JP3232902B2 - 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 controls the air-fuel ratio of air and fuel supplied to the internal combustion engine according to the operating state of the engine.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine, in order to optimize various performances such as output performance, exhaust characteristics, and drivability under all operating conditions, the ratio of air to fuel of a supplied air-fuel mixture, that is, Control of the air-fuel ratio has been performed. This control is based on the fact that the actual air-fuel ratio
This is performed by controlling the fuel supply amount so as to match the target air-fuel ratio that changes according to the load state, the warm-up state, and the like.

As one example, Japanese Patent Application Laid-open No. Sho 58-27
In the air-fuel ratio control method disclosed in Japanese Patent No. 848, the oxygen concentration in the exhaust gas discharged from the engine is detected by an oxygen sensor. An air-fuel ratio correction value is calculated by performing a proportional correction and an integral correction by a computer based on the detected value, and the actual air-fuel ratio is corrected to the target air-fuel ratio by correcting the fuel supply amount to the engine based on the correction value. To match. Here, the proportional constant and the integral constant when the detection value of the oxygen sensor is corrected for the proportional correction and the integral correction are not fixed values, and at least one of them is variably controlled according to the warm-up state of the engine. .

[0004]

However, in the above-mentioned conventional control method, the deviation between the actual air-fuel ratio and the target air-fuel ratio was not taken into account in setting the proportional constant and the integral constant. For this reason, the follow-up of the air-fuel ratio correction value with respect to the deviation of the air-fuel ratio is not good, and a delay occurs until the actual air-fuel ratio matches the target air-fuel ratio, which tends to cause deterioration of the exhaust characteristics. .

[0005] For example, a generally performed proportional correction (PC)
FIG. 7 is a time chart showing the operation of the integral correction (IC). That is, in a steady operation state in which the engine is operated at a constant rotation speed and a constant load, whether the detected value (Ox) of the oxygen sensor is rich indicating a high fuel concentration or lean indicating a low fuel concentration. Is determined, the air-fuel ratio correction value (FAF) is subjected to proportional correction (PC) based on a predetermined proportional constant value (skip value). afterwards,
Until the determination of the detection value (Ox) is reversed, the air-fuel ratio correction value (FAF) is subjected to integration correction (IC) based on the value (slope) of a predetermined integration constant.

Here, as shown in FIG. 1, at time t1, when the throttle valve opening (TA) changes from a certain opening state to an opening of "0%" and the engine shifts from steady operation to deceleration operation. Then, the amount of deviation between the actual air-fuel ratio and the target air-fuel ratio temporarily increases. Therefore, after that, the proportional correction (P
If the value (slope) of the integration constant in the integration correction (IC) after C) is simply kept constant, it takes a relatively long time to eliminate the deviation of the air-fuel ratio, and the air-fuel ratio correction value ( F
There is a delay before AF) is optimized. as a result,
There is a problem that a delay occurs until the fuel supply amount to the engine becomes an appropriate value, and the amount of hydrocarbons (HC) in the exhaust gas once increases.

In order to cope with such a problem, it is conceivable to previously set the integral constant and the proportional constant to large values. However, if the constants are simply increased, when the deviation amount of the air-fuel ratio is small, the air-fuel ratio correction value may be corrected more than necessary, leading to a phenomenon such as hunting.

The present invention has been made in view of the above-mentioned circumstances, and has as its object to change the air-fuel ratio correction value (product).
Minute time constant) according to the elapsed time since the latest proportional correction
By changing the air-fuel ratio to the target air-fuel ratio properly and promptly
It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine which is made to match the engine speed and to prevent deterioration of the exhaust characteristics of the engine.

[0009]

In order to achieve the above-mentioned object, according to the present invention, as shown in FIG. 1, the air-fuel ratio of air and fuel supplied to an internal combustion engine M1 is controlled by the operation of the internal combustion engine M1. An air-fuel ratio control device for controlling the amount of fuel to be supplied to an internal combustion engine M1 by a fuel supply means M2 in order to match a target air-fuel ratio according to a state, wherein exhaust gas discharged from the internal combustion engine M1 A concentration detecting means M3 for detecting the concentration of a specific component in the air and a proportional correction based on a detection value of the concentration detecting means M3 and a proportional correction based on a proportional constant followed by an integral correction based on an integration constant to obtain an air-fuel ratio Correction value calculating means M4 for calculating the air-fuel ratio correction value according to the above, and the correction value calculating means M4
In an air-fuel ratio control device for an internal combustion engine, comprising a fuel amount correcting means M5 for correcting the amount of fuel to be supplied to the internal combustion engine M1 in accordance with the calculated value of The purpose is to provide an integration time constant variable means M6 for increasing the integration time constant as time elapses after the latest proportional correction is performed.

