JPH0422725A - Air-fuel ratio control device for internal combustion engines - Google Patents

Abstract

PURPOSE:To enhance the converging characteristic to the target air fuel ratio in an air fuel ratio control, which is made on the basis of the values given by air fuel ratio sensors provided upstream and downstream a catalyst for purification of the exhaust gas, by modifying the correction amount for air fuel ratio control due to the dovmstream sensor according to the period of air fuel ratio controlling cycles due to sensor. CONSTITUTION:No.1 and No.2 air fuel ratio sensors A, B, whose output values vary according to the concentration of specific gas components of the exhaust gas, are mounted upstream and downstream of an exhaust gas purifying catalyst provided in the exhaust passage, and the air fuel ratio control amount is calculated C on the basis of the output value from the No.1 sensor A, while computation D is made for the air fuel ratio control correction amount to correct the air fuel ratio control amount on the basis of the output value from the No.2 air fuel ratio sensor B. The period of air fuel ratio controlling cycles due to the calculated C air fuel ratio control amount is sensed by an upstream control cycle period sensing means E, and on the basis of the result from sensing, the air fuel ratio control correction amount is modified F. The air fuel ratio control amount is corrected on the basis of this modified F air fuel ratio control correction amount, and the final air fuel ratio control amount is set G, and on the basis of this set amount an air fuel ratio controlling means H is controlled.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to an air-fuel ratio control device for an internal combustion engine, and in particular, the present invention relates to an air-fuel ratio control device for an internal combustion engine. The present invention relates to a device that performs feedback control of an air-fuel ratio with high accuracy based on a detected value of a fuel ratio sensor.

<Prior art> Conventionally, in order to maintain good conversion efficiency in a three-way catalyst installed in the exhaust system for exhaust purification, feedback control of the air-fuel ratio of the engine intake air-fuel mixture to the stoichiometric air-fuel ratio has been carried out. In order to ensure responsiveness, an oxygen sensor (air-fuel ratio sensor) that detects the air-fuel ratio via the oxygen concentration in the exhaust gas is installed at a gathering part of the exhaust manifold relatively close to the combustion chamber. Based on the oxygen concentration detected in the exhaust gas, the actual air-fuel ratio (rich/lean) relative to the stoichiometric air-fuel ratio is detected, and the amount of fuel supplied to the engine is feedback-controlled.

However, as mentioned above, the oxygen sensor installed in the exhaust system relatively close to the combustion chamber is exposed to high-temperature exhaust gas, so its characteristics tend to change due to thermal deterioration.
Because the exhaust gas from each cylinder was not sufficiently mixed, it was difficult to detect the average air-fuel ratio for all cylinders, resulting in variations in air-fuel ratio detection accuracy, which in turn worsened air-fuel ratio control accuracy. .

In view of this, an oxygen sensor is also installed downstream of the catalyst, and two
A method has been proposed in which the air-fuel ratio is feedback-controlled using the detected values of two oxygen sensors (Japanese Patent Laid-Open No. 58-487
(See Publication No. 56, etc.)

In other words, the downstream oxygen sensor has poor response due to its distance from the combustion chamber and the 02 storage effect of the three-way catalyst, but since it is located downstream of the catalyst, there is little thermal influence, and The amount of poisoning caused by toxic components is small, and because the exhaust mixture is well-mixed, the average air-fuel ratio of all cylinders can be detected, resulting in highly accurate and stable detection performance compared to oxygen sensors installed upstream. can get.

Therefore, we decided to perform independent feedback control of the air-fuel ratio based on the detected values of the two oxygen sensors.
By compensating the characteristics of air-fuel ratio feedback control by the upstream oxygen sensor with the downstream oxygen sensor, while ensuring responsiveness with the upstream sensor, and compensating for the accuracy of the control point downstream, the Accurate air-fuel ratio feed-hunk control is performed.

