JPH11264339A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce shock of an engine just after an air-fuel ratio control action is switched, and avoid deterioration of an operating performance by controlling an engine output just after switching of the air-fuel ratio control action is detected so as to nearly match integral values of cylinder internal pressure detecting signals after/before the switching of the air-fuel ratio control action is detected with each other. SOLUTION: A cylinder internal pressure data of one cycle obtained, for example, from a cylinder internal pressure sensor 5 is integrated, a net average effective pressure is calculated, and is memorized in a RAM 32. It is judged whether or not a control motion is switched from a stoichiometric control motion to a lean vane control motion. In the case of a switching time, an opening of a throttle 18a is set according to engine rotating speed and net average effective pressure, and a throttle valve driving command is generated to a driving device 35. After execution, net average effective pressure is found out by a data of cylinder internal pressure of one cycle newly obtained from the cylinder internal pressure sensor 5. In the case where an absolute value of a difference between previous and present net average effective pressure is larger than a prescribed value, the previous value is larger or smaller than a present value, a throttle opening is reduced or increased for a prescribed opening.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control device for controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine.

[0002]

2. Description of the Related Art A stoichiometric control operation for controlling the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine to a stoichiometric air-fuel ratio by feedback control and controlling the air-fuel ratio leaner than the stoichiometric air-fuel ratio to improve fuel efficiency. There is an air-fuel ratio control device that switches between a lean burn control operation and a lean burn control operation according to an operation state. In the stoichiometric control operation, the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the air-fuel ratio of the supplied air-fuel mixture is controlled according to the output of the oxygen concentration sensor. On the other hand, in the lean burn control operation, the pressure in the cylinder, that is, the in-cylinder pressure is detected by the in-cylinder pressure sensor, and the air-fuel ratio is controlled to be lean based on the in-cylinder pressure. For example, JP-A-62-150058 discloses that the air-fuel ratio of a supplied air-fuel mixture is controlled to a stoichiometric air-fuel ratio in accordance with an output signal of an exhaust oxygen sensor, and the maximum and minimum values of the in-cylinder pressure detected by an in-cylinder pressure sensor. It is disclosed that the air-fuel ratio is lean-controlled in accordance with the ratio.

[0003]

However, in such a conventional air-fuel ratio control device, the engine is, for example,
For example, when the air-fuel ratio control operation is switched from the stoichiometric control operation to the leak burn control operation because of the steady operation state such as the cruise operation, the engine output is reduced due to a sudden change in the combustion state, so that a shock (impact) is caused. There is a problem that the driving performance deteriorates due to the occurrence of.

An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can reduce the shock of the engine immediately after switching the air-fuel ratio control operation.

[0005]

An air-fuel ratio control apparatus according to the present invention includes a first air-fuel ratio control operation for controlling an air-fuel ratio control operation of an air-fuel mixture supplied to an internal combustion engine near a stoichiometric air-fuel ratio, and a leaner operation than the stoichiometric air-fuel ratio. An air-fuel ratio control device that selectively switches to one of a second air-fuel ratio control operation and a second air-fuel ratio control operation, wherein the switching between the first and second air-fuel ratio control operations is detected. Switching detection means, in-cylinder pressure detection means for generating an in-cylinder pressure detection signal corresponding to the pressure in the cylinder of the internal combustion engine, integration means for integrating the in-cylinder pressure detection signal to obtain an integrated value, And engine output control means for controlling the engine output immediately after the detection of the switching so that the integrated values before and after the detection of the switching between the second air-fuel ratio control operations are substantially the same.

That is, according to the present invention, the engine output immediately after the detection of the switching of the air-fuel ratio control operation is controlled such that the integral values of the in-cylinder pressure detection signals before and after the detection of the switching of the air-fuel ratio control operation are substantially the same. Since the engine operates so as to maintain the engine output immediately after the switching of the fuel ratio control operation, it is possible to reduce the shock of the engine and to avoid the deterioration of the driving performance.