[0010]

According to the above arrangement, as shown in FIG. 1, the correction value calculating means M4 performs a proportional correction based on the detected value of the density detecting means M3 with a proportional constant, and then performs an integral correction with an integration time constant. Is performed, the air-fuel ratio correction value is calculated. Here, the integration time constant is increased by the integration time constant varying means M6 as time passes after the proportional correction is performed. Then, in the fuel amount correcting means M5, the fuel amount to be supplied to the internal combustion engine M1 is corrected by the fuel supplying means M2 according to the calculated air-fuel ratio correction value.

Therefore, the integration time constant is increased in accordance with the amount of deviation between the actual air-fuel ratio and the target air-fuel ratio. If the amount of deviation of the air-fuel ratio is large, the correction value of the air-fuel ratio will increase over time. The value is gradually increased accordingly to reach an appropriate value. Therefore, the correction delay until the actual air-fuel ratio matches the target air-fuel ratio is shortened. On the other hand, when the deviation amount of the air-fuel ratio is small, the air-fuel ratio correction value is corrected to be relatively small at first, and reaches an appropriate value. Therefore, the actual air-fuel ratio is not excessively corrected with respect to the target air-fuel ratio.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention will be described in detail with reference to FIGS.

FIG. 2 is a schematic configuration diagram showing a gasoline engine system including an air-fuel ratio control device of an internal combustion engine mounted on an automobile in this embodiment. A plurality of cylinder bores 3 are formed in a cylinder block 2 constituting the engine 1 as an internal combustion engine. A cylinder head 4 is provided above the cylinder block 2 so as to close each cylinder bore 3.
Is assembled. A piston 5 is attached to each cylinder bore 3 so as to be vertically movable, and the piston 5 is connected to a crankshaft 1 a via a connecting rod 6. Inside the cylinder bore 3, a space surrounded by the piston 5 and the cylinder head 4 is a combustion chamber 7.

The cylinder head 4 is provided with an ignition plug 8 corresponding to each of the combustion chambers 7. The head 4 is provided with an intake port 9 and an exhaust port 10 communicating with each combustion chamber 7. Each port 9, 1
0 is connected to an intake passage 11 and an exhaust passage 12 respectively. Each of the ports 9 and 10 is provided with an intake valve 13 and an exhaust valve 14 for opening and closing, respectively. Each of the valves 13 and 14 is driven by a valve train (not shown) including a camshaft in conjunction with the rotation of the crankshaft 1a. The timing for opening and closing the valves 13 and 14 is synchronized with the rotation of the crankshaft 1a. That is, the valves 13 and 14 are opened and closed at a predetermined timing in synchronization with a series of strokes of an intake stroke, a compression stroke, an explosion / expansion stroke, and an exhaust stroke of the engine 1.

An air cleaner 1 is provided on the inlet side of the intake passage 11.
5 are provided. A surge tank 16 for smoothing the pulsation of air passing through the intake passage 11 is provided in the middle of the intake passage 11. On the downstream side of the surge tank 16, near the intake ports 9 corresponding to the respective cylinder bores 3, fuel injectors 17 as fuel supply means in the present invention are provided. Fuel in a fuel tank (not shown) is pumped to these injectors 17 by a fuel pump (not shown). By controlling the injector 17 based on a predetermined command signal, the amount and timing of fuel injection to the intake port 9 are controlled. That is, fuel injection amount control is performed. On the outlet side of the exhaust passage 12, a catalytic converter 18 having a built-in three-way catalyst for purifying exhaust gas is provided.

