JPH0233408A - Device for discriminating catalytic degradation of internal combustion engine - Google Patents

Abstract

PURPOSE:To get rid of wrong discrimination of catalytic degradation by measuring a discharging time of O2 from tree way catalyst at a time of forced conversion to the state of a rich or theoretical air fuel ratio so as to indirectly measure the maximum storage quantity of O2 of the three way catalyst. CONSTITUTION:An air fuel ratio adjusting means A adjusts an air fuel ratio of an engine according to outputs V1, V2 of air fuel ratio sensors on the upstream and downstream sides of three way catalyst CCRO. A time measuring means B measures a time TA since it is judged that an operating state has transited from a lean operating state to a rich or theoretical air fuel ratio operating stage by a rich/lean operation state transition discriminating means C until it is discriminated that the output V2 of the air fuel ratio sensor on the downstream side has reversed from the lean to the rich by a repeat discriminating means D. And a catalytic degradation discriminating means E discriminates that the tree way catalyst has dagraded when the measured discharging time TA of O2 from the three way catalyst is shorter than a fixed time. Thus it is possible to discriminate the degradation of the three way catalyst precisely.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (0□ sensor)) provided with an air-fuel ratio sensor (oxygen concentration sensor (0□ sensor)) on the upstream side and downstream side of a catalytic converter. The present invention relates to a catalyst deterioration determination device in a 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. □Due to variations in sensor output characteristics, it is difficult to improve air-fuel ratio control accuracy. It takes 02
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 1 is performed using the upstream AT sensor. In addition to this, a double 0□ 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). In this double 02 sensor system, although the O2 sensor installed downstream of the catalytic converter has a lower response speed than the upstream 02 sensor, it has the advantage of less variation in output characteristics for the following reasons. are doing.

(1) Downstream of the catalytic converter, the exhaust gas 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 0□ 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, the air-fuel ratio feedback control (double 0□ sensor system) based on the outputs of the two 0□ sensors allows the downstream 02 sensor to absorb variations in the output characteristics of the upstream 02 sensor. In fact, as shown in Figure 2, in the single 02 sensor system, 0□
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, whereas with the double 0□ sensor system, even if the output characteristics of the upstream Ot sensor deteriorate,
Exhaust emission characteristics are not deteriorated. That is, double 0
In a two-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, when the catalyst function deteriorates, the IC,
Due to the influence of unburned gas such as Co・, lh, etc., the downstream side is 0! The output characteristics of the sensor deteriorate. In other words, the number of times the output of the downstream 0□ sensor is reversed increases, and as a result, the downstream O
This causes disturbances in the air-fuel ratio feedback control by the t-sensor, making it impossible to obtain a good air-fuel ratio, resulting in poor fuel efficiency, poor drivability, HC, CO, and NOx.
There is a problem that this may lead to deterioration of emissions, etc.

For this reason, the applicant has already detected deterioration of the catalyst by comparing the output cycles of the upper and downstream Ot sensors, the output cycle of the downstream O2 sensor, or the number of reversals of the output of the downstream O2 sensor per unit time. It is proposed that
No. 1489).

[Problem to be solved by the invention]

However, in the above-described catalyst deterioration determination system, the 02
Changes in the output characteristics of the sensor are also included in the output of the 03 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 Ot sensors, the output cycle of the upstream 0□ sensor is on the order of 13, and the output cycle of the downstream 0□ is on the order of 1 win, indicating that the catalyst is burnt out. There was also the problem that only close conditions could be determined.

In addition, the applicant has further proposed that the downstream 0
．． Time from lean to rich reversal of sensor output and/or time from rich to lean reversal of downstream Ot sensor output when the engine is forcibly transitioned from stoichiometric air-fuel ratio operating state to clear lean state It is also proposed to determine the degree of deterioration of the three-way catalyst by measuring the time. However, in this case, the Oz storage a of the three-way catalyst at the end of the stoichiometric air-fuel ratio operating state is only clear to a certain extent, and therefore the degree of deterioration of the three-way catalyst cannot be determined with high precision.

Furthermore, 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 0□ 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 CCi+o provided in the exhaust passage of the internal combustion engine, and
A downstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage downstream of the three-way catalyst CC*o. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the output V1 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 downstream air-fuel ratio sensor is reversing from lean to rich or from rich to lean. On the other hand, the rich/lean operating state transition determining means determines whether the engine operating state has transitioned from a lean operating state to a rich or stoichiometric air-fuel ratio operating state.

