JPH07189815A - Exhaust reflux controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a target EGR quantity with good responsiveness and high precision so as to reduce NOx by feedback controlling a basic controlled variable for an EGR control valve according to a correction factor so that an indicated average effective pressure in an intake process is brought to approximation of a target indicated average effective pressure. CONSTITUTION:A basic controlled variable for an EGR control valve 7 is found on the basis of outputs of an air flow meter 3, a crank angle sensor 8, and a cylinder inner pressure sensor 9 by means of a control unit 50 and on the basis of a basic fuel injection quantity Tp and the number of engine revolutions N, while a final correction factor is found on the basis of the specific EGR quantity correction factor dEGR. An EGR controlled variable is computed on the basis of the obtained basic controlled variable and the final correction factor so as to control the EGR control valve 7. For the specific EGR quantity correction factor dEGR, a correction factor dEGR1 for bringing an actual EGR quantity close to the target EGR quantity with quick responsiveness and a correction factor dEGR2 for setting combustion stability in the predetermined range with a slow controlling speed are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a device for controlling the amount of exhaust gas recirculation (EGR) in an internal combustion engine, and more particularly to a technique for improving control response and control accuracy.

[0002]

2. Description of the Related Art Conventionally, exhaust gas emitted from an internal combustion engine
It reduces nitrogen oxides (NOx) contained in the air and reduces atmospheric pollution.
There is a strong desire to prevent the spread of dye. by the way,
The NOx is emptied at high temperature during combustion in the engine combustion chamber.
Nitrogen in the air (N₂) And oxygen (O ₂) Reacts with
Is produced by high oxygen concentration and combustion temperature
As it increases, the oxygen concentration and combustion temperature are reduced.
One of the effective ways to reduce NOx is to suppress the reaction
It becomes a step.

Therefore, as a device for reducing the oxygen concentration and the combustion temperature, part of the exhaust gas discharged from the engine is returned to the engine intake system and introduced into the combustion chamber to reduce the oxygen concentration of the intake air. At the same time, an exhaust gas recirculation (EGR) device has been proposed in which the combustion temperature is reduced via carbon dioxide (CO ₂ ) having a large heat capacity in the recirculated exhaust gas.

As a general control of such an exhaust gas recirculation system, the control amount (for example, opening degree or duty ratio) of an exhaust gas recirculation valve provided in an exhaust gas recirculation passage that connects the engine exhaust system and the engine intake system is So-called feed-forward control is employed which controls to a preset target value based on the operating state of the engine (load, rotation speed, etc.). However, in such a feedforward control, manufacturing variations and characteristic variations of the engine body and the exhaust gas recirculation valve, or changes over time in the engine body, changes in the exhaust gas recirculation valve, exhaust gas recirculation passage, etc. over time, Furthermore, environmental conditions (atmospheric pressure, atmospheric temperature,
If the actual exhaust gas recirculation amount differs from the target exhaust gas recirculation amount due to changes in humidity, etc., or the maximum exhaust gas recirculation amount itself that can be sucked while ensuring combustion stability due to deterioration of the engine body However, if exhaust gas recirculation control is performed at a target value that is set under a certain condition as in the conventional case, the NOx reduction effect is reduced, the fuel consumption is deteriorated due to excessive deterioration of combustion, or the engine drivability (combustion It is unavoidable that the stability) is deteriorated.

Therefore, for example, Japanese Patent Laid-Open No. 60-10475.
According to the method disclosed in No. 4, the indicated mean effective pressure is calculated from the combustion pressure, the engine fluctuation torque is detected by the degree of dispersion, and the fluctuation torque falls within a predetermined range.
The above problem is attempted to be solved by feedback-controlling the control value of the exhaust gas recirculation valve.

[0006]

However, in the conventional device as described above, even if the same operating condition is maintained, the variation of the combustion condition is large and the generated torque for each combustion has a predetermined distribution. Occurs. In particular, when the exhaust gas recirculation is recirculated to a maximum amount, this phenomenon becomes remarkable, and thus a sufficiently long time (data number) is required to determine its statistical properties. Therefore, it is difficult to estimate the global combustion state from the combustion result for each cycle (for example, the indicated mean effective pressure), and the reliability of the information is low when the number of data for obtaining the dispersion is small. Therefore, feedback control must be performed with a small correction amount, and if an attempt is made to obtain an appropriate correction amount by increasing the number of data items for which dispersion is to be calculated, it takes a long time to detect the state. It was a bad thing.