<Problem to be Solved by the Invention> By the way, when attempting to compensate for the air-fuel ratio feedback control based on the air-fuel ratio sensor on the upstream side of the catalyst with control using the air-fuel ratio sensor on the downstream side, as described above, the air-fuel ratio feedback control based on the air-fuel ratio sensor on the downstream side of the catalyst The request for the control amount based on the fuel ratio sensor differs depending on the rich/lean cycle relative to the target air-fuel ratio detected by the upstream air-fuel ratio sensor that appears as a result of air-fuel ratio control, and as shown in FIG. 5, the cycle is long. Sometimes, it is necessary to set a large control amount based on the detection result of the downstream air-fuel ratio sensor to ensure convergence to the target air-fuel ratio.

Figure 5 shows the air-fuel ratio feedback correction value for increasing/decreasing the fuel supply amount using the upstream air-fuel ratio sensor (oxygen sensor).
The proportional operation amount when proportional-integral control is performed based on the output of When the air-fuel ratio is corrected to the target air-fuel ratio, the larger the period of air-fuel ratio feedback control based on the upstream sensor (the rich/lean reversal period with respect to the target air-fuel ratio detected by the upstream sensor), the more the proportional Unless the change in the air-fuel ratio feedback correction value due to proportional operation is increased by increasing PH03, which is the correction amount of the manipulated variable, the rich/lean detection period at the downstream sensor that shows convergence to the true target air-fuel ratio will be shortened. It shows that it cannot be maintained.

In this way, depending on the control period based on the upstream sensor,
Although it is necessary to change the control amount by the downstream sensor,
The control period varies depending on the chip temperature of the air-fuel ratio sensor, the engine rotational speed, the degree of deterioration of the air-fuel ratio sensor, etc. (areas divided by engine load and engine load),
Because the conditions related to the control cycle are different in each region, the degree of learning progress varies between regions, and in regions with long control cycles and poor learning convergence, there is a difference between the learned value and the required value. This causes a problem in that the convergence and accuracy of learning are adversely affected, and desired air-fuel ratio control accuracy cannot be obtained.

The present invention has been made in view of the above problems, and is capable of correcting the air-fuel ratio control correction amount by the air-fuel ratio sensor on the downstream side according to the control cycle by the air-fuel ratio sensor on the upstream side of the catalyst, thereby achieving air-fuel ratio convergence. The purpose of the present invention is to provide an air-fuel ratio control device with improved performance.

<Means for solving the problem> Therefore, in the air-fuel ratio control device for an internal combustion engine according to the present invention,
As shown in Figure 1, the catalysts are installed upstream and downstream of an exhaust purification catalyst installed in the exhaust passage of an internal combustion engine, and output values are adjusted in response to the concentration of specific gas components in the exhaust gas, which changes depending on the air-fuel ratio. first and second air-fuel ratio sensors that change, air-fuel ratio control amount calculation means that calculates an air-fuel ratio control amount based on the output value of the first air-fuel ratio sensor, and an output value of the second air-fuel ratio sensor. an air-fuel ratio control correction amount calculation means for calculating an air-fuel ratio control correction amount for correcting the air-fuel ratio control amount based on the air-fuel ratio control amount; and detecting an air-fuel ratio control cycle based on the air-fuel ratio control amount calculated by the air-fuel ratio control amount calculation means. an upstream control cycle detection means for detecting an air-fuel ratio; a correction amount correction means for correcting an air-fuel ratio control correction amount based on the control cycle detected by the upstream control cycle detection means; and an air-fuel ratio corrected by the correction amount correction means. an air-fuel ratio control amount correction setting means for correcting the air-fuel ratio control amount based on the control correction amount and setting a final air-fuel ratio control amount; and an air-fuel ratio control means for controlling the air-fuel ratio of the engine intake air-fuel mixture based on the air-fuel ratio.

