JPH06249032A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] The present invention relates to an air-fuel ratio control device for an internal combustion engine having a three-way catalyst, and more effectively utilizes the O ₂ storage effect of the three-way catalyst to reduce exhaust emissions that occur during engine acceleration and deceleration. The purpose is to improve the deterioration. [Structure] Oxygen amount calculation means 6 for calculating the amount of oxygen currently stored in the three-way catalyst 2 using the amount of exhaust gas flowing into the three-way catalyst 2 and its oxygen concentration, and calculated by the oxygen amount calculation means 6. A fuel amount control means 8 for controlling the amount of fuel supplied to the engine combustion chamber in consideration of the amount of intake air so as to maintain the target amount of oxygen at the target amount of oxygen; And a target oxygen amount changing means 10 for decreasing the target oxygen amount and increasing the target oxygen amount from the scheduled engine deceleration until the engine deceleration is executed.

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 system for an internal combustion engine having a three-way catalytic converter in its exhaust system.

[0002]

2. Description of the Related Art Generally, an exhaust system of an internal combustion engine is provided with a catalytic converter for purifying harmful components in exhaust gas. As this catalytic converter, a three-way catalytic converter is widely used, which oxidizes carbon monoxide and hydrocarbons, which are harmful three components in exhaust gas, and also reduces nitrogen oxides, thereby harmless carbon dioxide and steam. , And nitrogen. It is known that the purification characteristic of the three-way catalytic converter depends on the air-fuel ratio of the air-fuel mixture formed in the combustion chamber, and the three-way catalytic converter functions most effectively when it is near the stoichiometric air-fuel ratio.
This is because when the air-fuel ratio is lean and the amount of oxygen in the exhaust gas is large, the oxidizing action becomes active but the reducing action becomes inactive, and when the air-fuel ratio is rich and the amount of oxygen in the exhaust gas is small, On the contrary, this is because the reducing action becomes active, but the oxidizing action becomes inactive, and it is impossible to satisfactorily purify all of the above-mentioned harmful three components. Therefore, an internal combustion engine having a three-way catalytic converter is provided with an output linear oxygen sensor in its exhaust passage, and the oxygen concentration measured thereby is used to feedback-control the air-fuel mixture in the combustion chamber to the stoichiometric air-fuel ratio. Is proposed. However, the oxygen concentration used in the present specification is a negative value corresponding to the extent of the exhaust gas when the air-fuel mixture mixture is in a rich state.

Even if such feedback control is executed, the air-fuel ratio of the air-fuel mixture temporarily becomes lean due to a rapid increase in the intake air amount during engine transient operation, for example, during engine acceleration, and during engine deceleration. On the contrary, the state becomes rich. At this time, although the exhaust gas purification performance of the three-way catalyst is usually reduced, it has been proposed to give the three-way catalyst the ability to store oxygen (O ₂ storage effect), and thereby the air-fuel ratio Stores excess oxygen when is lean and uses oxygen stored when it is rich,
Exhaust gas purification performance can be maintained.

Japanese Unexamined Patent Publication No. 3-217633 discloses an engine.
O of the three-way catalyst for transient operating conditions ₂Storage effect
The air-fuel ratio must be lean or lean for effective use.
The air-fuel ratio is intentionally changed to the opposite
To maintain the oxygen stored in the three-way catalyst at a specified amount.
Amount of oxygen newly stored under lean air-fuel ratio
And the amount of oxygen used in the air-fuel ratio rich state
The air-fuel ratio control which controls so that it may be changed is proposed.

[0005]

The above air-fuel ratio control is
It is intended to maintain a predetermined amount of oxygen stored in the three-way catalyst under all engine operating conditions. However, during rapid engine acceleration or when acceleration lasts for a relatively long time, it is preferable that oxygen is not stored in the three-way catalyst because there is a large amount of extra oxygen in the exhaust gas. At the same time, when the deceleration lasts for a relatively long time, a large amount of oxygen is required to purify the exhaust gas, and therefore it is preferable that the amount of oxygen stored in the three-way catalyst is large. As described above, the above-described air-fuel ratio control cannot fully utilize the O ₂ storage effect of the three-way catalyst.

