JPH07259605A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To surely prevent operating feeling such as deceleration feeling from growing worse at the time of switching the air-fuel ratio controller of an internal combustion engine applicable to a lean-burn internal combustion engine to a lean-burn operation. CONSTITUTION:An air fuel ratio controller 21 is provided with an intake air flow control means 201 which an intake air flow supplied to the combustion chamber of an internal combustion engine upon switching to an operation with a lean air-fuel ratio, an air-fuel ratio control means 210 having a target air-fuel ratio setting means 204 and a fuel amount setting means 205 to control an air-fuel ratio based on the operating state of the internal combustion engine, and a fuel feeding means for 211 feeding fuel to the internal combustion engine based on a set fuel amount. The target air-fuel ratio setting means 204 is provided with a following changing means 202 for continuously changing the air-fuel ratio depending on the change of an actual intake air quantity at the time of switching an operation with an excessively richer side air-fuel ratio than a lean side air-fuel ratio to the lean air-fuel ratio.

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 apparatus for an internal combustion engine suitable for use in a lean-burn internal combustion engine that performs lean-burn operation at a leaner air-fuel ratio than the stoichiometric air-fuel ratio under required operating conditions. Regarding

[0002]

2. Description of the Related Art In recent years, a lean burn internal combustion engine (so-called lean burn engine) has been provided which performs a lean burn operation at a leaner air-fuel ratio (lean) than a stoichiometric air-fuel ratio (stoichio) under required operating conditions. There is. In such a lean burn engine, during lean burn operation (lean burn operation), the air-fuel ratio is set as high as possible (that is, the air-fuel mixture becomes lean as much as possible), and the value of the air-fuel ratio is It is set near the limit (lean limit) that allows stable combustion.

By performing such a lean burn operation, fuel consumption can be greatly improved.

[0004]

Here, in order to perform the lean burn operation, the air-fuel ratio is controlled by the control device. In this control, it is necessary to introduce air for leaning. Done. When introducing air, a device is provided that controls the same output with the same accelerator operation amount (throttle opening) to prevent deceleration shock.

However, in the conventional apparatus, there is a possibility that deceleration shock may occur when the engine speed increases. That is, the switching to the lean burn operation is performed by the switching control from the stoichiometric mode to the lean mode as shown in FIG.
As shown in (b), the air-fuel ratio is changed from the target air-fuel ratio in the stoichio mode to the target air-fuel ratio in the lean burn mode.

Leaning air is supplied to change the air-fuel ratio to the lean side, and this air supply requires an air bypass valve (ABV) provided so as to bypass the throttle valve in the intake passage. It is performed by opening (see, for example, Japanese Patent Laid-Open No. 4-265475). Here, the air bypass valve is composed of a negative pressure driving diaphragm, and is driven by supplying negative pressure to the bypass passage.

By the way, the response (change in opening) of the air bypass valve is the sum of the dead time and the first-order delay, and does not depend on the number of strokes as the interval for switching determination. Further, the intake air amount changes with a primary delay with respect to this opening (see FIG. 16). Therefore, if the engine speed is increased while the number of strokes as the switching determination interval is kept constant, the increase in the air amount at the time of switching will be delayed relative to the switching operation, and the fuel injection amount will be corrected first. It is considered that there is a possibility that the state becomes leaner than the desired state.

When such a state occurs, a feeling of deceleration is generated, and in some cases, there is a possibility that the lean limit is exceeded and a misfire occurs, impairing the driving feeling. This state is shown in Figure 1.
Observed by the transient characteristic chart of No. 7. That is, when the set air-fuel ratio A / F (KA / F) changes due to switching from stoichio to lean burn operation, the fuel injection amount is changed in a situation where the volumetric efficiency Ev does not rise sufficiently, so that the output torque is indicated. A valley corresponding to the deceleration shock appears in the load cell output.

Further, this state changes depending on the engine speed Ne. That is, the diagram of FIG. 16 shows a plurality of intake air amount characteristics with the engine speed Ne as a parameter. The larger the engine speed Ne, the more to the left. Therefore, the engine speed Ne is 3
At 000 rpm, 85% of the intake air volume is achieved in 0.5 seconds, while at 1000 rpm, 8% is achieved.
It takes 0.85 seconds to achieve a 5% intake air volume.

Therefore, when performing the switching control to the lean burn operation in a fixed pattern, there arises a problem due to the intake delay depending on the engine speed Ne.
The present invention was devised in view of such problems, and when switching to lean burn operation, it is possible to reliably prevent deterioration of driving feeling such as deceleration feeling.
An object is to provide an air-fuel ratio control device for an internal combustion engine.

[0011]

For this reason, the air-fuel ratio control system for an internal combustion engine according to the present invention (claim 1) operates at a leaner air-fuel ratio than the stoichiometric air-fuel ratio and at a richer side than the lean-side air-fuel ratio. In an internal combustion engine capable of switching between operation at an air-fuel ratio depending on operating conditions, an intake air amount that increases the amount of intake air supplied to the combustion chamber of the internal combustion engine when switching to operation at the lean side air-fuel ratio Control means, target air-fuel ratio setting means for setting a target air-fuel ratio according to the operating state of the internal combustion engine, and the target air-fuel ratio setting means for controlling the air-fuel ratio according to the operating state of the internal combustion engine The air-fuel ratio control means having a fuel quantity setting means for setting the fuel quantity to achieve the desired target air-fuel ratio, and the fuel quantity set by the fuel quantity setting means in the air-fuel ratio control means. Fuel supply means for supplying fuel to the engine The target air-fuel ratio setting means in the air-fuel ratio control means, when switching from the lean side air-fuel ratio operation to the lean side air-fuel ratio operation to the actual intake air amount It is characterized in that it is provided with a follow-up changing means for continuously changing the air-fuel ratio following the change.

Further, in the air-fuel ratio control system for an internal combustion engine according to a second aspect of the present invention, the follow-up changing means sets the intake air amount immediately before the start of switching the operating state and the intake air amount during the switching transient operation. It is characterized in that it comprises a comparison means for comparing and a transient target air-fuel ratio setting means for setting a transient target air-fuel ratio based on the comparison result of the comparison means.

Further, in the air-fuel ratio control apparatus for an internal combustion engine according to claim 3 of the present invention, the follow-up changing means is configured to reach the final target air-fuel ratio after switching from the air-fuel ratio immediately before the start of switching the operating state. A backup air-fuel ratio setting means for setting a gradually changing backup air-fuel ratio is provided, and the fuel amount setting means has a fuel amount according to the larger one of the transient target air-fuel ratio and the backup air-fuel ratio. It is characterized in that it is configured to set.

Further, in the air-fuel ratio control device for an internal combustion engine according to a fourth aspect of the present invention, the follow-up change means is configured to reach the final target air-fuel ratio after switching from the air-fuel ratio immediately before the start of switching the operating state. The transient target air-fuel ratio setting means for setting the gradually changing transient target air-fuel ratio is provided, and the change speed of the transient target air-fuel ratio set by the transient target air-fuel ratio setting means is the above-mentioned internal combustion engine. It is characterized in that it is configured so that it becomes faster as the engine speed increases.

Further, in the air-fuel ratio control system for an internal combustion engine according to a fifth aspect of the present invention, the changing speed of the backup air-fuel ratio set by the backup air-fuel ratio setting means becomes faster as the rotational speed of the internal combustion engine becomes larger. It is characterized by being configured as follows. Further, in the air-fuel ratio control device for an internal combustion engine according to claim 6 of the present invention, the follow-up change means gradually changes from the air-fuel ratio immediately before the start of switching the operating state to the final target air-fuel ratio after the switching. The transient target air-fuel ratio setting means for setting the transient target air-fuel ratio is provided, and the change speed of the transient target air-fuel ratio set by the transient target air-fuel ratio setting means is higher than that of the internal combustion engine. It is characterized in that it is configured to change from the changing speed corresponding to the rotating operation state to the changing speed corresponding to the low rotation operation state.

Further, in the air-fuel ratio control apparatus for an internal combustion engine according to claim 7 of the present invention, the follow-up changing means is configured so as to reach the final target air-fuel ratio after switching from the air-fuel ratio immediately before the start of switching the operating state. A transient target air-fuel ratio setting means for setting a gradually changing transient target air-fuel ratio, and a change prohibiting / suppressing means for prohibiting or suppressing the change of the transient target air-fuel ratio immediately after switching the operating state are provided. It is characterized by being configured.

Further, in the air-fuel ratio control system for an internal combustion engine according to claim 8 of the present invention, the intake air amount during the switching transient operation compared by the comparison means is corrected in accordance with the change in the throttle opening due to the manual operation. It is characterized in that a correction means for performing is provided. Further, the air-fuel ratio control device for an internal combustion engine according to claim 9 of the present invention is characterized in that the correction means is configured to set the correction amount based on the intake air amount change information of the internal combustion engine. There is.

Further, in the air-fuel ratio control apparatus for an internal combustion engine according to claim 10 of the present invention, the transient target air-fuel ratio setting means sets the transient target air-fuel ratio based on the comparison result of the comparing means. It is configured to be performed for a predetermined period, and is configured to gradually change the transient target air-fuel ratio after the predetermined period so that the transient target air-fuel ratio after the predetermined period elapses to reach the final target air-fuel ratio. It is characterized by being done.

Further, in the air-fuel ratio control apparatus for an internal combustion engine according to claim 11 of the present invention, the correction means corrects the set target air-fuel ratio during transition in response to a change in throttle opening due to human operation. It is characterized in that it is provided with a storage means for storing the intake air amount which is not related to switching to the operation at the lean side air-fuel ratio as parameters of the throttle opening and the engine speed.

[0020]

In the above-described air-fuel ratio control apparatus for an internal combustion engine of the present invention (claim 1), the air-fuel ratio control means controls the air-fuel ratio in accordance with the operating state of the internal combustion engine. The target air-fuel ratio setting means sets the target air-fuel ratio according to the operating state of the internal combustion engine, and further the fuel amount setting means sets the fuel amount to realize the target air-fuel ratio set by the target air-fuel ratio setting means. To do. Then, the fuel is supplied from the fuel supply means to the internal combustion engine according to the fuel quantity set by the fuel quantity setting means. When the operation is switched to the lean side air-fuel ratio, the intake air amount control means increases the intake air amount supplied to the combustion chamber of the internal combustion engine.

By the way, when switching from the lean side air-fuel ratio to the rich side air-fuel ratio to the lean side air-fuel ratio, the follow-up changing means follows the change in the actual intake air amount. Is continuously changed. Further, in the air-fuel ratio control device for an internal combustion engine according to claim 2 of the present invention, in addition to the operation of claim 1, the follow-up change means has the comparison means, the intake air amount and the switching transient operation immediately before the start of switching the operating state. The transient target air-fuel ratio setting means sets the transient target air-fuel ratio on the basis of the comparison result by the comparing means by comparing the intake air amount therein.