On the other hand, Japanese Patent Application Laid-Open No. 4-272461 discloses an improvement by combining learning control with the above-mentioned device, but the basic information for feedback control and learning control is basically the combustion state. It is based on this, and basically has a poor responsiveness, and there is a problem similar to the above until the learning is completed. Further, Japanese Patent Application Laid-Open No. 4-81557 discloses a method in which a heat release rate is calculated based on the in-cylinder pressure in a compression stroke or a combustion stroke, and the control value of the exhaust gas recirculation valve is feedback-controlled using this as a target value. It has been disclosed that enables highly responsive control for each cycle.

However, since the heat release rate is obtained from the differential or differential processing of the detected values, high accuracy is required for all individual detected values. The obtained correction amount may be significantly different. Therefore, it is difficult to perform highly accurate feedback control. The present invention has been made in view of the above circumstances, and various error factors can be eliminated to quickly and accurately obtain a target exhaust gas recirculation amount.
An object of the present invention is to provide an exhaust gas recirculation control device for an internal combustion engine, which can maximize the Ox reduction effect.

[0009]

Therefore, in the exhaust gas recirculation control device for an internal combustion engine according to the present invention, as shown in FIG. 1, an exhaust gas recirculation passage A for recirculating a part of exhaust gas to an engine intake system, and an exhaust gas recirculation passage. Exhaust gas recirculation amount adjusting means B for adjusting the recirculation amount of
A cylinder pressure detecting means C for detecting the pressure in the cylinder; an operating state detecting means D for detecting the operating state of the engine; and a target value of the in-cylinder pressure state in the intake stroke based on the detected operating state. A target value setting means E for setting the cylinder pressure, an actual value detecting means F for detecting an actual cylinder pressure state in the intake stroke based on the cylinder pressure detected by the cylinder pressure detecting means C, and the set value. The target value of the in-cylinder pressure state,
An exhaust gas recirculation amount feedback control means G for feedback-controlling the exhaust gas recirculation amount adjusting means B so as to bring the in-cylinder pressure state closer to a target value on the basis of the actually measured value of the detected in-cylinder pressure state. Configured.

[0010]

In the present invention having the above-mentioned structure, the cylinder pressure state of the intake stroke set by the target value setting means (for example, the cylinder pressure at a predetermined crank angle of the intake stroke or the predetermined crank angle section of the intake stroke). Mean value of in-cylinder pressure of
Alternatively, it corresponds to the indicated mean effective pressure in the predetermined crank angle section of the intake stroke. ) And the actual measurement value of the actual in-cylinder pressure state detected by the actual measurement value detecting means, the exhaust gas is adjusted so that the actual in-cylinder pressure state approaches the target in-cylinder pressure state. The control value of the exhaust gas recirculation amount adjusting means is corrected and controlled by the recirculation feedback control means.
As a result, the actual exhaust gas recirculation amount can be controlled to the target exhaust gas recirculation amount with high responsiveness and high accuracy.

As will be described later, the actual in-cylinder pressure state in the intake stroke has little fluctuation in each cycle, and can be reliable as a sufficiently accurate value even with one cycle of measurement, and if the operating state and the exhaust gas recirculation amount are determined. Since it is determined definitely, detecting the in-cylinder pressure state in the intake stroke results in highly responsive and highly accurate detection of the exhaust gas recirculation amount.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. First, the basic idea of this embodiment will be described below. FIG. 10 is a diagram (P-V diagram) showing the experimental result of the in-cylinder pressure change with respect to the crank angle and the relationship between the in-cylinder volume and the in-cylinder pressure change. From these figures, the following can be understood.