<Operation> In such a configuration, the air-fuel ratio control amount calculation means calculates the air-fuel ratio control amount based on the output value of the first air-fuel ratio sensor provided upstream of the exhaust purification catalyst, while the air-fuel ratio The control correction amount calculation means calculates an air-fuel ratio control correction amount for correcting the air-fuel ratio control amount based on an output value of a second air-fuel ratio sensor provided downstream of the exhaust purification catalyst.

On the other hand, the upstream control cycle detecting means detects the control cycle of the air-fuel ratio based on the air-fuel ratio control amount based on the first air-fuel ratio sensor, and the correction amount correcting means detects the control cycle of the air-fuel ratio based on the air-fuel ratio control amount based on the control cycle. The air-fuel ratio control correction amount by the sensor is corrected, and the correction amount is set in response to a change in the required value of the correction amount due to the difference in the control cycle.

Based on the air-fuel ratio control correction amount corrected based on the control cycle by the first air-fuel ratio sensor as described above, the air-fuel ratio control amount correction setting means sets the air-fuel ratio control amount by the first air-fuel ratio sensor. is corrected to set the final air-fuel ratio control amount.

The air-fuel ratio control means controls the air-fuel ratio of the engine intake air-fuel mixture based on the air-fuel ratio control amount corrected by the air-fuel ratio control correction amount.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 2 showing the configuration of one embodiment, an air flow meter 13 for detecting the intake air flow rate Q and a throttle valve 14 for controlling the intake air flow rate Q in conjunction with an accelerator pedal (not shown) are installed in the intake passage 12 of the engine 11. An electromagnetic fuel injection valve 1 is installed for each cylinder in the downstream manifold part.
5 is provided.

The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 having a built-in microcomputer, and injects fuel that is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator.

Further, a water temperature sensor 17 is provided to detect the temperature Tw of cooling water in the cooling jacket of the engine 11.

On the other hand, the exhaust passage 18 is provided with a first air-fuel ratio sensor 19 that detects the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas at the manifold gathering part, and the exhaust gas A three-way catalyst 20 is provided as an exhaust purification catalyst that purifies exhaust gas by oxidizing Co and HC and reducing NOx.
A second air-fuel ratio sensor 2 having the same function as the air-fuel ratio sensor
1 is provided.

The first air-fuel ratio sensor 19 and the second air-fuel ratio sensor 21 are known oxygen concentration sensors whose output voltages change in response to the oxygen concentration in the exhaust gas. Rich/lean conditions relative to the stoichiometric air-fuel ratio, which is the target of air-fuel ratio control, can be detected by utilizing the sudden change in oxygen concentration.

Further, the distributor (not shown in FIG. 2) has a built-in crank angle sensor 22, and a crank angle signal outputted from the crank angle sensor 22 in synchronization with the engine rotation is counted for a certain period of time, or The engine rotation speed N is detected by measuring the period of the crank reference angle signal.

Next, the air/fi ratio control routine by the control unit 16 will be explained according to the flowcharts of FIGS. 3 and 4.

In this embodiment, the air-fuel ratio control amount calculation means.

air-fuel ratio control correction amount calculation means, upstream control cycle detection means,
The functions of the correction amount modifying means, the air-fuel ratio control amount correction setting means, and the air-fuel ratio control means are provided in the control unit 16 in the form of software, as shown in the flowcharts of FIGS. 3 and 4.

FIG. 3 shows a fuel injection amount setting routine, and this routine is performed at predetermined intervals (for example, every 1 (m)).

In step C (shown as S in the figure), the intake air per unit rotation is determined based on the intake air flow rate Q detected by the air flow meter 3 and the engine rotation speed N calculated based on the signal from the crank angle sensor 24. The basic fuel injection amount TP corresponding to the air amount is calculated using the following equation.

Tp=KxQ/N (K is a constant) In step 2, various correction coefficients C0EF are set based on the cooling water temperature Tw etc. detected by the water temperature sensor 17.

In step 3, an air-fuel ratio feedback correction coefficient α is read as an air-fuel ratio control amount set by a feedback correction coefficient setting routine to be described later.

