JP3099454B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine which always controls an air-fuel ratio of the internal combustion engine to an optimum value.

[0002]

2. Description of the Related Art Conventionally, in an air-fuel ratio control device for controlling an air-fuel ratio to a value close to a stoichiometric air-fuel ratio .lambda.0 in accordance with an output signal of a first O2 sensor provided upstream of a catalyst in a gasoline engine, the device is provided downstream of the catalyst. Control constants (integral constant, skip amount, delay time, comparison voltage, etc.) of the air-fuel ratio control by the first O2 sensor according to the output signal of the second O2 sensor
To prevent the controllability from deteriorating due to a change in the characteristics of the first O2 sensor.
286550).

[0003]

However, in practice, it takes time until fuel is supplied to the internal combustion engine and a change in the air-fuel ratio is detected by the first O ₂ sensor. Furthermore, it takes a longer time before the change in the air-fuel ratio is detected by the second O ₂ sensor provided downstream of the catalyst due to the storage effect of the catalyst.

Further, in recent years storage effect of many also need to have the catalyst further increases the amount of catalyst with the regulations of NOX, a tendency that the time until the change of the air-fuel ratio is detected in the second O ₂ sensor becomes longer It is in.

Therefore, a delay occurs in the control constant set by the detection signal of the second O ₂ sensor, and an optimum air-fuel ratio correction amount cannot be set. As a result, there is a problem that the air-fuel ratio is controlled to be over-rich or over-lean and the emission deteriorates.

Further, the output signal of the second O ₂ sensor fluctuates under the influence of the exhaust gas temperature. Specifically, as shown in FIG. 17, the output signal becomes larger as the exhaust gas temperature becomes lower. Therefore, even if the output signal changes in accordance with the exhaust gas temperature, the optimum correction value of the control constant of the first O ₂ sensor cannot be set, and the emission deteriorates even in such a case. There's a problem.

Accordingly, the present invention has been made to solve the above problems, and it is possible to prevent the deterioration of the emission due to the storage effect of the catalyst and to always provide the optimum correction value of the control constant even when the exhaust gas temperature changes. It is an object to provide a gas engine air-fuel ratio control that can be set.

[0008]

A catalyst provided in an exhaust system of an internal combustion engine for purifying exhaust gas, and a first oxygen concentration provided upstream of the catalyst and whose output signal changes rapidly at a stoichiometric air-fuel ratio. A second oxygen concentration sensor disposed downstream of the catalyst, the output signal of which is abruptly changed at a stoichiometric air-fuel ratio; and an exhaust temperature sensor disposed in an exhaust system of the internal combustion engine and detecting an exhaust gas temperature. The air-fuel ratio detected by the second oxygen concentration sensor at the current control timing and the air-fuel ratio detected by the second oxygen concentration sensor at the previous control timing are shifted to the same side with respect to the stoichiometric air-fuel ratio. The rich control constant and the rich control constant according to the detected air-fuel ratio.
A correction amount adjusting unit that adjusts a correction amount for correcting the lean control constant by the correction integral constant, Li according to the correction amount
A first control constant correction means for correcting the pitch control constants and the lean control constant, control the air-fuel ratio of the internal combustion engine in response to the output signal and the rich control constant and the lean control constant of the first oxygen concentration sensor Air-fuel ratio control means, and the second
The correction integration constant is set smaller as the output signal of the oxygen concentration sensor indicates a value closer to the stoichiometric air-fuel ratio, and the correction integration constant decreases as the exhaust gas temperature detected by the exhaust gas temperature sensor decreases, and Technical means of providing a correction integration constant setting means for setting a large value is adopted.

[0009]

With the above arrangement, the air-fuel ratio detected by the second oxygen concentration sensor at the current control timing by the correction amount increasing / decreasing means and the air-fuel ratio detected by the second oxygen concentration sensor at the previous control timing are obtained. In the same case, the correction amount for correcting the first control constant according to the detected air-fuel ratio is increased or decreased by the correction integration constant. The first control constant correction means corrects the first control constant in accordance with the correction amount, and the air-fuel ratio control means controls the internal combustion engine in accordance with the output signal of the first oxygen concentration sensor and the first control constant. The air-fuel ratio of the supplied mixture is controlled.