The outside air taken in from the air cleaner 15 is introduced into the intake passage 11. Each injector 1
The fuel injected from 7 forms a mixture with the outside air.
This air-fuel mixture is taken into the combustion chamber 7 when the intake valve 13 is opened during the intake stroke of the engine 1. Thereafter, when the ignition plug 8 operates in the combustion chamber 7, the air-fuel mixture burns, the piston 5 operates, and the driving force is obtained in the engine 1. The exhaust gas after combustion is guided to the exhaust passage 12 when the exhaust valve 14 is opened in the exhaust stroke of the engine 1, is purified by the catalytic converter 18, and is discharged to the outside.

On the upstream side of the surge tank 16, there is provided a throttle valve 19 which operates in conjunction with the operation of an accelerator pedal (not shown). By adjusting the opening degree (throttle opening degree) TA of the valve 19, the amount of outside air taken into the intake passage 11, that is, the intake air amount Q is adjusted.

In the vicinity of the throttle valve 19, a throttle sensor 31 is provided. The sensor 31 detects the throttle opening TA and outputs a signal corresponding to the detection result. The sensor 31 includes a well-known idle switch (not shown). This idle switch is turned "ON" when the throttle valve 19 is fully closed, and outputs an idle signal IDL indicating this. The air flow meter 3 is located downstream of the air cleaner 15.
2 are provided. The meter 32 detects the amount of intake air Q taken into the intake passage 11 and outputs a signal corresponding to the detection result. An intake air temperature sensor 33 is provided near the air cleaner 15. The sensor 33 detects the temperature of the intake air (intake temperature) THA taken into the intake passage 11 and outputs a signal corresponding to the detection result.

In the middle of the exhaust passage 12, there is provided an oxygen sensor 34 as a concentration detecting means in the present invention. The sensor 34 detects an oxygen concentration Ox as a concentration of a specific component in the exhaust gas discharged from the engine 1,
A signal corresponding to the detection result is output. This sensor 34
Is used for air-fuel ratio control in the present invention. That is, in order to match the air-fuel ratio of air and fuel supplied to the engine 1 with a target air-fuel ratio corresponding to the operating state of the engine 1, the amount of fuel to be supplied to the engine 1 by the injector 17 is detected by the sensor 34. It is controlled based on the result.

A water temperature sensor 35 is provided on the cylinder block 2.
Is provided. The sensor 35 detects the temperature (cooling water temperature) THW of the cooling water of the engine 1 and outputs a signal corresponding to the detection result.

Spark plugs 8 corresponding to each cylinder bore 3
, The ignition signal distributed by the distributor 20 is applied. The distributor 20 distributes the high voltage output from the igniter 21 to each spark plug 8 in synchronization with the rotation angle of the crankshaft 1a, that is, the crank angle (CA). The ignition timing of each ignition plug 8 is determined by the output timing of the high voltage output from the igniter 21. Then, by controlling the igniter 21 based on a predetermined command signal, the ignition timing of the ignition plug 8 is controlled. That is, ignition timing control is performed.

The distributor 20 has a built-in rotor (not shown) that rotates in conjunction with the rotation of the crankshaft 1a. The distributor 20 is provided with a rotation speed sensor 36 and a cylinder discrimination sensor 37. The rotation speed sensor 36 detects the rotation speed NE of the engine 1 (engine rotation speed) NE from the rotation of the rotor, and outputs a signal corresponding to the detection result. Cylinder discrimination sensor 37
Detects a reference position at a crank angle from the rotation of the rotor at a predetermined ratio, and outputs a reference signal GP indicating the detection result. In this embodiment, it is assumed that the crankshaft 1a makes two rotations during a series of strokes of the engine 1, and the rotation speed sensor 36 detects the crank angle at a rate of 30 ° per pulse. The cylinder angle sensor 37 detects the crank angle at a rate of 360 ° per pulse.

In this embodiment, an electronic control unit (EC
U) 51 inputs signals detected by the sensors 31 to 37 described above. The ECU 51 executes the ignition timing control, the fuel injection amount control, the air-fuel ratio control, and the like of the engine 1 based on these detection signals.
Each injector 17 and igniter 21 are controlled. In this embodiment, the ECU 51 constitutes a correction value calculating means, a fuel amount correcting means and an integral time constant varying means in the present invention.

As shown in the block diagram of FIG.
1 is a central processing unit (CPU) 52, a read-only memory (R
OM) 53, random access memory (RAM) 54,
A backup RAM 55 and a timer counter 56 are provided. In the ECU 51, these units 52 to 56, an external input circuit 57, an external output circuit 58, and the like are connected by a bus 59 to form a theoretical operation circuit.