As a result, the time measurement means measures the period from when the engine operating state changes from lean operating state to rich or stoichiometric air-fuel ratio operating state until the output V2 of the downstream air-fuel ratio sensor reverses from lean to rich. The time TA is measured, and the catalyst deterioration determining means determines that the three-way catalyst has deteriorated when the measured time TA is less than or equal to a predetermined time.

In FIG. 1B, instead of the lean/rich operating state transition determination means of FIG. 1A, the engine operating state determines whether the engine's operating state transitions from a rich operating state to a lean or stoichiometric air-fuel ratio operating state. Provide a means for determining transition,
The time measuring means starts when the operating state of the engine changes from a rich operating state to a lean or stoichiometric air-fuel ratio operating state.
Measure the time TB until the output (2) of the downstream air-fuel ratio sensor changes from rich to lean. In this case, the catalyst deterioration determination means determines that the three-way catalyst has deteriorated when the time TB is less than or equal to a predetermined time.

FIG. 1C is a combination of FIGS. 1A and 1B. In other words, the first time measuring means measures the period from when the engine operating state changes from a lean operating state to an empty state or to a stoichiometric air-fuel ratio operating state until the output vt of the downstream air-fuel ratio sensor reverses from lean to rich. The second time measuring means measures the output v of the downstream air-fuel ratio sensor from the time when the operating state of the engine transitions from the rich operating state to the lean or stoichiometric air-fuel ratio operating state.
Second time TB until 2 is reversed from rich to lean
Measure. The catalyst deterioration determining means determines that the three-way catalyst has deteriorated when the sum TA+TB of the measured first and second times is less than or equal to a predetermined time.

[For production]

According to the means shown in FIG. 1A, after the engine recognizes the 02 storage state of the three-way catalyst due to a lean operating state, such as a fuel cut state, the engine is forced to shift to a rich or stoichiometric air-fuel ratio state. The maximum 02 storage amount of the three-way catalyst is indirectly measured by measuring the 02 sweeping time TA from the original catalyst. Note that the 02 storage state of the three-way catalyst before the start of time TA measurement is preferably a complete 02 storage state B (full state B), so the above lean operating state (fuel cut state) must be maintained for a predetermined time or longer. It is preferable to check.

According to the means shown in FIG. 1B, when the engine is in a rich operating state, such as an output increase state or an OTP increase state, the three-way catalyst is
2 After confirming the empty state, the maximum 02 storage of the three-way catalyst is determined by measuring the storage time TB of 0□ storage to the three-way catalyst when the engine is forced to shift to a lean or stoichiometric air-fuel ratio state. Measuring quantity indirectly. In addition, time TB
It is preferable that the 02 empty state of the three-way catalyst before the start of measurement is a complete 02 empty state, so it is preferable to confirm that the rich operating state (output increase or OTP increase state B) is maintained for a predetermined time or longer. .

According to the means of FIG. 1C, the 0! of the three-way catalyst in the means of FIG. 1A! The maximum 02 storage amount of the three-way catalyst is indirectly measured by the sum of the sweep-out time TA and the 0□ storage time TB of the three-way catalyst in the means of FIG. 1B.

The degree of deterioration of the three-way catalyst is estimated by indirectly measuring the maximum o2 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 purifies NOX, CO, and HC at the same time, and its purification rate η is determined by the stoichiometric air-fuel ratio as shown by the dashed line in Figure 3. NO on the richer side than (λ=1)
The purification rate of x is large, and on the lean side, the purification rates of Co and HC are large (HC is not shown, but it has the same tendency as CO). In this case, the three-way catalyst is 0.0 when the air-fuel ratio is lean. When the air-fuel ratio becomes rich, CO
, IIc and reacts with 02 taken in when lean, which has an 02 storage effect. Air-fuel ratio feedback control actively utilizes this Ot storage effect, so it is possible to adjust the optimum frequency and amplitude. to control the air-fuel ratio. Generally, if a three-way catalyst is new, its 0□ storage effect is large, and therefore, as shown by the solid line in Fig. 3, the purification rate η improves during air-fuel ratio feedback control, and the required purification rate η becomes η. Then, the controllable air-fuel ratio window W is substantially wide < (w=w
,)Become. However, as the three-way catalyst deteriorates, its 02 storage effect decreases, and the air-fuel ratio window W becomes very narrow, as shown by the dashed line in Figure 3.
w ”= wz ), therefore, the air-fuel ratio feedback control for the stoichiometric air-fuel ratio is originally (W2) within this range.
must be done. As a result, HC.

This results in an increase in Co and NOX emissions.