Furthermore, the output signal of the second oxygen concentration sensor with the correction integration constant as showing a value close to the stoichiometric air-fuel ratio is set to a small value by the correction integration constant setting means, exhaust gas temperature
The lower the exhaust gas temperature detected by the sensor, the higher the correction product
The fractional constant is set to be small,
You.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment to which the present invention is applied will be described.
This will be described with reference to the drawings. FIG. 2 is a configuration diagram of the present embodiment. 1 is a gas engine. The intake system of the gas engine 1 includes an air cleaner 2 for purifying air, and an intake pipe 3 for guiding a mixture of air and fuel gas purified by the air cleaner 2 to the gas engine 1. Further, the intake pipe 3 has a mixer 4 for mixing air supplied from the air cleaner 2 from the upstream side and fuel gas supplied from a fuel gas supply source (not shown) to form a mixture slightly leaner than the stoichiometric air-fuel ratio. A throttle valve 5 for adjusting the amount of air-fuel mixture (total gas flow rate) supplied to the gas engine 1 is provided. Further, it has a main supply path 6 for supplying fuel gas directly from the gas supply source to the mixer 4 and a sub-supply path 7 for supplying fuel gas from the gas supply source to the downstream of the mixer 4. Further, an air-fuel ratio for controlling the air-fuel ratio of the air-fuel mixture supplied to the gas engine 1 to a desired value by adjusting the amount of fuel gas (by-pass flow rate) supplied from the auxiliary supply path 7 is provided in the auxiliary supply path 7. A control valve 8 for control is provided. Also, throttle valve 5
A pressure sensor 9 for detecting a downstream intake pressure PM is provided.

On the other hand, the exhaust system of the gas engine 1 is provided with an exhaust pipe 10 for guiding the exhaust gas from the gas engine 1, and the exhaust pipe 10 has a three-way system for purifying harmful components contained in the exhaust gas. A catalyst 11 is provided. further,
Upstream and downstream of the three-way catalyst 11, the oxygen concentration in the exhaust gas is detected to detect the air-fuel ratio of the air-fuel mixture supplied to the gas engine 1, and the output signal is inverted at the stoichiometric air-fuel ratio λ0. 1, 2 oxygen concentration sensors (O2 sensor) 12, 1
3 are provided.

The exhaust temperature T is located downstream of the three-way catalyst 11.
An exhaust gas temperature sensor 14 for detecting CR is provided. The exhaust temperature sensor 14 is of a thermocouple type, and outputs a linear output with respect to the temperature, and can accurately detect a relatively low temperature.

Reference numeral 15 denotes a spark plug provided in a cylinder of the gas engine 1, and 16 denotes a rotation speed sensor for detecting the rotation speed NE of the gas engine. Reference numeral 20 denotes an electronic control unit (ECU) for setting control amounts of various actuators such as the control valve 8 and the ignition plug 14 and outputting control signals according to the control amounts. As is well known, the ECU 20 includes a central processing unit (CPU) 20a that performs various operations, a read-only memory (ROM) 20 that stores a control program and the like.
b, a writable / readable random access memory (RAM) 20 for temporarily storing operation data and the like
c, an analog-to-digital converter (ADC) 20d for converting an analog signal into a digital signal, an input port 20e for taking in sensor signals from the various sensors described above into the ECU 20, and a control signal for outputting control signals to the various actuators described above. It comprises an output port 20f and a bus 20g interconnecting these.

Hereinafter, a method for setting the control amount of the control valve 8, that is, a method for controlling the air-fuel ratio of the gas engine will be described with reference to flowcharts shown in FIGS. FIG. 3 is a flowchart showing a control amount calculation routine for calculating the control amount D of the control valve 8.

First, in step 301, a basic control amount DB is calculated by the following equation (Equation 1) according to the intake pressure PM detected by the pressure sensor 9 and the rotational speed NE detected by the rotational speed sensor 15.

[0017]

## EQU1 ## DB ← (PM-PMOS) × KPMB × KNE × KDB
+ DOS Here, the PMOS has a relationship as shown in FIG. 8 between the intake pressure PM and the total gas flow rate, and is a value corresponding to the offset of this relationship and is a constant. KPMB is a conversion coefficient for converting the intake pressure PM into a duty ratio.
KNE is a rotation correction coefficient corresponding to the rotation speed NE, and there is a relationship between the rotation speed NE and the rotation correction coefficient KNE as shown in FIG. KDB is a correction coefficient set according to the intake pressure PM and the rotational speed NE. DOS has a relationship as shown in FIG. 10 between the duty ratio and the bypass flow rate, and is a value corresponding to the offset of this relationship and is a constant.

