JPH041440A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent a controlled air-fuel ratio from shifting to its rich side so as to and improve exhaust emission and the like by compensating a control constant of air fuel ratio feedback control based on an output of an oxygen sensor located upstream by means of the air-fuel ratio feedback control by an oxygen sensor located downstream. CONSTITUTION:An air-fuel ratio feedback control constant is calculated by a means B according to an output of an oxygen sensor A located downstream with respect to a catalyst used for purification of exhaust gas interposed in the exhaust system of an internal combustion engine. And also an air-fuel ratio compensation quantity is calculated by a means D according to the output of an oxygen sensor C located upstream and the calculated air-fuel ratio feedback control constant. The grade of deterioration of the catalyst is judged by a means E based on the oxygen sensors C, A located upstream and downstream. Furthermore the control constant by a means B is varied based on a judged result by a means E. An air-fuel ratio is adjusted by a means F based on an air-fuel ratio compensation quantity calculated by the means D.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention provides an internal combustion engine with oxygen sensors upstream and downstream of a catalyst for purifying exhaust gas, and performs air-fuel ratio feedback control using the upstream oxygen sensor. The present invention relates to an air-fuel ratio control device that performs air-fuel ratio feedback control using a downstream oxygen sensor in addition to the air-fuel ratio, and particularly relates to a device that controls the air-fuel ratio in consideration of deterioration of a catalyst and an oxygen sensor.

(Prior art) In normal air-fuel ratio feedback control using a single oxygen sensor, the oxygen sensor is installed in the exhaust system as close to the combustion chamber as possible, for example, in the exhaust manifold upstream of the catalytic converter for exhaust gas purification. However, due to variations in the output characteristics of the oxygen sensor, it is difficult to improve the accuracy of controlling the air-fuel ratio. In order to compensate for variations in output characteristics of oxygen sensors, variations in parts such as fuel injection valves, and changes over time, an oxygen sensor is also provided downstream of the catalytic converter, and in addition to air-fuel ratio feedback control by the upstream oxygen sensor, A dual oxygen sensor system has been proposed that performs air-fuel ratio feedback control using a side oxygen sensor.

In this dual oxygen sensor system, the oxygen sensor installed downstream of the catalytic converter has a lower response speed than the oxygen sensor installed upstream, but because it is downstream of the catalytic converter, the exhaust temperature is lower. The advantage is that there is little variation in output characteristics due to low heat, low thermal effects, low poisoning, sufficient mixing of exhaust gas, and oxygen concentration in exhaust gas close to equilibrium. have.

Therefore, by performing air-fuel ratio feedback control based on the outputs of the two oxygen sensors, variations in the output characteristics of the upstream oxygen sensor can be absorbed by the downstream oxygen sensor. for example,
With a system equipped with a single oxygen sensor, if the oxygen sensor output characteristics deteriorate, it will directly affect the exhaust emission characteristics, but with a dual oxygen sensor system, even if the output characteristics of the upstream oxygen sensor deteriorate, it will directly affect the exhaust emission characteristics. , the exhaust emission characteristics do not deteriorate.

Therefore, as shown in Japanese Unexamined Patent Publication No. 63-205441, there is a conventional device in which the deterioration of the upstream oxygen sensor is corrected and controlled based on the output of the downstream oxygen sensor.

<Problems to be Solved by the Invention> However, such a conventional dual oxygen sensor system has the following problems.

That is, when the deterioration of the catalyst increases, various poisons are no longer trapped, the amount of poisoning of the downstream oxygen sensor increases, and the downstream oxygen sensor also deteriorates further.

In this case, the output of this downstream oxygen sensor will be as shown in FIG.

As a result, even if the deterioration of the upstream oxygen sensor is corrected and controlled using the output of the downstream oxygen sensor, the controlled air-fuel ratio shifts to the rich side, resulting in deterioration of exhaust emissions.

In view of the above-mentioned conventional problems, the present invention has been developed to improve exhaust emissions in an internal combustion engine by preventing the controlled air-fuel ratio from shifting toward the rich side when the catalyst and oxygen sensor deteriorate. The purpose of the present invention is to provide an air-fuel ratio control device.

Means for Solving the Problems> Therefore, the air-fuel ratio control device for an internal combustion engine of the present invention has the following features:
As shown in the figure, oxygen sensors are installed on the upstream and downstream sides of a catalyst for exhaust gas purification installed in the exhaust system of an internal combustion engine to detect the oxygen concentration in the exhaust gas, and the downstream oxygen sensors output control constant calculation means for calculating an air-fuel ratio feedback control constant according to the output of the upstream oxygen sensor and an air-fuel ratio correction amount according to the output of the upstream oxygen sensor and the air-fuel ratio feedback control constant calculated by the control constant calculation means; a fuel ratio correction amount calculation means, a deterioration degree determination means for determining the degree of deterioration of the catalyst based on the outputs of the upstream and downstream oxygen sensors, and the control constant calculation means based on the determination result by the deterioration degree determination means. and an air-fuel ratio adjustment means that adjusts the air-fuel ratio based on the air-fuel ratio correction amount calculated by the air-fuel ratio correction amount calculation means.