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 4, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. The air flow meter 3 directly measures the intake air amount, has a built-in potentiometer, and generates an analog voltage output signal proportional to the intake air amount. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720° in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30' in terms of crank angle. A crank angle sensor 6 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 IO, and the output of the crank angle sensor 6 is sent to the CPU 10.
3 interrupt terminal.

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 boat 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 l. Water temperature sensor 9 indicates cooling water temperature TH
Generates an analog voltage electrical signal according to W. 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 harmful components HC, CO, and NOx in exhaust gas is provided in the exhaust system downstream of the exhaust manifold 11.

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 sensors 13 and 15 generate electrical signals corresponding to the concentration of oxygen components in the exhaust gas. That is, 0□ sensor 13
, 15, the control circuit 10 outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
This occurs in the 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 closed.
0 input/output interface 102. Furthermore, 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 has a certain opening, for example, 70" or more, and this output signal VL
is also supplied to the input/output interface 102 of the control circuit 10.

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

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102, a CPU 103, and a ROM 104, R
AM-105, bank amplifier ROM 106, clock generation circuit 107, etc. are provided.

Further, in the control circuit 10, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7. That is, in the routine described later, when the fuel injection amount TAU 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 the fuel injection valve 7. On the other hand, the down counter 108 receives the clock signal (
(not shown), and finally the carrier terminal is “
1" level, the flip-flop 109 is reset and the drive circuit 110 stops energizing the fuel injection valve 7. In other words, the fuel injection valve 7 is energized by the above-mentioned fuel injection NTAU, and therefore, An amount of fuel corresponding to the fuel injection ITAU 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 A/D conversion of step 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 data Q and cooling water temperature data THW of the air flow meter 3 are taken in by an A/D conversion routine executed every day for a predetermined period of time and stored in a predetermined area of the RAM 105. That is, data Q and THW in RAM 105 are updated at predetermined time intervals. Further, the rotational speed data Ne is calculated by interruption every 30° CA of the crank angle sensor 6 and is stored in a predetermined area of the RAM 105.

FIG. 9 shows a first air-fuel ratio feedback control routine that calculates an air-fuel ratio correction factor FAF based on the output of the upstream 02 sensor 13, and is executed every predetermined period of time, for example, every 4 ms.

In step 501, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 0□ 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 cant flag XFC in step 501
is executed by the routine shown in FIG. This routine is executed every predetermined time, for example, 4 ms, and is for setting the fuel cut flag XFC as shown in FIG. In FIG. 7, Nc indicates the fuel cut rotation speed, and Ne indicates the fuel cut return rotation speed, both of which are updated according to the engine cooling water temperature THW. Step 601
Now, it is determined whether the output signal LL of the idle switch 17 is "1", that is, whether there is an idle state. If it is in a non-idle state, the process proceeds to step 604; on the other hand, if it is in an idle state, the process proceeds to step 602. Step 6
In step 02, the rotation speed N is read out from the RAM 105 and compared with the fuel cut rotation speed NC, and in step 603, it is compared with the fuel cut return rotation speed NR. As a result,
When N0≦N, l, the fuel cut flag XFC is set to "0" in step 604, and when N0≧Nc, the process proceeds to step 705, where the fuel cut flag XFC is set to 1'. Nl<N.

<Nc, the flag XFC is held at the previous state. Then, the process ends at step 606.

Returning to FIG. 5, in step 502, the output of the upstream 0° sensor 13 is A/D converted and taken in, and in step 5
At step 03, it is determined whether or not Vl is less than the comparison voltage Vll+, for example, 0.45V.In other words, it is determined whether the air-fuel ratio is rich or lean.In other words, if the air-fuel ratio is lean (Vl ≦V□
), in step 504 the delay counter CD
It is determined whether LY is negative or not, and if CDLY>0, CDLY is set to O in step 505 and the process proceeds to step 506. In step 506, the delay counter CDLY is set to 1.
Then, in steps 507 and 508, the delay counter CDLY is guarded with 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 509.
(lean).

The minimum value TDL is a lean delay state in which the rich state is maintained even if the output of the upstream 02 sensor 13 changes from rich to lean, and is defined as a negative value. . On the other hand, rich (Vl > vH)
If so, in step 510 the delay counter CDL
It is determined whether Y is positive or not, and if CDLY<0, CDLY is set to O in step 511 and the process proceeds to step 512.

In step 512, the delay counter CDLY is incremented by 1, and in steps 513 and 514, the delay counter CDLY is incremented by 1.
Guard LY with maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the first air-fuel ratio flag F1 is set to "1" (
rich).