Further, according to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 3), in addition to the operation of claim 2, the follow-up change means is provided by the backup air-fuel ratio setting means immediately before the start of switching the operating state. The backup air-fuel ratio that gradually changes from the air-fuel ratio in step S1 to the final target air-fuel ratio after switching is set, and the fuel amount setting means determines the larger one of the transient target air-fuel ratio and the backup air-fuel ratio. Set the fuel amount.

According to the air-fuel ratio control apparatus for an internal combustion engine of the present invention (claim 4), in addition to the operation of claim 1, the following change means includes the transient target air-fuel ratio setting means.
The transient target air-fuel ratio is set so that it gradually changes from the air-fuel ratio immediately before the start of switching the operating state to the final target air-fuel ratio after switching, and the transient target air-fuel ratio changing speed is set by the transient target air-fuel ratio setting means. Is set so as to increase as the rotational speed of the internal combustion engine increases.

According to the air-fuel ratio control apparatus for an internal combustion engine of the present invention (claim 5), in addition to the operation of claim 3, the backup air-fuel ratio setting means changes the backup air-fuel ratio at a rotational speed of the internal combustion engine. It is set so that it becomes faster as becomes larger. Furthermore, according to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 6), in addition to the operation of claim 1, the following change means is set by the transient target air-fuel ratio setting means immediately before the start of switching the operating state. A transient target air-fuel ratio that gradually changes from the air-fuel ratio to the final target air-fuel ratio after switching is set, and the transient target air-fuel ratio setting means changes the transient target air-fuel ratio at a high rotation speed of the internal combustion engine. The changing speed corresponding to the state is set to change to the changing speed corresponding to the low rotation operation state.

According to the air-fuel ratio control system for an internal combustion engine of the present invention (claim 7), in addition to the operation of claim 1, the following change means uses the transient target air-fuel ratio setting means.
A transient target air-fuel ratio is set that gradually changes from the air-fuel ratio immediately before the start of switching the operating state to the final target air-fuel ratio after switching, and the transient target air-fuel ratio is set immediately after switching the operating state by the change prohibition / suppression means. Changes in the fuel ratio are prohibited or suppressed.

Further, according to the air-fuel ratio control system for an internal combustion engine of the present invention (claim 8), in addition to the operation of claim 2, the intake air amount during the switching transient operation in the comparison means,
The correction means performs the correction corresponding to the change in the throttle opening due to the manual operation. Further, according to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 9), in addition to the operation of claim 8, the correction amount in the correction means is set based on the intake air amount change information of the internal combustion engine.

According to the air-fuel ratio control system for an internal combustion engine of the present invention (claim 10), in addition to the operation of claim 2, the target air-fuel ratio setting means has a transient time based on the comparison result of the comparison means. The target air-fuel ratio is set for a predetermined period, and after the lapse of the predetermined period, the transient target air-fuel ratio that gradually changes from the transient target air-fuel ratio after the lapse of the predetermined period to the final target air-fuel ratio is set. .

According to the air-fuel ratio control system for an internal combustion engine of the present invention (claim 11), in addition to the operation of claim 7, the transient target air-fuel ratio set by the correction means is manually operated to open the throttle opening. When the correction is made in response to the change, the intake air amount that is not related to the switching to the lean side air-fuel ratio operation is set by the storage means that stores the throttle opening and the engine speed as parameters.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An air-fuel ratio control system for an internal combustion engine as an embodiment of the present invention will be described below with reference to the drawings.
Is a control block diagram of this device, FIG. 2 is an overall configuration diagram of an engine system having this device, FIG. 3 is a hardware block diagram showing a control system of an engine system having this device, and FIG. 4 is the first control of this device. 5 is a flowchart for explaining a first control mode of the present apparatus, FIG. 6 is a flowchart for explaining a second control mode, and FIG. 7 is a second control mode. FIG. 8 is a diagram for explaining the third control mode, FIG. 8 is a flowchart for explaining the third control mode,
FIG. 9 is a diagram for explaining the third control mode, FIG. 10 is a flowchart for explaining the fourth control mode, and FIG.
1 and 12 are diagrams for explaining the fourth control mode, and FIG.
3 is a flow chart for explaining the fifth control mode.

An engine (internal combustion engine) for an automobile equipped with the present device has a lean burn operation (lean burn operation) at a leaner side air-fuel ratio (lean) than the stoichiometric air-fuel ratio (stoichio) under required operating conditions. 2), the engine system is as shown in FIG. That is, in FIG. 2, an engine (internal combustion engine) 1 has an intake passage 3 and an exhaust passage 4 which communicate with a combustion chamber 2 of the engine 1.
The combustion chamber 2 and the combustion chamber 2 are controlled to communicate with each other by the intake valve 5, and the exhaust passage 4 and the combustion chamber 2 are controlled to communicate with each other by the exhaust valve 6.

The intake passage 3 is provided with an air cleaner 7, a throttle valve 8 and an electromagnetic fuel injection valve (injector) 9 in this order from the upstream side, and the exhaust passage 4 is provided in order from the upstream side. A three-way catalyst 10 and a muffler (silencer) not shown are provided. The injector 9 is provided for each cylinder of the engine 1. Further, the intake passage 3 is provided with a surge tank 3a.

The three-way catalyst 10 purifies CO, HC and NOx under stoichiometric operation and is a known one. Further, the throttle valve 8 is connected to an accelerator pedal (not shown) via a wire cable, and its opening degree is adjusted according to the depression amount of the accelerator pedal.

Further, the intake passage 3 is provided with a first bypass passage 11A for bypassing the throttle valve 8, and a stepper motor valve (hereinafter referred to as an STM valve) which functions as an ISC valve is provided in the first bypass passage 11A. 12 are installed. In addition, in the first bypass passage 11A,
A wax-type fast idle air valve 13 whose opening is adjusted according to the engine cooling water temperature is also provided, and is attached to the STM valve 12.

Here, the STM valve 12 is a valve body 12a which can abut against a valve seat portion formed in the first bypass passage 11A.
And a stepper motor (I
(SC actuator) 12b, and a spring 12c that urges the valve body in a direction that presses the valve body against the valve seat portion (a direction that closes the first bypass passage 11A). The stepper motor 12b performs stepwise adjustment of the position of the valve body 12a with respect to the valve seat portion (adjustment by the number of steps) to open the valve seat portion and the valve body 12a, that is, the STM valve 12
The opening degree of is adjusted.

Therefore, the opening degree of the STM valve 12 is an electronic control unit (ECU) 2 as a controller which will be described later.
By controlling with 5, the intake air can be supplied to the engine 1 through the first bypass passage 11A regardless of the operation of the accelerator pedal by the driver, and the throttle bypass intake air amount can be changed by changing the opening degree. It can be adjusted.

As an ISC actuator,
A DC motor may be used instead of the stepper motor 12b. Further, the intake passage 3 is provided with a second bypass passage 11B that bypasses the throttle valve 8, and an air bypass valve 14 is interposed in the second bypass passage 11B.

Here, the air bypass valve 14 has a second
It is composed of a valve body 14a capable of contacting a valve seat portion formed in the bypass passage 11B, and a diaphragm type actuator 14b for adjusting the position of the valve body, and a diaphragm chamber of the diaphragm type actuator 14b is provided with: A pilot passage 141 communicating with the intake passage on the downstream side of the throttle valve is provided.
An air bypass valve control solenoid valve 142 is provided at 41.

Therefore, by controlling the opening degree of the air bypass valve controlling solenoid valve 142 by the ECU 25, which will be described later, in this case also, regardless of the operation of the accelerator pedal by the driver, the second bypass passage 11B is used. The intake air can be supplied to the engine 1, and the throttle bypass intake air amount can be adjusted by changing the opening thereof. The basic operation of the solenoid valve 142 for controlling the air bypass valve is to be opened during lean burn operation and closed otherwise.

An exhaust gas recirculation passage (EGR passage) for returning exhaust gas to the intake system is provided between the exhaust passage 4 and the intake passage 3.
The EGR passage 80 is provided with an EG
The R valve 81 is interposed. Here, this EGR valve 81
Is composed of a valve body 81a capable of contacting a valve seat portion formed in the EGR passage 80, and a diaphragm type actuator 81b for adjusting the position of the valve body, and is provided in a diaphragm chamber of the diaphragm type actuator 81b. Is provided with a pilot passage 82 communicating with the intake passage downstream of the throttle valve.
An ERG valve control solenoid valve 83 is interposed in the.

Therefore, by controlling the opening degree of the EGR valve controlling solenoid valve 83 by the ECU 25, which will be described later, E
The exhaust gas can be returned to the intake system through the GR passage 80. In FIG. 2, reference numeral 15 denotes a fuel pressure regulator, which operates by receiving a negative pressure in the intake passage 3 and regulates the amount of fuel returned from a fuel pump (not shown) to the fuel tank. Thus, the pressure of fuel injected from the injector 9 is adjusted.

Various sensors are provided to control the engine system. First, as shown in FIG. 2, the intake air that has passed through the air cleaner 7 is introduced into the intake passage 3
An air flow sensor (intake air amount sensor) 17 for detecting the intake air amount from the Karman vortex information is provided at a portion flowing into the inside.
An intake air temperature sensor 18 and an atmospheric pressure sensor 19 are provided.

Further, the throttle valve 8 in the intake passage 3
In addition to the potentiometer-type throttle position sensor 20 that detects the opening of the throttle valve 8, an idle switch 21 is provided in the portion where is arranged. Further, on the exhaust passage 4 side, a linear oxygen concentration sensor (hereinafter, simply referred to as “linear O ₂ sensor”) 22 that linearly detects the oxygen concentration (O ₂ concentration) in the exhaust gas on the lean side of the air-fuel ratio is provided. In addition, as other sensors,
Water temperature sensor 23 for detecting the temperature of the cooling water for the engine 1
Or a crank angle sensor 24 for detecting the crank angle shown in FIG.
(It also functions as a rotation speed sensor that detects e).
A vehicle speed sensor 30 and the like are provided.

The detection signals from these sensors and switches are input to the ECU 25 as shown in FIG. Here, the hardware configuration of the ECU 25 is as shown in FIG.
Is configured as a computer having a CPU (arithmetic unit) 26 as its main part, and the CPU 26 includes an intake air temperature sensor 18, an atmospheric pressure sensor 19, a throttle position sensor 20, a linear O ₂ sensor 22, and a water temperature sensor 23. The detection signal from the input interface 28
And is input via the analog / digital converter 29.

The CPU 26 has an air flow sensor 17, an idle switch 21, a crank angle sensor 24,
A detection signal from the vehicle speed sensor 30 or the like is directly input through the input interface 35. Further, the CPU 26 is a ROM that stores various data in addition to program data and fixed value data via a bus line.
(Memory unit) 36 or RAM that can be updated and sequentially rewritten
Data is exchanged with 37.