That is, (1) the cylinder pressure waveform in the intake / exhaust stroke, particularly the cylinder pressure waveform in the intake stroke, is as long as the engine operating condition (basic fuel injection amount Tp and engine speed N) is constant. Compared to the expansion stroke (combustion stroke), which tends to be affected by variations in combustion, misfire, etc., there is little fluctuation in each cycle. That is, according to the in-cylinder pressure in the intake stroke, it is possible to determine the variation amount of the in-cylinder pressure by measuring only one cycle, and it is possible to determine the variation in the in-cylinder pressure in the expansion stroke as in the conventional case. It is not necessary to process the detection result by a statistical method to determine the fluctuation amount of the in-cylinder pressure afterwards.

(2) The cylinder pressure waveform during the intake stroke is
Even if the engine generated torque and the engine rotation speed are the same, they change in one direction according to the change of the EGR rate (exhaust gas recirculation amount / fresh air intake air flow rate). This is because the pressure of the exhaust gas is higher than the pressure in the intake passage during the intake stroke, so that a relatively simple relationship is established in which the cylinder pressure increases as the exhaust gas recirculation amount increases. . Therefore, the actual exhaust gas recirculation amount can be estimated with high accuracy by observing the in-cylinder pressure waveform in the intake stroke.

Based on the above basic idea,
In the present embodiment, the basic control amount of the exhaust gas recirculation amount adjusting means is a target value (basic control amount) determined based on the engine operating conditions such as the engine rotational speed and the intake air flow rate per cycle in a feedforward manner. ) And the actual cylinder pressure state detected by the cylinder pressure detecting means and the cylinder pressure state of the intake stroke which will be obtained by the target value, and the correction amount calculating means A correction amount for the basic control amount of the exhaust gas recirculation amount adjusting means is calculated. And
The exhaust gas recirculation amount adjusting means is feedback-controlled by a control amount obtained by correcting the basic control amount of the exhaust gas recirculation adjusting means by the correction amount. As a result, the actual exhaust gas recirculation amount can be controlled to the target exhaust gas recirculation amount with high responsiveness and high accuracy.

In the present embodiment, in addition to the above, based on the following concept, control is performed so that the combustion stability during exhaust gas recirculation control falls within a predetermined range. (3) The in-cylinder pressure waveform in the expansion stroke changes according to combustion fluctuations even when the engine operating condition is constant. In particular, if the combustion variation increases as the EGR rate increases,
The variation from cycle to cycle becomes large. Therefore, it is possible to estimate the combustion stability by obtaining a plurality of cycles of the in-cylinder pressure waveform in the expansion stroke and statistically processing the detection result.

Therefore, in this embodiment, the in-cylinder pressure state in the expansion stroke is detected, and the stability of the combustion state is detected based on the detection result, so that the combustion stability falls within a predetermined range. The corrected control amount is further corrected to ensure combustion stability. That is, in the present embodiment, the improvement of the control responsiveness to the target exhaust gas recirculation amount is achieved by the above (1) and (2), while the maintenance of the combustion stability by the exhaust gas recirculation is slightly performed in a relatively long cycle. It becomes possible to adjust. That is, it is possible to improve the control speed and accuracy of the exhaust gas recirculation control and maintain the combustion stability even when the suction limit value of the exhaust gas recirculation amount of the engine changes. .

The present embodiment will be specifically described below. In FIG. 2, the intake passage 2 of the engine 1 is provided with an air flow meter 3 for detecting a flow rate Q of intake air taken in via an air cleaner (not shown). A throttle valve 4 is provided downstream of the air flow meter 3 to adjust the intake air flow rate Q in conjunction with an accelerator pedal.

On the other hand, an exhaust gas recirculation passage 6 is provided which connects the exhaust passage 5 for guiding the exhaust gas discharged from the engine 1 to the outside air and the intake passage 2. An EGR control valve 7 for adjusting the exhaust gas recirculation amount is provided in the exhaust gas recirculation passage 6. The EGR control valve 7 constitutes exhaust gas recirculation amount adjusting means. In this embodiment, the EGR control valve 7 is a CPU, RO
Based on a drive signal (control amount) from a control unit 50 including a microcomputer including M, RAM, an A / D converter, an input / output interface and the like, via a step motor or a proportional solenoid. It is driven so that the opening degree (flow rate) can be adjusted.
Note that the present invention is not limited to this, and for example, a solenoid valve
An EGR control valve that opens and closes in an N / OFF manner may be provided, and the so-called duty control may be performed in which the exhaust gas recirculation amount is controlled by periodically opening and closing the valve and controlling the valve opening time and period.

