JPH084573A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To perform control in a preferable state without setting a period of control to a high value even when deterioration of a catalyst occurs. CONSTITUTION:In a double O2 system, a detecting means 502 is provided to detect an operation time on the rich side wherein the first output V1 of a first oxygen sensor positioned upper stream from a catalyst converter 11 is higher than a first comparison reference value VR1 by which the rich and the lean state of combustion are discriminated and an operation time on the lean side wherein it is lower than first comparison reference value. A comparison reference value correction means 503 is provided for setting the first comparison reference value VR1 to a value at which a ratio between an operation time on the rich side and an operation time on the lean side is set to 1 or approximately 1.

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 performing air-fuel ratio control required when purifying exhaust gas generated from an internal combustion engine or the like by a three-way catalyst method or the like.

[0002]

2. Description of the Related Art As an air-fuel ratio control device of this type, there is a so-called double O ₂ system. In recent years, Japanese Patent Laid-Open Nos. 61-286550 and 3-294634 have been reported as such systems. Now, in such a double O ₂ system,
A catalytic converter for purifying exhaust gas such as a three-way catalyst is arranged in the exhaust system of a combustion engine such as an internal combustion engine, and exhaust gas such as oxygen concentration is provided on the upstream side of the catalytic converter and the downstream side of the catalytic converter, respectively. First to detect the concentration of specific components in
An air-fuel ratio sensor and a second air-fuel ratio sensor are provided. Then, the air-fuel ratio feedback control for the combustion engine is performed based on the outputs from both air-fuel ratio sensors. Here, the second output, which is the output of the second air-fuel ratio sensor, is used to derive the delay time that is the control constant in the air-fuel ratio feedback control, and is the output of the first comparison reference value and the first air-fuel ratio sensor. The air-fuel ratio correction amount is calculated according to the difference from the one output and the delay time obtained in the above stroke, and the air-fuel ratio of the combustion engine is controlled according to the obtained air-fuel ratio correction amount. Now, in this system, the output from the first air-fuel ratio sensor arranged upstream of the catalytic converter directly represents the combustion state of the combustion engine under the air-fuel ratio control. The second air-fuel ratio sensor arranged on the downstream side represents the purification performance state of the catalyst.

[0003]

The first aspect of the control device
The output waveform of the air-fuel ratio sensor is shown in FIGS. In the figure, (a) shows the control state of the first output waveform and the air-fuel ratio when the catalyst is in a relatively new state,
(B) shows the first output waveform and the control state of the air-fuel ratio when the catalyst is deteriorating. The upper side shows the output from the first air-fuel ratio sensor, and the lower side shows the air-fuel ratio control amount. Has been done. Further, FIG. 14 shows the relationship between the air-fuel ratio λ and the output of the first air-fuel ratio sensor (● solid line), and the catalyst effective area (indicated by braiding on the figure). TD shown in the same figure shows the difference between the sensor effective range and the sensor output, which is the basis of the control described later. Now, when the current air-fuel ratio control device is used to control with a new catalyst, FIG.
As shown in (a), the effective range of the catalyst and the value range in which the sensor output greatly changes with respect to the air-fuel ratio substantially match. Therefore, TD is almost 0, the above-mentioned delay time is close to 0, and the delay times on the lean side and the rich side are almost the same value. That is, the output waveform of the sensor is shown in FIG.
As shown in (a), the region indicating that the combustion is occurring on the rich side and the region indicating that the combustion is occurring on the lean side appear almost evenly and alternately. On the other hand, when the catalyst deteriorates or when the sensor characteristics change, the effective range of the catalyst and the value range in which the sensor output greatly changes with respect to the air-fuel ratio deviate. That is, TD takes a certain value. In this state, the delay time, which is the above-mentioned control constant, changes and the air-fuel ratio control is inclined to the rich side or the lean side. Therefore, the output from the first air-fuel ratio sensor is as shown in FIG. 13B, and the ratio in the rich and lean regions is not 1: 1. If the control is performed in this state, the control cycle becomes large, the air-fuel ratio of the air-fuel mixture greatly fluctuates, the engine speed is influenced by the control, and the load fluctuates, causing a problem.

Therefore, it is an object of the present invention to obtain an air-fuel ratio control device in which load fluctuation is unlikely to occur even if the catalyst deteriorates or the characteristics of the sensor change, etc., without taking a large control cycle. .