The ROM 53 stores the above-described ignition timing control,
Predetermined programs related to fuel injection amount control, air-fuel ratio control, idle speed control, and the like are stored in advance. R
The calculation result of the CPU 52 and the like are temporarily stored in the AM 54. The backup RAM 55 stores data stored in advance. The timer counter 56 can perform a plurality of counting operations at the same time.

The external input circuit 57 is connected to the sensors 31 to 37 described above. The injector 17 and the igniter 21 are connected to the external output circuit 58, respectively. Then, the CPU 52 outputs each sensor 31 to 37 input via the external input circuit 57.
Is read as an input value. The CPU 51 controls the members 17, 21 and the like based on the input values.

Next, in the above gasoline engine system, of the various controls executed by the ECU 51,
The processing content of the air-fuel ratio control including the fuel injection amount control will be described with reference to FIGS.

FIG. 4 is a flowchart showing a "fuel injection amount calculation routine" executed by the ECU 51, which is periodically executed at predetermined intervals. When the process proceeds to this routine, first, in step 100, the values of the intake air amount Q, the intake air temperature THA, the cooling water temperature THW, and the engine speed NE are read based on the detection signals of the sensors 32, 33, 35, and 36, respectively. Put in.

Subsequently, in step 110, a basic injection amount TAUb is calculated based on the values of the intake air amount Q and the engine speed NE. This basic injection amount TAU
b is calculated by a known method with reference to a predetermined map (not shown). In this embodiment, this step 11
The ECU 51 executing the process 0 corresponds to a basic injection amount calculating means for calculating the basic injection amount TAUb according to the operating state of the engine 1.

Next, at step 120, the intake air temperature T
Based on the values of the HA and the cooling water temperature THW, the basic injection amount TA
A temperature correction value KTH for correcting Ub according to the degree of the intake air temperature THA and the cooling water temperature THW is calculated. This temperature correction value KTH is calculated by a known method with reference to a predetermined map (not shown). In this embodiment, the ECU 51 that executes the process of step 120 corresponds to a temperature correction value calculation unit for calculating a temperature correction value KTH according to a temperature condition.

Next, at step 130, the air-fuel ratio correction value FA relating to the air-fuel ratio A / F supplied to the engine 1 is determined.
Read F. This correction value FAF is calculated by a separate “air-fuel ratio correction value calculation routine” described later. This correction value FAF is for correcting the basic injection amount TAUb so that the actual air-fuel ratio A / F matches the target air-fuel ratio.

Thereafter, in step 140, each parameter TA obtained in each of the above steps 110 to 130 is obtained.
The target injection amount TAU is calculated by multiplying Ub, KTH, and FAF. That is, in this step 140,
The final target injection amount TAU to be supplied to the engine 1 is calculated by correcting the value of the basic injection amount TAUb based on the temperature correction value KTH and the air-fuel ratio correction value FAF. In this embodiment, the ECU 51 that executes the process of step 140 corresponds to the fuel amount correction unit in the present invention, and also corresponds to the target injection amount calculation unit for calculating the target injection amount TAU to be supplied to the engine 1. .

In step 150, the target injection amount TAU obtained this time is temporarily stored in the RAM 54,
Thereafter, the processing is temporarily terminated. Thereafter, the ECU 51 executes the processing in the RAM 54 according to a separate processing routine (not shown).
By driving each injector 17 based on the value of the target injection amount TAU read out from the above, fuel injection from each injector 17 to the intake port 9 is executed. The details of the processing relating to the execution of the fuel injection are generally well-known techniques, and thus description thereof is omitted here.

Next, the calculation of the air-fuel ratio correction value FAF used in the aforementioned "fuel injection amount calculation routine" will be described. FIG. 5 is a flowchart showing an “air-fuel ratio correction value calculation routine” executed by the ECU 51, which is periodically executed at predetermined intervals.