A crank angle sensor 8 is provided on a crank shaft, a cam shaft or the like not shown in FIG.
The control unit 50 counts the crank unit angle signal output from the crank angle sensor 8 in synchronization with the engine rotation for a certain period of time or measures the cycle of the crank reference angle signal to detect the engine rotation speed N. It is like this.

By the way, the air flow meter 3 and the crank angle sensor 8 constitute an operating condition detecting means according to the present invention. An in-cylinder pressure sensor 9 as an in-cylinder pressure detecting means for detecting the in-cylinder pressure is provided so as to face the inside of the cylinder of the engine 1. The in-cylinder pressure sensor 9 may be embedded in the washer of the spark plug and is often used as a knocking sensor. In this case, since it is not necessary to separately drill a mounting hole on the wall surface of the combustion chamber in the cylinder, damage due to thermal stress / mechanical stress can be prevented, the cylinder pressure sensor can be effectively used, and cost etc. Can be reduced. From the viewpoint of detection accuracy, it is preferable to use a piezo element to detect pressure. The in-cylinder pressure sensor 9 can be controlled most accurately if it is provided in each cylinder, but it may be provided in only one cylinder or in each bank in the case of a V-type engine. In this embodiment, for the sake of simplicity of explanation, a case where only one cylinder is provided will be described.

The control unit 50 according to this embodiment also has a function as a target value setting means, a measured value detection means, and an exhaust gas recirculation amount feedback control means. Exhaust gas recirculation control and combustion stabilization control during exhaust gas recirculation control performed by the control unit 50 will be described below with reference to the flowchart shown in FIG. FIG. 3 is a main routine, for example, a predetermined exhaust gas recirculation control cycle (for example,
It is executed every 10 msec or 1 rev).

In step 100 (denoted as S100 in the figure. The same applies hereinafter), the basic control amount EGRbase of the EGR control valve 7 is set based on the engine operating state (basic fuel injection amount Tp and engine speed N). Ask. In step 200, an exhaust gas recirculation amount correction coefficient (dEGR1, dEG described later
The final correction coefficient EGRadj is obtained based on R2).

In step 300, the basic control value EG
The final control amount is calculated based on Rbase and the final correction coefficient EGRadj, and the EGR control valve 7 is drive-controlled. This step constitutes exhaust gas recirculation amount feedback control means. The above is the main routine of the exhaust gas recirculation control and the combustion stabilization control during the exhaust gas recirculation control in the present embodiment, and each step will be described in detail below.

First, the above step 100, that is, EG
A routine for obtaining the basic control amount EGRbase of the R control valve 7 will be described with reference to the flowchart shown in FIG.
In step 110, the basic engine operating conditions (engine speed N, engine load Tp based on intake air flow rate Q, engine water temperature Tw, etc.) are detected. In step 120, the basic control amount EGR of the EGR control valve 7 is calculated based on the operating state.
The base is obtained by referring to, for example, a map stored in advance in the control unit 50.

The above is the basic control value EG of the EGR control valve 7.
This is a routine for obtaining Rbase. Next, step 2
The correction coefficient (d) necessary for calculating the final correction coefficient EGRadj of the control amount of the EGR control valve 7 at 00
A routine for obtaining EGR1, dEGR2) will be described with reference to the flowchart of FIG. The flowchart is executed once every two revolutions of the engine (in the present embodiment,
This is because the in-cylinder pressure sensor 9 is used only for one cylinder, so that data for one combustion cycle can be collected with two revolutions of the engine. If cylinder pressure sensors are provided in multiple cylinders, the calculation cycle is shortened in inverse proportion to the number of cylinder pressure sensors.