In step 4, a voltage correction numerator s is set based on the battery voltage value. This is to correct changes in the injection flow rate of the fuel injection valve 15 due to battery voltage fluctuations.

In step 5, the final fuel injection amount (fuel supply amount) T
i is calculated according to the following equation. The function of step 5, which sets the fuel injection amount Tt while correcting it using the air-fuel ratio feedback correction coefficient α (air-fuel ratio control amount) as shown in the equation below, corresponds to the air-fuel ratio control means.

T1-TpXCOEFXα+Ts In step 6, the calculated fuel injection valve Ti is set in the output register.

As a result, when the predetermined fuel injection timing is synchronized with the engine rotation, a drive pulse signal having a pulse width of the calculated fuel injection amount Ti is applied to the fuel injection valve 15 to perform fuel injection.

Next, the air-fuel ratio feedback correction coefficient (air-fuel ratio control amount)
The setting routine will be explained according to the flowchart in FIG. Note that this routine is executed in synchronization with engine rotation.

In step 11, it is determined whether the operating conditions are such that feedback control of the air-fuel ratio is performed. If the operating conditions are not satisfied, this routine is terminated. In this case, the air-fuel ratio feedback correction coefficient α is clamped to the value at the end of the previous feedback control or a constant reference value, and the feedback control is stopped.

In step 12, the signal voltage ■ from the first air-fuel ratio sensor 19 is detected. 2 and the signal voltage ■° from the second air-fuel ratio sensor 21. Enter 2.

In step 13, the signal voltage ■ of the first air-fuel ratio sensor 19 input in step 12 is determined. , and a reference value SL corresponding to the target air-fuel ratio (stoichiometric air-fuel ratio) to determine whether the air-fuel ratio is inverted from lean to rich or from rich to lean.

When it is determined that the inversion is occurring, the process proceeds to step 14, where the signal voltage of the first air-fuel ratio sensor 19 is set. The control period T is set based on the air-fuel ratio feedback correction coefficient α, which is determined as the inversion period of 2. That is, the cycle in which rich/lean reversal is determined in step 13 is measured, and the cycle is set to T.

Then, in the next step 15, the air-fuel ratio feedback correction coefficient α(
Based on the period T corresponding to the air-fuel ratio control period according to the air-fuel ratio control amount), a preset correction value FCONF is searched and determined.

In the next step 16, a proportional correction amount PH05x (air-fuel ratio The area-specific learned correction amount P) that has learned the control correction amount) Searches and obtains the correction amount P HOS corresponding to the current operating state from the map of IO5.

Note that the area-specific learning correction amount P HOS is the signal voltage V' from the second air-fuel ratio sensor 21, as will be described later. It is learned according to rich/lean for the stoichiometric air-fuel ratio detected based on 2.

In step 17, the output V'' of the second air-fuel ratio sensor 21 is
. 8 and a slice level SL corresponding to the stoichiometric air-fuel ratio to determine whether the air-fuel ratio is rich or lean.

When the air-fuel ratio is determined to be rich (V'., >SL), the process proceeds to step 18, where a predetermined value DPHO is calculated from the area-specific learning correction value PHOS retrieved in step 16.
5R is subtracted to correct the area-based learning correction value P HOSx corresponding to the current driving state.

Further, when the air-fuel ratio is determined to be lean (Vo., <SL), the process proceeds to step 19, and the area-specific learning correction value P is calculated by adding the predetermined value DP)IO5L to the searched area-specific learning correction value PHOS. Perform a correction calculation on HOSx.