When the process proceeds to this routine, first, at step 200, the value of the oxygen concentration Ox is read based on the detection signal of the oxygen sensor 34. Then, step 2
At 10, it is determined whether or not the actual value of the air-fuel ratio A / F is rich indicating a high fuel concentration based on the value of the oxygen concentration Ox. In this embodiment, the determination in step 210 is made with a delay of a predetermined delay time TDL. If the value of the air-fuel ratio A / F is rich, the process proceeds to step 220. On the other hand, the air-fuel ratio A
If the value of / F is not rich but lean indicating low fuel concentration, the process proceeds to step 230.

Step 22 shifts from step 210
At 0, it is determined whether or not the value of the air-fuel ratio A / F was rich last time. Here, if the value of the air-fuel ratio A / F is not rich last time, it is assumed that the air-fuel ratio A / F has changed from lean to rich this time, and in step 221 the air-fuel ratio correction value FAF is calculated using the lean proportional constant RSL.
Is performed for proportional correction PC. That is, the lean proportional constant RSL is subtracted from the previous air-fuel ratio correction value FAF, and the result of the subtraction is set as a new lean proportional constant RSL. Then, the value is temporarily stored in the RAM 54. Here, the lean proportional constant RSL is set in advance as a fixed value. The lean proportional constant RSL corresponds to a so-called “skip amount” for correcting the air-fuel ratio A / F to be lean when the air-fuel ratio A / F is rich, and is shown in FIG. At times t4 and t8, the waveform of the air-fuel ratio correction value FAF is shown.

Thereafter, in step 222, the count value CFS of the timer counter 56 is reset to "0", and the subsequent processing is temporarily terminated. On the other hand, step 22
If the air-fuel ratio A / F is rich last time at 0, it is determined that the air-fuel ratio A / F maintains a rich state, and the lean integration constant KLI is determined at step 223.
Performs the integral correction IC for the air-fuel ratio correction value FAF. That is, the count value CFS up to the previous time and the predetermined constant β
Is added to the multiplied value of, and the result of the addition is multiplied by a lean integration constant KLI. The multiplication result “KLB * (1
+ Β * CFS) ”indicates that the lean integration constant KLI changes over time, and corresponds to the lean integration time constant. Then, the multiplication result “KLB * (1 + β * CFS)” is subtracted from the previous value of the air-fuel ratio correction value FAF, and the result of the subtraction is set as a new air-fuel ratio correction value FAF. The value is temporarily stored in the RAM 54.
Here, the lean integration constant KLI is set in advance as a fixed value. The lean integration time constant obtained based on the lean integration constant KLI is used to correct the air-fuel ratio A / F to be lean when the air-fuel ratio A / F is rich. From time t4 to time t
6, the air-fuel ratio correction value F between time t8 and time t10.
This is shown in the AF waveform. That is, in this embodiment, the lean integration time constant increases and changes synergistically as time elapses after the proportional correction PC is performed, that is, as the count value CFS increases. More specifically, the lean integration time constant has a characteristic that it initially increases slightly, and then increases rapidly after a certain period of time.

Thereafter, in step 224, the count value CFS of the timer counter 56 is incremented by "1", and the subsequent processing is temporarily terminated. In contrast,
After step 210, in step 230, it is determined whether the value of the air-fuel ratio A / F was lean last time. Here, if the value of the air-fuel ratio A / F is not the previous lean value, it is determined that the air-fuel ratio A / F has changed from rich to lean this time, and in step 231 the rich proportional constant RSR is applied to the air-fuel ratio correction value FAF. The proportional correction PC is performed. That is, the rich proportional constant RSR is added to the previous air-fuel ratio correction value FAF, and the addition result is set as a new rich proportional constant RSR. Then, the value is temporarily stored in the RAM 54. Here, the rich proportional constant R
SR is set in advance as a fixed value. The rich proportional constant RSR corresponds to a so-called “skip amount” for correcting the air-fuel ratio A / F to be rich when the air-fuel ratio A / F is lean,
The air-fuel ratio correction value F at times t2, t6, and t10 in FIG.
This is shown in the AF waveform.

