rotationff1Q/No
In response to the output signal VL of the full switch 18, the output increase value I'l''DI [ER is calculated using a two-dimensional map stored in the ROM 104. In step 1005, the load, for example, intake air per revolution, is The OTP increase value POTP is RO according to the amount Q/Ne and the rotation speed Nll.
The calculation is performed using the two-dimensional map stored in M104. Note that the O'I''P increase value P[lTP is for preventing heating of the catalytic converter, exhaust pipe, etc. during high load. Then, in step 1006, the final injection amount TΔU is
to high U -T UP -FAF ・(FIIIL-
1-FP01'1BIl + f'OTP+β+1)+
Calculate by T. Note that β and γ are correction amounts determined by other operating state parameters, such as a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, battery voltage, etc., and these are also correction amounts determined by R. It is stored in M105. Next, in step 1007, the injection ITAU is set in the down counter 108 and the flip-flop 10 is set.
Set 9 to start fuel injection. The routine then ends at step 1008. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

FIG. 11 shows a catalyst deterioration determination routine, which is executed every predetermined period of time, for example, 4 ms. In step 11 old, it is determined whether or not the output is increased based on the output increase value FPOWBR. Here, the output increase state does not matter whether the value FPOWER is large or small. Unless the output is increased (FPOIII
ER=0), the flow of steps 1112 to 1115 is executed, and if the output is increased (IIPOIII
BR key 0), the flow advances to step 1102 and subsequent steps.

In addition, the output increase value FPOl'lER in step 11 old
The OTP increase value FOTP may be used instead.

Steps 1112 to 1114 set a catalyst deterioration determination execution flag XBXE for executing catalyst deterioration determination only when it is certain that the output V2 of the downstream 0□ sensor 15 is lean when the output increases. do ("1'"
) is for something. That is, step 1112
In step 1113, the output v2 of the downstream side 02 sensor 15 is A/D converted and taken in, and it is determined in step 1113 whether V2≦VR2, that is, whether the air-fuel ratio downstream of the catalyst is lean. As a result, if lean, the execution flag XBXB is set in step 1114 ('1'), and if rich, the execution flag XBXE is reset ("O"). Then, in step 1116, the counter CNT is cleared and step 1
Proceed to 117.

When the state is switched to the output increase state, the flow in step 1101 proceeds to step 1102, where it is determined whether the catalyst deterioration determination execution flag XIEX[E is Pa1''.
EXE="0" If the result is Xt!, the process directly proceeds to step 1116, without performing catalyst deterioration determination, and on the other hand, if Xt! XB=
If it is "1", the process proceeds to step 1103 and subsequent steps, and catalyst deterioration determination is performed.

In step 1103, the output V of the upstream 02 sensor 13 is
I is A/D converted and taken in, and in step 1104 V1
≧0゜8V (!J Petit or not is determined.The reason why the comparison voltage is higher than VRI<0.8V is because the upstream O
This is done depending on whether the RI has been crossed or not, but if the upstream 02 sensor 13 deteriorates and the output V1 of the upstream 0□ sensor 13 becomes unstable, even though the air-fuel ratio upstream of the catalyst is lean. This is to prevent erroneous judgments by setting the comparison voltage to a value relatively higher than VRI, since erroneous rich judgments may occur. Proceed to step 1105 only if V1≧0.8V.

In step 1105, the output V of the downstream 0□ sensor 15 is
2 is A/D converted and taken in, and in step 1106 V2
≧0.8V (to determine whether it is IJ small or not. The reason why the comparison voltage is set to be higher than Vl2 and <0.8V is for the same reason as mentioned above. As a result, when V2<0.8V, In step 1107, the counter CNT is counted up by +1 to measure time. When V2≧0.8V, the flow in step 1106 proceeds to step 1108.

In this way, the counter CNT measures the time from the time when Vl≧0.8V to the time when V2≧0.8V under the catalyst deterioration determination execution flag XEXB="1". This time depends on the 02 storage effect of the three-way catalyst, that is, the degree of deterioration of the three-way catalyst.

That is, if the three-way catalyst does not deteriorate and the 02 storage effect is large, this time is long; on the other hand, if the three-way catalyst deteriorates and the 02 storage effect is small, this time is short.