[0005]

In order to achieve the above object, the air-fuel ratio control device of the first specified invention according to claim 1 of the present application is characterized in that the first output is greater than the first comparison reference value. Is provided with detection means for detecting the rich side operating time at a high value and the lean side operating time at a low value, and the ratio between the rich side operating time and the lean side operating time is set to 1 or almost 1, It is provided with a comparison reference value correction means for setting the first comparison reference value.

Further, in the characteristic configuration of the air-fuel ratio control device of the second specified invention of the present application according to claim 2, in the region consisting of the first output and the time, the first output becomes higher than the first comparison reference value. Yes, and the rich side operation region area that is the area of the region surrounded by the first output and the first comparison reference value, and the first output is lower than the first comparison reference value, and the first output and the first comparison A quadrature unit is provided for detecting the lean side operation region area, which is the area of the region surrounded by the reference value, and the ratio between the rich side operation region area and the lean side operation region area is set to 1 or almost 1. It is provided with a comparison reference value correction means for setting one comparison reference value.

Further, in the above structure, it is preferable that both the first air-fuel ratio sensor and the second air-fuel ratio sensor are oxygen sensors. This is the invention according to claim 3.

Further, in the inventions of claims 1 and 2, when combustion in the combustion engine occurs in a lean combustion state in which fuel is insufficient and in a rich combustion state in which fuel is excessive, a delay time is present between both combustion states. It is a representative of the feedback control by delaying the change across, and it is preferable that the delay time is obtained based on the difference between the second comparison reference value and the second output of the second air-fuel ratio sensor. .
This is the invention according to claim 4.

Further, in the invention of claim 4, as the delay time, the rich delay time which is the delay time when the combustion in the combustion engine changes from the lean combustion state to the rich combustion state, and the rich combustion A lean delay time, which is the delay time when the state changes to the lean combustion state, is provided, and the control constant computing means computes either or both of the rich delay time and the lean delay time. Preferably there is. This is the invention according to claim 5.

Here, in the invention according to claim 1 or 2, it is preferable that the ratio is set between 0.9 and 1.1. This is the invention according to claim 6. Further, in the invention according to claim 1 or 2, it is preferable that the internal combustion engine uses a combustion gas containing methane as a main component as a fuel. This is the invention according to claim 7.

[0011]

In the air-fuel ratio control device of the present application, the criterion for judging whether the combustion in the combustion engine leans toward the lean side or leans at the component concentration detected by the first air-fuel ratio sensor. The first comparison reference value, which is the value, is corrected. In the configuration of the invention according to claim 1, this correction is performed by the detecting means for the time during which the first output is in a state of being higher or lower than the first comparison reference value (combustion is on the rich side or lean side, respectively). Based on the obtained detection result, the comparison reference value correction means corrects the first comparison reference value so that the time during which the combustion is on the rich side or the lean side is substantially the same. On the other hand, claim 2
In the invention according to, the quadrature means obtains the areas of a region where the output is higher than the air-fuel ratio comparison reference value and a region where the output is low in the time region of the first output, and similarly, The comparison reference value correction means corrects the first comparison reference value so that these areas are substantially the same. By performing such a correction, the correction requirement that is conventionally represented by the delay time from the output of the second air-fuel ratio sensor, which occurs due to catalyst deterioration and the like, is used as the first comparison reference of the output of the first air-fuel ratio sensor. As a time or a region area showing any tendency from the value, it can be captured prior to the control of the delay time. As a result, when this correction is performed, even if the catalyst deteriorates, as shown in FIG. 10B, a large increase in delay time can be avoided, and an increase in load fluctuation can be avoided. .

Here, the first air-fuel ratio sensor and the second air-fuel ratio sensor
If both the air-fuel ratio sensor is composed of an oxygen sensor, the air-fuel ratio control will be grasped by the oxygen concentration that can most effectively grasp the combustion state, so that the combustion state can be grasped surely and appropriate control can be performed.

Further, when combustion in the combustion engine occurs in a lean combustion state in which fuel is insufficient and in a rich combustion state in which fuel is excessive, a delay time delays a change between both combustion states to perform the feedback control. Assuming that the delay time is obtained based on the difference between the second comparison reference value and the second output of the second air-fuel ratio sensor, the output of the second air-fuel ratio sensor causes By representing the deterioration state and the like for each control cycle and representing it as a delay time, it is possible to perform accurate control in response to the transition state of the lean or rich combustion state of the engine.

Further, as the delay time, a rich delay time which is the delay time when the combustion in the combustion engine changes from the lean combustion state to the rich combustion state, and from the rich combustion state to the lean combustion state. A lean delay time, which is the delay time in the case of a change, is provided, and if the control constant computing means computes one or both of the rich delay time and the lean delay time, a sudden load change will occur. The air-fuel ratio can be satisfactorily followed.