The engine output control means includes a memory storing data of the opening degree of the throttle valve corresponding to the integral value and the engine speed as a data map, a speed detecting means for detecting the engine speed of the engine, When switching between the first and second air-fuel ratio control operations is detected by the switching detection means, the storage position corresponding to the current value of the integral value and the current value of the engine speed detected by the rotation speed detection means is set to 1 Means for retrieving and setting the opening data of the throttle valve from the data map, and controlling the opening of the throttle valve in accordance with the opening data of the first.
A throttle valve adjusting means for increasing or decreasing the opening of the throttle valve so that the magnitude of the difference between the integral value immediately before detection of switching between the air-fuel ratio control operations and the present value of the integral value is equal to or less than a predetermined value.

With the configuration of the engine output control means,
When the air-fuel ratio control operation is switched, the throttle valve is immediately controlled to a predetermined appropriate opening degree, so that a sudden drop in engine output can be prevented. Further, when the magnitude of the difference between the integral value immediately before the detection of the switching between the first and second air-fuel ratio control operations and the current value of the integral value becomes equal to or less than a predetermined value, the opening indicating the opening degree of the throttle valve at that time. The storage position of the data map is updated and stored with the degree data.

Thus, since each opening degree data of the data map is subjected to learning control, it is possible to cope with a temporal change of the engine.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a vehicle-mounted internal combustion engine body to which an air-fuel ratio control device according to the present invention is applied. The internal combustion engine main body has four cylinders 1 to 4, and an intake pipe 16 and an exhaust pipe 17 are connected to each of the cylinders 1 to 4. The intake pipe 16 is branched into four and connected to the cylinders 1 to 4, and the branch passages 16a to 16d are provided with throttle valves 18a to 18d, respectively. Each of the throttle valves 18a to 18d opens in conjunction with the operation of an accelerator pedal (not shown), and a drive circuit 3 which will be described later.
5 Throttle valve actuator 1 including motor
The valves are driven to open via 9a to 19d. The exhaust pipe 17 is provided with an oxygen concentration sensor 20 for detecting the oxygen concentration in the exhaust gas.

The cylinder heads of the cylinders 1 to 4 are provided with in-cylinder pressure sensors 5 to 8 as in-cylinder pressure detecting means for detecting the pressure in the cylinder. Specifically, each of the in-cylinder pressure sensors 5 to 8 integrates (or averages) and amplifies a voltage generated from the sensor element unit 9 including a piezoelectric element, as shown in FIG. And an amplifying unit 10.

As shown in FIG. 2, a spark plug 13 is screwed and fixed in a screw hole 12 of each cylinder head 11 of the engine body. Washer 13
a between the washer 1 and the sensor element 9 of the in-cylinder pressure sensor.
5 and crimped and fixed. The detection outputs of the in-cylinder pressure sensors 5 to 8 are supplied to an ECU (engine control unit) 21. EC
U21 includes a CPU 31, a ROM 32, as shown in FIG.
It comprises at least a RAM 33, an A / D converter 34, a drive circuit 35 and a counter 37, which are connected to each other by a common bus. The in-cylinder pressure sensors 5 to 8 and the oxygen concentration sensor 20 are connected to the A / D converter 34,
The drive circuit 35 includes the above-described actuators 19a to 19d.
And four injectors 41 to 44 are connected. The injectors 41 to 44 are provided in the intake pipe 16 near the intake port for each cylinder, and inject fuel by a driving operation of the driving circuit 35.

The A / D converter 34 has other sensors as follows:
Branches 16a to 16 downstream of throttle valves 18a to 18d
intake pipe internal pressure sensors 39a-39 for detecting the pressure inside
d, the cooling water temperature sensor 40 for detecting the temperature T _W of the cooling water of the internal combustion engine, there is an engine parameter sensors such as a throttle opening sensor (not shown) for detecting the degree of opening of the throttle valve. The A / D converter 34 uses the output pulse of the crank angle sensor 38 as the sampling timing. Since the crank angle sensor 38 generates a crank pulse each time the crankshaft rotates, for example, once, the A / D converter 34 determines the analog output voltage of each sensor in synchronization with the output crank pulse of the crank angle sensor 38. , And outputs the digital value for each sensor. The digital value is repeatedly updated. The counter 37 measures the generation interval of the crank pulse output from the crank angle sensor 38 by counting the number of clock pulses generated, and generates a signal indicating the engine speed Ne. The crank angle sensor 38 generates a TDC signal indicating the top dead center of the piston of each cylinder together with a reference position signal indicating the time when the rotation angle of the crankshaft is at a predetermined angle position.
31.