That is, each time this routine is executed, it is determined whether the actual air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio (target air-fuel ratio) based on the output V'02 of the second air-fuel ratio sensor 21, and the first air-fuel ratio sensor 19 The proportional operation amount in the proportional control of the air-fuel ratio feedback correction coefficient α based on the rich/lean discrimination based on the rich/lean discrimination is increased or decreased in the direction in which the air-fuel ratio detected by the second air-fuel ratio sensor 21 approaches the target (stoichiometric air-fuel ratio). As described later, the area-specific learning correction value P HOSx is added to the control amount (proportionality constant PL) that makes the air-fuel ratio rich, and conversely subtracted from the control amount that makes the air-fuel ratio lean (proportionality constant PI). Therefore, the second air-fuel ratio sensor 2
If the correction value P HOSx is reduced as described above when rich is detected in 1, the control amount to make it rich (proportionality constant PL) will decrease, and the control amount to make it lean (proportionality constant P) Since the amount subtracted from PH becomes smaller and the lean control amount becomes larger, as a result, the correction value PH
If the air-fuel ratio feedback correction coefficient α is manipulated using the corrected control amount in OSx, the air-fuel ratio control point will move in the lean direction.

In the next step 20, the area-specific learning correction value PH0Sx, which is increased or decreased based on the rich/lean ratio with respect to the target air-fuel ratio detected by the second air-fuel ratio sensor 21, is mapped as data corresponding to the current operating conditions. Rewrite the learning.

In addition, in step 21, the area-specific learning correction value P HOSx used for updating the map value in step 20 above and the correction value FCONF obtained in step 15 based on the control period T by the first air-fuel ratio sensor 19 are calculated. Here, the air-fuel ratio feedback correction coefficient α is increased by proportional control (in the air-fuel ratio rich direction).
The result of adding the correction value FCONF to the proportional constant PL to be manipulated and the area-specific learning correction value P HOSx is then determined as the final proportional constant P L (← P t
+P HOSx), while the area-specific learning correction value P HOSx was subtracted from the result of adding the correction value FCONF to the proportional constant Pa, which operates the air-fuel ratio feedback correction coefficient α to decrease (in the air-fuel ratio lean direction) by proportional control. Set the result to the final proportionality constant P1.

The correction value FCONF is set to a larger value as the control period T is longer. Therefore, when the control period T is longer, the proportionality constant P and the proportionality constant P1 are set to be larger, and the air-fuel ratio feedback correction coefficient α is proportionally controlled. Therefore, control is performed in the direction of shortening the control period T, thereby ensuring the convergence of the air-fuel ratio detected by the second air-fuel ratio sensor 21 to the target (the second air-fuel ratio sensor 21). (See FIG. 5).

As a result, even in an operating state where the control cycle based on the first air-fuel ratio sensor 19 is long, the learning convergence and accuracy of the area-based learning correction value P HOS that is learned corresponding to the area of the operating state can be improved. This prevents deterioration of the convergence to the target air-fuel ratio (the true target air-fuel ratio detected by the second air-fuel ratio sensor 21) due to the long control cycle, and also prevents deterioration of the learning convergence. Air-fuel ratio controllability in operating conditions with long control cycles can be improved. Note that when the control period T is short, the correction [FCONF is set relatively small, so the proportionality constant is set excessively and an overshoot error of the air-fuel ratio controlled by the air-fuel ratio feedback correction coefficient α occurs. This can be avoided.

In the next step 22, the output of the first air-fuel ratio sensor 19 is compared with the slice level SL corresponding to the stoichiometric air-fuel ratio to determine whether the stoichiometric air-fuel ratio is rich or lean, and if it is lean, the process proceeds to step 23. , the proportional constant PL is added to the previous air-fuel ratio feedback correction coefficient α, and the result is set as the new correction coefficient α, thereby enriching the air-fuel ratio. Further, when it is determined in step 22 that the fuel is rich, the process proceeds to step 24, and the proportional constant P is calculated from the previous air-fuel ratio feedback correction coefficient α.
5 is increased by 1jEX and the result is newly set as a correction coefficient α to make the air-fuel ratio leaner.