Further, the ratio R is 0.9-1.
If set to 1, the catalyst is effective in the state where the feedback control in the second air-fuel ratio sensor is effectively operated (the feedback control is performed on behalf of the catalyst deterioration state in a relatively narrow range). When a relatively large deviation occurs between the air-fuel ratio range that acts on the first air-fuel ratio sensor and the output characteristic of the first air-fuel ratio sensor, this is detected by the first air-fuel ratio sensor output (first
Appropriate control can be performed on behalf of the value change of the output-based first comparison reference value. Further, when the internal combustion engine uses a combustion gas containing methane as a main fuel, such an engine is often used in, for example, a power generation facility, so that output fluctuation can be prevented and the system It is effective in preventing synchronization congestion and frequency fluctuations in cooperation.

[0016]

Therefore, by performing such a correction, even if there is a deviation between the region where the catalyst effectively works and the output characteristic of the air-fuel ratio sensor, a large control cycle is not required. It was possible to obtain an air-fuel ratio control device capable of suppressing load fluctuations to a low level.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment to which the present invention is applied will be described below with reference to the drawings. FIG. 1 is a configuration diagram of this embodiment. 1 is a gas engine as an example of a combustion engine.
The air supply system of the gas engine 1 includes an air cleaner 2 that purifies air, and an air supply pipe 3 that guides a mixture of the air purified by the air cleaner 2 and fuel gas to the gas engine 1. Further, a mixer 4, which mixes the air supplied from the air cleaner 2 from the upstream side with the fuel gas supplied from a fuel gas supply source (not shown) in the air supply pipe 3 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 the fuel gas from the gas supply source directly to the mixer 4 and a sub supply path 7 for supplying the fuel gas from the gas supply source to the downstream of the mixer 4. Further, in the sub-supply path 7, an air-fuel ratio for controlling the air-fuel ratio of the air-fuel mixture supplied to the gas engine 1 by adjusting the amount of fuel gas (bypass flow rate) supplied from the sub-supply path 7 to a desired value. A control valve 8 for control is provided. Here, the control valve 8 is used for air-fuel ratio feedback control. Further, a pressure sensor 9 that detects the supply pressure PM downstream of the throttle valve 5 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. The exhaust pipe 10 serves as a catalytic converter for purifying harmful components contained in the exhaust gas. The original catalyst mounting portion 11 is provided. Above and downstream of the three-way catalyst mounting portion 11, first and second oxygen as air-fuel ratio sensors for detecting the oxygen concentration in the exhaust gas in order to detect the air-fuel ratio of the air-fuel mixture supplied to the gas engine 1. Sensors 12 and 13 are provided. This oxygen sensor 1
Reference numerals 2 and 13 are so-called λ sensors, and zirconia electromotive force type oxygen sensors, titania, and perovskite type power type oxygen sensors are used. Therefore, the three-way catalyst and this oxygen sensor 1
When the two are new, the characteristics of Nos. 2 and 13 are substantially the same as shown in FIG. Reference numeral 14 is an ignition plug provided in the cylinder of the gas engine, and 15 is a rotation speed sensor for detecting the rotation speed NE of the gas engine. An electronic control device (EC) 20 sets a control amount of the control valve 8, the spark plug 14 and the like and outputs a control signal according to the control amount.
U). As is well known, the ECU 20 is a central processing unit (CPU) that performs various calculations.
20a, a read-only read-only memory (ROM) 20b in which a control program and the like are stored, a writable / readable random access memory (RAM) 20c in which operation data and the like are temporarily stored, and an analog signal An analog-digital converter (ADC) 20d for converting into a digital signal, an input boat 20e for taking in sensor signals from the various sensors described above into the ECU 20, an output boat 20f for outputting control signals to the various actuators described above, and the like. And a bus 20g interconnecting the two.