Thereafter, in step 232, the count value CFS of the timer counter 56 is reset to "0", and the subsequent processing is temporarily terminated. On the other hand, step 23
If the air-fuel ratio A / F is lean at the previous time at 0, it is determined that the air-fuel ratio A / F maintains a lean state, and the rich integration constant KRI is determined at step 233.
Performs the integral correction IC for the air-fuel ratio correction value FAF. That is, “1” is added to the multiplied value of the count value CFS and the constant α up to the previous time, and the addition result is multiplied by the rich integration constant KRI. The result of this multiplication “KRB * (1 + α *
CFS) "indicates that the rich integration constant KRI changes over time, and corresponds to a lean integration time constant. Then, the above multiplication result “KRB * (1 + α * CFS)” is added to the previous value of the air-fuel ratio correction value FAF,
The result of the addition is set as a new air-fuel ratio correction value FAF. The value is temporarily stored in the RAM 54. here,
The rich integration constant KRI is set in advance as a fixed value. The rich integration time constant obtained based on the rich integration constant KRI is used to correct the air-fuel ratio A / F to be rich when the air-fuel ratio A / F is lean. Time t2 to time t4, time t6
The waveform of the air-fuel ratio correction value FAF is shown from time t8 to time t8. That is, in this embodiment, the rich integration time constant increases and changes in a synergistic manner as time elapses after the proportional correction PC is performed, that is, as the count value CFS increases. Like the lean integration time constant, the rich integration time constant has a characteristic that it initially increases slightly and then increases rapidly after a certain period of time.

Thereafter, in step 234, the count value CFS of the timer counter 56 is incremented by "1", and the subsequent processing is temporarily terminated. The calculation of the air-fuel ratio correction value FAF is performed as described above. In this embodiment, the ECU 51 that executes the “air-fuel ratio correction value calculation routine” as described above corresponds to the correction value calculation unit and the integration time constant variable unit in the present invention.

Here, the relationship between changes in various parameters Ox, A / F, FAF, and CFS according to the above processing routine will be described with reference to the time chart of FIG. At time t1, when the value of the oxygen concentration Ox exceeds the reference value a corresponding to the value of the target air-fuel ratio, time t2 delayed by the delay time TDL
In, the determination of the air-fuel ratio A / F is lean. At this time, the count value CFS is reset, and the increment is started. Further, the air-fuel ratio correction value FAF is proportionally corrected PC by the amount of the rich proportionality constant RSR, and thereafter, an integration correction IC based on the rich integration time constant is performed. Since the rich integration time constant increases synergistically with the increase of the count value CFS, the air-fuel ratio correction value FAF increases in a quadratic curve after time t2.

Thereafter, at time t3, the oxygen concentration Ox
Is smaller than the reference value a, the determination of the air-fuel ratio A / F becomes rich at time t4 delayed by the delay time TDL. At this time, the count value CFS is reset again,
The increment is started. Also, the air-fuel ratio correction value F
AF is proportionally corrected by the amount of the lean proportional constant RSL, and then the integral correction IC based on the lean integration time constant is performed. Since the lean integration time constant increases synergistically with the increase of the count value CFS, the air-fuel ratio correction value FAF decreases in a quadratic curve after time t4.

Thereafter, at times t6, t8, and t10, each time the determination of the air-fuel ratio A / F is inverted based on the change in the oxygen concentration Ox, the proportional correction PC is performed using the rich proportional constant RSR or the lean proportional constant RSL. At the same time, the integration correction IC is thereafter performed with the rich integration time constant or the lean integration time constant, and the air-fuel ratio correction value FAF changes.

As described above, in this embodiment, E
By executing the process of the “air-fuel ratio correction value calculation routine” by the CU 51, it is determined whether the air-fuel ratio A / F is rich or lean based on the detected value of the oxygen concentration Ox by the oxygen sensor. Then, based on the determination result, the proportional correction PC is performed with the lean proportional constant RSL, and then the integral correction IC is performed with the lean integration time constant related to the lean integration constant KLI, whereby the air-fuel ratio correction value FAF is calculated. . Alternatively, the air-fuel ratio correction value FAF is calculated by performing the proportional correction PC with the rich proportional constant RSR and then performing the integration correction IC with the rich integration time constant related to the rich integration constant KRI. Here, the rich integration time constant and the lean integration time constant are initially small and then multiplied synergistically so as to increase rapidly after the proportional correction PC is performed, that is, according to the count value CFS. . And the ECU 5
1 executes the “fuel injection amount calculation routine” to correct the target injection amount TAU to be supplied to the engine 1 by each injector 17 according to the air-fuel ratio correction value FAF calculated as described above. Asked to be.