The maximum value TDR is a rich delay time for maintaining the determination that the lean state is present even if the output of the upstream 0□ sensor 13 changes from lean to rich, and is defined as a positive value. Ru.

In step 516, 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, 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 518 FAF −FAF +R3
R and increases in a skip manner, and conversely, if it is a reversal from lean to rich, FAF 4-FA is increased in step 519.
F-RSL and skipping decrease. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 516, steps 520, 521, 522
In other words, in step 520, F
Determine whether 1="0' or not, F1="0" (lean)
If so, in step 521, FAF −FAF + is set to I
On the other hand, if F1="1" (rich), FAF 4-FAF-KIL is set in step 522. Here, the integral constants KIR and KIL are skipped il R2H
, is set sufficiently small compared to RSL, that is, K
iR(KIL)<R2H(RSL). Therefore,
Step 521 gradually increases the fuel injection amount in a lean state (F1="0"), and step 522 gradually increases the fuel injection amount in a rich state B (
Fl=“1”), the fuel injection amount is gradually decreased.

The air-fuel ratio correction coefficient FAF calculated in steps 518, 519, 521, and 522 is guarded at a minimum value of, for example, 0.8 in steps 523 and 524, and is guarded at a maximum value of, for example, 1.2 in steps 525 and 526. is guarded. As a result, for some reason, the air-fuel ratio correction coefficient F
When the AF becomes too large or too small, the air-fuel ratio of the engine is controlled using that value to prevent over-rich or over-lean conditions.

The FAF calculated as above is RA? ! 105, and the routine ends at 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 0□ 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 (I3). As a result, as shown in FIG. 8 (C), the delayed air-fuel ratio signal A/ F' (corresponding to flag F1) is formed.For example, even if the air-fuel ratio signal A/F' changes from lean to rich at time 1, the delayed air-fuel ratio signal A/F' is rich. Even if the air-fuel ratio signal A/F changes from rich to lean at time t, which changes to rich at time t2 after being held lean for the delay time TDR,
The delayed air-fuel ratio signal A/F' is f during lean delay.
At time t after being held rich by an amount equivalent to SF (TDL)
Changes to lean at 4. However, the air-fuel ratio signal A/F'
is the rich delay time TDR as time tSrt&+”l
If the delay counter CDLY is inverted in a short period of time, it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, the air-fuel ratio signal A/F' after the delay process is inverted at time t. In other words, 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 manner, the air-fuel ratio correction coefficient FAF shown in FIG. 8(D) is obtained based on the stable air-fuel ratio signal A/F' after the delay processing.

Next, downstream O! The second air-fuel ratio feedback control using the sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts R3R and RSL as the first air-fuel ratio feedback control constants, and an integral constant K.
IR, KIL, delay time TDR.

TDL or upstream 0! There is a system in which the comparison voltage V□ of the output ■1 of the sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAF2 is introduced.

For example, if the rich skip NR3R is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean skip IR3L is decreased, the controlled air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip amount RS L is increased,
The controlled air-fuel ratio can be shifted to the lean side, and even if the rich skip amount R5R is made small, the controlled air-fuel ratio can be shifted to the lean side.

Therefore, downstream side 0. The air-fuel ratio can be controlled by correcting the rich skip IR3R, upper and lean skip amount RSL in accordance with the output of the sensor 15.

In addition, the rich integral constant KIR can be increased (then the control air-fuel ratio can be shifted to the rich side, and the lean integral constant K I
Even if L is small, the control air-fuel ratio can be shifted to the rich side,
On the other hand, if the lean integral constant KIL is increased, the control air-fuel ratio can be shifted to the lean side, and the rich integral constant KIL can be shifted to the lean side.
Even if R is made small, the control n 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 K I I- according to the output of the downstream 0□ sensor 15. Increase the lean delay time "I'DR" or increase the lean delay time (-
By setting the lean delay time (-TDL) small, the control air-fuel ratio can shift to the rich side; conversely, by setting the lean delay time (-TDL) to a large value or by setting the lean delay time ("1'DR") small, the control air-fuel ratio can be shifted to the rich side. The air-fuel ratio can be shifted to the lean side.In other words,
Downstream side 0. Delay time TDI? according to the output of sensor 15?
- The air-fuel ratio can be controlled by correcting TDL.

Furthermore, if the comparison voltage V B 1 is increased, the controlled air-fuel ratio can be shifted to the rich side, and if the comparison voltage (2) is decreased, the controlled air-fuel ratio can be shifted to the lean side. Therefore,
By correcting the comparison voltage ■□ according to the output of the downstream 02 sensor 15, the air-fuel ratio can be controlled.