In the following step 302, the correction control amount DF is changed to the intake pressure PM, the rotational speed NE, and the air-fuel ratio correction coefficient F to be described later.
It is calculated by the following equation (Equation 2) according to AF.

[0019]

DF ← (PM−PMOS) × KPMF × KNE × FAF where KPMF is the intake pressure PM shown in FIGS. 8 and 10.
The following equation (Equation 3) is obtained from the slope α of the characteristic between the flow rate and the total gas flow rate, and the slope β of the characteristic between the duty ratio and the bypass flow rate.
Is the value set in.

[0020]

KPMF ← α / β Then, the control amount D is calculated by the following equation (Equation 4) according to the basic control amount DB and the correction control amount DF calculated in step 303 as described above.

[0021]

D ← DB + DF In step 304, a control signal corresponding to the control amount D is output to the control valve 8.

Thus, the control amount calculation routine ends. Next, the correction control DFs in step 302 of FIG.
A method of setting the air-fuel ratio correction coefficient FAF used for setting the parameter will be described. FIG. 4 shows an air-fuel ratio correction coefficient FAF based on the output value (first output value) V1 of the first O2 sensor 12.
Is a flowchart showing a main air-fuel ratio feedback control routine for calculating the following equation. This main air-fuel ratio feedback control routine is performed for a predetermined time (for example, 4 m in this embodiment).
s).

First, at step 401, it is determined whether a main air-fuel ratio feedback condition is satisfied. here,
The main air-fuel ratio feedback condition is, for example, in this embodiment, after the engine is started and the first O2 sensor 12 is in an active state. If it is determined in step 401 that the main air-fuel ratio feedback condition is not satisfied, the process proceeds to step 402, where the air-fuel ratio correction coefficient FAF
Is set to 0 (FAF ← 0), and this routine ends.

On the other hand, if it is determined in step 401 that the main air-fuel ratio feedback condition is satisfied, the processing from step 403 is executed. In step 403, the first output value V1 is fetched. In step 404, it is determined whether the first output value V1 is equal to or lower than a first comparison voltage VR1 (for example, 0.45 V in this embodiment), that is, whether the air-fuel ratio is rich or lean. Here, if the first output value V1 is equal to or lower than the first comparison voltage VR1, that is, if the air-fuel ratio is lean, the process proceeds to step 405, where the first delay counter CDLY1 is set.
Is decremented (CDLY1 ← CDLY1-
1). In the following steps 406 and 407, the first delay counter CDLY1 is subjected to guard processing with the first lower limit value TDR1. More specifically, in step 406, it is determined whether the first delay counter CDLY1 is less than a first lower limit TDR1. Here, when the first delay counter CDLY1 is smaller than the first lower limit TDR1, the process proceeds to step 407, and the first delay counter CDLY1 is reset to the first lower limit TDR1.

On the other hand, in step 403, the first output value V1
Is greater than the first comparison voltage VR1, that is, the air-fuel ratio is rich, the process proceeds to step 408, and the value of the first delay counter CDLY1 is incremented (CDL
Y1 ← CDLY1 + 1). Subsequent steps 409, 410
Sets the first delay counter CDLY1 to the first upper limit value T.
Guard processing is performed in DL1. More specifically, in step 409, the first delay counter CDLY1 sets the first upper limit value TD.
It is determined whether it is greater than L1. Here, when the first delay counter CDLY1 is larger than the first upper limit value TDL1, the process proceeds to step 410, and the first delay counter CDLY1 is reset to the first upper limit value TDL1.

The first lower limit value TDR1 is a first rich value for maintaining the determination that the output of the first O2 sensor 12 is in a lean state even when the output of the first O2 sensor 12 changes from lean to rich. Delay time, defined as a negative value. Further, the first upper limit value TDL1 is a first lean delay time for maintaining the determination that the output of the first O2 sensor 12 is in a rich state even when the output of the first O2 sensor 12 changes from rich to lean, Defined by a positive value. Then, the reference of the first delay counter CDLY1 is set to 0, and when the first delay counter CDLY1 is positive, the air-fuel ratio after the delay processing is regarded as rich, and when the first delay counter CDLY1 is negative, the delay processing after the delay processing is performed. Is regarded as lean. These first
Rich delay time TDR1, first lean delay time TR
L1 is set by the sub air-fuel ratio feedback control described later.