Therefore, if CNT≦m (predetermined value) in step 1108, the three-way catalyst is considered to have deteriorated, and step 1
In 109, set G to the deterioration diagnosis flag XDI.
1""), backup RAM1 at step 1110
06, and the alarm 19 is activated in step 1111. On the other hand, if the CN is 72m, the process directly proceeds to step 1116.

Then, the eleventh routine ends at step 1117 via step 1116.

FIGS. 12 and 13 are timing charts for supplementary explanation of the flowchart in FIG. 11. FIG. 12 shows a case where the three-way catalyst is normal. That is, time t. When the output increases, which is a clear rich state, at time t.

Catalyst deterioration determination is started under the condition that the catalyst deterioration determination flag XBXB set by the output v2 of the downstream side 02 sensor 15 is 1'', which does not indicate whether the air-fuel ratio downstream of the catalyst is clearly lean or not. In other words, the counter CNT changes from a clear lean state (time 1+) to a clear rich state (time t
Measure the forced transition time up to 2).

In the case of FIG. 12, this period is large, so the flow in step 1108 of FIG. 11 proceeds directly to step 1116 and no alarm is generated. On the other hand, FIG. 13 shows a case where the three-way catalyst has deteriorated. In this case, from a clear lean state (time 1+) to a clear rich state (time t2)
Since the forced transition time is short, the flow at step 1108 in FIG. 11 proceeds to step 1109, and an alarm is generated.

Figure 14 also shows the catalyst deterioration determination routine, and contrary to the case in Figure 11, the three-way catalyst deteriorates due to the 02 storage time to the three-way catalyst when transitioning to fuel cut, which is a clear lean state. Determine degree. In other words, in step 14 old,
It is determined whether or not the fuel is cut off based on the fuel cut flag XFC.

If it is not in the fuel cut state (XFC = “0”),
The flow of steps 1412 to 1415 is executed, and if the fuel cut state is (xFC=“1”), step 14
Proceed to the flow from 02 onwards.

Steps 1412 to 1414 set a catalyst deterioration determination execution flag XIEXB for executing catalyst deterioration determination only when it is confirmed that the output V2 of the downstream side 02 sensor 15 at the time of entering the fuel cut state is rich.
i''>. That is, in step 1412, the output v2 of the downstream 0° sensor 15 is set to A/
D conversion and import, in step 1413 V2 > VB
2, that is, whether the air-fuel ratio downstream of the catalyst is rich. As a result, if it is rich, step 141
4, the execution flag X [! Set XB to 1"), and if lean, reset the execution flag XBXB ("0'
°). Then, in step 1416, the counter CNT is cleared and the process proceeds to step 1417.

When the state is switched to the fuel cut state, the flow in step 1401 proceeds to step 1402, where it is determined whether the catalyst deterioration determination execution flag XEXE is "1'". As a result,
If BXB="0", the process directly advances to step 1416 and does not determine catalyst deterioration; on the other hand, if XBXB-"1°", the process advances to step 1403 and subsequent steps to determine catalyst deterioration.

In step 1403, the output v of the upstream 02 sensor 13 is
1 is A/D converted and imported, and in step 1404 v1
It is determined whether ≦VRI('J-n). In this case as well, it is possible to set the comparison voltage lower than VRI to prevent misjudgment even if the output VI of the upstream 0□ sensor 13 becomes unstable. Proceed to step 1405 only if v1≦VlH.

In step 1405, the output v of the downstream sensor 15
2 is A/D converted and taken in, and in step 1106 V2
It is determined whether ≦VR2 (!J-n). Note that the comparison voltage may be lower than VR2 for the same reason as described above. As a result, when V2 > VB2, step 14
At step 07, the counter CNT is counted up by +1 to measure time. When v2≦VR2, step 14
The flow at step 06 continues to step 1408.

In this way, the counter CNT measures the time from the time when V1≦VR2 becomes V2≦VR2 under the catalyst deterioration determination execution flag XBXB=“1”. This time also depends on the 02 storage effect of the three-way catalyst, that is, the degree of deterioration of the three-way catalyst. That is, if the three-way catalyst does not deteriorate and the 02 storage effect is large, this time is long; on the other hand, if the three-way catalyst deteriorates and the 02 storage effect is small, this time is short.