There are advantages to varying the skip amount, integral constant, delay time, and comparison voltage depending on the downstream side, the side O, and the sensor. 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, the air-fuel ratio feedback control constant and 1. A double O, send system with variable skip amount will be explained.

FIG. 9 shows a second air-fuel ratio feedback control routine that calculates skip 'FJ R5R and R5L based on the output of the downstream (+!1ot) sensor 15, and is executed every predetermined period of time, for example, every 512 m5.

In steps 901 to 905, it is determined whether the downstream side 02 sensor 15 is in a closed loop condition. For example, in addition to the failure of the closed loop condition determined by the upstream 02 sensor 13 (step 901), when the cooling water temperature THW is below a predetermined value (for example, 70°C) (step 902), the throttle valve 16 is fully closed cx-i, - “1”) (Step 903), when the downstream O8 sensor 15 is not activated (Step 7 904), when the load is light (Q/N ≦X, ) (Step 905), etc. The closed loop condition is not satisfied, and the closed loop condition is satisfied in other cases. 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, downstream 0. The output ■a of the sensor 15 is A/D converted and taken in, and in step 907 it is converted to v8.
is the comparison voltage■. For example, it is determined whether the voltage is 0.55V or less. In other words, it determines whether the air-fuel ratio is rich or lean. In addition, the comparison voltage ■. is set higher than the comparison voltage (1) of the output of the upstream side 02 sensor 13, taking into account that the output characteristics are different due to the influence of raw gas and the deterioration rate is different between the upstream and downstream of the catalytic converter 12. As a result, if ■yo≦VIE (lean), proceed to step 908;
On the other hand, if Vx>Vex (lean), the process proceeds to step 909. In step 908, rich sgip IR
3R is increased by a relatively small value ΔR3, and on the other hand, in step 909, the rich skip amount R8R is decreased by a value ΔR3. Note that the integral amount ΔR3 at steps 908 and 909 may be different or may be variable. Step 910 performs guard processing of R3R calculated as described above, for example, the minimum value MIN-2,
Guard at 5%, maximum value MAX = 7.5%. Note that the minimum value MIN is a value at a level that does not impair transient followability, and the maximum value MAX is a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

In step 911, reach skip 1iR3L is set to R
Calculate with AM105-RSR. That is, RSR+R3L=10%.

After the RSR calculated as described above is stored in the RAM 105, this routine ends in step 912.

FIG. 10 shows an injection amount 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”.
”, and if XFC="1", step 1
Proceed directly to 008 and do not perform fuel injection.

On the other hand, if XFC="O", the process advances to step 1002. In step 1002, the RAM 105 reads out the intake air amount data Q and the rotational speed data N0 to calculate the basic injection 11TAUP. For example, TAUP-α・
Q/N, (α is a constant). R at step 1003
Read the cooling water temperature data THW from AM105 and store it in ROM.
The warm-up increase value FW is determined by the one-dimensional map stored in 104.
Calculate L by interpolation. As shown in the figure, this warm-up increase value FWL is set to decrease as the current cooling water temperature THW increases.Next, in step 1004, a load such as intake air IQ/N per rotation, According to the output signal VL of the full switch 18, an output increase value FPOWII!R is calculated using a two-dimensional map stored in the ROM 104. N,
The 0TPIvI quantity value FOTP is calculated according to the two-dimensional map stored in the ROM 104. Note that the OTP increase value FOTP is for preventing heating of the catalytic converter, exhaust pipe, etc. during high load. Then, in step 1006, the final injection amount TAU is set as TAU←TAUP
-FAF ・(FWL +FPOenER+ POTP
+β+1)+T. Note that β and T 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. These are also correction amounts determined by the RAM 105. is stored in.

Next, in step 1007, the injection amount TAU is set in the down counter 108, and the flip-flop 1
Set 09 to start fuel injection. The routine then ends at step 1008.

As described above, when the time corresponding to the injection ff1TAU 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 1101,
Clear the counter CNT. In step 1102, it is determined whether the output LL of the idle switch 17 has changed from "1" (on) to "0" (off). It is determined whether the closed state has been released. On the other hand, in step 1108, the output VL of the full switch 18
It is determined whether the opening degree of the throttle valve 16 has changed from "1" (ON) to "O" (OFF), that is, the opening degree of the throttle valve 16 has left the state of 70 degrees or more, which is a clear rich state of the air-fuel ratio. Determine whether or not. Note that LL-“1” and LV=
In the state of "1", the air-fuel ratio feedback control by the downstream Ot sensor 15 shown in FIG. 9 is not executed.