Therefore, an object of the present invention is to provide O ₂ of a three-way catalyst.
It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which can more effectively utilize the storage effect to improve the deterioration of exhaust emission that occurs during engine acceleration / deceleration.

[0007]

SUMMARY OF THE INVENTION An air-fuel ratio control system for an internal combustion engine according to the present invention uses an amount of exhaust gas flowing into a three-way catalyst and its oxygen concentration to determine the amount of oxygen currently stored in the three-way catalyst. And a fuel amount control for controlling the fuel amount supplied to the engine combustion chamber in consideration of the intake air amount so as to maintain the oxygen amount calculated by the oxygen amount calculating means at the target oxygen amount. Means, between the scheduled and executed engine acceleration, the target oxygen amount is reduced,
Target oxygen amount changing means for increasing the target oxygen amount from the scheduled engine deceleration to the execution thereof.

[0008]

In the air-fuel ratio control device for an internal combustion engine, the oxygen amount calculating means calculates the amount of oxygen currently stored in the three-way catalyst by using the amount of exhaust gas flowing into the three-way catalyst and the oxygen concentration thereof. Then, the fuel amount control means controls the fuel amount to be supplied to the engine combustion chamber in consideration of the intake air amount in order to maintain this oxygen amount at the target oxygen amount, and the target oxygen amount changing means schedules the engine acceleration. The target oxygen amount is reduced during the period from the execution to the execution, and the target oxygen amount is increased during the period from the scheduled engine deceleration until the execution.

[0009]

1 is a block diagram showing the construction of an air-fuel ratio control system for an internal combustion engine according to the present invention. In the figure, 1
Is an internal combustion engine, 2 is a three-way catalyst installed in its exhaust system, 3
Is an output linear oxygen sensor (hereinafter referred to as a first oxygen sensor) provided upstream of the three-way catalyst 2 in the exhaust system, and 4 is a similar oxygen sensor (hereinafter referred to as a first oxygen sensor) provided downstream of the three-way catalyst 2 in the exhaust system. 2 oxygen sensor). The internal combustion engine 1 is
In particular, the throttle valve is not connected to the accelerator pedal and is driven by a step motor or the like. Reference numeral 5 is a basic fuel injection amount determination circuit that determines the basic fuel injection amount τ1 according to the engine operating state, 6 is a control circuit, 7 is a subtractor, and 8
Is a multiplier. The control circuit 6 is a circuit for adjusting dynamic characteristics, that is, a dynamic characteristic circuit 6a which is a circuit for speeding up closed loop control, an integrating circuit 6b, an integral control circuit 6c,
The connecting points 6d are arranged as shown in FIG. Further, 9 is a correction circuit for correcting the oxygen concentration λ0 (hereinafter referred to as stoichiometric value) of the exhaust gas in the stoichiometric air-fuel ratio combustion of the first oxygen sensor 3, and 10 is the target oxygen amount IS stored in the three-way catalyst 2. The target oxygen amount determination circuit 11 determines the maximum oxygen amount determination circuit 11 that determines the maximum oxygen amount FLMAX that can be stored in the three-way catalyst 2.

In the air-fuel ratio control system for an internal combustion engine having the above-described structure, the basic fuel injection amount determining circuit 5 has the first configuration shown in FIG.
Basic fuel injection amount τ every predetermined time according to the flowchart
1, and in synchronization with that, the controller 6 determines the correction coefficient k in accordance with the second flowchart shown in FIG.
Both are output to the multiplier 8, and fuel injection is executed based on the fuel injection amount τ calculated there.

In the first flowchart, in step 101, the engine speed N and the intake air amount Q are measured by a rotation sensor (not shown) and an air flow meter (not shown) provided in the internal combustion engine 1, and in step 102. The basic fuel injection amount τ1 is determined using a map or the like based on these values.