In step 411, it is determined whether or not the sign of the first delay counter CDLY1 set as described above has been inverted, ie, whether or not the air-fuel ratio after the delay processing has been inverted. When the air-fuel ratio after the delay processing is reversed, skip processing of steps 412 to 414 is performed. First, in step 412, it is determined whether or not the inversion is from the rich state to the lean state. Here, when it is determined that the inversion is from the rich state to the lean state, step 4 is performed.
Proceeding to 13, the air-fuel ratio correction coefficient FAF is increased by the first skip amount RS1 (FAF ← FAF + RS1). If it is determined in step 412 that the inversion is from the lean state to the rich state, the process proceeds to step 414, in which the air-fuel ratio correction coefficient FAF is reduced by the first skip amount RS1 (FAF ← FAF-RS1).

On the other hand, if it is determined in step 411 that the air-fuel ratio after the delay processing has not been inverted, then steps 415 to 4
17 integration processing is performed. First, in step 415, it is determined whether the first delay counter CDLY1 is equal to or less than 0, that is, whether the air-fuel ratio is in a rich state or a lean state. If it is determined that the vehicle is in the lean state, the process proceeds to step 416, where the air-fuel ratio correction coefficient FAF is increased by a first integration constant K1 (FAF ← FAF + K1). Step 4
If it is determined in step 15 that the vehicle is in the rich state, step 4
17, the air-fuel ratio correction coefficient FAF is set to the first integration constant K
Decrease by 1 (FAF ← FAF-K1).

Here, the first integration constant K1 is set sufficiently smaller than the first skip amount RS1. Therefore, when the air-fuel ratio is in a lean state, the supplied fuel gas gradually increases because the air-fuel ratio correction coefficient FAF gradually increases. Further, when the air-fuel ratio is in a rich state, the air-fuel ratio correction coefficient FAF gradually decreases, so that the supplied fuel gas gradually decreases.

Thus, the main air-fuel ratio feedback control routine ends. FIGS. 5 and 6 show the second O2 sensor 13.
Delay time (first rich delay time TD) as a first control constant based on the output value (second output value) V2 of
9 is a flowchart illustrating a sub air-fuel ratio feedback control routine for correcting R1, a first lean delay time TDL1). The sub air-fuel ratio feedback control routine is started every predetermined time (for example, 16 ms in the present embodiment).

First, at step 501, it is determined whether or not the sub-air-fuel ratio feedback condition is satisfied, that is, whether or not to execute the sub-air-fuel ratio feedback control. As the sub air-fuel ratio feedback condition, for example, the main air-fuel ratio feedback condition is satisfied, and the second O2 sensor 13 is in an active state. And the like are satisfied.

Here, if it is determined that the above condition is not satisfied, the sub air-fuel ratio feedback control after step 504 is not executed, and the routine proceeds to step 502, and will be described later in preparation for the next sub air-fuel ratio feedback control. Learning value DL
Substitute TDAV for the previous delay correction value DLTD0 (D
LTD0 ← DLTAV). In the following step 503, the learning value DLTDAV is substituted for the delay correction value DLTD (DLT
D ← DLTDAV), and the process proceeds to step 523.

On the other hand, if it is determined in step 501 that the sub air-fuel ratio feedback condition is satisfied, that is, if it is determined that the sub-air-fuel ratio feedback control is to be performed, the processing from step 504 is performed.

First, at step 504, the second output value V2
Take in. In step 505, the second output value V2 and the second
DLOXS from the comparison voltage VR2 (← V2-VR
2) is calculated. Here, the second comparison voltage VR2 is a second output value V2 corresponding to the stoichiometric air-fuel ratio λ0, and is set to, for example, 0.6 V in the present embodiment.