The CPU 31 of the ECU 21 performs a fuel injection control operation in synchronism with the TDC signal for each cylinder in accordance with a program stored in the ROM 32 in order to supply fuel into the cylinders 1 to 4 of the engine by the injectors 41 to 44. . Since the same fuel injection control operation is performed for each cylinder, the fuel injection control operation for the cylinder 1 will be described next. Further, the fuel injection control operation includes a stoichiometric control operation (first air-fuel ratio control operation) and a lean burn control operation (second air-fuel ratio control operation) as the air-fuel ratio control operations executed therein. The fuel injection control operation for performing the stoichiometric control operation will be described.

Fuel injection control operation for performing stoichiometric control operation
The operation is TD when an air-fuel ratio selection flag F described later is 0.
The interrupt is executed in response to the C signal, and the CPU 31
First, as shown in FIG.
Number of turns Ne and pressure P in the intake pipe _BSet according to
Step S1). The reference fuel injection time Ti is, for example, ROM
32 from the Ti data map stored in advance in the
Number of turns Ne and intake pipe pressure P_BAnd set according to the search
You. The engine speed Ne is obtained from the counter 37,
Tracheal pressure P_BIs detected by the intake pipe internal pressure sensor 39a.
And is obtained from the A / D converter 34.

After setting the reference fuel injection time Ti, the oxygen concentration
The output signal level of the sensor 20 is read from the A / D converter 34.
The air-fuel ratio is rich and lean with respect to the stoichiometric air-fuel ratio.
Is determined (step S2). acid
The output signal level of the element concentration sensor 20 indicates that the air-fuel ratio is stoichiometric.
When the air-fuel ratio is leaner than the fuel-
Since the level is high when the air-fuel ratio is richer than the stoichiometric air-fuel ratio,
From the output signal level of the element concentration sensor 20, the actual air-fuel ratio
Rich / lean can be determined. Step S2
If the air-fuel ratio is determined to be rich in
Air-fuel ratio feedback to make the air-fuel ratio lean.
Correction coefficient K_O2Is reduced by a predetermined value I (for example, 0.05).
(Step S3). On the other hand, the air-fuel ratio was judged to be lean.
If separate, enrich the air-fuel ratio of the supply mixture
The air-fuel ratio feedback correction coefficient K_O2Is the predetermined value I
(Step S4). Therefore, rich air-fuel
If the ratio state continues, the air-fuel ratio feedback correction coefficient K
_O2Gradually decreases and the lean air-fuel ratio condition continues,
Air-fuel ratio feedback correction coefficient K_O2Gradually increases.
The air-fuel ratio feedback correction coefficient K_O2The initial value of is
1.0. Also, the air-fuel ratio is reversed from rich to lean
Immediately after the air-fuel ratio feedback correction coefficient K _O2Predetermined
Decrease by a predetermined value P larger than the value I, and
Immediately after the reversal of the air-fuel ratio feedback correction coefficient K
_O2May be increased by a predetermined value P.

After setting the air-fuel ratio feedback correction coefficient K _O2 , the CPU 31 calculates the fuel injection time Tp (step S5). The fuel injection time Tp is obtained by multiplying the reference fuel injection time Ti obtained in step S1 and the air-fuel ratio feedback correction coefficient K _O2 obtained in step S3 or S4 as Ti × K _O2 . Fuel injection time Tp
Is calculated, a drive command for the fuel injection time Tp of the injector 41 is issued to the drive circuit 35 (step S).
6). The drive circuit 35 drives the injector 41 for a fuel injection time Tp from a specific point in time (for example, immediately before the intake stroke) in synchronization with the TDC signal to inject and supply fuel.

On the other hand, when the air-fuel ratio selection flag F is 1, the fuel injection control operation for performing the lean burn control operation is TD.
The interrupt is executed in response to the C signal, and the CPU 31
First, as in step S1, the reference fuel injection time Ti is set to the engine speed Ne and the intake pipe pressure P _B.
(Step S11). After setting the reference fuel injection time Ti, a net average effective pressure Pme is calculated based on the data of the in-cylinder pressure Pi for one cycle obtained from the in-cylinder pressure sensor 5 (step S12).

The net mean effective pressure Pme is the difference between the indicated mean effective pressure Pmi and the pumping loss Pmf as shown in equation (1).