In step 400, the actual exhaust gas recirculation amount is brought close to the target exhaust gas recirculation amount with a quick response based on the in-cylinder pressure PV1 in the intake stroke by executing steps 410 to 440 in the flowchart shown in FIG. 6 described later. The correction coefficient dEGR1 for Step 500
Then, step 5 of the flowchart shown in FIG. 7 described later.
By executing 10 to 590, the combustion stability is obtained based on the in-cylinder pressure in the expansion stroke, and the relatively slow control speed correction coefficient dEGR2 is set so that the combustion stability falls within a predetermined range. Ask.

The above is the correction coefficient (dEGR1, dEGR
This is a routine for obtaining 2). Here, the step 4
A method of obtaining the correction coefficient dEGR1 in 00 will be described with reference to the flowchart shown in FIG. In step 410, the indicated mean effective pressure PV1 of only the intake stroke is obtained.
That is, only the portion of the intake stroke is extracted from the indicated average effective pressure obtained based on the normal crank angle 720 ° and the in-cylinder pressure for the entire one combustion cycle. If noise due to ignition signals of other cylinders, intake pulsation during intake / exhaust valve seating, etc., causes an error in the detection of cylinder pressure in the cylinder, a crank angle range that avoids such a range is used. May be set, and the indicated mean effective pressure PV1 may be obtained in this section. At this time, if the in-cylinder pressure is detected only in that section, the memory capacity of the control unit 50 can be reduced.

The step 410 constitutes the actual measurement value detecting means according to the present invention. In step 420, the engine operating state is detected as in step 110. In step 430, the target value PV10 of the indicated mean effective pressure in the intake stroke when the predetermined exhaust gas recirculation amount that is predetermined and set in the operating state is recirculated is obtained by referring to a map or the like.

The step 430 constitutes a target value setting means according to the present invention. In step 440, the correction coefficient dEGR1 is calculated based on the actually detected indicated mean effective pressure PV1 and the target value PV10 predetermined from the operating state. As a method of calculating the correction coefficient, for example, as shown in FIG. 9, | PV1 | − for the purpose of avoiding hunting or the like due to unnecessary frequent correction control.
A dead zone with a certain width is provided near | PV10 | = 0 to avoid this, and then | PV1 |-| PV10 |
The correction coefficient dEGR1 corresponding to The indicated mean effective pressure PV1 in the actual intake stroke is equal to the target value PV
When it is larger than 10, the PV1 tends to increase as the exhaust gas recirculation amount increases as described above. Therefore, the correction coefficient dEGR1 is set to a negative value in order to decrease the exhaust gas recirculation amount in order to approach the target value PV10. To do. on the other hand,
In the opposite case, the correction coefficient dEGR1 is set to a positive value in order to increase the exhaust gas recirculation amount so as to approach the target value PV10.

Next, how to obtain the correction coefficient dEGR2 in step 500 will be described with reference to the flowchart shown in FIG. The correction coefficient dEGR2 is
A correction coefficient for correcting the control amount of the EGR control valve 7 for the purpose of keeping the combustion stability within a predetermined range during the exhaust gas recirculation control. Therefore, the correction coefficient dEGR
When determining 2, the operating condition (steady state, etc.) where the combustion stability can be detected is the execution condition of this flow.

In step 510, it is determined whether or not the current operating state is a state in which combustion stability can be detected (or a meaningful state). Specifically, when the operating state is changing, or when the vehicle is moving between regions where the criteria for determining stability are significantly different, stability cannot be detected, so the condition is not satisfied. Go to step 590. In step 590, a combustion stability detection permission condition satisfaction flag is set.
FLAG EGR con is set to 0, and Sidx, which is an index of combustion stability, is initialized to 0.

On the other hand, if it is determined in step 510 that the condition is satisfied, the process proceeds to step 521. In step 521, the combustion stability detection permission condition satisfaction flag Flag EGR con is set to 1. Step 522
Then, the indicated mean effective pressure PV3 of the expansion stroke is obtained.

At step 523, Sidx, which is an index of combustion stability, is calculated based on the PV3 and its past history. As a specific method of calculating Sidx, for example, there is a method of calculating the variance of PV3 a predetermined number of times and taking the reciprocal thereof. In step 530, it is determined whether or not the combustion stability index Sidx is confirmed (updated), and if confirmed (updated), the process proceeds to step 541. NO
If so, the process proceeds to step 581. Here, the determination as to whether or not the combustion stability index Sidx has been determined is made, for example, when Sidx is calculated as the reciprocal of the predetermined number of dispersions of PV3 as described above, based on whether or not this predetermined number of times has elapsed. You can Therefore, while the predetermined number of times has not elapsed, the process proceeds to step 581, and when the predetermined number of times has elapsed, the process proceeds to step 541.