Next, the second flow chart will be described. First, in step 201, the oxygen concentration λ1 in the exhaust gas is measured by the first oxygen sensor 3, and in step 202, the deviation Δλ between this oxygen concentration λ1 and the stoichiometric value λ0 output from the correction circuit 9 is subtracted by the subtractor 7. calculate. This Δλ has a positive value when the air-fuel mixture is in a lean state, and has a negative value when the air-fuel mixture is in a rich state.

Next, at step 203, this Δλ is input to the integration circuit 6b of the control circuit 6, time integration is performed in consideration of the exhaust gas amount E per unit time at this time, and it is currently stored in the three-way catalyst 2. The oxygen amount FL that is being stored is calculated.
This oxygen amount FL is approximately calculated by adding the product of Δλ, the processing interval Δt of this flowchart and the exhaust gas amount E per unit time to the previous oxygen amount FL. The exhaust gas amount E may be directly measured, but the intake air amount Q measured in the first flow chart may be approximately used.

Next, at step 204, the maximum oxygen amount F that can be stored in the three-way catalyst 2 from the maximum oxygen amount determination circuit 11 is stored.
LMAX is input to the integration controller 6c, and in step 205, the flag F1 determined by the correction circuit 9 is 1
Is judged, and when this judgment is denied,
In step 206, it is determined whether the flag F1 is 2, and when this determination is negative, step 20
At 7, the integral controller 6c determines whether the oxygen amount FL is larger than the maximum oxygen amount FLMAX. When this determination is negative, it is as it is, and when it is positive, the oxygen amount FL is set to FLMAX in step 208. When the determination in step 206 is affirmative, the process proceeds to step 208.

Next, at step 209, the oxygen amount FL
However, it is determined whether or not the minimum oxygen amount that can be stored in the three-way catalyst, that is, is less than 0. When this judgment is denied, it is as it is, and when it is affirmed, step 210.
In, the oxygen amount FL is set to 0. When the determination in step 205 is affirmative, this step 21
Go to 0. Next, at step 211, the target oxygen amount determination circuit 10 inputs the target oxygen amount IS to be stored in the three-way catalyst to the integral controller 6c, and at step 212, it is judged whether or not the oxygen amount FL is larger than the target oxygen amount IS. When the determination is affirmative, the control value FI is increased by 1 in step 213, and when the determination is negative, the control value FI is decreased by 1 in step 214.

Next, in step 215, the deviation Δλ is input to the dynamic characteristic circuit 6a of the controller 6 to calculate the dynamic control value FD, and in step 216, the connection point 6 is calculated.
At d, the correction coefficient k is calculated from the control value FI and the dynamic control value FD.

In the correction circuit 9, the third flowchart shown in FIG. 4 is executed in synchronization with the second flowchart. First, in step 301, the oxygen concentration λ2 in the exhaust gas downstream of the three-way catalyst 2 is measured by the second oxygen sensor 4, and in step 302, it is determined whether or not the oxygen concentration λ2 is larger than the upper limit M1 indicating the theoretical mixture combustion. When the determination is negative, in step 303, it is determined whether the oxygen concentration λ2 is smaller than the lower limit M2 indicating stoichiometric air-fuel ratio combustion. When the three-way catalyst 2 is functioning well including the O ₂ storage effect, all of these judgments are denied, and the flag F1 is set to 0 in step 304 and the process ends.

However, when the determination in step 302 is affirmative, the maximum amount of oxygen is stored in the three-way catalyst 2 and the air-fuel ratio is in the lean state, and the flag F1 is set in step 305. Is set to 2, and then, in step 306, the stoichiometric value λ0 of the first oxygen sensor 3 is decreased by α and corrected to the rich side.
When the determination in step 303 is affirmative, oxygen is not stored in the three-way catalyst 2 and the air-fuel ratio is in a rich state, and the flag F1 is set to 1 in step 307. Then, in step 308, the stoichiometric value λ0 is increased by α to correct the lean side.

