JPH048854A - Air-fuel ratio control device of gas engine - Google Patents

Abstract

PURPOSE:To prevent deterioration in emission cause by a storage effect of a catalyzer by setting a correction integration constant small when an output signal of an oxygen concentration sensor on the lower stream side of the catalyzer shows a value close to a theoretic air-fuel ratio. CONSTITUTION:A first and second oxygen concentration sensors C and D whose output signals are reversed by a theoretic air fuel ratio are provided respectively at the upper and the lower streams of a catalyzer B for purifying exhaust gas arranged in an exhaust system of a gas engine A. At this time, when each of the air-fuel ratio detected by the second oxygen concentration sensor D at control timing of the present and the previous time are deviated to the same side as the theoretic air-fuel ratio, a correction amount of a first control constant is increased or decreased according to the detected air-fuel ratio by a means E only by a correction integration constant. Also, the first control constant is corrected according to the correction amount by a first means F. Moreover, the air-fuel ratio is controlled by a means G according to an output signal of the first oxygen concentration sensor C and the first control constant. And the correction integration constant is set by a means H so that the smaller it becomes the closer the output signal of the second oxygen concentration sensor D to the theoretic air fuel ratio.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gas engine, and in particular, to a gas engine, in which oxygen concentration sensors (02 sensors) are provided upstream and downstream of a catalyst, and the air-fuel ratio is controlled according to the output signals of these sensors. This invention relates to an air-fuel ratio control device for a gas engine.

[Conventional technology]

Conventionally, in an air-fuel ratio control device that controls the air-fuel ratio to near the stoichiometric air-fuel ratio λ0 in response to an output signal from a first 02 sensor provided upstream of a catalyst in a gasoline engine, a second 02 sensor provided downstream of the catalyst is used. Control constants (integral constant, skip amount, delay time, comparison voltage, etc.) for air-fuel ratio control by the first 02 sensor are corrected according to the output signal of the sensor, and control is performed based on changes in characteristics of the first 02 sensor. Devices for preventing sexual decline have been disclosed (for example, Japanese Patent Laid-Open No. 61286
No. 550).

[Problem to be solved by the invention]

In gas engines, it is necessary to increase the amount of catalyst in accordance with NOx regulations, and the catalyst has a larger capacity than in gasoline engines. Therefore, the storage effect of the catalyst increases, and it takes a considerable amount of time until the second 02 sensor detects the air-fuel ratio of the air-fuel mixture that is actually being supplied, causing a delay in correction of the control constant. Therefore, there is a problem in that the air-fuel ratio is controlled to be over-rich or over-lean, resulting in worsening of emissions.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide an air-fuel ratio control device for a gas engine that prevents deterioration of emissions due to the storage effect of a catalyst.

[Means to solve the problem]

As shown in FIG. 1, the present invention includes a catalyst disposed in the exhaust system of a gas engine to purify exhaust gas, and a first catalyst disposed upstream of the catalyst whose output signal is inverted at the stoichiometric air-fuel ratio. an oxygen concentration sensor, a second oxygen concentration sensor that is disposed downstream of the catalyst and whose output signal is inverted at the stoichiometric air-fuel ratio, and an air-fuel ratio detected by the second oxygen concentration sensor at the current control timing. If the air-fuel ratio detected by the second oxygen concentration sensor at the previous control timing is on the same side as the stoichiometric air-fuel ratio, the first control constant is corrected according to the detected air-fuel ratio. a correction amount increase/decrease means for increasing/decreasing a correction amount by a correction integral constant; a first control constant correction means for correcting a first control constant according to the correction amount; and an output of the first oxygen concentration sensor. an air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the gas engine according to the signal and the first control constant; and an output signal of the second oxygen concentration sensor that has a value close to the stoichiometric air-fuel ratio. The gist of the present invention is an air-fuel ratio control device for a gas engine, which includes a correction integral constant setting means for setting the correction integral constant to a smaller value as shown.

[Effect]

With the above configuration, if the air-fuel ratio detected by the second oxygen concentration sensor at the current control timing is the same as the air-fuel ratio detected by the second oxygen concentration sensor at the previous control timing by the correction amount increase/decrease means, A correction amount for correcting the first control constant is increased or decreased by the correction integral constant in accordance with the detected air-fuel ratio. The first control constant correction means corrects the first control constant according to the correction amount, and the air-fuel ratio control means corrects the first control constant according to the output signal of the first oxygen concentration sensor and the first control constant. The air-fuel ratio of the air-fuel mixture supplied to the air-fuel mixture is controlled.

