JPH08165946A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To reduce worsening of an exhaust emission after it is completed that an air-fuel ratio is rendered lean, in an internal combuston engine wherein the reference output of a first air-fuel ratio sensor arranged upper stream from a second air-fuel ratio sensor situated downstream from a catalytic converter having O2 storage capacity is corrected. CONSTITUTION: When control to bring an air-fuel ratio into a lean state is not executed, a fuel injection amount is controlled based on a first air-fuel ratio sensor 21, and based on an output from a second air-fuel ratio sensor 22, the reference output of the first air-fuel ratio sensor is corrected by using an integratedly changing correction amount. An air-fuel ratio control device for an internal combustion engine comprises a memory means to store a value of a correction amount right before control to bring an air-fuel ratio into a lean state is completed; and a varying means to vary a correction amount to a value stored by the memory means when a-n air-fuel ratio of exhaust gas detected by a second air-fuel ratio sensor is adjusted to a stoichiometric air-fuel ratio after completion of control to bring an air-fuel ratio into a lean state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention feedback-controls a mixture air-fuel ratio by means of a first air-fuel ratio sensor arranged upstream of a catalytic converter in an exhaust passage and a second air-fuel ratio sensor arranged downstream thereof. The present invention relates to an air-fuel ratio control device for an internal combustion engine.

[0002]

2. Description of the Related Art In the exhaust passage of an internal combustion engine, a three-way catalytic converter that reduces nitrogen oxide and simultaneously oxidizes carbon monoxide and hydrocarbons is generally arranged. Since the three-way catalytic converter exhibits good exhaust gas purification performance as described above when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, the fluctuation of the air-fuel ratio of the exhaust gas, An O ₂ storage capacity is provided for storing excess oxygen from lean exhaust gas and releasing the stored oxygen when the exhaust gas is in a rich state.

A first one arranged upstream of the catalytic converter
In an air-fuel ratio control device comprising an air-fuel ratio sensor and a second air-fuel ratio sensor arranged on the downstream side, a linear output type air-fuel ratio sensor capable of detecting the air-fuel ratio of exhaust gas is used as the first air-fuel ratio sensor. However, there has been proposed an air-fuel ratio control device that corrects and controls the basic fuel injection amount that is determined by the engine operating state, based on the difference between the exhaust gas air-fuel ratio and the theoretical air-fuel ratio on the upstream side of the catalytic converter.

In this air-fuel ratio control device, the second air-fuel ratio sensor has a correction amount for correcting the reference output corresponding to the theoretical air-fuel ratio of the first air-fuel ratio sensor, which is detected by the downstream side of the catalytic converter. This is for making an integral change based on the difference between the exhaust gas air-fuel ratio and the stoichiometric air-fuel ratio.

In such an air-fuel ratio control device, when a fuel cut is performed to save fuel when the vehicle is decelerating, the fuel injection amount control by the first air-fuel ratio sensor and the second air-fuel ratio sensor are performed. The reference output correction control of the first air-fuel ratio sensor is stopped together. When the fuel cut is finished and fuel injection is started, the oxygen stored in the fuel cut is gradually released due to the O ₂ storage capacity of the three-way catalytic converter. Even if the fuel ratio is maintained near the stoichiometric air-fuel ratio, the air-fuel ratio of the exhaust gas on the downstream side of the three-way catalytic converter becomes lean.

At this time, if the reference output correction control of the first air-fuel ratio sensor by the second air-fuel ratio sensor is restarted, the correction amount becomes excessively large on the rich side due to this exhaust gas lean state and is stored in the catalytic converter. This correction amount is gradually returned to an appropriate value when all the oxygen is released, but during this time, the air-fuel ratio of the exhaust gas on the downstream side of the three-way catalyst becomes rich, and the hydrocarbon and carbon monoxide of the catalytic converter are reduced. However, there is a problem that the purification performance of the engine deteriorates and the exhaust emission deteriorates.

In order to solve this problem, Japanese Patent Laid-Open No. 6-1
No. 01536 discloses that after the fuel cut is completed, all the oxygen stored in the catalytic converter is released, and the second air-fuel ratio sensor is used until the air-fuel ratio of the exhaust gas on the downstream side of the catalytic converter becomes the stoichiometric air-fuel ratio. (1) An air-fuel ratio control device for an internal combustion engine is described that stops the reference output correction of an air-fuel ratio sensor.

[0008]

In the air-fuel ratio control device described above, in order to maintain the air-fuel ratio of the air-fuel mixture near the stoichiometric air-fuel ratio by the first air-fuel ratio sensor after the fuel cut is completed,
The air-fuel ratio of the exhaust gas on the downstream side of the catalytic converter is maintained in a lean state for a considerably long time, and during this period, the catalytic converter's nitrogen oxide purification performance deteriorates,
After all, exhaust emission deteriorates.