Further, as a result of calculation by the CPU 26, EC
From U25, a signal for controlling the operating state of the engine 1, such as a fuel injection control signal, an ignition timing control signal,
Various control signals such as an ISC control signal, a bypass air control signal and an EGR control signal are output. Here, the fuel injection control (air-fuel ratio control) signal is sent to the CPU 26.
Is output to the injector solenoid 9a for driving the injector 9 (accurately, the transistor for the injector solenoid 9a) via the injection driver 39, and the ignition timing control signal is output from the CPU 2
6 is output to a power transistor 41 via an ignition driver 40, and a spark is sequentially generated from the power transistor 41 to an ignition plug 42 by a distributor 43 via an ignition coil 42.

The ISC control signal is output from the CPU 26 to the stepper motor 12b via the ISC driver 44, and the bypass air control signal is output from the CPU 26 via the bypass air driver 45 to the air bypass valve controlling solenoid valve. It is adapted to be output to the solenoid 142a of 142. Further, the EGR control signal is sent to the CPU2.
6 through the EGR driver 46 to the solenoid 83a of the ERG valve control solenoid valve 83.

Now, focusing on the air-fuel ratio control,
For this air-fuel ratio control, the ECU 25 controls the intake air amount control means 201 and the air-fuel ratio control means 21 as shown in FIG.
0, the fuel supply means 211 is provided. Here, the intake air amount control means 201 controls the air bypass valve 14 when switching to the lean side air-fuel ratio operation (lean burn operation).
Is opened to increase the amount of intake air supplied to the combustion chamber 2 of the engine 1.

The air-fuel ratio control means 210 controls the engine 1 to control the air-fuel ratio in accordance with the operating state of the engine 1.
Target air-fuel ratio setting means 204 for setting the target air-fuel ratio in accordance with the operating state of the vehicle, and fuel amount setting means 205 for setting the fuel amount to realize the target air-fuel ratio set by the target air-fuel ratio setting means 204. ing. The fuel supply means 211 supplies fuel to the engine 1 according to the fuel amount set by the fuel amount setting means 205 in the air-fuel ratio control means 210, and the injector 9 corresponds to this.

Further, the target air-fuel ratio setting means 204 in the air-fuel ratio control means 210 changes the operation from the lean side air-fuel ratio to the rich side air-fuel ratio (including the operation in the stoichiometric state) to the lean side air-fuel ratio operation. Switching (this switching
-> L switching "), the follow-up change means 20 for continuously changing the air-fuel ratio by following the change in the actual intake air amount.
It has two functions.

Further, the follow-up changing means 202 includes a comparing means 203, a transient target air-fuel ratio setting means 207, a backup air-fuel ratio setting means 206, a change prohibiting / suppressing means 20.
8. Each function of the correction means 209 is provided. here,
The comparison means 203 compares the intake air amount immediately before the start of the S → L switching and the intake air amount during the switching transient operation.

The transient target air-fuel ratio setting means 207 is configured to set the transient target air-fuel ratio based on the comparison result of the comparing means 203. Further, the transient target air-fuel ratio setting means 207 is configured to set the transient target air-fuel ratio based on the comparison result of the comparison means 201 for a predetermined period, and after the predetermined period has elapsed, a predetermined period. The transient target air-fuel ratio may be gradually changed so as to reach the final target air-fuel ratio from the transient target air-fuel ratio at the time of elapse.

Further, the transient target air-fuel ratio setting means 207
May be configured to set a transient target air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of the S → L switch to the final target air-fuel ratio after the switch. At this time, the changing speed of the transient target air-fuel ratio set by the transient target air-fuel ratio setting means 207 is set so as to increase as the rotation speed of the engine 1 increases. The transition target air-fuel ratio change speed set in 201 may be set to change from the change speed corresponding to the high rotation operation state of the engine 1 to the change speed corresponding to the low rotation operation state.

The backup air-fuel ratio setting means 206 uses the S
The backup air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of L switching to the final target air-fuel ratio after switching is set. Change prohibition / suppression means 2
08 is for prohibiting or suppressing the change of the target air-fuel ratio during transition immediately after the switching from S to L.

The correcting means 209 corrects the intake air amount during the switching transient operation compared by the comparing means 203 in accordance with the change in the throttle opening due to the manual operation. The correcting means 209 corrects the corrected amount. The setting is made based on the intake air amount change information of the engine 1. Also,
This correcting means 209 adjusts the intake air amount not related to S → L switching between the throttle opening and the engine speed in order to correct the set target air-fuel ratio during transition in response to a change in the throttle opening due to human operation. A map is provided as a storage means that stores the parameters.

If necessary, the fuel amount setting means 205 may be configured to set the fuel amount in accordance with the larger one of the transient target air-fuel ratio and the backup air-fuel ratio. Then, in order to achieve the air-fuel ratio determined by using the above-mentioned functions, the fuel injection pulse width Tinj is adjusted to a desired state by the control signal from the fuel amount setting means 205, and the lean air-fuel ratio to be realized is obtained. It is configured to perform a burn operation.

Here, the fuel injection pulse width Tinj is expressed by the following equation (1). Tinj (j) = TB · K · KAFL + Td or Tinj (j) = TB · K + Td ·· (1) TB in this equation is the basic drive time of the injector 9 and the intake air amount A information from the air flow sensor 17 And the engine speed N information from the crank angle sensor (engine speed sensor) 24, the intake air amount A / N information per engine revolution is obtained, and the basic drive time TB is determined based on this information. There is.

KAFL is a lean correction coefficient, which is determined so as to achieve the air-fuel ratio determined by each of the control modes described later, and the operation is performed in the desired air-fuel ratio state. Further, the correction coefficient K is set according to the engine cooling water temperature, the intake air temperature, the atmospheric pressure, etc., and the dead time (ineffective time) Td is corrected according to the battery voltage.

The lean burn operation is performed when the lean operation condition determining means (not shown) determines that a predetermined condition is satisfied. By the way, each control mode in this embodiment is as follows. (A) First, the first control mode will be described. The first control mode mainly includes a comparison unit 203 that compares the intake air amount immediately before the start of the S → L switching with the intake air amount during the switching transient operation, and a transition time based on the comparison result of the comparison unit 203. A transient target air-fuel ratio setting means 201 for setting a target air-fuel ratio, and a backup air-fuel ratio for setting a backup air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of S → L switching to the final target air-fuel ratio after switching. The setting means 206 is used, and in this case, the fuel amount setting means 205 sets the fuel amount according to the larger one of the transient target air-fuel ratio and the backup air-fuel ratio.

Then, in this first control mode,
The target air-fuel ratio AFN is set by performing the operation according to the flowchart of FIG. 4 while using each of the above means. First, in step A1, it is judged whether or not the state is the state of switching to the lean burn operation. If not, the return operation is performed through the "NO" route because the state is not the lean burn operation (for example, the stoichiometric operation state). Done.

On the other hand, if it is in the state of switching to the lean burn operation, the step A2 is performed through the "YES" route.
Is executed and the lean target air-fuel ratio AFS is set. The lean target air-fuel ratio AFS is the air-fuel ratio in the lean burn operation state that should be finally achieved, and is set in the same manner as the conventional system. Then, in step A3,
It is determined whether or not the actual intake air amount Q (0) to the engine 1 has been measured, and if not, step A4 is executed through the "NO" route.

At step A4, the air flow sensor 17
Detection signal, the initial actual intake air amount Q (0) to the engine 1 immediately after switching to the lean burn operation is performed.
Is calculated. Then, in step A5, the backup air-fuel ratio AFL is set to the theoretical air-fuel ratio 1 as an initial value.
It is set to 4.7.

On the other hand, if the initial actual intake air amount Q (0) has already been calculated and the transition to the lean burn operation has been entered, a "YES" determination is made from step A3.
Step A6 is executed through the route. Step A6
Then, the actual intake air amount Q (n) at that time in the transient state
Is calculated from the detection signal of the air flow sensor 17.

Next, at step A7, the target air-fuel ratio AFQ considering the actual intake air amount Q (n) is calculated by the following equation (2).
Set by. AFQ = (Q (n) / Q (0)) × 14.7 ... (2) This value corresponds to the characteristic AFQ shown in FIG. 5, and corresponds to the actual intake air amount. The target air-fuel ratio AFQ is set.

That is, in the tracking changing means 202,
Intake air amount Q immediately before the start of operating state switching
(0) and the intake air amount Q (n) during the switching transient operation are compared by the comparison means 203, and the target air-fuel ratio setting means 2
04, the comparison result Q (n) / Q of the comparison means 203
The target air-fuel ratio AFQ is set based on (0). Then, in step A8, the backup air-fuel ratio AFL
Is set by the following equation (3-1).

AFL = AFL + ΔAFL (3−1) where ΔAFL is an increment for increasing the backup air-fuel ratio AFL from the stoichiometric air-fuel ratio 14.7 toward the air-fuel ratio in lean burn operation, and is a predetermined fixed value. Is used. The backup air-fuel ratio AFL is the characteristic AF shown in FIG.
Corresponds to L.

That is, in the tracking change means 202,
The backup air-fuel ratio AFL that gradually changes from the initial backup air-fuel ratio AFL (= 14.7) immediately before the start of switching the operating state to the final target air-fuel ratio AFS when the switching is completed is the backup air-fuel ratio setting means 20.
6 is set. Next, an upper limit check is performed in steps A9 and A10, and step A1
1, the target air-fuel ratio AFN during transition that is actually adopted
Is set.

That is, in step A11, the target air-fuel ratio AFQ obtained in step A7 and step A
The backup air-fuel ratio AFL obtained in 8 is compared, and the larger value is adopted as the transient target air-fuel ratio AFN. AFN = MAX (AFQ, AFL) As a result, the target air-fuel ratio setting means 204 sets the transient target air-fuel ratio AFN, and the fuel amount setting means 205 sets the fuel amount for realizing the transient target air-fuel ratio AFN. It

As a result, in the fuel amount setting means 205, the target air-fuel ratio A corresponding to the actual intake air amount Q (n) is obtained.
The fuel amount is set according to the larger air-fuel ratio of FQ and the backup air-fuel ratio AFL that is set by increasing the time from the initial air-fuel ratio toward the final target air-fuel ratio AFS during lean burn operation. By the way, step A9,
When the backup air-fuel ratio AFL exceeds the final target air-fuel ratio AFS (step A9), the backup air-fuel ratio AFL is set to the final target air-fuel ratio AFS (step A10). The operation of sticking AFL to the final target air-fuel ratio AFS is performed.

Since the first control mode is as described above, when switching from S to L, as shown in FIG. 5, first, the target air-fuel ratio AFQ larger than the backup air-fuel ratio AFL is set to the target air-fuel ratio during transition. The operation adopted as the fuel ratio AFN is performed. In this state, control corresponding to the actual intake air amount Q (n) at that time in the transient state is performed.