Further, the correction integral constant setting means sets the correction integral constant to a smaller value as the output signal of the second oxygen concentration sensor shows a value closer to the stoichiometric air-fuel ratio. That is, the correction integral constant is set small before and after the air-fuel ratio detected by the second oxygen concentration sensor changes.

〔Example〕

An embodiment to which the present invention is applied will be described below based on the drawings.

FIG. 2 is a configuration diagram of this embodiment. ■ is a gas engine. The intake system of the gas engine 1 includes an air cleaner 2 that purifies air, and an intake pipe 3 that guides a mixture of air and fuel gas purified by the air cleaner 2 to the gas engine 1. Further, in the intake pipe 3, a mixer 4 is provided which mixes air supplied from the air cleaner 2 from the upstream side with 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 that adjusts the amount of air-fuel mixture (total gas flow rate) supplied to the gas engine 1 is provided. Also, a main supply path 6 that supplies fuel gas directly from the gas supply source to the mixer 4
and an auxiliary supply path 7 for supplying fuel gas downstream of the mixer 4 from the gas supply source. Furthermore, in the sub supply path 7,
Amount of fuel gas supplied from the sub-supply path 7 (bypass flow rate)
An air-fuel ratio control control valve 8 is provided to adjust the air-fuel ratio of the air-fuel mixture supplied to the gas engine 1 to a desired value. Further, a pressure sensor 9 is provided to detect the intake pressure PM downstream of the throttle valve 5.

On the other hand, the exhaust system of the gas engine 1 is provided with an exhaust pipe 10 that guides exhaust gas from the gas engine 1, and a three-way catalyst 11 that purifies harmful components contained in the exhaust gas is installed in the exhaust pipe 10. It is arranged. Furthermore, upstream and downstream of this three-way catalyst 11, the oxygen concentration in the exhaust gas is detected in order to detect the air-fuel ratio of the air-fuel mixture supplied to the gas engine 1, and the output signal is reversed at the stoichiometric air-fuel ratio λ0. 1st and 2nd
Oxygen concentration sensors (02 sensors) 12 and 13 are provided.

14 is a spark plug provided in the cylinder of the gas engine 1, and 15 is a rotation speed sensor that detects the rotation speed NE of the gas engine.

20 is an electronic control unit (ECU) that sets control amounts for various actuators such as the aforementioned control valve 89 and spark plug 14, and outputs a control signal according to the control amount.
As is well known, 0 is a central processing unit (CPU) 20a that performs various calculations, a read-only memory (ROM) 20b that stores control programs, etc., and a read-only memory (ROM) 20b that temporarily stores calculation data, etc. A writable/readable random access memory (RAM) 20c for storing data in the memory, an analog-to-digital converter (for converting analog signals into digital signals)
ADC) 20d, an input port 1-20e for taking sensor signals from the various sensors mentioned above into the ECU 20, an output port 20f for outputting control signals to the various actuators mentioned above, and a bus 20g interconnecting these. It is configured.

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 explained using flowcharts shown in FIGS. 3 to 5.

FIG. 3 is a flowchart showing a control amount calculation routine for calculating the control amount of the control valve 8.

First, in step 301, the basic control amount DB is set to the pressure sensor 9.
It is calculated by the following formula according to the intake pressure PM detected by the rotation speed sensor 15 and the rotation speed NE detected by the rotation speed sensor 15.

DB ←(PM-PMOS)XKPMBXKNEXKD
B+DOS Here, PMOS has a relationship between the intake pressure PM and the total gas flow rate as shown in FIG. 6, and is a value corresponding to the offset of this relationship and is a constant. KPMB is a conversion coefficient for converting intake pressure PM into a duty ratio. KNE is a rotation correction coefficient corresponding to the rotation speed N,
There is a relationship between the rotation speed NE and the rotation correction coefficient NKE as shown in FIG. KDB is intake pressure PM and rotation speed N
This is a correction coefficient set according to E. There is a relationship between the duty ratio and the bypass flow rate as shown in FIG. 8, and DO5 is a value corresponding to the offset of this relationship and is a constant.

In the following step 302, the correction side! ll amount DF is intake pressure PM
, the rotational speed NE, and an air-fuel ratio correction coefficient FAF, which will be described later, using the following equation.