The above is the hardware configuration of the present application, but the configuration of the air-fuel ratio control processing is shown in FIG. 2 as a block diagram.
As shown in the figure, the air-fuel ratio control device of the present application includes a processing system from the first oxygen sensor 12 and a processing system from the second oxygen sensor 13. First, the system from the second oxygen sensor 13 will be described. This is to calculate the delay times TDR1 and TDL1 as the control constants in the air-fuel ratio feedback control from the second output V2 of the second oxygen sensor 13. The control constant calculation means 501 of the flow shown in FIGS. Further, the system from the first oxygen sensor 12 will be described. This is a characteristic configuration of the present application, that is, the detection means 502 and the comparison reference value correction means 50.
3, and an air-fuel ratio correction amount calculation means 504. Here, the detecting means 502 will be described later with reference to FIG.
0, as shown in FIG. 12, the first output V1 that is the output of the first oxygen sensor 12 has a rich side operation time that is higher than the first comparison reference value VR1 and a lean side operation time that is low. And the comparison reference value correction means 5
03 is a value that makes the ratio R of the rich side operation time and the lean side operation time 1 or almost 1, and the first comparison reference value V
R1 is set. Further, with respect to the first comparison reference value VR1 determined in this way, the air-fuel ratio correction amount FAF1 is previously described according to the difference between the first comparison reference value VR1 and the first output V1 and the delay time. It is obtained from the air-fuel ratio correction amount calculation means 504 according to the flow shown in FIGS. The air-fuel ratio of the engine 1, which is a combustion engine, is adjusted by the air-fuel ratio adjusting means 505 according to the obtained air-fuel ratio correction amount. The injection amount calculation routine in the air-fuel ratio adjusting means 505 is shown in FIG. Although the above is the basic configuration, as shown by the broken line in FIG.
Instead of 02, in the region consisting of the first output V1 and time, the first output V1 is higher than the first comparison reference value VR1 and the rich side operation region sandwiched between the first output V1 and the reference value VR1. A quadrature means 506 for detecting the area and a lean side operation area area which is at a low value and is similarly sandwiched between the first output V1 and the reference value VR1 is provided, and the comparison reference value correction means 503 is set to the rich side operation area. The first comparison reference value VR1 may be set to a value that makes the ratio of the area and the lean side operation region area to 1 or almost 1.

Each routine will be described below.
FIG. 3 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, 360 °. R in step 301
The intake air amount data Q and the rotation speed data Ne are read from the AM 20c to calculate the basic injection amount TAUP. For example, TAUP ← K × Q / Ne (K is a constant). In step 302, the cooling water temperature data THW is read from the RAM 20c.
Is read out and the warm-up increase value FWL is interpolated by the one-dimensional map stored in the ROM 20b. In step 303, the final injection amount TAU is calculated by TAU ← TAUP × FAF1 × (FWL + α) + β. Note that α and β are correction amounts determined by other operating state parameters. Here, FAF1 is an air-fuel ratio correction coefficient as an air-fuel ratio correction amount determined from the first feedback control routine shown in FIGS. Next, at step 304, the fuel is injected to the fuel injection operation side by the injection amount TAU. In this way,
In step 305, this routine ends.

FIGS. 4 and 5 show a first feedback control routine for calculating the air-fuel ratio correction coefficient FAF1 based on the output of the first oxygen sensor 12, which is executed every predetermined time, for example, 4 ms. At step 401, it is judged if the closed loop (feedback) condition of the air-fuel ratio by the first oxygen sensor 12 is satisfied. During the engine start, during the fuel increase operation after the start, during the warm-up increase operation, during the power increase operation, during the lean control, when the first oxygen sensor 12 is in the inactive state, etc., the closed loop condition is not satisfied,
In other cases, the closed loop condition is satisfied. The RAM 20c is used to determine whether the first oxygen sensor 12 is active or inactive.
The water temperature data THW is read to determine whether or not THW ≧ 70 ° C. has once been reached, or the first oxygen sensor 1
This is done by determining whether the output level of 2 has once risen or falled. When the closed loop condition is not satisfied, the routine proceeds to step 417, where the air-fuel ratio correction coefficient FAF1 is set to 1.0.
And On the other hand, if the closed loop condition is satisfied, step 40
Go to 2. In step 402, after the first output V1 of the first oxygen sensor 12 is binarized to obtain an A / F1 signal (see FIG. 6A), it is A / D converted and captured, and in step 403 V1 Is the first comparison reference value VR1
For example, it is determined whether it is 0.45 V or less. That is, it is determined whether the air-fuel ratio is rich or lean. Lean (V1 ≦ V
R1), the first delay counter CDLY1 is decremented by 1 in step 404, and steps 405 and 406 are executed.
The first delay counter CDLY1 to the minimum value TDR
Guard with 1. The minimum value TDR1 is a rich delay time for holding the determination that the output is the lean state even if the output of the first oxygen sensor 12 changes from lean to rich, and is defined as a negative value. . On the other hand, if it is rich (V1> VR1), the first delay counter CDLY1 is incremented by 1 in step 407, and step 40 is performed.
At 8,409, the first delay counter CDLY1 is guarded with the maximum value TDL1. It should be noted that the maximum value TDL1 is a lean delay time for holding the determination that the output is in the rich state even when the output of the first oxygen sensor 12 changes from rich to lean, and is defined by a positive value. . Here, the reference of the first delay counter CDLY1 is set to 0, the air-fuel ratio after delay processing is considered rich when CDLY1> 0, and the air-fuel ratio after delay processing is considered lean when CDLY ≦ 0. To do. That is, these are delay times as feedback control constants.