As described above, the correction circuit 9 can correct the stoichiometric value λ0 of the first oxygen sensor 3 and can grasp the maximum oxygen amount and minimum oxygen amount (0) storage state of the three-way catalyst 2, This is reflected in the determination of the stored oxygen amount of the three-way catalyst 2 in the second flowchart.

The maximum oxygen amount FLMAX determined by the maximum oxygen amount determination circuit 11 is set to a lean air-fuel ratio in the engine steady operation state by using the oxygen amount calculation method described in the second flowchart, for example. The post-rich state is established, and the output of the second oxygen sensor 4 is obtained by time integration from the lean air-fuel ratio state to the rich state.

In the target oxygen amount determination circuit 11, the fourth flow chart shown in FIG. 5 is executed in synchronization with the second flow chart. First, in step 401, it is determined whether or not a flag F2 described later is 1. Initially, this judgment is denied, and the routine proceeds to step 402. Step 40
2, the accelerator pedal stroke L1 is measured by the accelerator pedal stroke sensor, and step 40
In 3, the deviation ΔL between the current accelerator pedal stroke L1 and the previous accelerator pedal stroke L0 is calculated. Next, at step 404, the accelerator pedal stroke L1 is stored as the previous accelerator pedal stroke L0 in preparation for the next processing.

Next, at step 405, ΔL is the first
It is determined whether or not the predetermined value K1 or more, that is, whether or not the engine acceleration state in which the air-fuel ratio of the air-fuel mixture inevitably becomes considerably lean is intended. When this determination is denied, the routine proceeds to step 406, where it is intended whether ΔL is less than or equal to the negative second predetermined value K2, that is, the engine deceleration state where the air-fuel mixture mixture is inevitably a considerably rich state. Is determined. When this determination is denied, the change in the accelerator pedal stroke is in a relatively small state including 0, and the air-fuel ratio of the air-fuel mixture can be maintained substantially at the stoichiometric air-fuel ratio.
At 7, the target oxygen amount IS is set to about half of the maximum oxygen amount FLMAX, and the process ends.

When the determination in step 405 is affirmative, the air-fuel ratio of the air-fuel mixture is in a considerably lean state, so that the three-way catalyst 2 not storing oxygen has a larger amount of excess oxygen. It can be absorbed, and the purification performance of the three-way catalyst 2 is maintained. Therefore, the target oxygen amount IS is set to 0 in step 408. On the other hand, step 4
When the determination in 06 is affirmative, the air-fuel mixture is in a considerably rich state, so that the maximum oxygen amount stored in the three-way catalyst 2 uses more oxygen and the three-way catalyst is used. The purification performance of the catalyst 2 can be maintained, and the target oxygen amount IS is set to FLMAX in step 409.

In both cases, the routine proceeds to step 410, where the flag F2 is set to 1. As a result, the determination in step 401 is affirmed in the next process, and step 411
Proceed to. In step 411, the count value T initially set to 0 is incremented by 1, and in step 412 it is determined whether or not the count value T is equal to or more than the predetermined value N. This judgment is initially denied and the processing ends, but it is eventually judged affirmative and proceeds to step 413, the flag F2 is reset to 0, and at step 414, the count value T
Is reset to 0.

Therefore, the target oxygen amount IS is 0 or FLMA.
When set to X, the subsequent accelerator pedal stroke L
Regardless of this, the count value T is maintained at that value until it becomes N, and in particular during this period, the throttle valve opening does not change in accordance with the accelerator pedal stroke. As a result, the actual acceleration / deceleration is executed after the oxygen amount of the three-way catalyst 2 has actually reached the target oxygen amount of 0 or FLMAX, and good exhaust including the O ₂ storage effect of the three-way catalyst 2 is achieved. Gas purification is realized.

FIG. 6 is a time chart of the amount of oxygen stored in the three-way catalyst 2 under the air-fuel ratio control of this embodiment. In the figure, t1 is when the engine acceleration / deceleration is intended,
At t2, actual engine acceleration / deceleration is executed. The solid line A is when the accelerator pedal stroke change is small, and since the air-fuel ratio is maintained at the stoichiometric air-fuel ratio, the oxygen amount stored in the three-way catalyst 2 is maintained at about half the maximum oxygen amount FLMAX. There is.