Therefore, the rich integration time constant or the lean integration time constant is increased according to the amount of deviation between the actual value of the air-fuel ratio A / F and the reference value a corresponding to the target air-fuel ratio. When the deviation amount of the air-fuel ratio A / F is large,
The air-fuel ratio correction value FAF is gradually increased over time to reach an appropriate value. Therefore, the actual air-fuel ratio A / F
The correction delay until the value of? Coincides with the value of the target air-fuel ratio is shortened. On the other hand, when the deviation amount of the air-fuel ratio A / F is small,
At first, the value of the air-fuel ratio correction value FAF is corrected to be relatively small and reaches an appropriate value. Therefore, the actual value of the air-fuel ratio A / F is not excessively corrected with respect to the value of the target air-fuel ratio.

As a result, the air-fuel ratio correction value FA is always determined according to the amount of deviation between the actual air-fuel ratio A / F value and the target air-fuel ratio value.
F can be determined appropriately and without a large delay. Further, since the air-fuel ratio correction value FAF is obtained without delay, an appropriate air-fuel ratio correction value FAF can be promptly obtained even when the operating state of the engine 1 changes suddenly. An appropriate target injection amount TAU according to the change can be quickly obtained. In this sense, it is possible to prevent the exhaust characteristics of the engine 1 from being deteriorated due to the correction delay related to the target injection amount TAU.

For example, when the engine 1 shifts from the steady operation state to the deceleration operation, the difference between the actual value of the air-fuel ratio A / F and the value of the target air-fuel ratio temporarily increases. But,
In this embodiment, unlike the conventional example in which the value of the integration constant is constant, the rich integration time constant or the lean integration time constant increases synergistically with the passage of time after the proportional correction PC, and the air-fuel ratio A
The time required to resolve the deviation of / F is reduced, and the air-fuel ratio correction value FAF is optimized in a short time. Therefore, the target injection amount TAU is not excessively corrected beyond the necessary period, and in that sense, the hydrocarbon (H
C) can be suppressed from increasing.

Further, since the correction delay of the air-fuel ratio correction value FAF can be prevented as described above, the rich integration constant KRI
Or the value of the lean integration constant KLI is set large in advance,
There is no need to previously set the values of the rich proportional constant RSR and the lean proportional constant RSL large. In that sense, when the deviation amount of the air-fuel ratio A / F is small, the air-fuel ratio correction value FAF
Is not excessively corrected, and the air-fuel ratio correction value FAF does not lead to a phenomenon such as unnecessary hunting.

In addition, since the rich integration time constant and the lean integration time constant of this embodiment increase slightly immediately after the proportional correction PC, the rich and lean proportional constants RS
It is also possible to set the values of R and RSL large in advance to some extent. In that case, the proportional constants RSR, RS
Integral correction I after proportional correction PC by the amount of increasing L
The time required for C can be reduced, and the time required for correcting the air-fuel ratio correction value FAF can be reduced as a whole. In that sense, the proportional constants RSR, RSL
Can be increased.

The present invention can be embodied in another embodiment as follows. In another example below,
The same operation and effect as those of the above embodiment can be obtained. (1) In the above embodiment, the oxygen concentration Ox is detected by the oxygen sensor 34 as the concentration of the specific component in the exhaust gas. On the other hand, the concentration of carbon dioxide may be detected by a special sensor as the concentration of the specific component in the exhaust gas.

(2) In the above embodiment, the integration time constant of rich and lean is increased synergistically with the lapse of time after the proportional correction is performed. On the other hand, the rich and lean integration time constants are uniformly set to a small value within a predetermined time after the proportional correction is performed, and then set to a uniformly large value thereafter, in two stages according to the passage of time. You may comprise so that it may increase.

(3) In the above embodiment, the air-fuel ratio control device of the present invention is applied to the "El Jetronic" type engine 1 using the air flow meter 32, but the "Die Jetronic" using a vacuum sensor is used. "Type engine.

(4) In the above embodiment, the air-fuel ratio control device of the present invention is embodied in a gasoline engine as an internal combustion engine, but may be embodied in an LPG engine or a diesel engine.

The embodiments of the present invention have been described above. However, it is to be noted that each of the embodiments includes the following various embodiments according to the technical idea described in the claims. Are described together with the effects.