Therefore, if CNT≦m (predetermined value) in step 1408, the three-way catalyst is considered to have deteriorated, and step 1
In 409, set the deterioration diagnosis flag XDIAG.
1”), backup RAM 10 at step 1410
6 and energizes Arano 19 in step 1411. On the other hand, if the CN is 12m, the process directly proceeds to step 1416.

Thus, the 14th routine ends at step 1417 via step 1416.

FIGS. 15 and 16 are timing diagrams for supplementary explanation of the flowchart in FIG. 14. FIG. 15 shows a case where the three-way catalyst is normal. That is, as shown in the figure, the vehicle speed SPD and the immediately preceding Q/Ne change, and at time t. When the fuel cut state, which is a clear lean state, is entered at time t. Catalyst deterioration determination is started under the condition that the catalyst deterioration determination flag XEXB, which is set by the output V2 of the downstream side 02 sensor 15, which indicates whether the air-fuel ratio downstream of the catalyst is in a clear rich state or not, is "1". Ru. That is, the counter CNT measures the forced transition time from a clear rich state (time 1+) to a clear lean state (time t2).

In the case of FIG. 15, this period is large, so the flow in step 1408 of FIG. 14 proceeds directly to step 1416 and no alarm is generated. On the other hand, FIG. 16 shows a case where the three-way catalyst has deteriorated. In this case, a clear rich state (time 1+) to a clear lean state (time tz)
Since the forced transition time is short, the flow at step 1408 in FIG. 14 proceeds to step 1409, and an alarm is generated.

Note that it is also possible to combine the routine in FIG. 11 and the routine in FIG. 14. In other words, from a clear lean state (XfEXE="1") to a clear rich state (FP
OW[! Calculate the reversal time TΔ of the output V2 of the downstream side 02 sensor 15 to rich when shifting to Itkey 0 or FOTP40 (routine in Figure 11), and also from a clear rich state (XEXB="1") Clear lean state (X
Find the reversal time TB of the output V2 of the downstream side 02 sensor 15 to lean when shifting to FC="l" (routine in Figure 14), and calculate the time TΔ, the sum of TB T A -1-T B
The degree of deterioration of the three-way catalyst can be determined by That is, in this case the value TΔ.

TA+TB is larger than TB, and therefore the accuracy of determining the deterioration of the three-way catalyst is higher.

In the above-described embodiment, when catalyst deterioration is determined, the closed loop by the downstream 02 sensor 15 may be stopped, thereby preventing deterioration of emissions.

In addition, the first air-fuel ratio feedback control is performed every 4 ms, and the second air-fuel ratio feedback control is performed every 512 m5.
The reason for this is that the air-fuel ratio feedback control is primarily controlled by the upstream O2 sensor, which has good responsiveness, and the downstream O2 sensor, which has poor responsiveness, is used as a secondary control.

In addition, other control constants in the air-fuel ratio feedback control by the upstream 0□ sensor, such as delay time, integral constant, and comparison voltage of the upstream 0□ sensor (reference: JP-A-55-3
The present invention can also be applied to a double 02 sensor system that corrects the air-fuel ratio (No. 7562) etc. using the output of a downstream 02 sensor, or a double 02 sensor system that introduces a second air-fuel ratio correction coefficient.

Furthermore, instead of the air flow meter, a Karman vortex sensor, a heat wire sensor, or the like may be used as the intake air amount sensor.

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 the amount of fuel injected, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (BACV) is used to control the air-fuel ratio by adjusting the intake air amount of the engine, and an electric bleed air control valve is used to adjust the amount of air bleed from the carburetor to control the main system passage and slow air. The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into system passages, devices that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic injection lTA[IP
A corresponding basic fuel injection amount is determined by the carburetor itself, that is, depending on the intake pipe negative pressure depending on the intake air amount and the engine rotational speed, and in step 1004, the final fuel injection, the supply air corresponding to 1 TAU The quantity is calculated.

Furthermore, in the above-described embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a CO sensor, lean mixture sensor, etc. may also be used.

Furthermore, although the embodiments described above are constructed using a microcomputer, that is, a digital circuit, they may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, deterioration of a three-way catalyst can be controlled with high accuracy.