At step 410, it is judged if the sign of the first delay counter CDLY1 is reversed, that is, if the air-fuel ratio after the delay processing is reversed. If the air-fuel ratio is reversed, it is determined in step 411 whether the reversal from rich to lean or the reversal from lean to rich. If it is the inversion from rich to lean, it is increased in a skip manner as FAF1 ← FAF1 + RS1 in step 412. Conversely, if it is the inversion from lean to rich, FAF1 ← FAF1-RS1 in step 413.
And reduce like a skip. That is, step processing is performed. In step 410, the first delay counter CDL
If the sign of Y1 is not inverted, steps 414, 4
Integral processing is performed at 15,416. That is, step 4
At 14, it is determined whether or not CDLY1 <0, and CDLY1
If ≦ 0 (lean), FAF1 ← in step 415
FAF1 + KI1. On the other hand, if CDLY1> 0 (rich), FAF1 ← FAF1 + in step 416.
It is KI1. Here, the integration constant KI1 is set to be sufficiently smaller than the skip constant RS1, that is, KI
1 << RS1. Therefore, step 415 gradually increases the fuel injection amount in the lean state (CDLY1 ≦ 0), and step 916 gradually reduces the fuel injection amount in the rich state (CDLY1> 0). Steps 412 and 41
Air-fuel ratio correction coefficient FA calculated at 3,415,416
F1 has a minimum value of 0.8 and a maximum value of 1.
2, the air-fuel ratio correction coefficient FAF1 becomes too large or too small for some reason, and the air-fuel ratio of the engine is controlled by that value to cause overrich or over lean. prevent. The FAF1 calculated as described above is stored in the RAM 20c, and this routine ends at step 418.

FIG. 6 is a timing chart for supplementarily explaining the operation according to the flow charts of FIGS. When the air-fuel ratio signal A / F1 for rich / lean determination is obtained from the output of the first oxygen sensor 12 as shown in FIG. 6 (a), the first delay counter CDLY1 is rich as shown in FIG. 6 (b). The state is counted up, and the lean state is counted down. As a result, as shown in FIG. 6C, the delayed air-fuel ratio signal A / F1 ′ is formed. For example, even if the air-fuel ratio signal A / F1 changes from lean to rich at time t ₁ , the delayed air-fuel ratio signal A / F1 ′ is held lean for the rich delay time (−TDR1) and then It changes to rich at t ₂ . Be changed from the air-fuel ratio signal A / F1 is rich at time t ₃ to lean, the delayed air-fuel ratio signal A / F1 'is at time t ₄ after being held rich only equivalent lean delay time TDL1 Change to lean. However, the air-fuel ratio signal A / F
1 indicates the rich delay time (-T) at times t ₅ , t ₆ , and t _7.
If it is inverted in a shorter period than DR1), it takes time for the first delay counter CDLY1 to cross the reference value 0. As a result, at the time t _{8, the} delayed air-fuel ratio signal A
/ F1 'becomes more stable than the air-fuel ratio signal A / F1 before the delay processing. In this way, the air-fuel ratio correction coefficient FAF1 shown in FIG. 6D is obtained based on the stable air-fuel ratio signal A / F1 ′ after the delay processing.

Next, the second feedback routine for determining the delay time as the air-fuel ratio feedback control constant will be described with reference to FIGS. 7 and 8 are the second
Based on the output of the oxygen sensor 13, the delay time TDR1,
It is an air-fuel ratio feedback control routine that calculates TDL1, and is executed every predetermined time, for example, every 1 second. In step 601, it is determined whether or not the catalyst of the catalytic converter 12 is deteriorated, and also it is determined whether or not the closed loop condition of the air-fuel ratio is satisfied (this catalyst deterioration is detected by a deterioration detection mechanism separately provided). Done and the results are used). If the catalyst described as F / B condition in the drawing is deteriorated or if the closed loop condition is not satisfied, the routine proceeds to steps 623 and 624, where the rich delay time T
DR1 and lean delay time TDL1 are set to constant values. For example, TDR1 ← -12 (equivalent to 48 ms) TDL1 ← 6 (equivalent to 24 ms). Here, the rich delay time (-TDR1) is set to be larger than the lean delay time TDL1 because the comparison voltage VR1 is set to a low value, for example, 0.45V on the lean side. The catalyst has not deteriorated,
If the closed loop condition is satisfied, the process proceeds to step 602.