Then, the actual intake air amount Q in the transient state
As for (n), as shown in FIG. 5, the increase amount is gradually reduced, and after a certain period of time, the change is leveled off, and the target air-fuel ratio AFQ also has the same tendency. Also in this state, if the target air-fuel ratio AFQ is adopted as the transient target air-fuel ratio AFN, the transient target air-fuel ratio AFN will not reach the final target air-fuel ratio AFS.

That is, when the transitional state progresses and exceeds the state where the characteristics of the target air-fuel ratio AFQ and the characteristics of the backup air-fuel ratio AFL shown in FIG.
The backup air-fuel ratio AFL is adopted as N, and the target air-fuel ratio AFN during transition smoothly transitions toward the final target air-fuel ratio AFS. About this part, a sufficient amount of time has passed since the start of the switching to the lean burn operation, and a sufficient increase in the air amount has been achieved. Therefore, control is not performed corresponding to the actual intake air amount Q (n) at this time, Even if the control for changing to the final target air-fuel ratio AFS is performed, the feeling of deceleration does not occur.

When the final target air-fuel ratio AFS is adopted as the transient target air-fuel ratio AFN, the switching transient state ends and the same final target air-fuel ratio AFS as in the conventional case is reached.
Feedback control is performed. With such a control mode, when switching to the lean burn operation, the control that follows the actual change in the intake air amount is performed, and it is possible to prevent the state in which the air amount control is delayed with respect to the fuel injection amount control. Therefore, the generation of deceleration is surely prevented.

That is, since the air-fuel ratio is shifted to the lean side in accordance with the increase of the actual air amount, the output of the engine 1 becomes almost constant and the driving mode switching shock is not generated. Further, even if there is a manual accelerator operation, the operating state of the target air-fuel ratio is finally achieved.

Furthermore, the control mode as described above does not require additional equipment for the sensor, and the algorithm is simple,
Reliable control is performed. (B) Next, the second control mode will be described. The second control mode mainly includes a comparison unit 203 for comparing the intake air amount immediately before the start of the S → L switching and the intake air amount during the switching transient operation, and a transition time based on the comparison result of the comparison unit 203. A transient target air-fuel ratio setting means 201 for setting a target air-fuel ratio, and a backup air-fuel ratio for setting a backup air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of S → L switching to the final target air-fuel ratio after switching. The setting means 206 is used, and in this case, the backup air-fuel ratio setting means 206 for setting the backup air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of the S → L switching start to the final target air-fuel ratio after the switching. , S → L gradually changes from the air-fuel ratio immediately before the start of switching to the final target air-fuel ratio after switching. A transient target air-fuel ratio setting means 207 for setting the transit target air-fuel ratio is used, and in this case, the backup air-fuel ratio changing speed set by the backup air-fuel ratio setting means 206 becomes faster as the engine speed increases. The fuel amount setting means 205 sets the fuel amount according to the larger one of the transient target air-fuel ratio and the backup air-fuel ratio.

Then, in this second control mode,
The target air-fuel ratio AFN is set by performing the operation according to the flowchart of FIG. 6 while using each of the above means. First, in step B1, it is judged whether or not the state is the state of switching to the lean burn operation. If not, the state is not the lean burn operation (for example, the stoichiometric operation state), so the return operation is performed through the “NO” route. Done.

On the other hand, if it is in the state of switching to the lean burn operation, the step B2 is performed through the "YES" route.
Is executed and the lean target air-fuel ratio AFS is set. The lean target air-fuel ratio AFS is the air-fuel ratio in the lean burn operation state that should be finally achieved, and is set in the same manner as the conventional system. Then, in step B3,
It is determined whether or not the actual intake air amount Q (0) to the engine 1 has been measured, and if not, step B4 is executed through the "NO" route.

At step B4, the air flow sensor 17
Detection signal, the initial actual intake air amount Q (0) to the engine 1 immediately after switching to the lean burn operation is performed.
Is calculated. Next, in step B5, the backup air-fuel ratio AFL is set to the theoretical air-fuel ratio 1 as an initial value.
It is set to 4.7.

On the other hand, if the initial actual intake air amount Q (0) has already been calculated and the transition to the lean burn operation has been entered, a transition from step B3 to "YES".
Step B6 is executed through the route. Step B6
Then, the actual intake air amount Q (n) at that time in the transient state
Is calculated from the detection signal of the air flow sensor 17.

Next, at step B7, the target air-fuel ratio AFQ considering the actual intake air amount Q (n) is calculated by the following equation (2).
Set by. AFQ = (Q (n) / Q (0)) × 14.7 ·· (2) This value corresponds to the characteristic AFQ shown in FIG. 7, and corresponds to the actual intake air amount. The target air-fuel ratio AFQ is set.

That is, in the tracking change means 202,
Intake air amount Q immediately before the start of operating state switching
(0) and the intake air amount Q (n) during the switching transient operation are compared by the comparison means 203, and the target air-fuel ratio setting means 2
04, the comparison result Q (n) / Q of the comparison means 203
The target air-fuel ratio AFQ is set based on (0). Then, in step B12, the engine speed Ne is read, and in step B8, the backup air-fuel ratio A
FL is set in accordance with the read engine speed Ne by the following expression (3-2).

AFL = AFL + ΔAFL (Ne) (3-2) Here, ΔAFL (Ne) is backed up from the theoretical air-fuel ratio 14.7 to the lean-burn operation air-fuel ratio (final target air-fuel ratio AFS). This is an increment for increasing the air-fuel ratio AFL and is set corresponding to the engine speed Ne, and the engine speed Ne is read as a parameter from a predetermined map, or the engine speed Ne is determined by a predetermined equation.
Is calculated as a variable.

The backup air-fuel ratio AFL thus set is the characteristics AFL1, AFL shown in FIG.
The backup air-fuel ratio AFL is set so as to follow the characteristic AFL1 having a large inclination when the engine speed Ne is large and the characteristic AFL2 having a small inclination when the engine speed Ne is small. That is, in the follow-up change means 202, the initial backup air-fuel ratio AFL (= 14.7) immediately before the start of switching the operating state.
The backup air-fuel ratio AFL is set by the backup air-fuel ratio setting means 206 so that the backup air-fuel ratio AFL gradually changes from the above to the final target air-fuel ratio AFS at the completion of the switching.

Next, the upper limit value check is carried out in steps B9 and B10, and the actually adopted transient target air-fuel ratio AFN is set in step B11. That is, at step B11, the target air-fuel ratio AFQ obtained at step B7 and the backup air-fuel ratio AFL obtained at step B8 are compared, and the larger value is adopted as the transient target air-fuel ratio AFN.

AFN = MAX (AFQ, AFL) As a result, the target air-fuel ratio setting means 204 sets the transient target air-fuel ratio AFN, and the fuel amount setting means 205 sets the fuel amount for realizing the transient target air-fuel ratio AFN. Is set. Then, in the fuel amount setting means 205, the target air-fuel ratio A corresponding to the actual intake air amount Q (n)
The fuel amount is set according to the larger air-fuel ratio of FQ and the backup air-fuel ratio AFL that is set by increasing the time from the initial air-fuel ratio toward the final target air-fuel ratio AFS during lean burn operation.

When the backup air-fuel ratio AFL exceeds the final target air-fuel ratio AFS (step B9), the upper limit value check in steps B9 and B10 sets the backup air-fuel ratio AFL to the final target air-fuel ratio AFS (step B10). ), After this, backup air-fuel ratio A
The operation of sticking FL to the final target air-fuel ratio AFS is performed.

Since the second control mode is configured as described above, when the stoichio operation is switched to the lean burn operation (S → L switching), first, as shown in FIG. 7, the backup air-fuel ratio AFL is set. An operation is performed in which a larger target air-fuel ratio AFQ is adopted as the transient target air-fuel ratio AFN. In this state, control corresponding to the actual intake air amount Q (n) at that time in the transient state is performed.

Then, the actual intake air amount Q in the transient state
As for (n), as shown in FIG. 7, the increase amount is gradually reduced, and after a certain period of time, the change is leveled off, and the target air-fuel ratio AFQ also has the same tendency. Also in this state, if the target air-fuel ratio AFQ is adopted as the transient target air-fuel ratio AFN, the transient target air-fuel ratio AFN will not reach the final target air-fuel ratio AFS.

That is, when the transitional state progresses and exceeds the state where the characteristics of the target air-fuel ratio AFQ and the characteristics of the backup air-fuel ratio AFL shown in FIG.
The backup air-fuel ratio AFL is adopted as N, and the target air-fuel ratio AFN during transition smoothly transitions toward the final target air-fuel ratio AFS. In this part, a sufficient amount of time has passed from the start of switching to the lean burn operation, and a sufficient increase in the air amount has been achieved. Therefore, the control does not correspond to the actual intake air amount Q (n) at that time, Even if the control for changing to the final target air-fuel ratio AFS is performed, the feeling of deceleration does not occur.

Since the backup air-fuel ratio AFL is set corresponding to the engine speed Ne, accurate control is performed. When the final target air-fuel ratio AFS is adopted as the transient target air-fuel ratio AFN, the switching transient state ends, and the final target air-fuel ratio AF similar to the conventional one is reached.
Feedback control by S is performed.

By the way, according to such a control mode, when switching to the lean burn operation, the control following the actual change of the intake air amount is performed, and the control of the air amount is delayed with respect to the fuel injection amount control. The state can be prevented, and the occurrence of deceleration feeling is surely prevented. That is, since the air-fuel ratio is shifted to the lean side in accordance with the increase in the actual air amount, the output of the engine 1 becomes almost constant and the driving mode switching shock is not generated.

In addition, even if there is an artificial accelerator operation,
Eventually, the operating state of the target air-fuel ratio is achieved. further,
The control mode as described above does not require additional equipment for the sensor, the algorithm is simple, and reliable control is performed. (C) Next, the third control mode will be described.

In the above-described second control mode, step B7
As in step B11 and step B11, the larger one of the target air-fuel ratio AFQ in consideration of the actual intake air amount and the backup air-fuel ratio AFL corresponding to the engine speed Ne is employed for the control. The control mode is to set the transition target air-fuel ratio AFN without the backup air-fuel ratio AFL by setting the increment ΔAFN (Ne) of the transition target air-fuel ratio AFN in consideration of the actual intake air amount.

In this case, the transient target air-fuel ratio setting means 207 for setting the transient target air-fuel ratio AFN that gradually changes from the air-fuel ratio immediately before the start of the S → L switch to the final target air-fuel ratio after the switch is performed. use. The processing flow at this time is as shown in FIG. That is, first, in step B1, it is determined whether or not the state is the state of switching to the lean burn operation. If not, the state is not the lean burn operation (for example, the stoichiometric operation state), and therefore the return is made through the “NO” route. The operation is performed.

On the other hand, if it is in the state of switching to the lean burn operation, the step B2 is performed through the "YES" route.
Is executed and the lean target air-fuel ratio AFS is set. The lean target air-fuel ratio AFS is the air-fuel ratio in the lean burn operation state that should be finally achieved, and is set in the same manner as the conventional system. Then, in step B3 ', it is determined whether or not the initial value has been set, and if not set, step B5' is executed through the "NO" route.