Therefore, the object of the present invention is to control the air-fuel ratio by correcting the reference output of the first air-fuel ratio sensor arranged on the upstream side by the second air-fuel ratio sensor arranged on the downstream side of the catalytic converter in the exhaust passage. (EN) Provided is an air-fuel ratio control device for an internal combustion engine, which can reduce deterioration of exhaust emission after the end of air-fuel ratio leaning control.

[0010]

An air-fuel ratio control system for an internal combustion engine according to the present invention comprises a catalytic converter having an O ₂ storage capacity, and a first air-fuel ratio sensor arranged in an exhaust passage upstream of the catalytic converter. A lean air-fuel ratio sensor arranged downstream of the catalytic converter in the exhaust passage, and lean control means for performing lean control of the air-fuel mixture in the engine specific operating state. When the lean control is not performed by the control means, the fuel injection amount is controlled based on the output of the first air-fuel ratio sensor, and the correction amount that changes in an integral manner based on the output of the second air-fuel ratio sensor is set. In an air-fuel ratio control device which is used to correct the reference output of the first air-fuel ratio sensor, storage means for storing the value of the correction amount immediately before the start of the lean control, Changing means for changing the correction amount to a value stored by the storage means when the air-fuel ratio of the exhaust gas detected by the second air-fuel ratio sensor becomes the stoichiometric air-fuel ratio after the end of lean control. It is characterized by further comprising.

[0011]

In the air-fuel ratio control device for an internal combustion engine described above, after the lean control is completed, the fuel injection amount is controlled based on the output of the first air-fuel ratio sensor and the integral injection is performed based on the output of the second air-fuel ratio sensor. The reference output of the first air-fuel ratio sensor is corrected using the correction amount that changes to, and then the oxygen stored in the catalytic converter is completely released by the O ₂ storage capacity during the lean control and the second air-fuel ratio is When the air-fuel ratio of the exhaust gas detected by the sensor reaches the stoichiometric air-fuel ratio, the changing unit changes the correction amount to the value stored in the storage unit immediately before the start of the lean control.

[0012]

1 is a schematic sectional view of an internal combustion engine equipped with an air-fuel ratio control device according to the present invention. In the figure, 1 is a piston, 2 is a combustion chamber, and 3 is an ignition plug that faces the combustion chamber 2. An intake passage 5 is connected to the combustion chamber 2 via the intake valve 4, and an exhaust passage 7 is connected to the combustion chamber 2 via the exhaust valve 6. A fuel injection valve 8 is arranged in the intake passage 5 for each cylinder.

The exhaust passage 7 is provided with a three-way catalytic converter 9 for reducing nitrogen oxide and oxidizing carbon monoxide and hydrocarbons. This three-way catalytic converter 9
It has an O ₂ storage capacity that stores excess oxygen when the air-fuel ratio of the exhaust gas is lean and releases this oxygen when the air-fuel ratio of the exhaust gas becomes rich. A linear output type first air-fuel ratio sensor 21 capable of detecting the air-fuel ratio of the exhaust gas is located upstream of the three-way catalytic converter 9, and the air-fuel ratio of the exhaust gas is close to the theoretical air-fuel ratio downstream. Step output type second air-fuel ratio sensors 22 whose output voltage suddenly changes when
It is electrically connected to 0. The control device 20 includes a rotation sensor 23 for detecting the engine speed, an air flow meter 24 for detecting the intake air amount, a cooling water temperature sensor 25 for detecting the cooling water temperature, and other sensors for grasping the engine operating state. Are further connected.

The fuel injection amount control by the control device 20 usually determines the basic fuel injection amount for realizing the theoretical air-fuel ratio with respect to the intake air amount measured by the air flow meter 24, and the first air-fuel ratio sensor 21 Based on the difference between the actual air-fuel ratio and the theoretical air-fuel ratio measured by, the basic fuel injection amount is corrected to determine the actual fuel amount to be injected. This internal combustion engine executes fuel cut to save fuel by stopping fuel injection at the time of deceleration of the engine, etc. As a matter of course, the fuel injection amount control is stopped during execution of fuel cut. It is like this.

In such fuel injection amount control, the first
Since the output of the air-fuel ratio sensor 21 is required to have high reliability, the control device 20 is arranged on the downstream side of the three-way catalytic converter 9 and therefore the first air-fuel ratio sensor 21 on the upstream side.
By using the second air-fuel ratio sensor 22 that is less likely to deteriorate as compared with the above, the deviation of the reference output from the theoretical air-fuel ratio of the first air-fuel ratio sensor 21 is corrected according to the flowchart shown in FIG.