In the following step 506, the deviation DLOXS is set to 0.
Is determined, that is, whether the air-fuel ratio is rich or lean. If the difference DLOXS is less than 0, that is, if the air-fuel ratio is lean, the process proceeds to step 507, and the value of the second delay counter CDLY2 is decremented (CDL).
Y2 ← CDLY2-1). Subsequent steps 508, 509
To set the second delay counter CDLY2 to the second lower limit value T.
A guard process is performed in DR2, and the process proceeds to step 513. More specifically, in step 508, the second delay counter CD
It is determined whether LY2 is less than a second lower limit value TDR2.
Here, when the second delay counter CDLY2 is smaller than the second lower limit TDR2, the process proceeds to step 509, and the second delay counter CDLY2 is reset to the second lower limit TDR2.

On the other hand, if the difference DLOXS is equal to or larger than 0 in step 506, that is, if the air-fuel ratio is rich, step 51
The process proceeds to 0, and the value of the second delay counter CDLY2 is incremented (CDLY2 ← CDLY2 + 1). In subsequent steps 511 and 512, the second delay counter C
Guard processing is performed on DLY2 with the second upper limit value TDL2,
Proceed to step 513. Specifically, in step 511, the second delay counter CDLY2 sets the second upper limit value TDL
It is determined whether it is greater than two. Here, when the second delay counter CDLY2 is smaller than the second upper limit value TDL2, the process proceeds to step 412, and the second delay counter CDLY
LY2 is reset to the second upper limit value TDL2.

The aforementioned second lower limit value TDR2 is equal to the second O
This is the second rich delay time for maintaining the determination that the output of the second sensor 13 is in the lean state even when the output changes from lean to rich, and is defined as a negative value. The second upper limit value TDL2 is a second lean delay time for maintaining the determination that the output of the second O2 sensor 13 is in a rich state even when there is a change from rich to lean, Defined by a positive value. Then, the reference of the second delay counter CDLY2 is set to 0, and when the second delay counter CDLY2 is positive, the air-fuel ratio after the delay processing is regarded as rich, and when the second delay counter CDLY2 is negative,
The air-fuel ratio after the delay processing is regarded as lean.

In step 513, it is determined whether or not the second delay counter CDLY2 has inverted, that is, whether or not the air-fuel ratio after the delay processing has changed. If the air-fuel ratio after the delay processing has changed, the process proceeds to step 514, and the average of the previous delay correction value DLTD0 and the delay correction value DLTD is substituted for the learning value DLTDAV (DLTDAV ← (DLTD
0 + DLTD) / 2). In the following step 515, the delay correction value DLTD is set as the previous delay correction value DLTD0 (DL
TD0 ← DLTD), and the process proceeds to step 516.

At step 516, it is determined whether or not the inversion is from the rich state to the lean state. Here, if it is determined that the inversion is from the rich state to the lean state, the process proceeds to step 517, where the delay correction value DLTD is reduced by the second rich skip amount SSR (DLTD ← DLTD).
-SSR), and proceed to step 523. Step 5
If it is determined in step 16 that the inversion is from the lean state to the rich state, the process proceeds to step 518, where the delay correction value DLT
D is increased by the second lean skip amount SSL (DL
TD ← DLTD + SSL), and the process proceeds to step 523. Here, the second rich skip amount SSR is set to a value equal to or larger than the second lean skip amount SSL (in the present embodiment, the second rich skip amount SSR is the second lean skip amount SSL).
Rich skip amount SSR and second lean skip amount S
SL is set to an equal value).

On the other hand, if the air-fuel ratio after the delay processing has not been inverted at step 513, the process proceeds to step 519, where a second integration constant SK calculated by a sub-feedback constant setting routine described later is read.

In step 520, it is determined whether the second delay counter CDLYYZ is equal to or less than 0, that is, whether the air-fuel ratio is in a rich state or a lean state. If it is determined that the vehicle is in the lean state, the process proceeds to step 521, where the delay correction value DLTD is reduced by the second integration constant SK (DLTD ← DLTD-SK), and the process proceeds to step 523. If it is determined in step 520 that the vehicle is in the rich state, the process proceeds to step 522, where the delay correction value DLTD
Is increased by a second integration constant SK (DLTD ← DLT
D + SK), and proceeds to step 523.