At step B5 ', the transient target air-fuel ratio A
FN is set to the theoretical air-fuel ratio of 14.7 as an initial value. On the other hand, if the initial value has already been set and the transition to the lean burn operation has been entered, step B3 ′ to step B1 through the “YES” route.
2 is executed.

At step B12, the engine speed Ne
Is read, and in step B8 ', the target air-fuel ratio AFN during transition is set by the following equation (3-3) corresponding to the read engine speed Ne. AFN = AFN + ΔAFN (Ne) (3-3) where ΔAFN (Ne) is the target air-fuel ratio during transition from the theoretical air-fuel ratio of 14.7 to the air-fuel ratio of lean burn operation (final target air-fuel ratio AFS). It is an increment to increase the fuel ratio AFN,
It is set corresponding to the engine speed Ne and is read from a predetermined map with the engine speed Ne as a parameter, or is calculated with a predetermined formula using the engine speed Ne as a variable.

The target air-fuel ratio during transient A set by this
FN is the characteristic AFL1, AFL2 shown in FIG.
The transient target air-fuel ratio AFN is set so as to follow the characteristic AFL1 having a large inclination when the engine speed Ne is large and the characteristic AFL2 having a small inclination when the engine speed Ne is small. That is, in the follow-up change means 202, the transient target air-fuel ratio that gradually changes from the initial target air-fuel ratio AFN (= 14.7) immediately before the start of switching the operating state to the final target air-fuel ratio AFS when the switching is completed. The fuel ratio AFN is set by the transient target air-fuel ratio setting means 207.

Next, the upper limit value check is performed in steps B9 'and B10'. As a result, the target air-fuel ratio setting means 204 sets the transient target air-fuel ratio AFN, and the fuel amount setting means 205 sets the fuel amount for realizing the transient target air-fuel ratio AFN. Then, in the fuel amount setting means 205, the fuel amount is set according to the set target air-fuel ratio AFN during the transition.

The upper limit value check in steps B9 'and B10' is carried out when the transient target air-fuel ratio AFN exceeds the final target air-fuel ratio AFS (step B9 '). AFS is set (step B10 '), and then the target air-fuel ratio A during transition is set.
The operation of sticking FN to the final target air-fuel ratio AFS is performed.

According to this third control mode, the above-mentioned second
In addition to the advantage of the control mode, it is not necessary to calculate the target air-fuel ratio AFQ, and almost the same operation is realized by simpler control. (D) Next, the fourth control mode will be described. In the fourth control mode, mainly, a transient target air-fuel ratio setting that sets a transient target air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of S → L switching to the final target air-fuel ratio after switching is performed. The means 207 and the change prohibition / suppression means 208 for prohibiting or suppressing the change of the target air-fuel ratio during the transition immediately after the S → L switching are used. In this case, the changing speed of the transient target air-fuel ratio set by the transient target air-fuel ratio setting means 207 is changed from the changing speed corresponding to the high rotation operating state of the engine 1 to the changing speed corresponding to the low rotation operating state. Is composed of.

In the fourth control mode,
The target air-fuel ratio AFN is set by performing the operation according to the flowchart of FIG. 9 while using each of the above means. First, in step C1, it is judged whether or not it is in the lean burn operation region. If it is not in the switching state, it is in the stoichiometric operation state, so "NO".
A return operation is performed through the route.

On the other hand, in the lean burn operation range, switching to the lean operation state is started, and "YE
Step C2 is executed through the "S" route. That is, the countdown of the number of strokes from the start of switching is started in step C2, and the time t corresponding to this number of strokes is compared with the predetermined value t0 in step C3.

The predetermined value t0 is set by the engine speed Ne immediately before switching, and for example, the predetermined values t0 corresponding to the following respective rotation speeds are stored in the map in advance,
It is read from the same map and set. Ne (rpm) = 750,1000,1250,1500,2000,2500,3000,
3500 Note that the predetermined value t0 is set smaller as the engine speed Ne is larger.

Then, until the time t corresponding to the number of strokes reaches the set predetermined value t0, step C4 is executed through the "YES" route from step C3 to set the transient target air-fuel ratio AFT immediately before switching. The target air-fuel ratio AFTI is adopted. When the time t corresponding to the number of strokes reaches the set predetermined value t0, the steps C3 to “N
Step C5 is executed through the "O" route.

This operation is performed by the change prohibiting / suppressing means 208, and the change of the transient target air-fuel ratio AFT is suppressed for a predetermined time t0 immediately after switching to the lean burn operation. That is, immediately after switching to the lean burn operation, the actual intake air amount starts to increase with a dead time, but by suppressing the increase in the target air-fuel ratio during the time corresponding to this dead time, the sense of deceleration is reduced. Occurrence is prevented.

This state corresponds to the portion on the horizontal axis from time "0" to "t0" shown in FIG. 10, and the transient target air-fuel ratio AFT is maintained at the target air-fuel ratio AFTI immediately before switching. Then, in step C5, the transient target air-fuel ratio A
FT is a predetermined value AFT1 (AFTI <AFT1 <AFT
F), and step C6 is initially executed through the “YES” route.

At step C6, the transient target air-fuel ratio AFT is calculated by the following equation (4-1). AFT = (1−AFTTL) × AFTI + AFTTL × AFT1 (4-1) where AFTTL is an initial value “0” and an end value “1.
0 "corresponds to the elapsed time from the switching of the operating state in which AFTTL1 is added for each stroke. As shown in FIG. 10, at time t0, AFTTL =" 0 ", and the transient target air-fuel ratio AFT becomes AFT1. AFTTL = "1" is taken at the time to reach.

That is, for the portion of the transient target air-fuel ratio AFT from the target air-fuel ratio AFTI immediately before switching to the intermediate predetermined air-fuel ratio AFT1, the transient target air-fuel ratio AFT at that time is obtained by linear interpolation. Also,
The intermediate predetermined air-fuel ratio AFT1 is set so as to correspond to the lean side upper limit of the region where NO _x is likely to occur, and the transition in the portion from the target air-fuel ratio AFTI immediately before switching to the intermediate predetermined air-fuel ratio AFT1. Target air-fuel ratio A
By increasing the rate of change of FT, it is possible to quickly pass through a region where NO _x is likely to be generated.

Thus, the calculation of the transient target air-fuel ratio AFT by the above equation (4-1) is continued until the intermediate predetermined air-fuel ratio AFT1 is reached, and when the intermediate predetermined air-fuel ratio AFT1 is exceeded, in step C5 The "NO" route is taken and step C7 is executed. In step C7, the following equation (4-
The target air-fuel ratio AFT during transition is calculated by 2).

AFT = (1-AFTTL) × AFT1 + AFTTL × AFTF (4-2) Here, AFTTL is an initial value “0” and an end value “1.
"0" is obtained by adding AFTTL2 for each stroke, and corresponds to the elapsed time from the time when the transient target air-fuel ratio AFT reaches the intermediate predetermined air-fuel ratio AFT1.

That is, as shown in FIG. 10, during the time when the transient target air-fuel ratio AFT is the intermediate predetermined air-fuel ratio AFT1, AFTTL = “0”, the transient target air-fuel ratio AFT.
Takes AFTTL = “1” at the time when the final target air-fuel ratio AFTF is reached at the end of switching. Therefore, the portion from the time when the transient target air-fuel ratio AFT is the intermediate predetermined air-fuel ratio AFT1 to the time when the transient target air-fuel ratio AFT reaches the final target air-fuel ratio AFTF at the end of switching is linearly interpolated at that time point. The target air-fuel ratio AFT at the time of transition is calculated.

The coefficients AFTTL1 and AFTTL2
Is set by the volumetric efficiency Ev immediately before switching to the lean burn operation and the engine speed Ne. For example, predetermined values corresponding to the following values are stored in advance as a map, and from the map Read and set. Ne (rpm) = 750,1000,1250,1500,2000,2500,3000,
3500 Ev (%) = 20,30,40,50,60,70 When the transient target air-fuel ratio AFT reaches the final target air-fuel ratio AFTF at the end of switching to the lean burn operation, “YES” in step C8. The route is taken, the switching operation is completed, and the feedback control by the final target air-fuel ratio AFTF similar to the conventional one is performed.

By the way, the change of the target air-fuel ratio AFT during the transition during the switching operation becomes like the characteristic shown in FIG.
As a whole, a change similar to the actual change of the intake air amount (see FIG. 18) is performed. Therefore, it is possible to avoid a feeling of deceleration caused by a change in intake air amount accompanied by a dead time and a first-order delay, and at the portion from the target air-fuel ratio AFTI immediately before switching to the intermediate predetermined air-fuel ratio AFT1, the transient target air-fuel ratio Since the rate of change of the fuel ratio AFT is set to a large value, it is possible to quickly pass through a region where NO _x is likely to be generated.

Since the transient target air-fuel ratio AFT is set in correspondence with the engine speed Ne, accurate control is performed. Also, when switching to lean burn operation, control that follows the actual change in intake air amount is performed, and it becomes possible to prevent the state in which the air amount control is delayed relative to the fuel injection amount control, and it is possible to reduce the deceleration. The generation of feeling is surely prevented.

That is, since the air-fuel ratio is shifted to the lean side in accordance with the increase of the actual air amount, the output of the engine 1 becomes almost constant and the driving mode switching shock is not generated. Further, even if there is a manual accelerator operation, the operating state of the target air-fuel ratio is finally achieved.

Furthermore, the above control mode does not require additional equipment for the sensor, the algorithm is simple, and reliable control is performed. (E) Next, the fifth control mode will be described. In the fifth control mode, the transient target air-fuel ratio is set mainly for a predetermined period based on the comparison result of the comparison unit 203, and after the predetermined period has elapsed, the transient target after the predetermined period has elapsed. The transient target air-fuel ratio setting means 207 for gradually changing the transient target air-fuel ratio from the air-fuel ratio to the final target air-fuel ratio and the intake air amount during the switching transient operation compared by the comparing means 203 are artificially operated. Correction means 209 for correcting in response to changes in throttle opening
Use and. In this case, the correction unit 209 is configured to set the correction amount based on the intake air amount change information of the internal combustion engine.

In the fifth control mode,
By performing the operation according to the flowchart of FIG. 11 while using each of the above means, the target air-fuel ratio AFN
Is set. First, in step D0, the intake air amount change rate dQI _n is calculated by the following equation (5).

DQI _n = ALPH × dQI _n-1 + (1-ALPH) × (Q _n −Q _n-1 ) ·· (5) where dQI _n−1 is the previously calculated intake air amount change rate. , Q _n is the intake air amount measured this time, Q _n-1 is the intake air amount measured last time, and the previous intake air amount change rate d
The QI _n-1 and the current intake air amount change rate dQI _n are subjected to the primary smoothing processing by the weighting coefficient ALPH.