Proceed to steps 1103 to 11o5 only when LL changes from “1” (on) to “0” (off), and proceed to steps 1103 to 11o5 only when VL changes from “1” (on) to “0” (off). 1109~! Proceed to the flow of step 111, otherwise proceed directly to step 1118.

In steps 1103 to 1105, the counter CNT measures the time until the output v2 of the downstream 08 sensor 15 changes from lean to rich. That is, step 1
In step 103, the counter CNT is counted up by +1, in step 1104, the output vt of the downstream sensor 15 is A/D converted and taken in, and in step 1105, V t
> V lit, that is, whether the air-fuel ratio is rich or not. In this case, Vt >V.

The flow of steps 1103 to 1105 is repeated until the value becomes (rich). Note that an idle step between time adjustments may be inserted between flows 1103 to 1105.

As a result, only when the output V2 of the downstream 0□ sensor 15 indicates rich, the process proceeds to step 110G, and it is determined whether the output VL of the full switch 18 is 1'' (on) or not. That is, step 11f) The time CNT measured by the flow of 3 to 11o5 has a clear lean shape [(L
Clear rich state (Vl, -“1”) from L-“1”)
Determine whether it is time for a forced transition to . Therefore, if V l is -“0” in step 1106, the process directly proceeds to step 1118. On the other hand, if VL-“1”, the value of the counter CN T is set to TA in step 7 block 1107, and the response time from lean to rich is set to TA, which is not shown in FIG.
get.

Similarly, in steps 1109 to 1ull, the counter CN
0 on the downstream side due to T. The time required for the output (2) of the sensor 15 to change from lean to rich is measured. Next, in step 1109, the counter CNT is counted up by 1-1, and in step 1110, the downstream side o.

The output vt of the sensor 15 is converted into A/Di and taken in, and in step 1111 it is determined whether V≦Vat, that is, whether the air-fuel ratio is lean or not. □(
The flow of steps 1109-111i is repeated until the state becomes lean (lean). Note that an idle step 1.2 for time adjustment may be inserted between flows 1109 and 1111. As a result, only when the output V of the downstream side 02 sensor 15 indicates lean, does the process proceed to step 1112, where it is determined whether the outputs of the idle switch 17 ), (2), are "1" (on). That is, steps 1109 to 1111
The time CNT measured by the flow changes from a clear rich state acvh=゛x'') to a clear lean state a<t, i,
It is determined whether it is time for a forced transition to "1"). Therefore, if I, [, -0' is determined in step 1112, the process directly proceeds to step 1118. On the other hand, if Ll, -1'', the counter sets the value of CNT to TB in step 1113, and obtains the rich-to-lean response time 'r13 shown in FIG.

In step 1114, steps 1107 and 1113
The sum of the response times T A + T B is the predetermined value T
It is determined whether or not it is smaller than O, and as a result, T A -1-
Steps 1115 to 1117 only when T B < TO
Proceed to. In step 1115, the deterioration diagnosis flag XI)
[AG should be set.l.], is stored in the backup RAM 106 in step 1116, and the alarm 19 is activated in step 1117. On the other hand, if TA+TB≧To, the process directly proceeds to step 1118.

Then, in step 1118, the routine of FIG. 11 ends.

As described above, according to the routine shown in FIG. 11, when the operating state shifts between a clear rich state and a clear lean state, the time until the downstream side O, the output 2 of the sensor 15 is reversed. TA and TB depend on the 01 storage effect of the three-way catalyst, that is, the degree of deterioration of the three-way catalyst. Therefore, the degree of deterioration of the three-way catalyst can be determined accurately from the sum of times TA and TB.
(LL-“1”) to a clear rich state (VL-“1”)
Lean-rich response time TA only or clear when transitioning to ``)'' Rich-lean response time TB when transitioning from a notch state (VL-``1'') to a clear lean condition (LL=゛1'') It is also possible to determine the degree of deterioration of the three-way catalyst only based on =. For example, when TA<TA0 (predetermined value) or TB<TBO (predetermined value)6.
It is determined that the two-way catalyst has deteriorated, and steps 1115 to 1
7. However, as in step 1114 in FIG. 11, T A + T B < T O
The absolute value of the force increases, and the accuracy of determining the deterioration of the three-way catalyst increases.

FIG. 13 and FIG. 14 also show other examples of determining deterioration of a three-way catalyst.

FIG. 13 shows an Otfulst 1/-ji determination routine, in which the 1. This will be executed.