DF←(PM-PMOS)xKPMF XKNEXFAF Here, KPMF is the intake pressure P shown in Figs. 6 and 8.
This is a value set by the following equation based on the slope α of the characteristic between M and the total gas flow rate, and the slope β of the characteristic between the duty ratio and the bypass flow rate.

KPMF←α/β Then, in step 303, a control amount is calculated according to the following equation according to the basic control amount DB and the corrected control amount DF calculated as described above.

D4-DB+DF In step 304, a control signal corresponding to the control amount is output to the control valve 8.

This completes the control amount calculation routine.

Next, a method of setting the air-fuel ratio correction coefficient FAF will be explained. FIG. 4 is a flowchart showing the main air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output value (first output value) Vl of the first 02 sensor 12. This main air-fuel ratio feedback control routine is activated at predetermined intervals (for example, every 4 m5 in this embodiment).

First, in step 401, it is determined whether the main air-fuel ratio feedback condition is satisfied. Here, as the main air-fuel ratio feedback condition, for example, in this embodiment, the first 02 sensor 12 is in an active state after the engine is started. If it is determined in step 401 that the main air-fuel ratio feedback condition is not satisfied, step 40
Proceed to step 2 and set the air-fuel ratio correction coefficient FAF to 1 (FAF
F←■).

On the other hand, if it is determined in step 401 that the main air-fuel ratio feedback condition is satisfied, the processes from step 403 onwards are executed. In step 403, the first output value ■1 is taken in. In step 404, it is determined whether the first output value (1) is less than or equal to the first comparison voltage VRI (for example, 0.45V in this embodiment), that is, whether the air-fuel ratio is rich or lean.

Here, if the first output value Vl is less than or equal to the first comparison voltage VRI, that is, if the air-fuel ratio is lean, the process proceeds to step 405, where the first delay counter CDLYIO value is decremented (CDLYI←CDLYI-1). In subsequent steps 406 and 407, the first delay counter CDLYI
is subjected to guard processing using the first lower limit value TDR1. For more information,
In step 406, it is determined whether the first delay counter CDLYI is less than the first lower limit value TDRI. here,
The first delay counter CDLYI is the first lower limit value TD.
If it is less than RI, the process proceeds to step 407, where the first delay counter CDLYI is reset to the first lower limit value TDR1.

On the other hand, if the first output value V1 is larger than the first comparison voltage VRI in step 403, that is, the air-fuel ratio is rich, the process proceeds to step 408, and the first delay counter CD
Increment the LYIO value (CDLY1←CDL
Y1+1). In subsequent steps 409 and 410, the first delay counter CDLY1 is guarded with the first upper limit value TDLI. Specifically, in step 409, it is determined whether the first delay counter CDLYI is greater than the first upper limit value TDLI. Here, when the first delay counter CDLYI is larger than the first upper limit value TDLI, 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 TDRI described above is the first lower limit value TDRI of the first 02 sensor 12.
This is the first rich delay time for maintaining the determination that the state is lean even if the output changes from lean to rich, and is defined as a negative value. In addition, the first upper limit value T
DLI is a first lean delay time for maintaining the judgment that the rich state is reached even when the output of the first 02 sensor 12 changes from rich to lean, and is defined as a positive value. . And the first delay counter CDLYI
The reference of the first delay counter CDLY 1 is set to 0.
is positive, the air-fuel ratio after the delay process is considered rich, and the first
When the delay counter CDLY 1 is negative, the air-fuel ratio after the delay processing is regarded as lean.

These first rich delay time TDRI and first lean delay time TRLI are set by side fuel ratio feedback control which will be described later.

In step 411, it is determined whether the sign of the first delay counter CDLY1 set as described above has been inverted, that is, whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio after the delay processing is reversed, steps 412 to 414 are skipped. First, step 4
At step 12, it is determined whether or not there is a reversal from the rich state to the lean state. Here, if it is determined that there is a reversal from the rich state to the lean state, the process proceeds to step 413, and the air-fuel ratio correction coefficient FAF is increased by the first skip amount R31 (FAF 4 - FAF + RS 1).

Further, if it is determined in step 412 that the state is a reversal from a lean state to a rich state, the process proceeds to step 414;
The air-fuel ratio correction coefficient FAF is decreased by the first skip amount R3I (FAF 4-FAF-R3I).