[0020]

Pme = Pmi−Pmf (1) The indicated mean effective pressure Pmi is

[0021]

(Equation 2)

It is calculated as follows. Here, TDC is the cylinder capacity at the top dead center position, and BDC is the cylinder capacity at the bottom dead center position. DV is a shilling capacitance change amount. The relationship between the in-cylinder pressure Pi and the cylinder capacity V can be illustrated as shown in FIG. 6 in one cycle including intake, compression, explosion, and exhaust. The indicated average effective pressure Pmi corresponds to the range indicated by the symbol A in FIG. Equation (2)
The first integral term corresponds to the area surrounded by 1-2-3-4-5-1 in FIG. 6, and the second integral term corresponds to 1-2-3′-4 ′ in FIG.
It corresponds to the area enclosed by -5-1.

The pumping loss Pmf is

[0024]

(Equation 3)

It is calculated as follows. Pumping loss Pm
f corresponds to the range indicated by reference numeral B in FIG. The first integral term in equation (3) corresponds to the area enclosed by 1-2-3-6-1 in FIG. 6, and the second integral term is 1-2-3′-6′-1 in FIG. It corresponds to the area enclosed by. After calculating the net average effective pressure Pme, the CPU 31 sets a threshold value a (Ne) (step S13), and determines whether the net average effective pressure Pme is equal to or greater than the threshold value a (Ne) (step S14). Threshold a (N
e) is set according to the engine speed Ne. For example, the threshold value a (Ne) is set smaller as the engine speed Ne is higher. According to the determination in step S14, Pme ≧ a
In the case of (Ne), the air-fuel ratio leaning correction coefficient K _AF is reduced by a predetermined value I in order to make the air-fuel ratio of the supplied air-fuel mixture lean (step S15). On the other hand, Pme <a (Ne)
In this case, the air-fuel ratio leaning correction coefficient K _AF is increased by a predetermined value I in order to enrich the air-fuel ratio of the supplied air-fuel mixture (step S16). Therefore, if the state of Pme ≧ a (Ne) continues, the air-fuel ratio leaning correction coefficient K _AF gradually decreases, and if the state of Pme <a (Ne) continues, the air-fuel ratio leaning correction coefficient K _AF Gradually increases. The initial value of the air-fuel ratio leaning correction coefficient K _AF is 1.0.

The CPU 31 calculates an air-fuel ratio lean correction coefficient K
After setting the _AF , the fuel injection time Tp is calculated as in step S5 (step S17). The fuel injection time Tp is obtained by multiplying the reference fuel injection time Ti obtained in step S11 by the air-fuel ratio leaning correction coefficient K _AF obtained in step S15 or S16 as Ti × K _AF . After calculating the fuel injection time Tp, a drive command for the fuel injection time Tp of the injector 41 is issued to the drive circuit 35 (step S18). The drive circuit 35 drives the injector 41 for a fuel injection time Tp from a specific point in time (for example, immediately before the intake stroke) in synchronization with the TDC signal to inject and supply fuel. Here, when performing the lean burn control operation, the air-fuel ratio feedback correction coefficient K _O2 is fixed to a fixed value (for example, 1.0).

By performing the fuel injection control operation for performing the lean burn control operation, Pme ≧ a (Ne)
In this state, the engine combustion is performed well without misfiring, and the air-fuel ratio of the supplied air-fuel mixture is made lean, whereby lean combustion is performed. When the state of Pme <a (Ne) is detected, the air-fuel ratio is made rich so as not to cause misfire, and excessive leaning is prevented. If the combustion of the internal combustion engine is normal, the in-cylinder pressure during expansion in the explosion stroke is higher than that in the compression stroke, and the internal combustion engine performs a positive work. However, in the case of misfiring due to abnormal combustion, FIG.
Is not substantially equal to or higher than the 3′-4′-5 line, and the indicated mean effective pressure Pmi becomes smaller than that during normal combustion. Therefore, by comparing the net average effective pressure Pme (or the indicated average effective pressure Pmi) with the threshold value, the air-fuel ratio can be made lean while preventing abnormal combustion. Further, since the fuel injection control operation is performed for each cylinder, appropriate lean combustion can be performed in any cylinder.