The step puffer 1301 determines whether a fuel cut is in progress or not based on a fuel cut flag XFC. Fuel can 1-medium (X F
C=“1”), the fuel cut continuous counter CFC is incremented by +1 in step 13o2, and on the other hand, if the fuel cut is not in progress, the fuel cut continuous counter CFC is cleared in step 1305.

In step 1303, fuel cut! ! +Continuation counter C
It is determined whether FC is greater than or equal to n. Note that n is a value equivalent to 2 to 5 seconds. Only when CFC≧n, it is assumed that the three-way catalyst is completely filled by 02, and step 130
4, set the catalyst deterioration determination execution flag XEXE (“
13) Do.

Then, in step 1306, the routine of FIG. 13 ends.

FIG. 14 shows a catalyst deterioration determination routine, which is executed every predetermined period of time, for example, every 4 ms. Steps 1401-14
Step 05 is the same as steps 901 to 905 in FIG. 9, and it is determined whether the downstream side 02 sensor 15 is in a closed loop condition. Here, the closed loop control by the downstream O2 sensor 15 indicates that the air-fuel ratio is stoichiometric air-fuel ratio control, which is different from the lean state where the air-fuel ratio is clear.

Only when the closed loop condition is satisfied, it is determined in step 1406 whether the catalyst deterioration determination execution flag
Proceed to flow 414. Otherwise, step 141
At step 5, the counter CNT is cleared and the process directly proceeds to step 1416.

Steps 1407 to 1409 are the time (C
NT). That is, in step 1407, the output ■2 of the downstream Ot sensor 15 is changed to A/
D conversion and import, in step 1408 ■2≦Vat
(lean) or not.

■! ≦Vll! If so, the counter CNT is incremented by +1 in step 1409, and the process proceeds to step 1416.

In the above state, when the output ■2 of the downstream side 0□ sensor 15 is reversed from lean to rich, the flow at step 1408 proceeds to step 1410, where the catalyst deterioration determination execution flag XEXE is cleared, and at step 1411, the downstream side 0□
It is determined whether the inversion time CNT of the output V2 of the sensor 15 from lean to rich is less than or equal to m.

Note that m is a value equivalent to 5 to 10 seconds. As a result, C.N.
Only when the distance is 75 m, the process proceeds to steps 1412 to 1414. In step 1412, the deterioration diagnosis flag MDIAG is set to '1'), in step 1413 it is stored in the back amplifier RAM 106, and in step 1414 the alarm 19 is activated.On the other hand, if CNT>m, it is directly move on.

Then, in step 1416, the routine of FIG. 14 ends.

FIG. 15 is a timing diagram illustrating the flowchart of FIG. 14. That is, at time t0, the fuel power is changed from 7 to 7 (XFC-“1”) to non-fuel cut (XFC=“0”).
”), from the oven loop (0/L) to the downstream O
When the closed loop condition determined by the x-sensor 15 is satisfied, the air-fuel ratio moves from a clear lean state to near the stoichiometric air-fuel ratio (λ=1). In this case, the air-fuel ratio upstream of the catalyst immediately becomes near λ-1, and therefore, the output ■1 of the upstream 02 sensor 13 also crosses the comparison voltage ■□. However, the air-fuel ratio downstream of the catalyst takes time to reach the stoichiometric air-fuel ratio due to the degree of the 0□ storage effect of the three-way catalyst, and therefore, the output Vt of the downstream 0□ sensor 15 is equal to the comparison voltage V. It takes time to reach. In this case, if the Ot storage effect of the three-way catalyst is large (if the three-way catalyst is normal), this time will be long;
On the other hand, if the 02 storage effect of the three-way catalyst is small (if the three-way catalyst has deteriorated), this time will be short, but the 15th
In the figure, the threshold value of this time is set to m, and the deterioration of the three-way catalyst is determined.

In the routines shown in FIGS. 13 and 14, the sustained state of the fuel cut state is determined as a clear lean state, and then the stoichiometric air-fuel ratio control state is determined based on the closed loop condition established by the downstream 02 sensor 15. The degree of deterioration of the three-way catalyst is determined based on the time it takes to return to FP.
[IL (FOTP)] The degree of deterioration of the three-way catalyst can be determined by determining the duration of the (FOTP) state and then determining the degree of deterioration of the three-way catalyst based on the time it takes for the downstream 02 sensor 15 to return to the stoichiometric air-fuel ratio control state when the closed loop condition is established. good. In this case, in step 1301 of FIG. 13, it is determined whether FPOWER is not O or FOTP is not O, and in step 1408 of FIG. 14, it is determined whether Vt > VII2 (rich). .