On the other hand, if the air-fuel ratio after the delay processing is not reversed in step 411, then the integration processing in steps 415 to 417 is performed. First, in step 415, it is determined whether the first delay counter CDLYI is less than or equal to 0, that is, whether the air-fuel ratio is in a rich state or a lean state. Here, if it is determined that the state is lean, the process proceeds to step 416, where the air-fuel ratio correction coefficient FAF is increased by 1 to the first integral constant (F
1) for AF-FAF+. Further, if it is determined in step 415 that the state is rich, the process proceeds to step 417;
Decrease the air-fuel ratio correction coefficient FAF by 1 to the first integral constant (1 to FAF-FAF-).

Here, 1 for the first integral constant is the first skip amount R5I
It is set sufficiently small compared to . Therefore, when the air-fuel ratio is in a lean state, the air-fuel ratio correction coefficient FAF gradually increases, so the amount of supplied fuel gas gradually increases. Further, when the air-fuel ratio is in a rich state, the air-fuel ratio correction coefficient FAF gradually decreases, so the supplied fuel gas gradually decreases.

This completes the main air-fuel ratio feedback control routine.

FIG. 5 shows the first delay time (first rich delay time TDR1, first lean delay time TDR1, first lean delay time) as the first control constant based on the output value (second output value) V2 of the second 02 sensor 13. 12 is a flowchart showing a side fuel ratio feedback control routine for correcting the time TDLI). This side fuel ratio feedback control routine is activated at predetermined time intervals (eg, is in this embodiment).

First, in step 501, it is determined whether or not a side injection fuel ratio feedback condition is satisfied, that is, whether side injection fuel ratio feedback control is to be executed. As this side side fuel ratio feedbank condition, for example, the fuel ratio feedback condition (2) is satisfied.

(2) The second 02 sensor 13 is in an active state.

■Three-way catalyst 11 has not deteriorated.

This is a case where all of the conditions (■) to (■) are satisfied.

Here, if it is determined that the above-mentioned condition is not satisfied, the side injection fuel ratio feedback control from step 504 onwards is not executed, and the process proceeds to step 502, in which the learned value DLTDAV, which will be described later, is prepared for the next side injection fuel ratio feedback control. is assigned to the previous delay correction value DLTDO (DLTDO4-
DLTDAV).

In the following step 503, the learning value DLTDAV is substituted into the delay correction value DLTD (DLTD4-DLTDAV), and the process proceeds to step 523.

On the other hand, if it is determined in step 501 that the side injection fuel ratio feedback condition is satisfied, that is, it is determined that the side injection fuel ratio feedback control is to be executed, the processes from step 504 onwards are executed.

First, in step 504, the second output value ■2 is taken in.

In step 505, the second output value ■2 and the second comparison voltage V
Calculate the deviation DLOXS (-V2-VR2) from R2. Here, the second comparison voltage VR2 is the second output value ■2 corresponding to the stoichiometric air-fuel ratio λ0, and is set to 0.6■ in this embodiment, for example.

In the following step 506, it is determined whether the deviation DLOXS is less than 0 or not.
That is, it is determined whether the air-fuel ratio is rich or lean. Here, if the deviation DLOXS is less than 0, that is, the air-fuel ratio is lean, the process advances to step 507, and the second delay counter CD
Decrement the value of LY2 (CDLY2←CDLY
2-1). In subsequent steps 508 and 509, the second delay counter CDLY2 is guarded with the second lower limit value TDR2, and the process proceeds to step 513. Specifically, in step 508, it is determined whether the second delay counter CDLY2 is less than the second lower limit value TDR2. Here, when the second delay counter CDLY2 is less than the second lower limit value TDR2, the process proceeds to step 509, and the second delay counter CDLY2 is reset to the second lower limit value TDR2.

On the other hand, if the deviation DLOXS is 0 or more in step 506, that is, the air-fuel ratio is rich, the process proceeds to step 510, where the value of the second delay counter CDLY2 is incremented (CDLY2←CDLY2+1). Next step 5
At step 11,512, the second delay counter CDLY2 is guarded at the second upper limit value DL2, and at step 51
Proceed to step 3. Specifically, in step 511, it is determined whether the second delay counter CDLY2 is larger than the second upper limit value TDL2. Here, the second delay counter C
If DLY2 is less than the second upper limit TDL2, step 4
12, and set the second delay counter CDLY2 to the second delay counter CDLY2.
is reset to the upper limit value TDL2.