As a result, the influence of the instantaneous noise component
Intake air amount change rate dQI _nIs calculated stably
Be done. Intake air amount change rate dQI_nCalculation of the calculation cycle
The engine 1 is in a lean operating state.
It continues until it enters the burn operation area. Engine 1
When the operating state of the vehicle enters the lean burn operating area, the
At D1, switching to lean operation state starts
And the step D2 is executed through the “YES” route.
It

That is, the countdown of the number of strokes from the start of switching is started in step D2, and the time t corresponding to this number of strokes is set to the predetermined value t in step D3.
Compared to 1. The predetermined value t1 is set by the engine speed Ne immediately before switching, and for example, the predetermined value t1 corresponding to each of the following rotation speeds is stored in the map in advance and is read and set from the map.

Ne (rpm) = 750,1000,1250,1500,200
0,2500,3000,3500 Then, until the time t corresponding to the number of strokes reaches the set predetermined value t1, step D4 is executed through the “YES” route from the step D3, and the transient target air-fuel ratio A
FT is calculated by the following equation (6). AFT = AFTI × Qr / QI (6) Here, AFTI is the target air-fuel ratio immediately before switching, QI is the intake air amount immediately before switching, and Qr is calculated by the following equation (7).

Qr = Qn-Qacc (7) Here, Qn is the intake air amount measured at that time, and Qa
cc is a correction value, and the correction value Qacc is an initial value "0".
Then, the intake air amount change rate dQ immediately before switching for each stroke
The value obtained by adding I _n is taken. Therefore, the correction value Qa
cc is the intake air increase amount after the switching, _assuming that the intake air amount change rate dQI _n immediately before the switching is maintained after the switching, and corresponds to the amount indicated by Qacc in FIG.

That is, the intake air amount change rate dQI _n immediately before switching to the lean burn operation corresponds to the change in the throttle opening due to the manual operation performed at that time, and the change is the dotted line in FIG. Corresponds to the change (slope) indicated by. This change (slope) is continued regardless of switching to the lean burn operation, and is maintained even after the switching operation to the lean burn operation is started. Therefore, the correction value Qacc is assumed to be due to the manual operation and the actual inhalation is performed. It is subtracted from the air amount Qn.

The value Qr obtained by subtracting the correction value Qacc from the actual intake air amount Qn excludes the intake air amount caused by the change in the throttle opening due to the manual operation, and is the air bypass when switching to the lean burn operation. This is due to the opening of the valve 14. As a result, the actual intake air amount Q _{r associated} with switching to the lean burn operation is calculated, and its transient characteristic is shown by the characteristic shown in FIG.

The transient transition control to the lean burn operation by such characteristics is performed, and the intake air amount Q _n during the transition transient operation in the comparison unit 203 is changed by the correction unit 209 to the throttle opening change due to the manual operation. Correspondingly corrected. Further, the correction amount Qacc by the correction means 209 is the intake air amount change information dQI _{n of the} engine 1.
It is set based on.

Then, using the actual intake air amount Q _r calculated as a result of the correction as described above, the transient target air-fuel ratio AFT is used.
Is calculated by the above equation (6). As a result, the transient target air-fuel ratio AFT is set in correspondence with the actual intake air amount Q _r . The transient target air-fuel ratio AFT is set by such means until the intermediate predetermined air-fuel ratio AFT1 is reached.

That is, the transient target air-fuel ratio AFT is obtained in correspondence with the actual intake air amount for the portion from the target air-fuel ratio AFTI immediately before switching to the intermediate predetermined air-fuel ratio AFT1, and the target air-fuel ratio is obtained. Control is performed.
By the way, the intermediate predetermined air-fuel ratio AFT1 is set so as to correspond to the lean side upper limit of the region where NO _x is likely to occur, and the actual intake air amount Q _r of the portion exceeding the intermediate predetermined air-fuel ratio AFT1 is , As shown in FIG. 13, the characteristics are such that a gradual change is made.

For this portion, the control in step D6 is performed. That is, after a lapse of time t1 from the start of switching to the lean burn operation, step D6 is executed through the “NO” route from step D3.
At step D6, the transient target air-fuel ratio AFT is calculated by the following equation (7). AFT = (1−AFTTL) × AFT1 + AFTTL × AFTF (7) Here, AFTTL has an initial value “0” and an end value “1.
"0" is obtained by adding AFTTL1 for each stroke, and corresponds to the elapsed time from the time when the transient target air-fuel ratio AFT reaches the intermediate predetermined air-fuel ratio AFT1.

That is, as shown in FIG. 13, during the time when the transient target air-fuel ratio AFT is the intermediate predetermined air-fuel ratio AFT1, AFTTL = "0", the transient target air-fuel ratio AFT.
Takes AFTTL = “1” at the time when the final target air-fuel ratio AFTF is reached at the end of switching. Therefore, the portion from the time when the transient target air-fuel ratio AFT is the intermediate predetermined air-fuel ratio AFT1 to the time when the transient target air-fuel ratio AFT reaches the final target air-fuel ratio AFTF at the end of switching is linearly interpolated at that time point. The target air-fuel ratio AFT at the time of transition is calculated.

The coefficient AFTTL1 is set by the volumetric efficiency Ev immediately before switching to the lean burn operation and the engine speed Ne. For example, a predetermined value corresponding to each of the following values is set in advance. It is stored as a map, read from the map, and set. Ne (rpm) = 750,1000,1250,1500,2000,2500,3000,
3500 Ev (%) = 20,30,40,50,60,70 In this way, the transient target air-fuel ratio AFT for the control after exceeding the intermediate predetermined air-fuel ratio AFT1 is set by linear interpolation. The transitional target air-fuel ratio AFT is appropriately increased toward the final target air-fuel ratio AFTF, and the final target air-fuel ratio AFTF is achieved in a timely manner.

That is, the actual intake air amount Q _r after exceeding the intermediate predetermined air-fuel ratio AFT1 has a gradual change characteristic, and if the transient target air-fuel ratio AFT is set corresponding to this actual intake air amount Q _r. However, the achievement of the final target air-fuel ratio AFTF is delayed, but as described above, linear interpolation is performed for this portion, so that the final target air-fuel ratio AFTF is reduced.
Accurate control is performed by preventing the delay in achieving TF.

When the transient target air-fuel ratio AFT reaches the final target air-fuel ratio AFTF at the end of switching to the lean burn operation, "YES" in step D8.
The route is taken, the switching operation is completed, and the feedback control by the final target air-fuel ratio AFTF similar to the conventional one is performed. By the way, the transitional target air-fuel ratio AFT during the switching operation has a characteristic shown in FIG. 13, and as a whole, a variation similar to the actual variation of the intake air amount is performed. Therefore, it is possible to avoid the occurrence of a sense of deceleration due to the dead time and the first-order delay in the change in the intake air amount, and to linearly increase the transient target air-fuel ratio AFT in the portion where the change in the intake air amount becomes gentle. ,
Switching control is completed in a timely manner, and accurate control is performed.

Since the target air-fuel ratio AFT during transition is set in correspondence with the engine speed Ne, accurate control is performed. Also, when switching to lean burn operation, control that follows the actual change in intake air amount is performed, and it becomes possible to prevent the state in which the air amount control is delayed relative to the fuel injection amount control, and it is possible to reduce the deceleration. The generation of feeling is surely prevented.

That is, since the air-fuel ratio is shifted to the lean side in accordance with the increase of the actual air amount, the output of the engine 1 becomes almost constant and the driving mode switching shock is not generated. Further, even if there is a manual accelerator operation, the correction corresponding to the accelerator operation is performed to perform the control, so that the generation of deceleration feeling is prevented.

Further, the above control mode does not require additional equipment for the sensor, has a simple algorithm, and performs reliable control. (F) Next, a sixth control mode will be described. In the sixth control mode, the transient target air-fuel ratio is mainly set for a predetermined period based on the comparison result of the comparison unit 203, and after the predetermined period has elapsed, the transient target after the predetermined period has elapsed. The transient target air-fuel ratio setting means 207 for gradually changing the transient target air-fuel ratio from the air-fuel ratio to the final target air-fuel ratio and the intake air amount during the switching transient operation compared by the comparing means 203 are artificially operated. Correction means 209 for correcting in response to changes in throttle opening
Use and. In this case, the correction unit 209 corrects the set target air-fuel ratio during transition in response to a change in the throttle opening due to an artificial operation, so that the intake air amount not related to switching to the lean burn operation is adjusted to the throttle opening and the engine. It has a map (storage means) that stores the number of rotations as a parameter.

In the sixth control mode,
By performing the operation in accordance with the flowchart of FIG. 14 while using each of the above means, the target air-fuel ratio AFN
Is set. First, when the operating state of the engine 1 enters the lean burn operating region, switching to the lean operating state is started in step E1, and step E2 is executed through the “YES” route.

That is, in step E2, the countdown of the number of strokes from the start of switching is started, and the time t corresponding to this number of strokes is the predetermined value t in step E3.
Compared to 1. The predetermined value t1 is set by the engine speed Ne immediately before switching, and for example, the predetermined value t1 corresponding to each of the following rotation speeds is stored in the map in advance and is read and set from the map.

Ne (rpm) = 750,1000,1250,1500,200
0,2500,3000,3500 And, until the time t corresponding to the number of strokes reaches the set predetermined value t1, step E4 is executed through the “YES” route from the step E3, and the transient target air-fuel ratio A
FT is calculated by the following equation (8). AFT = AFTI × Qr / QI (8) Here, AFTI is the target air-fuel ratio immediately before switching, QI is the intake air amount immediately before switching, and Qr is calculated by the following equation (9).

Qr = Qn-Qacc = Qn- (Qthne-QI) (9) where Qn is the intake air amount measured at that time, and Qa
cc is a correction value, and the correction value Qacc is an initial value "0".
Then, for each stroke, the predetermined value Qth stored in the map in advance
ne and the intake air amount QI at the start of switching to the lean burn operation.

That is, the predetermined value Qthne is the intake air amount during stoichiometric operation, and the throttle opening TH
(V) and engine speed Ne (rpm) are stored in advance as parameters. These values are stored corresponding to the following characteristic values, for example. Ne (rpm) = 750,1000,1250,1500,2000,2500,3000,
3500 TH (V) = 0.635,1.26,1.885,2.510,3.135,3.76,4.38
5 Here, as in the case of the fourth control mode, the correction value Qacc is the intake air amount change rate dQI _n immediately before switching.
Is the amount of increase in intake air after switching, which corresponds to the amount indicated by Qacc in FIG.

That is, the intake air amount change rate dQI _n immediately before the switching to the lean burn operation corresponds to the change in the throttle opening due to the manual operation performed at that time, and the change is the dotted line in FIG. Corresponds to the change (slope) indicated by. This change continues regardless of switching to lean burn operation, and continues even after the start of switching operation to lean burn operation.
This correction value Qacc is subtracted from the actual intake air amount Qn, assuming that it is due to a manual operation.