It should be noted, compared with the At step S14 brake mean effective pressure Pme a threshold a (Ne), but sets the air-fuel ratio direction in accordance with the comparison result, a brake mean effective pressure Pme _n calculated this time The difference ΔPme from the net average effective pressure Pmen ₋₁ calculated one cycle before may be compared with a threshold α (Ne), and the air-fuel ratio direction may be set according to the comparison result. This threshold α (Ne) is set according to the engine speed Ne.

Further, the threshold value a (Ne) is the engine speed Ne.
Is set according to, but other than the engine speed, for example,
The threshold may be set according to an engine parameter such as a throttle valve opening. In executing the above-described fuel injection control operation, the CPU 31 determines which of the stoichiometric control operation and the lean burn control operation should be selectively executed according to the operating state of the engine. That is, as shown in FIG. 7, the CPU 31 determines whether the air-fuel ratio control operation should be a stoichiometric control operation or a lean burn control operation (step S21). If it is determined that the air-fuel ratio control operation is the stoichiometric control operation, the process proceeds to step S1. In step S22, the air-fuel ratio selection flag F is set to 0 in order to perform the fuel injection control operation in which the air-fuel ratio control operation is set to the stoichiometric control operation (step S22). The air-fuel ratio selection flag F is set to 1 in order to perform a fuel injection control operation in which the control operation is a lean burn control operation (step S23). Step S
As a determination at 21, the CPU 31 selects the fuel injection control operation by the lean burn control operation when the engine speed Ne is in a predetermined engine speed range and is in a stable engine operating state, for example. The fuel injection control operation by the stoichiometric control operation is selected. This air-fuel ratio control selection operation may be repeatedly executed in synchronization with a clock pulse or a crank pulse output from the crank angle sensor 38.

The CPU 31 performs a throttle valve control operation as engine output control means in order to reduce a shock generated in the engine due to an abrupt change in the combustion state when shifting from the stoichiometric control operation to the air-fuel ratio control operation of the lean burn control operation. This throttle valve control operation is performed for each cylinder, and the throttle valve control operation for each cylinder is the same. Therefore, the throttle valve control operation for the cylinder 1 will be described below.

In this throttle valve control operation, the CPU
8, first, a net average effective pressure Pme is calculated based on the data of the in-cylinder pressure Pi for one cycle obtained from the in-cylinder pressure sensor 5 (step S31).
This is the same as step S12, and the one obtained in step S12 may be used. Calculated net average effective pressure P
me is stored in the RAM 32 as Pme1. After execution of step S31, it is determined whether or not it is time to switch from the stoichiometric control operation to the lean burn control operation (step S31).
32). This determination is made by detecting that the air-fuel ratio selection flag F has just changed from 0 to 1.

When switching from the stoichiometric control operation to the lean burn control operation, the throttle opening TH is set according to the engine speed Ne and the net average effective pressure Pme1 (step S33), and the opening of the throttle valve 18a is reduced. A throttle valve drive command is issued to the drive circuit 35 so as to achieve the throttle opening TH (step S34). R
OM32 has an engine speed Ne and a net average effective pressure P
Since the throttle opening TH corresponding to “me” is stored in advance as a TH data map, the CPU 31 determines the engine speed Ne at that time and the calculated net average effective pressure Pm.
The throttle opening TH (opening data) corresponding to e1 is retrieved from the TH data map of the ROM 32 and read out. The drive circuit 35 drives the throttle valve 18a in response to the throttle valve drive command so that the opening thereof becomes equal to the throttle opening TH.

After execution of step S34, the in-cylinder pressure sensor 5
Then, the net average effective pressure Pme is calculated as the current value Pme2 based on the data of the in-cylinder pressure Pi for one cycle newly obtained from (step S35). This is step S12
Alternatively, it is calculated in the same manner as in S31. Net average effective pressure Pme1
It is determined whether or not the absolute value | Pme1-Pme2 | of the difference between Pme2 and Pme2 is greater than a predetermined value a (step S3).
6). If | Pme1-Pme2 |> a, the difference Pme1-Pme2 between the net mean effective pressures Pme1 and Pme2 is 0
It is determined whether the value is larger (step S37). That is, if Pme1> Pme2, the throttle opening T
H is reduced by a predetermined opening Δθ (step S38), and a throttle valve drive command is issued to the drive circuit 35 so that the opening of the throttle valve 18a becomes the new throttle opening TH (step S39). On the other hand, if Pme1 ≦ Pme2, the throttle opening TH is increased by the predetermined opening Δθ (step S40), and the process proceeds to step S29 so that the drive circuit 35 sets the opening of the throttle valve 18a to the new throttle opening TH. Generates a throttle valve drive command.