Further, in the above-described embodiment, when catalyst deterioration is determined, the closed loop by the downstream 94 t sensor 15 may be set to medium+ht, thereby preventing deterioration of the emissive con.

In addition, the first air-fuel ratio feedback control is performed every 4 ws.
Also, the second air-fuel ratio feedpack control is 512m5
The reason for this is that air-fuel ratio feed hack control is primarily controlled by the upstream 0□ sensor, which has good responsiveness, and secondary control is performed by the downstream 02 sensor, which has poor responsiveness. , other control constants in the air-fuel ratio feed control by the upstream 02 sensor, such as delay time, integral constant, comparison voltage of the upstream or sensor (reference: Japanese Patent Application Laid-Open No. 55-37562), etc., are determined by the downstream 02 sensor. (±
Output B, double 0. corrected from 2. The present invention can also be applied to a sensor system or a double 02 sensor system in which a second air-fuel ratio correction coefficient is introduced.

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 amount of air for the official and the rotational speed of the engine. The fuel injection amount may be calculated according to the fuel injection amount.Furthermore, in the above embodiment, an internal combustion engine is shown in which the fuel injection amount to the intake system is controlled based on the fuel injection amount.

However, the present invention can also be applied to a carbureted internal combustion engine. For example, engineering 1. / Trick Air Control Valve (EACν) to control the air-fuel ratio by adjusting the engine intake air amount 1. The electric link bleed air control valve adjusts the amount of air bleed from the carburetor and controls the air-fuel ratio by introducing atmospheric air into the main system passage and slow system passage, and the amount of secondary air sent to the engine exhaust system. The present invention can be applied to things such as those that adjust In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1001 is
/ is determined by itself, that is, it is determined according to the intake pipe negative pressure corresponding to the intake air amount and the rotational speed of the engine, and in step 1003, the supply air amount corresponding to the final fuel injection amount TA[J is calculated. Ru.

Furthermore, in the above embodiment, the air-fuel ratio sensor is 0. Although a sensor was used, a CO sensor, a 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 invention■]

As described above in Explanation 1, according to the present invention, deterioration of a three-way catalyst can be determined with high accuracy.

[Brief explanation of the drawing]

1A to 1C are overall block diagrams for explaining the present invention in detail, and FIG. 2 is a single OR, a sensor system, and a double 0.
．． An exhaust emission characteristic diagram explaining the sensor system, FIG. 3 is a timing 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. 13
Figure 14 is a flowchart for explaining the operation of the control circuit in Figure 4, Figure 7 is an evening/timing diagram for supplementary explanation of the flowchart in Figure 6, and Figure 8 is a flowchart for Figure 5. 12 is a timing diagram for supplementary explanation of flowchart 1 of FIG. 11. FIG. 15 is a timing diagram for supplementary explanation of the flowchart of 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 0. Sensor, 17... Idle switch, 8... Full 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) 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 determining whether the operating state of the engine is transitioning from a lean operating state to a rich or stoichiometric air-fuel ratio operating state. a lean/rich operating state transition determining means, and an output of the downstream air-fuel ratio sensor is reversed from lean to rich when the operating state of the engine changes from the lean operating state to the rich or stoichiometric air-fuel ratio operating state. A catalyst deterioration determining device for an internal combustion engine, comprising: a time measuring device that measures the time until the catalyst deterioration occurs; 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. The apparatus according to claim 1, wherein the lean/rich operating state transition determining means is replaced by a rich/lean operating state that determines whether the engine operating state transitions from a rich operating state to a lean or stoichiometric air-fuel ratio operating state. Transition determining means is provided, and the time measuring means reverses the output of the downstream air-fuel ratio sensor from rich to lean when the operating state of the engine transitions from a rich operating state to a lean or stoichiometric air-fuel ratio 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 lean to rich or from rich to lean; and determining whether the operating state of the engine is transitioning from a lean operating state to a rich or stoichiometric air-fuel ratio operating state. a lean/rich operating state transition selection means to select a lean/rich operating state; and an output of the downstream air-fuel ratio sensor is reversed from lean to rich when the operating state of the engine changes from a lean operating state to a rich or stoichiometric air-fuel ratio operating state. The first step is to measure the time until
a rich/lean operating state transition determining means for determining whether the operating state of the engine changes from a rich operating state to a lean or stoichiometric air-fuel ratio operating state; or a second time measuring means for measuring a second time from the transition to the stoichiometric air-fuel ratio operating state until the output of the downstream air-fuel ratio sensor reverses from rich to lean; 1. 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 second times is less than or equal to a predetermined time.