This flowchart is started at the same time when the engine is started, and is repeated every predetermined period. First, at step 101, it is judged if the fuel cut is being executed. When this determination is denied, the routine proceeds to step 102, where the reference voltage Vref (for example, 0.4 that corresponds to the stoichiometric air-fuel ratio of the second air-fuel ratio sensor 22).
5 V) and the current output voltage V difference Vd is calculated.

Next, in step 103, it is determined whether the flag F is 1. Since the flag F is initially 0, this determination is denied and the routine proceeds to step 104,
The difference dV of this time is added to the previously integrated value TdV of the difference dV (reset to 0 at the time of engine start), and the new integrated value TdV of the difference up to this time is calculated.

Next, in step 113, the following equation (1)
Thus, the reference output correction voltage Vc corresponding to the theoretical air-fuel ratio of the first air-fuel ratio sensor 21 is calculated. Vc = KP * dV + KI * TdV + KD * dV / dt-(1) where KP is a coefficient in the proportional term, KI is a coefficient in the integral term, dV / dt is a time differential value of the difference dV, K
D is a coefficient in the differential term. This equation (1) is an equation used to calculate a correction amount in general PDI control.

When the fuel cut is not executed, the reference voltage of the first air-fuel ratio sensor 21 is corrected as usual by the correction voltage Vc thus calculated, and the air-fuel ratio of the air-fuel mixture is close to the stoichiometric air-fuel ratio. It is possible to maintain.

When the fuel cut is executed, the determination in step 101 is affirmed, and the routine proceeds to step 105, where it is determined whether or not the flag F is 1. Initially,
This determination is negative and the routine proceeds to step 106, where the integrated value TdV of the difference calculated in step 104 in the execution of the previous flowchart, that is, the integrated value TdV of the difference immediately before the start of the fuel cut is stored as A. Next, in step 107, the flag F is set to 1. During the fuel cut, the first air-fuel ratio sensor 21
Since the fuel injection amount control by is also stopped, the process ends without calculating the correction voltage Vc. In the next process, if the fuel cut is still executed, the determination in step 105 is affirmative,
It ends as it is.

When the fuel cut is completed, the determination at step 101 is denied again, and the routine proceeds through step 102 to step 103. At this time, since the flag F is set to 1, the determination at step 103 is affirmative and the routine proceeds to step 108. In step 108,
It is determined whether or not a predetermined time T has elapsed after the fuel cut is completed. This predetermined time T is equal to the second air-fuel ratio sensor 2
In consideration of the response delay of 2, the second air-fuel ratio sensor 22 is the time when it is possible to detect the accurate air-fuel ratio of the exhaust gas in the restarted combustion.

Therefore, when the determination at step 108 is negative, the reliability of the output of the second air-fuel ratio sensor 22 is low, and the routine proceeds to step 109, at which the correction voltage Vc of the first air-fuel ratio sensor 21 is as described above. In equation (1) of
Integral value A of the difference immediately before the start of fuel cut (Step 1
(Stored in 06).

When the predetermined time T elapses after the fuel cut is completed, the determination at step 108 is affirmed and the routine proceeds to step 110, where the output voltage V of the second air-fuel ratio sensor 22 is equal to or higher than the voltage Vref corresponding to the theoretical air-fuel ratio. It is determined whether or not. Initially, during the fuel cut, the oxygen stored in the catalytic converter 9 is gradually released due to the O ₂ storage capacity, and the air-fuel ratio of the air-fuel mixture becomes the first air-fuel ratio sensor 2
Even if the stoichiometric air-fuel ratio is maintained at 1, the air-fuel ratio of the exhaust gas on the downstream side of the catalytic converter 9 becomes lean, so the determination at step 110 is denied and the routine proceeds to step 104.

In step 104, the difference dV of this time is added to the integrated value TdV of the difference immediately before the start of the fuel cut to calculate a new integrated value TdV of the difference, and step 11
3, the integrated value TdV of this new difference and the current difference dV
And the time differential value dV / t are used to calculate the correction voltage Vc.

While the reference output of the first air-fuel ratio sensor 21 is corrected using the correction voltage Vc calculated in this way, the oxygen stored in the catalytic converter 9 is almost exhausted and the oxygen is stored in the downstream side. When the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio, the determination at step 110 is affirmed, the routine proceeds to step 111, and the flag F is reset to 0. Next, in step 112, the integrated value of the difference TdV
Is returned to the integral value A of the difference immediately before the start of the fuel cut, and the correction voltage Vc of the first air-fuel ratio sensor 21 is calculated in step 113.