[Brief explanation of the drawing]

Figures 1A to 1C are overall block diagrams for explaining the present invention in detail. Figure 2 is a single 02 sensor system and a double 02 sensor system.
An exhaust emission characteristic diagram explaining the sensor system, FIG. 3 is a graph diagram explaining the 02 storage effect of the three-way catalyst, and FIG. 4 is an overall schematic diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention. Fig. 5, Fig. 6, Fig. 9, Fig. 10, Fig. 11, Fig. 14
Figure 7 is a flowchart for explaining the operation of the control circuit in Figure 4, Figure 7 is a timing diagram for supplementary explanation of the flowchart in Figure 6, and Figure 'fIJ8 is a flowchart for supplementary explanation of the flowchart in Figure 5. 12 and 13 are timing diagrams for supplementary explanation of the flowchart in FIG. 11, and FIGS. 15 and 16 are timing diagrams for supplementary explanation of the flowchart in FIG. 14. . 1... Engine body, 3... Air flow meter, 4
... Distributor, 5, 6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side 02 sensor, 15... Downstream side 02 sensor, 17...・Idle switch, 18...Full switch. NOx Diagram XFC=''1'' (Fuel power) Amendment (voluntary) July 1999/D date

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) that is provided in the exhaust passage upstream of the three-way catalyst and detects the air-fuel ratio of the engine; and an upstream air-fuel ratio sensor (13) that is provided downstream of the exhaust passage of the three-way catalyst that detects the air-fuel ratio of the engine. a downstream air-fuel ratio sensor (15) for detecting the air-fuel ratio of the engine; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor; Reversal determining means for determining whether the output of the downstream air-fuel ratio sensor is reversed from lean to rich or from rich to lean; and a theory for determining whether the operating state of the engine changes from a stoichiometric air-fuel ratio operating state to a rich operating state. an air-fuel ratio/rich operating state transition determination means; and an air-fuel ratio/rich operating state transition determination means; A catalyst deterioration determining device for an internal combustion engine, comprising: a time measuring device that measures time; and a catalyst deterioration determining device that determines that the three-way catalyst has deteriorated when the measured time is less than or equal to a predetermined time. 2. In the apparatus of claim 1, instead of the stoichiometric air-fuel ratio/rich operating state transition determining means, a stoichiometric air-fuel ratio/lean operating state for determining whether the operating state of the engine changes from a stoichiometric air-fuel ratio operating state to a lean operating state. An operating state transition determining means is provided, and the time measuring means is configured to invert the output of the downstream air-fuel ratio sensor from rich to lean from when the operating state of the engine transitions from the stoichiometric air-fuel ratio operating state to the lean operating state. A catalyst deterioration determination device for internal combustion engines that measures the time until 3. Three-way catalyst (12) installed in the exhaust passage of an internal combustion engine
an upstream air-fuel ratio sensor (13) that is provided in the exhaust passage upstream of the three-way catalyst and detects the air-fuel ratio of the engine; and an upstream air-fuel ratio sensor (13) that is provided downstream of the exhaust passage of the three-way catalyst that detects the air-fuel ratio of the engine. a downstream air-fuel ratio sensor (15) for detecting the air-fuel ratio of the engine; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor; Reversal determining means for determining whether the output of the downstream air-fuel ratio sensor is reversed from rich to lean or from lean to rich; and a theory for determining whether the operating state of the engine changes from a stoichiometric air-fuel ratio operating state to a rich operating state. an air-fuel ratio/rich operating state transition selection means; and an air-fuel ratio/rich operating state transition selection means; a first time measuring means for measuring a first time; a stoichiometric air-fuel ratio lean operating state transition determining means for determining whether the operating state of the engine changes from a stoichiometric air-fuel ratio operating state to a lean operating state; a second time measuring means for measuring a second time from when the operating state changes from the stoichiometric air-fuel ratio operating state to the lean operating state until the output of the downstream side air/fuel efficiency sensor reverses from rich to lean; A catalyst deterioration determining device for an internal combustion engine, comprising: catalyst deterioration determining means for determining that the three-way catalyst has deteriorated when the sum of the measured first and second times is less than or equal to a predetermined time.