In step 523, it is detected whether or not the delay correction value DLTD set as described above is less than the reference value DLTD1. Here, the delay correction value DLTD is equal to the reference value DL.
If it is less than TD1, the process proceeds to step 524, where the first lean delay time TDL1 is set to the lean minimum value TDLMIN. In the following step 525, a value obtained by adding the rich initial value TDR0 to the delay correction value DLTD is substituted for the first rich delay time TDR1 (TDR1 ← TDR0 + DLTD),
The guard processing of steps 526 and 527 is performed. Specifically, in step 526, it is determined whether the first rich delay time TDR1 is less than a lower limit TR1. Here, if the first rich delay time TDR1 is less than the lower limit value TR1, the process proceeds to step 527, where the first rich delay time TDR1 is reset to the lower limit value TR1 (TDR1 ← TR1), and this routine ends.

On the other hand, the delay correction value DLTD is equal to the reference value DLT.
If it is equal to or longer than D1, the process proceeds to step 528, where the first lean delay time TDL1 is set by the following equation. TDL1 ← T
DL0 + (DLTD-100) Here, TDL0 is a lean initial value. In a succeeding step 529, the first rich delay time TDR1 is set to the first rich delay time TDR1 to the rich minimum value TDRMIN, and in step 530,
531 guard processing is performed. For details, see step 530
It is determined whether the first lean delay time TDL1 is larger than the upper limit value TL1. Here, if the first lean delay time TDL1 is larger than the upper limit value TL1, step 53
1 to increase the first lean delay time TDL1 to the upper limit value TL.
1 (TDL1 ← TL1), and this routine ends.

Here, since the second integration constant SK obtained in the processing described later is set sufficiently smaller than the second skip amounts SSR and SSL, when the air-fuel ratio is in a lean state, the delay correction is performed. Since the amount DLTD gradually decreases,
The first rich delay time TDR1 gradually increases, or the first lean delay time TDL1 decreases. When the air-fuel ratio is in a rich state, the delay correction amount DLTD gradually increases, so that the first rich delay time TDR1 gradually decreases or the first lean delay time TDL1 increases. Therefore, the control center of the air-fuel ratio of the air-fuel mixture supplied to the gas engine 1 is controlled so that the stoichiometric air-fuel ratio λ0 is centered.

FIG. 7 shows the second characteristic used in the above-described sub-feedback control routine, which is the most characteristic part of the present invention.
9 is a flowchart showing a routine for setting an integration constant SK of the first embodiment. The second integration constant SK setting routine is started every predetermined time (for example, 1S in this embodiment).

First, at step 701, the deviation DOXS between the second output value V2 calculated at step 505 in FIG. 5 and the second comparison voltage VR2 is read, and this deviation DLOS is read.
Obtain the absolute value of XS | DLOXS |. Step 702
In step 701, a basic integration constant SK0 is set according to the absolute value | DLOXS | calculated in step 701. Specifically, the basic integration constant SK0 is set from the map shown in FIG. Note that the absolute value | DLOXS | of the basic integration constant SK0 decreases as shown in FIG. 11, that is, the second integration constant SK decreases before and after the output signal of the second O ₂ sensor 13 changes abruptly. It is set as follows.

In the following step 703, the exhaust gas temperature sensor 14
The exhaust gas temperature TCR downstream of the three-way catalyst is taken in based on the signal from. In step 704, a correction coefficient FSK is obtained according to the exhaust gas temperature TCR. Specifically, it is obtained from a map as shown in FIG. That is, the above-described map of FIG. 11 is a map for obtaining the basic integration constant SKO when the exhaust gas temperature is a predetermined temperature T (750 ° C. in the present embodiment).
2 is a correction coefficient FS when the exhaust temperature TCR is a predetermined temperature T.
It is set in advance so that K becomes 1.0.

In step 705, a second integration constant SK is calculated based on the following equation (Equation 14).

[0049]

SK ← SKO × FSK The second integration constant SK may be obtained from a map of the absolute value | DLOXS | and the exhaust gas temperature TCR as shown in FIG.

Thus, the routine for setting the second integral constant SK is completed. That is, the exhaust temperature TC
The second integration constant SK corrected and determined according to R is used in the above-described auxiliary air-fuel ratio feedback routine, and optimal first rich delay time TDR1 and first lean delay time TRL1 are set.