The second lower limit value TDR2 mentioned above is determined by the second o2 sensor 13.
This is the second rich delay time for maintaining the determination that the state is in the lean state even if the output changes from lean to rich, and is defined as a negative value. In addition, the second upper limit value T
DL2 is a second lean delay time for maintaining the judgment that the engine is in a rich state even if the output of the second 02 sensor 13 changes from rich to lean, and is defined as a positive value. . And the second delay counter CDLY2
When the second delay counter CDLY2 is positive, the air-fuel ratio after the delay process is considered rich, and when the second delay counter CDLY2 is negative, the air-fuel ratio after the delay process is considered lean.

In step 513, it is determined whether the second delay counter CDLY2 has been inverted, that is, whether the air-fuel ratio after the delay processing has changed. If the air-fuel ratio after the delay processing has changed, the process advances to step 514, and the previous delay correction value DLT is
The average of DO and delay correction value DLTD is set as learning value DLTDA.
Assign to V (DLTDAV←(D LTD O+D
LTD) /2).

In the following step 515, the delay correction value DLTD is substituted into the previous delay correction value DLTDO (DLTDO←DLTD).
, the process proceeds to step 516. In step 516, it is determined whether or not there is a reversal from the rich state to the lean state. Here, if it is determined that there is a reversal from the rich state to the lean state, the process advances to step 517, and the delay correction value DLTD
is decreased by the second rich skip amount SSR (DLT
D←DLTD-3SR), the process proceeds to step 523. If it is determined in step 516 that the lean state is reversed to the rich state, the process proceeds to step 518, where the delay correction value DLTD is increased by the second lean skip amount SSL (DLTD 4-DLTD+5SL), and step 523 Proceed to. Here, the second rich skip amount SS
R is set to a value greater than or equal to the second lean skip amount SSL (in this embodiment, the second rich skip amount SSR and the second lean skip amount SSL are set to be equal).
.

On the other hand, if it is determined in step 513 that the air-fuel ratio after the delay processing has not been reversed, the process proceeds to step 519, where a second integral constant SK is set in accordance with the deviation DLOXS. Here, the deviation D
As shown in FIG. 9, LOXS and the second integral constant SK are such that the smaller the deviation DLOXS, that is, the smaller the second integral constant SK becomes before and after the output signal of the second 02 sensor 13 changes. Set.

In the following step 520, the second delay counter CDLY
2 is below O, that is, whether the air-fuel ratio is in a rich state or a lean state. Here, if it is determined that the state is lean, the process proceeds to step 521, in which the delay correction value DLTD is decreased by the second integral constant SK set in step 519 (DLTD-DLTD-SK), and step 523
Proceed to.

If it is determined in step 520 that the state is rich, the process proceeds to step 522, where the delay correction value DLTD is increased by the second integral constant SK set in step 519 (DLTD + - DLTD + 5KL), and step 5
Proceed to 23.

In step 523, it is detected whether the delay correction value DLTD set as described above is less than the reference value DLTD1. Here, if the delay correction value DLTD is less than the reference value DLTD1, the process proceeds to step 524, and the first lean delay time TDLI is set to the lean minimum value TDLMIN. In the following step 525, the rich initial value T is set to the delay correction value DLTD.
The value obtained by adding DRO is substituted into the first rich delay time TDRI (TDRI←TDRO+DLTD), and the guard processing for the steering knobs 526 and 527 is performed. Specifically, in step 526, the first rich delay time TDRI is set to the lower limit T.
It is determined whether or not it is less than R1. Here, if the first rich delay time TDR1 is less than the lower limit value TR1, step 52
Proceed to step 7 and set the first sea/Sochi delay time TDRI to the lower limit T.
Reset to RI (TDRI←TR1) and end this routine.

On the other hand, if the delay correction value DLTD is equal to or greater than the reference value DLTD1, the process proceeds to step 528, where the first lean delay time TD
LI is set using the following formula.

TDLI←TDLO+ (DLTD-100) Here,
TDLO is a lean initial value. In the following step 529, the first rich delay time TDR1 is set to the rich minimum value TDRMIN, and the guard processing in steps 530 and 531 is performed. Specifically, step 530 determines whether the first lean delay time TDLI is greater than the upper limit TLI. Here, if the first lean delay time TDLI is larger than the upper limit value TLI, the process advances to step 531, and the first lean delay time TDLI
is reset to the upper limit value TLI (TDL1←TL1), and this routine ends.