The solid line B shows the case where the engine is suddenly decelerated, and the oxygen amount stored in the three-way catalyst until the actual deceleration is the maximum oxygen amount FLMAX. A good purification using the stored oxygen is realized for the exhaust gas. In the conventional air-fuel ratio control, the oxygen storage amount becomes 0 on the way as shown by the dotted line, and the three-way catalyst 2 does not function in the region shown by the hatched line, and the exhaust emission deteriorates. Further, the solid line C is a case where the engine is intended to be accelerated rapidly, the oxygen amount stored in the three-way catalyst by the actual acceleration is 0, and the exhaust gas in the lean air-fuel ratio state generated at the time of engine acceleration is Thus, the three-way catalyst 2 stores this extra oxygen, and good purification is realized. In the conventional air-fuel ratio control, the oxygen storage amount reaches the maximum oxygen amount FLMAX on the way as shown by the one-dot chain line, and the three-way catalyst 2 does not function in the region shown by the diagonal line, and exhaust emission deteriorates.

In this embodiment, the case of the internal combustion engine having the throttle valve which is not connected to the accelerator pedal has been described, but in the case of the internal combustion engine in which both are mechanically connected,
For example, the schedule of engine acceleration can be grasped by the minimum accelerator pedal stroke, and the schedule of engine deceleration can be grasped by the maximum accelerator pedal stroke. The target oxygen amount IS is 0, half of the maximum oxygen amount FLMAX, or the maximum oxygen amount FLMAX is adopted as the target oxygen amount IS, but the present invention is not particularly limited to this, and at least during engine acceleration. It is obvious that the exhaust emission can be improved as compared with the conventional case if the target oxygen amount IS is relatively small and the target oxygen amount IS is relatively large during deceleration of the engine. Furthermore, the target oxygen amount IS can be set more finely according to the engine operating state.

[0029]

As described above, according to the air-fuel ratio control system for an internal combustion engine according to the present invention, the target oxygen amount is reduced from the scheduled to the execution of the engine acceleration that causes the lean state of the air-fuel ratio. Therefore, the amount of oxygen stored in the three-way catalyst becomes small, the excess oxygen at this time can be sufficiently stored, and the three-way catalyst can function sufficiently to purify the exhaust gas at this time well. it can. In addition, from the scheduled execution of the engine deceleration to bring the air-fuel ratio rich state to the execution,
Since the target oxygen amount is increased, the amount of oxygen stored in the three-way catalyst increases, and the oxygen can be used to make the three-way catalyst fully function and to purify the exhaust gas at this time well. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 2 is a first flowchart executed in a basic fuel injection amount determination circuit.

FIG. 3 is a second flowchart executed in a control circuit.

FIG. 4 is a third flowchart executed in the correction circuit.

FIG. 5 is a fourth flowchart executed in a target oxygen amount determination circuit.

FIG. 6 is a time chart of the amount of oxygen stored in the three-way catalyst by the air-fuel ratio control device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Three-way catalyst 3 ... 1st oxygen sensor 4 ... 2nd oxygen sensor 5 ... Basic fuel injection amount determination circuit 6 ... Control circuit 7 ... Subtractor 8 ... Multiplier 9 ... Correction circuit 10 ... Target oxygen amount Decision circuit

Claims (1)

[Claims] 1. An oxygen amount calculation means for calculating the amount of oxygen currently stored in the three-way catalyst using the amount of exhaust gas flowing into the three-way catalyst and its oxygen concentration, and the oxygen amount calculation means. A fuel amount control means for controlling the amount of fuel supplied to the engine combustion chamber in consideration of the amount of intake air so as to maintain the above-mentioned amount of oxygen at the target amount of oxygen; An air-fuel ratio of an internal combustion engine, comprising: a target oxygen amount changing means for decreasing the target oxygen amount and increasing the target oxygen amount from the time when the engine deceleration is scheduled to the time when it is executed. Control device.