Next, the operation of the second integration constant SK and the setting routine will be described in more detail with reference to time charts shown in FIGS. FIG. 14 shows the exhaust gas temperature T.
FIG. 15 shows a change in each control amount and output signal when the CR is 750 ° C., and FIG. 15 shows a change in each control amount and output signal when the exhaust temperature is 600 ° C.

14 and 15, (a) shows the output waveform of the second O ₂ sensor 13, (b) shows the change in the second integration constant SK, and (c) shows the second integration constant SK. FIG. 9D is a diagram showing a change in the delay correction value DLTD calculated in the sub air-fuel ratio feedback routine described above using the integral constant SK of FIG. It is a figure showing a characteristic.

First, the present invention will be described in detail with reference to FIG. In FIG. 14A, the second comparison voltage V
The distance between R2 and the actual output of the second O ₂ sensor 13 is the deviation DLOXS, and the larger the deviation DLOXS is, the more the air-fuel ratio is shifted from the stoichiometric air-fuel ratio inlet. Here, based on this deviation DSOXS, FIG.
By setting the basic integration constant SK0 as shown in the step 701, the integration constant SK is increased as the deviation DLOXS is larger (in other words, as the deviation from the stoichiometric air-fuel ratio λ0 is larger). The stoichiometric air-fuel ratio λ0 can be approached with good efficiency. Further, the deviation DL
When OXS is small, the integration constant SK is set small, so that it is possible to prevent the air-fuel ratio from being controlled to be over-rich or over-lean.

The characteristics of the integration constant SK set by the method described above are shown by the solid line in FIG.
It can be seen that the larger LOXS, the larger the integration constant SK. The broken line in FIG. 14B shows the characteristic of the conventional integration constant SK, which is always a constant value regardless of the magnitude of the deviation DLOXS.

The solid lines in FIGS. 14 (c) and 14 (d) show the characteristics when the air-fuel ratio feedback control is performed by obtaining the integration constant SK by the method described above, and the broken lines show the characteristics when the integration constant SK is constant. . From this figure, it can be seen that the air-fuel ratio can be controlled near the stoichiometric air-fuel ratio λ0 by varying the integration constant SK.

Next, the present invention will be described in more detail with reference to FIG. FIG. 14 described above has a characteristic in which the exhaust temperature TCR is 750 ° C., whereas FIG.
The characteristics at 0 ° C. are shown. That is, FIG. 14A and FIG.
As can be seen from (a), the amplitude of the output signal of the second O ₂ sensor 13 changes according to the exhaust gas temperature TCR. Specifically, the lower the exhaust gas temperature TCR, the larger the amplitude. Therefore, if the integral constant SK is set only from the deviation DLOXS, the optimal integral constant SK will not be set when the exhaust gas temperature TCR greatly varies, and the control will be over-rich or over-lean.

In FIG. 15, the solid line indicates the exhaust gas temperature T.
The characteristic when the integration constant SK is corrected according to the CR, the broken line is the characteristic when the integration constant SK is constant, and the one-dot chain line is the characteristic when the correction is not performed according to the exhaust temperature TCR (in this embodiment, the exhaust temperature TCR is 750). 2nd O ₂ sensor 1 at ℃
3 shows a case where correction is performed using an integral constant SK obtained from a two-dimensional map of a deviation DLOXS determined based on the output of No. 3 and an integral constant SK.

Accordingly, by detecting the exhaust gas temperature TCR and correcting the basic integral constant SK0 based on the exhaust gas temperature TCR to set the integral constant SK, a more optimal integral constant SK can be set. As a result, the air-fuel ratio can always be controlled near the stoichiometric air-fuel ratio λ0 (FIG. 15D).

In the above embodiment, the sub-supply passage 7 is opened upstream of the throttle valve 5 and the fuel gas is bypassed upstream of the throttle valve 5, but the fuel gas flows downstream of the throttle valve 5. The bypass structure may be such that the intake air is bypassed instead of the fuel gas.

In the above embodiment, the second control constant is set according to the deviation DLOXS.
May be set according to the output value V2. In the above embodiment, the second comparison voltage VR2 is set to a predetermined value. However, the comparison voltage VR2 may be set in accordance with the intake pressure PM using characteristics as shown in FIG.

Further, in the above embodiment, the gas engine system has been described. However, the present invention may be applied to a gasoline engine having an injector and determining a fuel supply amount by electronic control.