On the other hand, if it is determined in step 13 that the rich-lean inversion is not occurring, the process proceeds to step 25 and onward to perform integral control of the air-fuel ratio feedback correction coefficient α. In step 25, the output ■ of the first air-fuel ratio sensor 19 is determined. 2 and the slice level SL, and if it is rich, a predetermined integral constant ■ is subtracted from the air-fuel ratio feedback correction coefficient α in step 26, and if it is lean, the air-fuel ratio feedback correction coefficient α is subtracted in step 27. A predetermined integral constant It is added.

In this embodiment, the correction value PH03 of the proportional operation amount of the air-fuel ratio feedback correction coefficient α as the air-fuel ratio control amount is set as the air-fuel ratio control correction amount, and this correction 4fiPHO5 is corrected according to the control period T. is the air-fuel ratio feedback correction coefficient α based on the output of the first air-fuel ratio sensor 19
The integral or differential bone, which is the control operation amount, may be corrected according to the control period T. Furthermore, based on the output of the second air-fuel ratio sensor 2J, the air-fuel ratio feedback correction coefficient α is a unique air-fuel ratio feedback correction coefficient α2.
In this case, the air-fuel ratio feedback correction coefficient α2 based on the second air-fuel ratio sensor 21 may be set as the correction coefficient α( based on the first air-fuel ratio sensor 19).
The correction coefficient α2 may be corrected based on the control cycle T by regarding the correction (air-fuel ratio control amount) as 1 (air-fuel ratio control correction amount).

<Effects of the Invention> As explained above, according to the present invention, air-fuel ratio sensors are provided on the upstream and downstream sides of the exhaust purification catalyst, and the air-fuel ratio is controlled based on the detected values of these rain air-fuel ratio sensors. By correcting the air-fuel ratio control correction amount by the air-fuel ratio sensor on the downstream side according to the air-fuel ratio control period by the air-fuel ratio sensor on the upstream side of the catalyst, the air-fuel ratio control period can be shortened in the operating state where the control period is long. This has the effect of improving convergence with respect to the true target air-fuel ratio detected by the second air-fuel ratio sensor.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, FIG. 3 is a flowchart showing the fuel injection amount setting routine of the same embodiment, and FIG. Similarly, FIG. 5 is a flowchart showing the air-fuel ratio feedback correction coefficient setting routine, and FIG. 5 is a diagram showing the required correction value of the proportionality constant with respect to the air-fuel ratio control period (frequency) by the upstream air-fuel ratio sensor. 11...Internal combustion engine 12...Intake passage elevation resistance 16.
...Air-fuel ratio sensor of control unit 20...Three-way catalyst air-fuel ratio sensor 15...Fuel injection 19...1st 21...2nd patent applicant Japan Electronics Co., Ltd. Agent Patent attorney Sasa Fujio ShimaFigure 2Figure 3

Claims (1)

[Scope of Claims] The catalyst is provided on the upstream and downstream sides of an exhaust purification catalyst provided in the exhaust passage of an internal combustion engine, and the output value changes in response to the concentration of a specific gas component in the exhaust gas that changes depending on the air-fuel ratio. first and second air-fuel ratio sensors that calculate the air-fuel ratio, air-fuel ratio control amount calculation means that calculates an air-fuel ratio control amount based on the output value of the first air-fuel ratio sensor, and an output value of the second air-fuel ratio sensor. an air-fuel ratio control correction amount calculation means for calculating an air-fuel ratio control correction amount for correcting the air-fuel ratio control amount based on the air-fuel ratio control amount; and an air-fuel ratio control period based on the air-fuel ratio control amount calculated by the air-fuel ratio control amount calculation means. upstream control period detection means for detecting; correction amount correction means for correcting the air-fuel ratio control correction amount based on the control period detected by the upstream control period detection means; an air-fuel ratio control amount correction setting means for correcting the air-fuel ratio control amount based on the air-fuel ratio control correction amount to set a final air-fuel ratio control amount; and an air-fuel ratio set by the air-fuel ratio control amount correction setting means. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio control means for controlling an air-fuel ratio of an engine intake air-fuel mixture based on a control amount.