FIG. 3 is a time chart of the output of the second air-fuel ratio sensor for comparing the conventional two types of control for correcting the reference voltage of the first air-fuel ratio sensor with the control of the present embodiment. In the figure, A is the case of the first conventional example in which the normal reference output correction of the first air-fuel ratio sensor is performed immediately after the fuel cut is completed, and the exhaust gas on the downstream side of the catalytic converter is in the lean state after the fuel cut is completed. Therefore, the correction is performed to make the air-fuel mixture rich, and at the time when all the oxygen stored in the catalytic converter is released, the total difference TdV becomes excessively large on the rich side. , And then the integrated value Td of this difference
V is gradually returned to an appropriate value, but during that time, the air-fuel ratio of the exhaust gas on the downstream side of the catalytic converter becomes rich, so the exhaust emission deteriorates.

B is the case of the second conventional example in which the reference output correction of the first air-fuel ratio sensor is stopped until the air-fuel ratio of the exhaust gas on the downstream side of the catalytic converter which becomes lean after the fuel cut becomes the stoichiometric air-fuel ratio. After the fuel cut is completed, the air-fuel ratio on the downstream side of the catalytic converter is in the lean state for a relatively long period, and the exhaust emission is deteriorated during this period.

C is the case of the present embodiment. Immediately after the end of the fuel cut, correction of only the integral term using the integrated value of the difference immediately before the start of the fuel cut is performed, and then exhaust gas on the downstream side of the catalytic converter is corrected. Since the correction using the proportional term, the integral term, and the differential term as usual is performed until the air-fuel ratio becomes the stoichiometric air-fuel ratio, compared to the second conventional example, the catalytic converter after the fuel cut is completed. The time during which the air-fuel ratio of the exhaust gas on the downstream side is kept lean can be considerably shortened, and the deterioration of exhaust emission during this time can be reduced.

Further, when the air-fuel ratio of the exhaust gas on the downstream side of the catalytic converter reaches the stoichiometric air-fuel ratio, in order to return the integrated value of the difference to the value just before the start of the fuel cut, as in the first conventional example, It is prevented that the air-fuel ratio of the exhaust gas on the downstream side of the converter becomes rich and the exhaust emission is deteriorated.

The method of correcting the reference output of the first air-fuel ratio sensor in this embodiment can be applied not only after the end of fuel cut but also after the engine operation in which the air-fuel ratio of the air-fuel mixture is intentionally made lean.

[0031]

As described above, according to the air-fuel ratio control system for an internal combustion engine of the present invention, after the lean control is completed,
The fuel injection amount is controlled based on the output of the first air-fuel ratio sensor, and the reference output of the first air-fuel ratio sensor is corrected using the correction amount that changes in an integrated manner based on the output of the second air-fuel ratio sensor. Therefore, the air-fuel ratio of the exhaust gas on the downstream side of the catalytic converter can be set to the stoichiometric air-fuel ratio relatively early, and the deterioration of the exhaust emission during this period can be reduced. When the air-fuel ratio becomes the stoichiometric air-fuel ratio, the exhaust gas on the downstream side of the catalytic converter is changed in order to change the correction amount that has become excessively large on the rich side by the changing means to the value just before the start of lean control stored by the storage means. The air-fuel ratio of the gas can be maintained near the stoichiometric air-fuel ratio, and it is possible to prevent deterioration of exhaust emission at this time.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an internal combustion engine equipped with an air-fuel ratio control device according to the present invention.

FIG. 2 is a flow chart for determining a correction voltage for a first air-fuel ratio sensor.

FIG. 3 is a time chart of the output of the second air-fuel ratio sensor for comparing the related art with the present invention.

[Explanation of symbols]

 2 ... Combustion chamber 7 ... Exhaust passage 9 ... Three-way catalytic converter 20 ... Control device 21 ... First air-fuel ratio sensor 22 ... Second air-fuel ratio sensor

Claims (1)

[Claims] 1. A catalytic converter having an O ₂ storage capacity, a first air-fuel ratio sensor arranged in an exhaust passage upstream of the catalytic converter, and a second air-fuel ratio sensor arranged in an exhaust passage downstream of the catalytic converter. An air-fuel ratio sensor, and lean control means for performing lean control of the air-fuel ratio of the air-fuel mixture in an engine specific operating state, and when the lean control is not performed by the lean control means, the first A fuel injection amount is controlled based on the output of the air-fuel ratio sensor, and the reference output of the first air-fuel ratio sensor is corrected using a correction amount that changes in an integrated manner based on the output of the second air-fuel ratio sensor. In the fuel ratio control device, a storage unit that stores the value of the correction amount immediately before the start of the lean control and the second air-fuel ratio sensor after the end of the lean control are used. An air-fuel ratio control of an internal combustion engine, further comprising: a changing unit that changes the correction amount to a value stored by the storage unit when the air-fuel ratio of the exhaust gas to be emitted becomes a stoichiometric air-fuel ratio. apparatus.