The rich / lean determination is made in step 603 by comparing the second output V2 with the second comparison reference value VR2. The result of this determination is delayed in steps 604-609. Then, the rich / lean discrimination subjected to the delay processing is performed in step 610. Step 61
At 0, the second delay counter CDLY2 is set to CDLY2.
It is determined whether or not ≤0. As a result, if CDLY2≤0, the air-fuel ratio is determined to be lean, and steps 611 to 61 are executed.
6, and on the other hand, if CDLY2> 0, it is determined that the air-fuel ratio is rich, and the routine proceeds to steps 617-622. In step 611, TDR1 ← TDR1-1, that is,
The rich delay time (-TDR1) is increased to further delay the change from rich to lean to shift the air-fuel ratio to the rich side. In steps 612 and 613, TDR1 is guarded with the minimum value TR1. Here, TR1 is also a negative value, and therefore (-TR1) means the maximum rich delay time. Further, in step 614, TDL1 ← T
DL1-1, that is, the lean delay time TDL1 is reduced, the delay of the change from lean to rich is reduced, and the air-fuel ratio is shifted to the rich side. Steps 615, 61
At 6, TDL1 is guarded by the minimum value TL1. Here, TL1 is a positive value, so TL1 means the minimum lean delay time. In step 617, the TDR
1 ← TDR1 + 1, that is, the rich delay time (-T
DR1) is decreased to reduce the delay in the change from rich to lean to shift the air-fuel ratio to the lean side. In steps 618 and 619, TDR1 is guarded with the maximum value TR1. Here, TR2 is also a negative value, and therefore (-T
R2) means the minimum rich delay time. Further, in step 620, TDL1 ← TDL1 + 1, that is,
The lean delay time TDL1 is increased to further delay the change from lean to rich to shift the air-fuel ratio to the lean side. In steps 621 and 622, TDL1 is guarded with the maximum value TL2. Here, TL2 means the maximum lean delay time. TDR1, calculated as described above
After the TDL1 is stored in the RAM 20c, step 6
At 25, this routine ends. Note that step 62
3, 624, TDR1 and TDL1 are set to constant values, but values immediately before the air-fuel ratio feedback is stopped, average values, or other parameters such as Ne, Q, intake air pressure,
It may be a value according to the exhaust temperature or the like. FAF1, TDR1, TDL1 calculated during air-fuel ratio feedback can be converted to other values FAF1 ', TDR1', TDL1 'and stored in the backup RAM, thereby improving drivability at the time of restart, etc. Is useful for.

FIG. 9 is a timing chart of the delay times TDR1 and TDL1 obtained by the flow charts of FIGS. 4, 5, 7 and 8. As shown in FIG. 9A, when the output voltage V2 of the second oxygen sensor 13 changes, FIG.
As shown in, the delay times TDR1 and TDL1 are both increased in the lean state (V2 ≦ VR2), while the delay times TDR1 and TDL1 are both reduced in the rich state. At this time, both TDR1 and TDL1 are reduced. At this time, TDR1 changes in the range of TR1 to TR2, and TDL1 changes in the range of TL1 to TL2. When the catalyst of the catalytic converter 12 has deteriorated, FIG.
Control of TDR1 and TDL1 of
Hold at R1 = -12 and TDL1 = 6. In addition,
The first air-fuel ratio feedback control is performed every 4 ms,
The second air-fuel ratio feedback control is performed every 1 s. The air-fuel ratio feedback control is mainly performed by the control of the first oxygen sensor having a good responsiveness, and the control of the second oxygen sensor having a poor responsiveness is performed as a subordinate. To do so.