Here, the second integral constant SK is the second skip amount SSR
, is sufficiently small (setting) compared to SSL, so when the air-fuel ratio is in a lean state, the delay correction amount DLTD gradually increases, so the first rich delay time TDR1 gradually increases or In addition, when the air-fuel ratio is in a rich state, the delay correction amount DLTD gradually decreases, so the first rich delay time TDRI gradually decreases, or the first lean delay time TDL1 decreases. The lean delay time TDLI increases.Therefore, the air-fuel ratio of the air-fuel mixture supplied to the gas engine 1 is controlled to be centered around the stoichiometric air-fuel ratio λO.

Furthermore, the second integral constant SK is the second output value ■2 and the second integral constant SK.
The characteristics shown in FIG. 9 are set according to the deviation DLOXS from the comparison voltage VR2. Therefore, when the deviation DLOXS is small as shown in the time chart of Fig. 10,
In other words, when the air-fuel ratio is close to the stoichiometric air-fuel ratio λO, the delay correction amount D
Since the change in LTD becomes smaller, the amount of correction change in the first control constant becomes smaller, and it is possible to prevent the air-fuel ratio from being controlled to be over-rich or over-lean. That is, since the control constant can be corrected without being influenced by the storage effect of the catalyst, deterioration of emissions can be prevented.

In the embodiment described above, 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 a structure in which the fuel gas is bypassed downstream of the throttle valve 5 may also be used. Alternatively, a structure may be adopted in which intake air is bypassed instead of fuel gas.

In addition, in the embodiment, the second control constant is the deviation DLOXS
I try to set it according to the second output value ■2
Further, in the above embodiment, the second comparison voltage VR2 was set to a predetermined value, but the intake pressure P may be set according to the characteristics shown in FIG.
The comparison voltage VR2 may be set according to M.

〔effect〕

As described in detail above, in the present invention, when the output signal of the second oxygen concentration sensor shows a value close to the stoichiometric air-fuel ratio, the correction integral constant is set to be small by the correction integral constant setting means. Therefore, the amount of correction change in the first control constant becomes smaller before and after the air-fuel ratio detected by the second oxygen concentration sensor changes, so it is possible to prevent the air-fuel ratio from being over-rich or over-lean. That is, there is an excellent effect of being able to prevent deterioration of emissions due to the storage effect of the catalyst.

[Brief explanation of drawings]

FIG. 1 is a diagram corresponding to claims, FIG. 2 is a configuration diagram of an embodiment to which the present invention is applied, FIGS. 3 to 5 are flowcharts for explaining the operation of the embodiment, and FIG. Figure 7 is a characteristic diagram of the intake pressure PM, Figure 7 is a characteristic diagram of the rotational speed NE and the rotational speed correction coefficient KNE, Figure 8 is a characteristic diagram of the duty ratio and bypass flow rate, and Figure 9 is a characteristic diagram of the deviation DLOXS and the rotational speed correction coefficient KNE.
FIG. 10 is a time chart for explaining the operation of the embodiment, and FIG. 11 is a characteristic diagram between the second comparison voltage VR2 and the intake pressure PM. DESCRIPTION OF SYMBOLS 1... Gas engine, 8... Control valve, 11... Catalyst, 12... First 02 sensor, 13... Second 0
2 sensors. 20...ECU.

Claims (1)

[Scope of Claims] A catalyst disposed in an exhaust system of a gas engine to purify exhaust gas; a first oxygen concentration sensor disposed upstream of the catalyst and whose output signal is inverted at a stoichiometric air-fuel ratio; A second oxygen concentration sensor is disposed downstream of the catalyst and whose output signal is inverted at the stoichiometric air-fuel ratio, and the air-fuel ratio detected by the second oxygen concentration sensor at the current control timing and at the previous control timing. If the air-fuel ratio detected by the second oxygen concentration sensor is on the same side as the stoichiometric air-fuel ratio, a correction amount for correcting the first control constant according to the detected air-fuel ratio is determined. a correction amount increase/decrease means for increasing or decreasing the first control constant by a correction integral constant; a first control constant correction means for correcting the first control constant according to the correction amount; and an output signal of the first oxygen concentration sensor and the first control constant. an air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the gas engine according to a control constant; and the correction integral constant increases as the output signal of the second oxygen concentration sensor indicates a value closer to the stoichiometric air-fuel ratio An air-fuel ratio control device for a gas engine, comprising: correction integral constant setting means for setting a small value.