In such a device, the air-fuel ratio feedback control by the downstream oxygen sensor controls the differential amount and integral constant as control constants for the air-fuel ratio feedback control based on the output of the upstream oxygen sensor, the delay time for air-fuel ratio determination, or the upstream The slice level etc. compared with the side oxygen sensor are corrected. That is, since the control constant is corrected according to the output of the downstream oxygen sensor, variations in the output characteristics of the upstream oxygen sensor are absorbed by the downstream oxygen sensor. Moreover, since the above-mentioned correction amounts such as the differential amount and the integral constant are changed according to the degree of deterioration of the catalyst, if the deterioration of the catalyst becomes large and the downstream oxygen sensor also deteriorates, the controlled air-fuel ratio will become richer. This prevents the engine from shifting to the side, thereby preventing deterioration of exhaust emissions.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 2, an exhaust pipe 2 of an engine 1 is provided with a catalytic converter 3 that houses a three-way catalyst that simultaneously purifies harmful components HC, Co, and NOx in exhaust gas.

Oxygen sensors 4 and 5 are provided in the exhaust pipes 2 on the upstream and downstream sides of the catalytic converter 3, respectively.

These oxygen sensors 4 and 5 each generate an electric signal according to the oxygen component concentration in the exhaust gas, and output this signal to the A/D converter 9 through the input circuit 7.8 of the engine control device 6. do. That is, both oxygen sensors 4 and 5 generate different output voltages to the A/D converter 9 depending on whether the air-fuel ratio is on the lean side or the lean side with respect to the stoichiometric air-fuel ratio.

The input/output circuit 10 of the engine control device 6 includes an intake pipe 11
An intake air amount detection signal from an air flow meter 13 installed upstream of the throttle valve 12, an engine rotation speed detection signal from a crank angle sensor 14, and a water temperature sensor 15.
In addition to the engine cooling water temperature detection signal from the engine cooling water temperature detection signal, detection signals from various engine operating condition detection sensors are input.
A signal (including an air-fuel ratio feedback signal) for controlling the fuel injection amount by the fuel injection valve 6 is output to the fuel injection valve 6.

The engine control device 6 is configured as a microcomputer, for example, and includes the input circuits 7, 8, A/
In addition to the D converter 9 and the input/output circuit 10, the CPU 17 and the RO
M1B, RAM19, etc. are provided.

Next, an example of air-fuel ratio control according to the present invention based on the above hardware structure will be explained based on the flowcharts shown in FIGS. 3 to 5.

FIG. 3 is a flowchart showing an air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient α.

In step 1, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream oxygen sensor 4 is satisfied.

When the closed loop (feedback) condition is satisfied, the process proceeds to step 2 and the air-fuel ratio correction coefficient α is set to 1.0. Further, when the closed loop (feedback) condition is not satisfied, the process proceeds to step 3. In step 3, the output O3R'l of the upstream oxygen sensor 4 is A/D converted and read.
It is determined whether or not 03RI is equal to or lower than the slice level voltage SLF. In other words, it determines whether the air-fuel ratio is rich or lean. If rich is determined, the process proceeds to step 5 and the air-fuel ratio flag F1 is set to 1 (rich). If lean is determined, proceed to step 6 and set the air-fuel ratio flag F1.
is O (lean). In step 7, it is determined whether the sign of the air-fuel ratio flag Fl has been inverted. That is, it is determined whether the air-fuel ratio has been reversed. If the air-fuel ratio is reversed, the process proceeds to step 8, where an operation is performed to add 1 to the number of inversions N1, and the process proceeds to step 9. Note that this calculation is necessary for determining the degree of deterioration of the catalyst, which will be described later.

In step 9, it is determined based on the value of the air-fuel ratio flag F1 whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, proceed to step 10 and calculate the correction amount PH05 of the rich differential amount PL as an air-fuel ratio feedback control constant using a subroutine to be explained later, then proceed to step 11 and skip to α=α+PL+PH03. If you want to increase the amount of money and reverse from lean to rich, step 1
Proceeding to step 2, the subroutine also determines the correction amount PH of the lean differential 1iPR as the air-fuel ratio feedback control constant.
After calculating 03, proceed to step 13 and calculate α=α−P
Decrease R+PH05 in a skip manner. In other words, differential processing is performed.

If the sign of the air-fuel ratio flag F1 is not inverted in step 7, integration processing is performed in steps 14, 15, and 16. That is, in step 14, it is determined whether F1=0. If F1=0 (lean), set α=α±IL (rich integral constant) in step 15, and if F1=1 (rich), set α=α−IR (lean integral constant) in step 16. shall be.