In step 541, the combustion stability index Sid
Since x has been determined, the combustion stability detection completion flag FLAG indicating that the combustion stability in the current operating state has been detected.
Set EGRjdg to 1. In step 542, the target combustion stability index S0 to be compared with the obtained combustion stability index Sidx in the present operating state is calculated. The target combustion stability index S0 may also be obtained by referring to a preset map or the like based on the operating state or the like.

In step 550, the Sidx and S
0 is compared to determine whether or not Sidx ≧ S0 (this relationship is set as a state where the combustion stability is high). If YES, the process proceeds to step 560, and if NO, the process proceeds to step 570. In step 560, a correction coefficient dEGR2 for keeping the combustion stability within a predetermined range
On the other hand, since the combustion is stable at a predetermined level or more, the combustion stability flag Flag stb indicating whether or not the combustion is stable is set to 1. The correction coefficient d
As a calculation method of EGR2, in a simple example, there is a method of multiplying a difference between Sidx and S0 by a predetermined gain.

In step 570, the correction coefficient dEG
While R2 is calculated, combustion is unstable in this state, so the combustion stability flag Flag stb is set to -1. By the way, if it is determined NO in step 530, the process proceeds to step 581, but step 581.
Now, if the detection of combustion stability is not completed, Flag
Set EGR jdg to 0.

In step 582, the combustion stability flag Flag stb is maintained in the current state, although it is not necessary to newly operate it. As described above, the correction coefficient dEGR2 for keeping the combustion stability during exhaust gas recirculation control within the predetermined range is obtained. Next, a routine for obtaining the final correction coefficient EGRadj necessary in step 200 of the main routine shown in FIG. 3 will be described with reference to the flowchart shown in FIG.

In step 210, it is determined whether the combustion stability detection permission condition satisfaction flag Flag EGR con is 0 or not. If YES, the process proceeds to step 220, and if NO, the process proceeds to step 230. In step 220, Fla
Since g EGR con is 0 and the permission condition for detecting the combustion stability is not satisfied, basically, the correction coefficient EGRadj holds the previous value, and this flow ends. Note that dE
Since GR1 is calculated independently of the detection of combustion stability, in this step 220, EGRadj may be calculated based only on dEGR1.

In step 230, Flag EGR con is 1
Since the permission condition for detecting the combustion stability is satisfied, it is further checked with the combustion stability detection completion flag Flag EGR jdg whether or not the detection of the combustion stability has already been completed. If Flag EGR jdg is 1 (that is, completed), the process proceeds to step 240. On the other hand, Flag EGR jdg is 0 (that is,
If not completed), go to step 270.

At step 240, it is subsequently checked whether or not the combustion is stable by the combustion stability flag Flag stb. If Flag stb = 1 (stable), step 25
0, and if Flag stb = -1 (unstable), proceed to step 260. In step 250, since the combustion is stable, it is determined that the exhaust gas recirculation amount can be further increased, and in order to control the EGR control valve 7 in the direction of increasing the exhaust gas recirculation amount, for example, a final correction coefficient EGRadj On the other hand, a larger value of dEGR1 and dEGR2 is added as the correction increase amount. As a result, the exhaust gas recirculation amount can be maximized while stabilizing the combustion within a predetermined range, and thus NOx can be maximally reduced.

On the other hand, in step 260, it is judged that the combustion is not stable and the exhaust gas recirculation amount should be decreased in order to increase the stability of the combustion, and the EGR control valve 7 is moved in the direction of decreasing the exhaust gas recirculation amount. Control. For example, with respect to the final correction coefficient EGRadj, dE
Try to deduct GR2. In addition, the dEGR2
Is a correction coefficient that is set so that the current combustion fluctuation amount approaches the target combustion fluctuation amount.
Subtracting dEGR2 from GRadj results in the combustion stability being restored to within a predetermined range.