The correction value Qacc is obtained via the intake air amount Qthne which is a map value. This intake air amount Qthne is an amount corresponding to the display in FIG. It is obtained by subtracting the intake air amount QI at the start of switching to operation. The value Qr obtained by subtracting the correction value Qacc from the actual intake air amount Qn excludes the intake air amount caused by the change in the throttle opening due to the manual operation, and the air bypass valve at the time of switching to the lean burn operation. 14 due to the opening of 14.

As a result, the actual intake air amount Q _{r associated} with the switch to the lean burn operation is calculated, and its transient characteristic is shown by the characteristic shown in FIG. The transient transition control to the lean burn operation based on such characteristics is performed, and the intake air amount Q _n during the transition transient operation in the comparison unit 203 is corrected by the correction unit 209 in response to the change in the throttle opening due to the manual operation. Will be corrected.

Then, using the actual intake air amount Q _r calculated as a result of the correction as described above, the transient target air-fuel ratio AFT is used.
Is calculated by the above equation (8). As a result, the transient target air-fuel ratio AFT is set in correspondence with the actual intake air amount Q _r . The transient target air-fuel ratio AFT is set by such means until the intermediate predetermined air-fuel ratio AFT1 is reached.

That is, the transient target air-fuel ratio AFT is obtained in correspondence with the actual intake air amount for the portion from the target air-fuel ratio AFTI immediately before switching to the intermediate predetermined air-fuel ratio AFT1, and the target air-fuel ratio is obtained. Control is performed.
By the way, the intermediate predetermined air-fuel ratio AFT1 is set so as to correspond to the lean side upper limit of the region where NO _x is likely to occur, and the actual intake air amount Q _r of the portion exceeding the intermediate predetermined air-fuel ratio AFT1 is , As shown in FIG. 13, the characteristics are such that a gradual change is made.

For this portion, control in step E6 is performed. That is, after the time t1 has elapsed from the start of switching to the lean burn operation, step E6 is executed through the "NO" route from step E3.
At step E6, the transient target air-fuel ratio AFT is calculated by the following equation (10). AFT = (1−AFTTL) × AFT1 + AFTTL × AFTF (7) Here, AFTTL has an initial value “0” and an end value “1.
"0" is obtained by adding AFTTL1 for each stroke, and corresponds to the elapsed time from the time when the transient target air-fuel ratio AFT reaches the intermediate predetermined air-fuel ratio AFT1.

That is, as shown in FIG. 13, during the time when the transient target air-fuel ratio AFT is the intermediate predetermined air-fuel ratio AFT1, AFTTL = “0”, the transient target air-fuel ratio AFT.
Takes AFTTL = “1” at the time when the final target air-fuel ratio AFTF is reached at the end of switching. Therefore, the portion from the time when the transient target air-fuel ratio AFT is the intermediate predetermined air-fuel ratio AFT1 to the time when the transient target air-fuel ratio AFT reaches the final target air-fuel ratio AFTF at the end of switching is linearly interpolated at that time point. The target air-fuel ratio AFT at the time of transition is calculated.

The coefficient AFTTL1 is set by the volumetric efficiency Ev immediately before switching to the lean burn operation and the engine speed Ne. For example, a predetermined value corresponding to each of the following values is set in advance. It is stored as a map, read from the map, and set. Ne (rpm) = 750,1000,1250,1500,2000,2500,3000,
3500 Ev (%) = 20,30,40,50,60,70 In this way, the transient target air-fuel ratio AFT for the control after exceeding the intermediate predetermined air-fuel ratio AFT1 is set by linear interpolation. The transitional target air-fuel ratio AFT is appropriately increased toward the final target air-fuel ratio AFTF, and the final target air-fuel ratio AFTF is achieved in a timely manner.

That is, the actual intake air amount Q _r after exceeding the intermediate predetermined air-fuel ratio AFT1 has a gradual change characteristic, and the transient target air-fuel ratio AFT is set in correspondence with this actual intake air amount Q _r. However, the achievement of the final target air-fuel ratio AFTF is delayed, but as described above, linear interpolation is performed for this portion, so that the final target air-fuel ratio AFTF is reduced.
Accurate control is performed by preventing the delay in achieving TF.

When the transient target air-fuel ratio AFT reaches the final target air-fuel ratio AFTF at the end of switching to the lean burn operation, "YES" in step E8.
The route is taken, the switching operation is completed, and the feedback control by the final target air-fuel ratio AFTF similar to the conventional one is performed. By the way, the transitional target air-fuel ratio AFT during the switching operation has a characteristic shown in FIG. 13, and as a whole, a variation similar to the actual variation of the intake air amount is performed. Therefore, it is possible to avoid the occurrence of a sense of deceleration due to the dead time and the first-order delay in the change in the intake air amount, and to linearly increase the transient target air-fuel ratio AFT in the portion where the change in the intake air amount becomes gentle. ,
Switching control is completed in a timely manner, and accurate control is performed.

Since the target air-fuel ratio AFT during transition is set corresponding to the engine speed Ne, accurate control is performed. Also, when switching to lean burn operation, control that follows the actual change in intake air amount is performed, and it becomes possible to prevent the state in which the air amount control is delayed relative to the fuel injection amount control, and it is possible to reduce the deceleration. The generation of feeling is surely prevented.

That is, since the air-fuel ratio is shifted to the lean side in accordance with the increase of the actual air amount, the output of the engine 1 becomes almost constant and the driving mode switching shock is not generated. Further, even if there is a manual accelerator operation, the correction corresponding to the accelerator operation is performed to perform the control, so that the generation of deceleration feeling is prevented.

Further, the control mode as described above does not require additional equipment for the sensor, the algorithm is simple, and reliable control is performed.

[0154]

As described in detail above, according to the air-fuel ratio control apparatus for an internal combustion engine (Claim 1) of the present invention, operation at a leaner air-fuel ratio than the stoichiometric air-fuel ratio and overrunning at the lean-side air-fuel ratio is performed. In an internal combustion engine capable of switching between operation with a rich side air-fuel ratio depending on the operating state, intake air that increases the amount of intake air supplied to the combustion chamber of the internal combustion engine when switching to operation with the lean side air-fuel ratio Air amount control means, target air-fuel ratio setting means for setting a target air-fuel ratio according to the operating state of the internal combustion engine, and the target air-fuel ratio setting means for controlling the air-fuel ratio according to the operating state of the internal combustion engine According to the fuel amount set by the fuel amount setting means in the air-fuel ratio control means, and an air-fuel ratio control means having a fuel amount setting means for setting the fuel amount to achieve the target air-fuel ratio set by Fuel supplier for supplying fuel to the internal combustion engine The target air-fuel ratio setting means in the air-fuel ratio control means, when switching from the lean side air-fuel ratio operation to the lean side air-fuel ratio operation, the actual intake air amount With a simple configuration in which a follow-up changing means for continuously changing the air-fuel ratio in accordance with the change of 1 is provided, there are the following effects or advantages.

(1) At the time of switching to the lean burn operation, the control following the actual change in the intake air amount is performed, and it is possible to prevent the state in which the air amount control is delayed with respect to the fuel injection amount control. Therefore, it is possible to reliably prevent the generation of deceleration. (2) Since the air-fuel ratio is shifted to the lean side in accordance with the increase in the actual air amount, the output of the engine becomes almost constant and the driving mode switching shock is not generated.

(3) Even if there is an artificial accelerator operation,
Eventually, the operating state of the target air-fuel ratio is achieved. (4) No additional equipment is required for the sensor, the algorithm is simple, and reliable control is performed. Further, according to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 2), the follow-up changing means in claim 1 changes the intake air amount immediately before the switching of the operating state and the intake air during the switching transient operation. The apparatus according to claim 1, which has a simple configuration including a comparing means for comparing the quantity and a transient target air-fuel ratio setting means for setting a transient target air-fuel ratio based on a comparison result in the comparing means. Similar effects or advantages are obtained.

According to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 3), the follow-up change means in claim 2 has the final target after switching from the air-fuel ratio immediately before the start of switching the operating state. The backup air-fuel ratio setting means for setting a backup air-fuel ratio that gradually changes to reach the air-fuel ratio is provided, and the fuel amount setting means is the larger of the transient target air-fuel ratio and the backup air-fuel ratio. With a simple configuration in which the fuel amount is set according to the air-fuel ratio of
In addition to the effect of (4), there are the following effects and advantages.

(5) When the transient state progresses and exceeds the state where the target air-fuel ratio setting characteristic and the backup air-fuel ratio setting characteristic intersect, the backup target air-fuel ratio is adopted as the transient target air-fuel ratio. As the air-fuel ratio smoothly transitions to the final target air-fuel ratio, a sufficient amount of time has elapsed from the start of switching to lean burn operation and a sufficient increase in air amount has been achieved for this part. Even if control is performed to change to the final target air-fuel ratio instead of control corresponding to the actual intake air amount at that time, deceleration feeling is not generated and accurate control is performed.

Further, according to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 4), the follow-up change means in claim 1 has the final target after switching from the air-fuel ratio immediately before the start of switching the operating state. The transient target air-fuel ratio is set so as to set the transient target air-fuel ratio that gradually changes to reach the air-fuel ratio, and the transient target air-fuel ratio is set by the transient target air-fuel ratio setting means. In addition to the effects (1) to (4) described above, the following effects and advantages are provided by a simple configuration in which the changing speed of (1) becomes faster as the rotation speed of the internal combustion engine increases.

(6) Since the target air-fuel ratio during transition is set corresponding to the engine speed Ne, accurate control is performed. Further, according to the air-fuel ratio control apparatus for an internal combustion engine of the present invention (Claim 5), the change speed of the backup air-fuel ratio set by the backup air-fuel ratio setting unit according to Claim 3 increases as the rotational speed of the internal combustion engine increases. Since the speed is increased, the following effects and advantages are provided in addition to the effects (1) to (4) described above.

(7) Since the backup air-fuel ratio is set corresponding to the engine speed Ne, accurate control is performed. According to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 6), the follow-up change means according to claim 1 changes from the air-fuel ratio immediately before the start of switching the operating state to the final target air-fuel ratio after switching. A transition target air-fuel ratio setting means for setting a transition target air-fuel ratio that gradually changes so that the transition target air-fuel ratio changing speed set by the transition target air-fuel ratio setting means is set. Is a simple configuration in which the changing speed corresponding to the high rotation operating state of the internal combustion engine is changed to the changing speed corresponding to the low rotation operating state.
In addition to the effect of (4), there are the following effects and advantages.

(8) The transitional change in the target air-fuel ratio during the transition operation is similar to the actual change in the intake air amount as a whole. Therefore, it is possible to avoid the occurrence of a feeling of deceleration due to a change in the intake air amount with a dead time and a first-order delay. (9) at a portion extending from the target air-fuel ratio immediately before switching to a predetermined air-fuel ratio of the intermediate is because it is largely set the change rate of the transitional target air-fuel ratio, the possibility of the NO _x generation is to quickly pass through regions of high be able to.