Here, the above integral constants IL and IR are the differential amount PL
, is set sufficiently small compared to PR.

Therefore, step 15 is a lean L! (F1=0), the fuel injection amount is gradually increased, and step 16 is a rich m
1 (F1=1), the fuel injection amount is gradually decreased.

The air-fuel ratio correction coefficient α calculated as described above is stored in the RAM 19 shown in FIG. 2, and this routine ends.

Next, the operation of the subroutine in step 10.12 of the flowchart of FIG. 3 will be explained based on FIG.

This subroutine is the calculation routine of PH03 as described above.

That is, in step 21, the output 03R2 of the downstream oxygen sensor 5 is A/D converted and read, and in step 22
It is determined whether or not 03R2 is equal to or lower than the slice level voltage SLR. In other words, it determines whether the air-fuel ratio is rich or lean. If rich is determined, the process proceeds to step 23 and the air-fuel ratio flag F2 is set to 1 (rich). If lean is determined, the process proceeds to step 24 and the air-fuel ratio flag F2 is set to O (lean). In step 25,
It is determined whether the sign of the air-fuel ratio flag F2 has been inverted, that is, whether the air-fuel ratio has been inverted.

If the air-fuel ratio is reversed, the process proceeds to step 26, where an operation is performed to add 1 to the number of inversions N2, and the process proceeds to step 27. Note that this calculation is necessary to determine the degree of deterioration of the oxygen sensor, which will be described later.

In step 27, it is determined based on the value of the air-fuel ratio flag F2 whether the reversal is from rich to lean or from lean to rich. If it is a reversal from rich to lean, proceed to step 28 and set PH03=PHO3+ΔPH
03L is calculated to increase PH03. Conversely, if it is a reversal from lean to rich, proceed to step 29 and increase PH03.
3=PHO5-ΔPH03R is calculated to decrease PH03.

Next, based on the base flow of the control of the present invention shown in FIG. 5, ΔPH03L and ΔPH03L in the above subroutine
The setting method for PH03R will be explained.

In step 31, PH05=O, N1=O, N
2=0, and execute these initial value settings. In step 32, a timer is set to 0 and starts counting a certain elapsed time.

In step 33, the air-fuel ratio correction coefficient α is calculated by the routine explained based on FIG. 3, in step 34 the fuel injection amount is calculated, and in step 35, the fuel injection valve 16 shown in FIG. 2 is driven. Execute.

In the next step 36, it is determined whether a predetermined time (for example, 20 seconds) has been counted by the timer, and if it has been counted, the process proceeds to step 37,
If not counted, repeat steps 33 to 35.

In steps 37 and 38, the degree of deterioration DCAT of the catalyst is determined based on the number of inversions Nl and N2. In other words, it is determined whether the number of times the output of the downstream oxygen sensor 5 changes between lean and rich is larger or smaller than the number of times the output of the downstream oxygen sensor 5 changes between lean and rich. In step 37, the ratio of N2/Nl is calculated, and in step 38, the degree of deterioration of the catalyst is determined from the value of this ratio. In this case, if the number of switching times of the downstream oxygen sensor 5 output is large and the above ratio is large, the degree of deterioration is large, and if the number of switching times of the downstream oxygen sensor 5 output is small and the above ratio is small. If so, the degree of deterioration is small.

In the determination at step 38, it is determined whether DCAT exceeds a predetermined reference value (for example, 0.5 to 0.7), and
If AT exceeds the predetermined base value (high degree of deterioration), the process proceeds to step 39, and if DCAT is below the predetermined reference value (small degree of deterioration), the process proceeds to step 40.

Then, in steps 39 and 40, ΔPH03R and ΔPH0SL are set, respectively.

Here, when the degree of deterioration is large, in step 39, for example, ΔPH03R=7X10"', ΔPH03L-7X1
0-, and when the degree of deterioration is small, in step 40, for example, ΔPH03R=7X10ΔPH03L=15X10
-'.

That is, when the degree of deterioration is large, ΔPH03L is made smaller than when the degree of deterioration is small, the lean differential amount PL is made smaller, and the control air-fuel ratio is shifted to the lean side.

In this case, when the degree of deterioration is large, 8PH03R may be made larger than when the degree of deterioration is small, the lean differential amount PR may be increased, and the control air-fuel ratio may be shifted to the lean side.

As is clear from the above explanation, the degree of deterioration of the catalyst is determined, and when the degree of deterioration is large, that is, the downstream oxygen sensor 5
As a result of shifting the air-fuel ratio to the lean side when deterioration has also occurred, when the output of the downstream oxygen sensor 5 is used to correct the deterioration of the upstream oxygen sensor 4, the controlled air-fuel ratio shifts to the rich side. It is possible to prevent this, and it is possible to prevent deterioration of emissions.