[0062]

As described above, according to the present invention, when the output signal of the second oxygen concentration sensor indicates a value close to the stoichiometric air-fuel ratio, the correction integration constant is set small and the exhaust gas temperature sensor is set.
The lower the exhaust gas temperature detected by the above, the more the correction integration
The smaller the constant, the larger the higher the constant.

As a result, the second O ₂
Even if the output signal of the sensor changes, the optimal integration constant can always be set, and the air-fuel ratio can be controlled to be close to the stoichiometric air-fuel ratio without being over-rich or over-lean. It has excellent effects.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention.

FIG. 2 is an overall configuration diagram of an apparatus according to an embodiment of the present invention.

FIG. 3 is a flowchart for explaining an operation of setting a control amount of a control valve 8;

FIG. 4 is a flowchart for explaining an operation of a main air-fuel ratio feedback control by a first O ₂ sensor 12;

FIG. 5 is a flowchart for explaining the operation of the secondary air-fuel ratio feedback control by the second O ₂ sensor 13;

FIG. 6 is a flowchart for explaining the operation of the secondary air-fuel ratio feedback control by the second O ₂ sensor 13;

FIG. 7 is a flowchart illustrating an operation for setting a second integration constant SK.

FIG. 8 is a characteristic diagram of a total gas flow rate and an intake pressure PM.

FIG. 9 is a characteristic diagram of a rotation speed NE and a rotation speed correction coefficient KNE.

FIG. 10 is a characteristic diagram of a duty ratio and a bypass flow rate.

FIG. 11 is a characteristic diagram of an absolute value | DLOGS | of a deviation DLOXS and a second integration constant.

FIG. 12 is a characteristic diagram of an exhaust gas temperature TCR and a correction coefficient FSK.

FIG. 13 is a characteristic diagram of an absolute value | DLOGS | of a difference DLOXS and a second integration constant SK.

FIG. 14 is a time chart for explaining the operation of this embodiment.

FIG. 15 is a time chart for explaining the operation of this embodiment.

FIG. 16 is a characteristic diagram of the second comparison voltage VR2 and the intake pressure PM.

FIG. 17 is a diagram illustrating output voltage characteristics of a second oxygen concentration sensor.

[Explanation of symbols]

Reference Signs List 1 gas engine (internal combustion engine) 11 three-way catalyst 12 first O ₂ sensor (first oxygen concentration sensor) 13 second O ₂ sensor (second oxygen concentration sensor) 14 exhaust temperature sensor 20 electronic control device ( ECU)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-195351 (JP, A) JP-A-2-45635 (JP, A) JP-A-61-101646 (JP, A) JP-A 55-195 5440 (JP, A) Special Table 3-500565 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/00-14/40 F02D 43/00-45/00

Claims (1)

(57) [Claims] 1. A catalyst disposed in an exhaust system of an internal combustion engine for purifying exhaust gas; a first oxygen concentration sensor disposed upstream of the catalyst and whose output signal changes rapidly at a stoichiometric air-fuel ratio; A second oxygen concentration sensor disposed downstream of the catalyst and whose output signal changes abruptly at the stoichiometric air-fuel ratio; an exhaust temperature sensor disposed in the exhaust system of the internal combustion engine and detecting exhaust gas temperature; When the air-fuel ratio detected by the second oxygen concentration sensor at the timing and the air-fuel ratio detected by the second oxygen concentration sensor at the previous control timing are shifted to the same side with respect to the stoichiometric air-fuel ratio Are the rich control constant and the lean control constant according to the detected air-fuel ratio.
Correction amount increasing / decreasing means for increasing / decreasing a correction amount for correcting the number by a correction integration constant; a rich control constant and a lean control constant in accordance with the correction amount
A first control constant correction means for correcting the following: an output signal of the first oxygen concentration sensor and a rich control constant
Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine in accordance with the lean control constant, and the correction integration constant is set smaller as the output signal of the second oxygen concentration sensor shows a value closer to the stoichiometric air-fuel ratio. An air-fuel ratio control device for an internal combustion engine, comprising: a correction integration constant setting unit that sets the correction integration constant to be smaller as the exhaust gas temperature detected by the exhaust gas temperature sensor is lower, and to be larger as the exhaust gas temperature is higher.