Further, according to the air-fuel ratio control apparatus for an internal combustion engine of the present invention (claim 7), the follow-up changing means in claim 1 is the final target after switching from the air-fuel ratio immediately before the start of switching the operating state. A transient target air-fuel ratio setting means for setting a transient target air-fuel ratio that gradually changes to reach the air-fuel ratio, and a change prohibition that suppresses or suppresses the change of the transient target air-fuel ratio immediately after switching the operating state.
With a simple configuration that is configured with suppression means,
In addition to the above effects (1) to (4), there are the following effects and advantages.

(10) Immediately after switching to the lean burn operation, the actual intake air amount starts to increase with a dead time, but the increase of the target air-fuel ratio during the time corresponding to this dead time is prohibited or suppressed. As a result, a sense of deceleration is prevented. Further, according to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 8), in claim 2, for the intake air amount during the switching transient operation in the comparison means, the intake air amount is throttled by an artificial operation. With a simple configuration in which correction means for correcting the change in opening is provided, in addition to the effects (1) to (4), the following effects and advantages are provided.

(11) Even if there is an artificial accelerator operation, the correction corresponding to the accelerator operation is performed to perform the control, so that the deceleration feeling is prevented from occurring. According to the air-fuel ratio control apparatus for an internal combustion engine of the present invention (claim 9), the correction means in claim 8 sets the correction amount based on the intake air amount change information of the internal combustion engine, which is simple. With the configuration, substantially the same effects and advantages as the device according to claim 8 are obtained.

Further, according to the air-fuel ratio control system for an internal combustion engine of the present invention (claim 10), the transient target air-fuel ratio setting means in claim 2 is in a transient time based on the comparison result by the comparing means. The target air-fuel ratio is set for a predetermined period, and after the predetermined period has elapsed, the transient target air-fuel ratio is gradually increased from the transient target air-fuel ratio after the predetermined period has passed to the final target air-fuel ratio. With a simple configuration that is configured to change to (1) to
In addition to the effect of (4), there are the following effects and advantages.

(12) Even if there is an artificial accelerator operation, the correction corresponding to the accelerator operation is performed to perform the control, so that the feeling of deceleration is prevented. (13) The actual intake air amount after exceeding the intermediate predetermined air-fuel ratio has a gradual change characteristic, and if the transient target air-fuel ratio is set corresponding to this actual intake air amount, the final target air-fuel ratio will be achieved. Although this causes a delay, a linear interpolation is performed for this portion to prevent a delay in the achievement of the final target air-fuel ratio, the switching control is completed in a timely manner, and accurate control is performed.

Further, according to the air-fuel ratio control device for an internal combustion engine of the present invention (claim 11), the correction means according to claim 7 changes the set target air-fuel ratio at the time of transition into a change in throttle opening due to human operation. In order to make a corresponding correction, since the intake air amount not related to switching to the lean air-fuel ratio is stored as a storage means for storing the throttle opening and the engine speed as parameters, In addition to the effects (1) to (4) and (10), the following effects and advantages are obtained.

(14) Even if there is an artificial accelerator operation, the correction corresponding to the accelerator operation is performed to perform the control, so that the feeling of deceleration is prevented. (15) Since the correction corresponding to the accelerator operation can be performed without detecting the actual intake air amount, there is an advantage that the control device can be realized at low cost.

[Brief description of drawings]

FIG. 1 is a control block diagram of an air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of an engine system having an air-fuel ratio control device as an embodiment of the present invention.

FIG. 3 is a hardware block diagram showing a control system of an engine system having an air-fuel ratio control device as one embodiment of the present invention.

FIG. 4 is a flow chart for explaining a first control mode of an air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 5 is a diagram for explaining a first control mode of an air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 6 is a flowchart for explaining a second control mode of the air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 7 is a diagram for explaining a second control mode of the air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 8 is a flowchart for explaining a third control mode of the air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 9 is a flowchart for explaining a fourth control mode of the air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 10 is a diagram for explaining a fourth control mode of the air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 11 is a flowchart for explaining a fifth control mode of the air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 12 is a diagram for explaining a fifth control mode of an air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 13 is a diagram for explaining a fifth control mode of an air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

FIG. 14 is a flowchart for explaining a sixth control mode of an air-fuel ratio control device for an internal combustion engine as an embodiment of the present invention.

15A and 15B are diagrams for explaining the air-fuel ratio control characteristic.

FIG. 16 is a diagram for explaining the air-fuel ratio control characteristic.

17 (a) to 17 (c) are diagrams for explaining the air-fuel ratio control characteristic.

FIG. 18 is a diagram for explaining the air-fuel ratio control characteristic.

[Explanation of symbols]

1 engine (internal combustion engine) 2 combustion chamber 3 intake passage 3a surge tank 4 exhaust passage 5 intake valve 6 exhaust valve 7 air cleaner 8 throttle valve 9 electromagnetic fuel injection valve (injector) 9a injector solenoid 10 three-way catalyst 11A first bypass passage 11B 2nd bypass passage 12 Stepper motor valve (STM valve) 12a Valve body 12b Stepper motor (ISC actuator) 12c Spring 13 First idle air valve 14 Air bypass valve 14a Valve body 14b Diaphragm type actuator 15 Fuel pressure regulator 16 Spark plug 17 an air flow sensor (intake air amount sensor) 18 intake air temperature sensor 19 atmospheric pressure sensor 20 throttle position sensor 21 the idle switch 22 linear O ₂ sensor 23 water temperature sensor 24 crank angle sensor Engine speed sensor) 25 ECU as air-fuel ratio control means 26 CPU (arithmetic unit) 28 Input interface 29 Analog / digital converter 30 Vehicle speed sensor 35 Input interface 36 ROM (storage means) 37 RAM 39 Injection driver 40 Ignition driver 41 Power transistor 42 Ignition coil 43 Distributor 44 ISC driver 45 Bypass air driver 46 EGR driver 80 Exhaust gas recirculation passage (EGR passage) 81 EGR valve 81a Valve body 81b Diaphragm actuator 82 Pilot passage 83 ERG valve control solenoid valve 83a Solenoid 201 Intake air Quantity control means 202 Tracking change means 203 Comparison means 204 Target air-fuel ratio setting means 205 Fuel amount setting means 206 Backup air-fuel ratio setting Stage 207 transitional target air-fuel ratio setting means 208 changes prohibiting, restraining means 209 compensation means 210 air fuel ratio control unit 211 the fuel supply means

Claims (11)

[Claims] 1. An internal combustion engine capable of switching between operation at a leaner side air-fuel ratio than the stoichiometric air-fuel ratio and operation at a richer side air-fuel ratio than the lean side air-fuel ratio in an internal combustion engine, the lean-side air-fuel ratio Intake air amount control means for increasing the amount of intake air supplied to the combustion chamber of the internal combustion engine, and an air-fuel ratio of the internal combustion engine for controlling the air-fuel ratio according to the operating state of the internal combustion engine. Air-fuel ratio control having target air-fuel ratio setting means for setting a target air-fuel ratio according to operating conditions, and fuel amount setting means for setting a fuel amount to realize the target air-fuel ratio set by the target air-fuel ratio setting means Means and fuel supply means for supplying fuel to the internal combustion engine in accordance with the fuel amount set by the fuel amount setting means in the air-fuel ratio control means, and the target air-fuel ratio setting in the air-fuel ratio control means. The means is the lean side sky When the operation at the air-fuel ratio on the rich side of the ratio is switched to the operation on the lean-side air-fuel ratio, the follow-up changing means is provided for continuously changing the air-fuel ratio by following the change in the actual intake air amount. An air-fuel ratio control device for an internal combustion engine, characterized in that 2. The following change means compares the intake air amount immediately before the start of the switching of the operating state with the intake air amount during the switching transient operation, and the transient target based on the comparison result of the comparison means. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, further comprising: a target air-fuel ratio setting means for setting a transient air-fuel ratio. 3. The follow-up changing means includes backup air-fuel ratio setting means for setting a backup air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of switching the operating state to the final target air-fuel ratio after the switching. 3. The fuel amount setting means is configured to set the fuel amount according to the larger one of the transient target air-fuel ratio and the backup air-fuel ratio. Air-fuel ratio controller for internal combustion engine. 4. The transient target air-fuel ratio, wherein the follow-up changing means sets a transient target air-fuel ratio that gradually changes from the air-fuel ratio immediately before the switching of the operating state to the final target air-fuel ratio after switching. It is configured to include setting means, and the changing speed of the transient target air-fuel ratio set in the transient target air-fuel ratio setting means is configured to become faster as the rotational speed of the internal combustion engine increases. The air-fuel ratio control device for an internal combustion engine according to claim 1. 5. The internal combustion engine according to claim 3, wherein the backup air-fuel ratio setting means sets the changing speed of the backup air-fuel ratio to increase as the rotational speed of the internal combustion engine increases. Air-fuel ratio controller. 6. The transient target air-fuel ratio, wherein the follow-up changing means sets a transient target air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of switching the operating state to the final target air-fuel ratio after switching. The change target speed of the transient target air-fuel ratio set in the transient target air-fuel ratio setting means is changed from the change speed corresponding to the high rotation operating state of the internal combustion engine to the low rotation operating state. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control device is configured to change to a corresponding change speed. 7. The transient target air-fuel ratio, wherein the follow-up changing means sets a transient target air-fuel ratio that gradually changes from the air-fuel ratio immediately before the start of switching the operating state to the final target air-fuel ratio after switching. 2. The air-conditioner for an internal combustion engine according to claim 1, further comprising: setting means and change prohibiting / suppressing means for prohibiting or suppressing a change in the target air-fuel ratio during transition immediately after the switching of the operating state. Fuel ratio control device. 8. The correction means for correcting the intake air amount during the switching transient operation compared by the comparison means in response to a change in the throttle opening due to an artificial operation is provided. Air-fuel ratio control device for internal combustion engine. 9. The air-fuel ratio control apparatus for an internal combustion engine according to claim 8, wherein the correction means is configured to set the correction amount based on the intake air amount change information of the internal combustion engine. 10. The transient target air-fuel ratio setting means is configured to set the transient target air-fuel ratio based on the comparison result of the comparing means for a predetermined period, and after the predetermined period has elapsed. The air-fuel ratio of the internal combustion engine according to claim 2, wherein the transient target air-fuel ratio is gradually changed so as to reach the final target air-fuel ratio from the transient target air-fuel ratio after the lapse of the predetermined period. Control device. 11. The intake air, which is not related to switching to operation at the lean side air-fuel ratio, so that the correction means corrects the set target air-fuel ratio during transition in response to a change in throttle opening due to human operation. 8. A storage means for storing the quantity as parameters of the throttle opening and engine speed.
An air-fuel ratio control device for an internal combustion engine as described.