In the above embodiment, each step of the flowchart in FIG. 4 corresponds to the control constant calculation means of the present invention that calculates the air-fuel ratio feedback control constant according to the output of the downstream oxygen sensor 5.

Further, each step of the flowchart in FIG. 3 is an air-fuel ratio correction amount calculation according to the present invention, which calculates an air-fuel ratio correction amount according to the output of the upstream oxygen sensor and the air-fuel ratio feedback control constant calculated by the control constant calculation means. It corresponds to the means.

Furthermore, steps 37 and 38 in the flowchart of FIG. 5 correspond to the deterioration degree determining means of the present invention which determines the deterioration degree of the catalyst based on the output cams of the upstream and downstream oxygen sensors 4 and 5, respectively.

Further, steps 39 and 40 in the same flowchart correspond to the control constant changing means of the present invention which changes the control constant by the control constant calculating means based on the determination result by the deterioration degree determining means.

In the above embodiment, a differential amount is adopted as a control constant in the control constant calculation means for calculating an air-fuel ratio feedback control constant according to the output of the downstream oxygen sensor 5, and this is changed according to the degree of deterioration. However, a configuration may also be adopted in which an integral constant, a delay time, and a slice level as a comparison voltage of the output of the downstream oxygen sensor 5 are employed as control constants, and these are changed according to the degree of deterioration.

For example, when correcting the integral constant, when the degree of deterioration is large, the lean integral constant is changed to be smaller than when the degree of deterioration is small, or the lean integral constant is changed to be increased, and the control air-fuel ratio is All you have to do is shift it to the lean side.

Also, the relationship between the lean delay time to maintain the judgment that the state is rich even when there is a change from rich to lean and the rich delay time to maintain the opposite judgment (lean delay time > rich delay time) ) according to the degree of deterioration,
The control air-fuel ratio may be shifted to the lean side.

Furthermore, the control air-fuel ratio may be shifted to the lean side by changing the comparison voltage of the output of the downstream oxygen sensor 5 depending on the degree of deterioration.

Further, the delay time for determining the air-fuel ratio or the comparison voltage of the output of the upstream oxygen sensor may be changed.

<Effects of the Invention> As explained above, according to the air-fuel ratio control device for an internal combustion engine according to the present invention, the exhaust gas is connected to the upstream side and the downstream side of the exhaust gas purifying catalyst installed in the exhaust system of the internal combustion engine. Equipped with an oxygen sensor that detects the oxygen concentration in gas, and as air-fuel ratio feedbank control using the downstream oxygen sensor, corrects the differential amount, integral constant, etc. as control constants for air-fuel ratio feedback control based on the output of the upstream oxygen sensor. That is, in a device that performs control to correct the control constant according to the output of the downstream oxygen sensor, the correction amount of the differential amount, integral constant, etc. is changed depending on the degree of deterioration of the catalyst. With air-fuel ratio feedback control based on the outputs of the two oxygen sensors, variations in the output characteristics of the upstream oxygen sensor can be absorbed by the downstream oxygen sensor, and if the catalyst deteriorates significantly and the downstream oxygen sensor also deteriorates. In addition, it is highly useful in that it can prevent the controlled air-fuel ratio from shifting toward the rich side, thereby preventing deterioration of exhaust emissions.

[Brief explanation of the drawing]

Fig. 1 is a diagram corresponding to claims of an air-fuel ratio control device for an internal combustion engine according to the present invention, Fig. 2 is a system diagram of a device for carrying out the present invention, and Figs. 3 to 5 are control contents of the present invention, respectively. FIG. 6 is a downstream oxygen sensor output characteristic diagram explaining the problems of the conventional system. 1... Engine 2... Exhaust pipe 3... Catalytic converter 4, 5... Oxygen sensor 6... Engine control device 16... Fuel injection valve

Claims (1)

[Claims] Oxygen sensors that detect the oxygen concentration in exhaust gas are installed on the upstream and downstream sides of a catalyst for purifying exhaust gas that is installed in the exhaust system of an internal combustion engine, and air-fuel ratio feedback is provided according to the output of the downstream oxygen sensor. control constant calculation means for calculating a control constant; and air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the output of the upstream oxygen sensor and the air-fuel ratio feedback control constant calculated by the control constant calculation means. , a deterioration degree determination means for determining the degree of deterioration of the catalyst based on the outputs of the upstream and downstream oxygen sensors, and a control constant by the control constant calculation means based on the determination result by the deterioration degree determination means. An air-fuel ratio adjusting means for an internal combustion engine, comprising: a control constant changing means; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio based on the air-fuel ratio correction amount calculated by the air-fuel ratio correction amount calculating means. Fuel ratio control device.