After execution of step S39, the CPU 31 returns to step S35, and repeats the operation from step S35. In step S36, | Pme1-Pme2 | ≦ a
When it is determined that this is the case, the throttle valve control operation ends. By controlling the opening of the throttle valve 18a in this manner, the net average effective pressure Pm can be reduced when the air-fuel ratio control operation is switched from the stoichiometric control operation to the lean burn control operation.
The opening of the throttle valve 18a is controlled such that e2 becomes equal to Pme1 before switching. As a result, engine output fluctuation due to switching from the stoichiometric control operation to the lean burn control operation can be prevented.

It should be noted that step S31 in this embodiment is performed.
Execution by the CPU 31 corresponds to the integration means, the determination in step S32 corresponds to the switching detection means, and
Steps S40 to S40 executed by the CPU 31, the drive circuit 35 and the actuators 19a to 19d correspond to engine output control means. Further, a TH data map is formed using the RAM 33 as a non-volatile memory.
Using the TH data map of M33, the engine speed Ne
And the throttle opening TH according to the net average effective pressure Pme.
Can be set. With this configuration, TH
The throttle opening TH of the data map can be learned and controlled. That is, as shown in FIG.
6, when it is determined that | Pme1−Pme2 | ≦ a,
Proceeding to step S41, the throttle opening T at that time
H is written to the storage position corresponding to the engine speed Ne and the net average effective pressure Pme in the TH data map.

In the above-described embodiment, the opening of the throttle valve 18a is increased or decreased. However, the opening of the throttle valves 18b to 18d corresponding to the other cylinders is also increased by the above-described throttle valve control operation. Increased or decreased. Further, instead of changing the throttle valve opening to adjust the net average effective pressure Pme, the ignition timing may be changed as another engine output control means. That is, when it is determined that Pme1> Pme2 in step S37 as shown in FIG.
42, the ignition timing is retarded by a predetermined angle, and Pm
If it is determined that e1 ≦ Pme2, the process proceeds to step S43 to advance the ignition timing by a predetermined angle.

In each of the above embodiments, the control of the throttle valve opening or the ignition timing at the time of switching from the stoichiometric control operation to the lean burn control operation as the switching of the air-fuel ratio control operation has been described. The control of the throttle valve opening or the ignition timing at the time of switching from the control to the stoichiometric control operation can be similarly performed.

Further, in the above-described embodiment, the net average effective pressure Pme is obtained as the integral value of the in-cylinder pressure detection signal, but the indicated average effective pressure Pmi may be used as the integral value. In the above embodiment, the throttle valve 1
8a to 18d are provided for each cylinder.
The present invention can also be applied to an internal combustion engine in which a throttle valve common to each cylinder is provided in 6.

[0039]

As described above, according to the present invention, switching of the air-fuel ratio control operation is detected, an in-cylinder pressure detection signal corresponding to the pressure in the cylinder is generated, and the in-cylinder pressure detection signal is integrated and integrated. The engine output is controlled based on the throttle valve opening, ignition timing, and the like immediately after the detection of the air-fuel ratio control operation so that the integrated values before and after the detection of the air-fuel ratio control operation substantially coincide with each other. Therefore, since the engine operates so as to maintain the engine output immediately after switching of the air-fuel ratio control operation such as switching from the stoichiometric control operation to the lean burn control operation, it is possible to reduce engine shock,
Deterioration of driving performance can be avoided.

The throttle valve opening data corresponding to the integrated value of the in-cylinder pressure detection signal and the engine speed is stored in a memory as a data map, the engine speed of the engine is detected, and the air-fuel ratio control operation is switched. Is detected, the opening degree data at the storage position corresponding to the current value of the integral value and the current value of the detected engine speed is retrieved from the data map and set, and according to the opening degree data, Control the opening of the throttle valve, and then increase or decrease the opening of the throttle valve so that the magnitude of the difference between the integrated value immediately before the detection of switching of the air-fuel ratio control operation and the current value of the integrated value becomes a predetermined value or less. By doing so, the throttle valve is controlled to a predetermined appropriate opening immediately when the air-fuel ratio control operation is switched, so that a sudden decrease in engine output can be prevented.