Although the above is the basic configuration, in the present application, the detecting means 502 (or the quadrature calculating means 506) is provided as described above, and the first comparison reference value is based on the detection results. The comparison reference value correction means 503 for correcting the comparison voltage VR1 is provided. This routine is shown in FIG. 12, which is performed, for example, every 10 cycles and every 1 minute. In step 1001, the first output V1 of the first oxygen sensor 12 is A / D converted and taken in. Then, in step 1002, the time h when the first output V1 is higher than the first comparison reference value VR1 and the time i when it is lower than the first comparison reference value VR1 are obtained based on the stored waveform of the first output V1. These times are shown in FIG. Then, in step 1003,
The ratio R = h / i of these times is determined. Then, in step 1004, R is in a predetermined value range (0.9
.About.1.1). Step 1
When R is in the predetermined range in 004, the routine is finished as it is. On the other hand, when R is not within the predetermined range, the first comparison reference value VR1 is increased or decreased (Δ
VR1 addition or subtraction) steps 1005, 10
06, 1007. By repeating this routine, R falls within a predetermined range in the configuration of the present application.

FIGS. 10A and 10B show the output waveform of the first oxygen sensor and the control state of the air-fuel ratio when the control is performed by the air-fuel ratio control device of the present application. here,
(A) shows the case where the catalyst is in a relatively new state,
(B) shows that there is a considerable time lapse. FIG.
At 0 (b), VR1 is the first comparison reference value.
a is the initial one, and VR1b is the one after correction. As a result, in the case of this example, it can be seen that R does not significantly change as compared with that shown in FIG. Here, when the relationship between the effective range of the catalyst and the first comparison reference values VR1a and VR1b for the first oxygen sensor is shown, the values change as shown in FIG.

Further, the time lapse (8000h, 16) in the conventional air-fuel ratio control device and the air-fuel ratio control device of the present application
The experimental results of the load fluctuation state of the engine after 000 h) are shown below. The thing shown in Table 1 shows the thing of a 100 kW gas engine, and the thing shown in Table 2 shows the thing of a 450 kW gas engine.

[0029]

[Table 1]

[0030]

[Table 2] As a result, it can be seen that the load fluctuation of the engine can be greatly suppressed by adopting the configuration of the present application.

[Other Embodiment] Another embodiment of the present application will be described below. (A) In the above embodiment, an example in which a pair of oxygen sensors is used for the catalytic converter has been shown, but this may use a NOx sensor, a CO sensor, etc. on the downstream side of the catalyst. (B) In the above embodiment, the rich delay time TDR1 and the lean delay time TDL1 are both calculated as the delay time. However, the control constant calculating means 501 calculates either one of them. It may be calculated. In this case, responsiveness is poor, but tentative control is possible. (C) Furthermore, in the above-mentioned embodiment, an example in which the configuration of the present application is adopted for the treatment of exhaust gas from a gas engine has been shown. However, as a vehicle that performs exhaust gas treatment with air-fuel ratio control, automobiles, tractors, etc. Therefore, the device of the present application is generally applicable to combustion engines.

It should be noted that although reference numerals are given in the claims for convenience of comparison with the drawings, the present invention is not limited to the configuration of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a diagram showing a gas engine air-fuel ratio control configuration adopting an air-fuel ratio control device of the present application.

FIG. 2 is a block diagram showing a configuration of gas engine air-fuel ratio control.

FIG. 3 is a diagram showing a fuel injection amount calculation routine.

FIG. 4 is a diagram showing an air-fuel ratio feedback control routine.

FIG. 5 is a diagram showing an air-fuel ratio feedback control routine.

FIG. 6 is a timing chart of the routine shown in FIGS. 4 and 5.

FIG. 7 is a diagram showing an air-fuel ratio feedback control routine related to delay time.

FIG. 8 is a diagram showing an air-fuel ratio feedback control routine relating to delay time.

9 is a timing diagram of the routine shown in FIGS. 7 and 8. FIG.

FIG. 10 is a diagram showing an output of the first air-fuel ratio sensor of the present application and a state of corresponding air-fuel ratio control.

11 is a diagram showing the relationship between the air-fuel ratio and the sensor output in FIG.

FIG. 12 is a diagram showing a routine for correcting a first comparison reference value.

FIG. 13 is a diagram showing an output of a conventional first air-fuel ratio sensor and a state of corresponding air-fuel ratio control.