(A) In the invention according to the first aspect, the change of the integration time constant by the integration time constant variable means is initially small and then rapidly changed in accordance with the lapse of time after the proportional correction has been performed. An air-fuel ratio control device for an internal combustion engine which is set so as to increase in a synergistic manner so as to increase.

According to this configuration, since the integration time constant increases at first, the value of the proportionality constant can be set to a large value in advance, and the time required for the integral correction after the proportionality correction can be shortened accordingly. Thus, the time required for correcting the air-fuel ratio correction value can be shortened.

In this specification, means, members, and the like according to the configuration of the present invention are defined as follows. (A) The air-fuel ratio means a weight ratio of air / fuel,
It refers to the air / fuel ratio of the air-fuel mixture sucked into the internal combustion engine.
Assuming complete combustion, the air-fuel ratio at the minimum theoretically necessary air amount is called the stoichiometric air-fuel ratio. The air-fuel ratio when the fuel is thinner than the stoichiometric air-fuel ratio is called "lean", and the air-fuel ratio when it is rich is called "rich".

[0058]

According to the first aspect of the present invention, when calculating the air-fuel ratio correction value for correcting the amount of fuel to be supplied to the internal combustion engine, the detected value indicating the concentration of the specific component in the exhaust gas is used. , The proportional correction is performed using the proportional constant, and thereafter the integral correction is performed using the integration time constant. Then, the integration time constant is increased as time elapses after the proportional correction is performed.

Accordingly, when the deviation amount of the air-fuel ratio is large, the correction value of the air-fuel ratio is gradually increased over time to reach an appropriate value, so that the actual air-fuel ratio matches the target air-fuel ratio. The correction delay until is shortened. On the other hand, when the deviation amount of the air-fuel ratio is small, the air-fuel ratio correction value is corrected to a relatively small value at first and reaches an appropriate value, so that the actual air-fuel ratio is excessively corrected with respect to the target air-fuel ratio. There is no.
As a result, the air-fuel ratio correction value can always be obtained properly and without delay in accordance with the amount of deviation between the actual air-fuel ratio and the target air-fuel ratio, and the effect of preventing deterioration of the exhaust characteristics of the engine can be prevented. Demonstrate.

[Brief description of the drawings]

FIG. 1 is a conceptual configuration diagram illustrating a basic conceptual configuration of the present invention.

FIG. 2 is a schematic configuration diagram showing a gasoline engine system including an air-fuel ratio control device for an internal combustion engine according to the present invention, in one embodiment of the present invention;

FIG. 3 is a block diagram showing a configuration of an ECU and the like in one embodiment.

FIG. 4 is a flowchart illustrating a “fuel injection amount calculation routine” executed by an ECU in one embodiment.

FIG. 5 is a flowchart illustrating an “air-fuel ratio correction value calculation routine” executed by an ECU in one embodiment.

FIG. 6 is a time chart showing changes in various parameters according to the routine of FIG. 5 in one embodiment.

FIG. 7 is a time chart showing a change in an air-fuel ratio correction value and a parameter related thereto in a conventional technique.

DESCRIPTION OF SYMBOLS 1 ... Engine as internal combustion engine, 17 ... Injector as fuel supply means, 34 ... Oxygen sensor as concentration detection means, 51 ... ECU (51 is a correction value calculation means, fuel amount correction means and integration time Constituting the constant variable means).

Claims (1)

(57) [Claims] In order to match the air-fuel ratio of air and fuel supplied to an internal combustion engine with a target air-fuel ratio corresponding to an operating state of the internal combustion engine, the amount of fuel to be supplied to the internal combustion engine by a fuel supply means is determined. An air-fuel ratio control device configured to control, a concentration detecting means for detecting a concentration of a specific component in exhaust gas discharged from the internal combustion engine, and a proportional constant based on a detection value of the concentration detecting means. A correction value calculating means for calculating an air-fuel ratio correction value related to the air-fuel ratio by performing a proportional correction with the integration constant after that, and An air-fuel ratio control device for an internal combustion engine, comprising: a fuel amount correction unit for correcting a fuel amount to be supplied to the internal combustion engine, wherein the integration constant is an integration time constant that changes with time. Air-fuel ratio control system for an internal combustion engine, characterized in that the integration time constant latest proportional correction provided integral time constant varying means for increasing in accordance with the elapsed time after it has been made.