Further, when the magnitude of the difference between the integral value immediately before the detection of the switching of the air-fuel ratio control operation and the present value of the integral value becomes equal to or smaller than a predetermined value, the opening degree data indicating the opening degree of the throttle valve at that time is used. By updating and storing the storage position of the data map, each opening degree data of the data map is subjected to learning control, so that it is possible to cope with a temporal change of the engine.

[Brief description of the drawings]

FIG. 1 is a diagram showing an internal combustion engine main body.

FIG. 2 is a diagram showing a configuration of an in-cylinder pressure sensor.

FIG. 3 is a block diagram illustrating a configuration of an ECU.

FIG. 4 is a flowchart showing a fuel injection control operation by stoichiometric control.

FIG. 5 is a flowchart showing a fuel injection control operation by lean burn control.

FIG. 6 is a diagram showing a relationship between in-cylinder pressure and cylinder volume.

FIG. 7 is a flowchart showing an air-fuel ratio control selection operation.

FIG. 8 is a flowchart showing a throttle valve control operation.

FIG. 9 is a flowchart showing another throttle valve control operation.

FIG. 10 is a flowchart showing another throttle valve control operation.

[Description of Signs of Main Parts]

 1-4 cylinder 5-8 in-cylinder pressure sensor 16 intake pipe 17 exhaust pipe 21 ECU 38 crank angle sensor 39a-39d intake pipe internal pressure sensor 40 cooling water temperature sensor 41-44 injector

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/04 310 F02D 41/04 310B 43/00 301 43/00 301E 301K (72) Inventor Kazuto Sawamura Central in Wako-shi, Saitama 1-4-1 within Honda R & D Co., Ltd. (72) Inventor Hironao Fukuchi 1-4-1 Chuo, Wako-shi, Saitama Pref. Inside Honda R & D Co., Ltd. (72) Inventor Hiroaki Kato Wako-shi, Saitama 1-4-1, Chuo, Honda R & D Co., Ltd. (72) Inventor Kenji Abe 1-4-1, Chuo, Wako-shi, Saitama Pref., Honda R & D Co., Ltd.

Claims (3)

[Claims] 1. A first air-fuel ratio control operation for controlling an air-fuel ratio control operation of an air-fuel mixture supplied to an internal combustion engine near a stoichiometric air-fuel ratio, or a second air-fuel ratio control operation for controlling leaner than the stoichiometric air-fuel ratio. On the other hand, there is provided an air-fuel ratio control device that selectively switches according to an operation state of the engine, wherein a switch detection unit that detects a switch between the first and second air-fuel ratio control operations; An in-cylinder pressure detection means for generating an in-cylinder pressure detection signal corresponding to a pressure; an integrator means for integrating the in-cylinder pressure detection signal to obtain an integrated value; and a first and a second air-fuel ratio control operation by the switching detection means. An engine output control means for controlling an engine output immediately after the detection of the switching so that the integrated values before and after the detection of the switching substantially match. 2. The engine output control means includes: a memory storing a throttle valve opening degree data corresponding to the integral value and the engine speed as a data map; and a speed detection for detecting the engine speed of the engine. Means for detecting the switching between the first and second air-fuel ratio control operations by the switching detecting means, the current value of the integral value and the current value of the engine speed detected by the speed detecting means. Means for retrieving and setting one opening degree data at a storage position corresponding to the above from the data map; and controlling the opening degree of the throttle valve in accordance with the one opening degree data. The throttle valve is controlled such that the difference between the integrated value immediately before the detection of the switching between the first and second air-fuel ratio control operations and the current value of the integrated value becomes a predetermined value or less. Air-fuel ratio control apparatus according to claim 1, characterized in that it comprises a throttle valve adjusting means for increasing or decreasing the degree of opening. 3. When the magnitude of the difference between the integral value immediately before detection of switching between the first and second air-fuel ratio control operations and the current value of the integral value becomes equal to or less than a predetermined value, the throttle at that time is used. 3. The air-fuel ratio control device according to claim 2, wherein the storage position of the data map is updated and stored with the opening data indicating the opening of the valve.