14 is a diagram showing the relationship between the air-fuel ratio and the sensor output in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Combustion engine 11 Catalytic converter 12 1st air-fuel ratio sensor 13 2nd air-fuel ratio sensor 501 Control constant calculation means 502 Detection means 503 Comparison reference value correction means 504 Air-fuel ratio correction amount calculation means 505 Air-fuel ratio adjustment means V1 1st output V2 1st 2 outputs VR1 1st comparison reference value TDR1 delay time TDL1 delay time FRF1 air-fuel ratio correction amount

Claims (7)

[Claims] 1. An upstream side of the catalytic converter (11) and a downstream side of the catalytic converter (11) with respect to an exhaust gas purifying catalytic converter (11) provided in an exhaust system of a combustion engine (1). , A first air-fuel ratio sensor (12) and a second air-fuel ratio sensor (13) for detecting the concentration of a specific component in the exhaust gas are separately provided, and the both air-fuel ratio sensors (1
2) A configuration in which air-fuel ratio feedback control for the combustion engine (1) is performed by the output of (13), and the delay time (TDR1, TDL1) as a control constant in the air-fuel ratio feedback control is set to the second air-fuel ratio sensor ( 13) a control constant calculation means (501) for calculating according to the second output, a first comparison reference value (VR1) and the first air-fuel ratio sensor (1).
2) difference from the first output (V1) and the delay time (TD)
R1, TDL1) and the air-fuel ratio correction amount (FRF1)
Air-fuel ratio control means (504) for calculating the air-fuel ratio correction amount, and air-fuel ratio adjustment means (505) for adjusting the air-fuel ratio (R) of the engine according to the air-fuel ratio correction amount (FRF1). A device, wherein the first output (V1) is the first comparison reference value (VR
Detection means (502) for detecting the rich side operation time which is higher than 1) and the lean side operation time which is lower than 1).
Is set to a value that makes the ratio of the rich side operation time and the lean side operation time 1 or almost 1, and the first comparison reference value (V
An air-fuel ratio control device comprising a comparison reference value correction means (503) for setting R1). 2. An upstream side of the catalytic converter (11) and a downstream side of the catalytic converter (11) with respect to an exhaust gas purifying catalytic converter (11) provided in an exhaust system of a combustion engine (1). , A first air-fuel ratio sensor (12) and a second air-fuel ratio sensor (13) for detecting the concentration of a specific component in the exhaust gas are separately provided, and the outputs of the both air-fuel ratio sensors (12) and (13) are used to A configuration for performing air-fuel ratio feedback control for the combustion engine (1), the delay time (TDR1, TDL1) as a control constant in the air-fuel ratio feedback control, the second output (V2) of the second air-fuel ratio sensor (13) Control constant calculation means (501) that calculates according to the first comparison reference value (VR1) and the first air-fuel ratio sensor (1
2) difference from the first output (V1) and the delay time (TD)
R1, TDL1), an air-fuel ratio correction amount calculation means (504) for calculating an air-fuel ratio correction amount, and an air-fuel ratio adjustment means for adjusting the air-fuel ratio of the combustion engine (1) according to the air-fuel ratio correction amount. (505) and an air-fuel ratio control device comprising: a first output (V1) and time;
The first output (V1) is the first comparison reference value (VR1)
The rich side operation region area having a higher value and being the area of the region surrounded by the first output (V1) and the first comparison reference value (VR1) and the first output (V1) are the first Quadrature means for detecting a lean side operation area area which is lower than the comparison reference value (VR1) and which is the area of the area surrounded by the first output (V1) and the first comparison reference value (VR1). (506) is provided, and the ratio (R) of the rich side operation region area and the lean side operation region area is 1 or almost 1.
An air-fuel ratio control device comprising a comparison reference value correction means (503) for setting the first comparison reference value (VR1) to a value that 3. The air-fuel ratio control device according to claim 1, wherein both the first air-fuel ratio sensor (12) and the second air-fuel ratio sensor (13) are oxygen sensors. 4. The delay time (TDR1, TDL) when combustion in the combustion engine (1) occurs over a lean combustion state with insufficient fuel and a rich combustion state with excessive fuel.
1) is representative of the feedback control by delaying the change between the combustion states, and includes the second comparison reference value (VR2) and the second comparison of the second air-fuel ratio sensor (13).
Based on the difference from the output (V2), the delay time (TDR
The air-fuel ratio control device according to claim 1 or 2, wherein (1, TDL1) is required. 5. The rich delay time (TDR1), which is the delay time when the combustion in the combustion engine (1) changes from the lean combustion state to the rich combustion state, as the delay time, and the rich combustion state. The lean delay time (TDL1) which is the delay time when the lean combustion state is changed to the lean combustion state, and the control constant calculation means (501) compares the rich delay time (TDR1) or the lean delay time (TDL1). The air-fuel ratio control device according to claim 4, which calculates one or both of them. 6. The air-fuel ratio control device according to claim 1, wherein the ratio (R) is set between 0.9 and 1.1. 7. The combustion engine (1) uses combustion gas containing methane as a main component as fuel.
The air-fuel ratio control device described.