By the way, in the step 230,
When it is determined that the detection of the combustion stability is not completed yet, the process proceeds to step 270, but the step 270.
Then, the previous combustion stability flag Flag stb is used to check whether the previous combustion was stable. Flag stb = 1
If it is (stable), proceed to Step 280 and set Flag.
If stb = -1 (unstable), step 290
Then, the process proceeds to step S30, and the last correction coefficient EGRadj of the last time is held as it is, and this flow ends.

On the other hand, in step 280, since the combustion was stable until the last time, in order to prioritize effectively reducing NOx by approaching the target exhaust gas recirculation amount with good responsiveness, the last final The correction coefficient dEGR1 is added to the correction coefficient EGRadj, and this flow ends. The final correction coefficient EGRadj thus obtained is shown in FIG.
The main control amount EGRbase is multiplied in order to obtain the final control amount in step 300 of the main routine shown in FIG. Then, the EGR control valve 7 is drive-controlled by the final control amount.

As described above, according to this embodiment,
A predetermined EG for obtaining the target recirculation amount according to the operating state
The basic control amount of the R control valve 7 is detected with high responsiveness and high accuracy of the actual exhaust gas recirculation amount based on the indicated mean effective pressure PV1 of the intake stroke obtained for each cycle, and based on the detection result, promptly Then, feedback control is performed so that the actual exhaust gas recirculation amount becomes the target exhaust gas recirculation amount. This makes it possible to obtain the target exhaust gas recirculation amount with high responsiveness and high accuracy.

On the other hand, on the other hand, by statistically processing the indicated mean effective pressure PV3 in the expansion strokes of a plurality of cycles, the combustion stability is detected at a relatively slow speed with high accuracy, and the combustion stability is not less than a predetermined value. If so, the NOx reduction effect is maximized by giving priority to the increase in the exhaust gas recirculation amount, and when the combustion stability decreases, the exhaust gas recirculation amount is set so that the combustion stability becomes a priority in order to give priority to the improvement of the combustion stability. Since feedback control is performed at a relatively slow control speed, it is highly accurate and completely prevents control hunting due to too fast control speed, while changing the suction limit of the exhaust gas recirculation amount of the engine. It is possible to obtain the maximum exhaust gas recirculation amount including. Therefore, while maximizing the NOx reduction effect, it is possible to prevent deterioration of fuel consumption due to hunting and the like.

That is, according to this embodiment, the combustion stability is ensured by the relatively slow control speed while realizing the control of the target exhaust gas recirculation amount with high responsiveness and high accuracy. It is possible to maximize the NOx reduction effect by the exhaust gas recirculation amount, and at the same time achieve prevention of problems associated with control hunting and maintenance of combustion stability.

In the present embodiment, it has been explained that the best exhaust gas recirculation control is performed by combining the exhaust gas recirculation control and the combustion stabilization control during exhaust gas recirculation control. Of course, the exhaust gas recirculation control (dEGR1) according to this embodiment has been described. It is obvious that the exhaust gas recirculation control alone is an effective technique because the responsiveness and control accuracy of the exhaust gas recirculation control can be sufficiently improved by executing only the exhaust gas recirculation control. is there.

The present embodiment is further provided with a learning function, so that the correction coefficient dEGR1
By storing (learning) or dEGR2 or EGRadj and using this for the final calculation of the control amount in step 300, the correction coefficients dEGR1, dEGR
The target exhaust gas recirculation amount can be obtained with high responsiveness and high accuracy without correction by 2.

In this embodiment, the cylinder pressure is detected for one cylinder and the control is performed. However, for example, the cylinder pressure is detected for all cylinders, and the exhaust gas recirculation amount is the highest. Needless to say, the most accurate control can be performed if the control is performed on the basis of a cylinder in which the number of cylinders increases and combustion stability decreases. Further, when the above control is performed in one cylinder, if the cylinder in which the exhaust gas recirculation amount becomes the largest and the combustion stability is lowered is specified in advance by an experiment or the like, and the above control is performed for the cylinder, The lowest cost and most accurate control can be obtained.

In this embodiment, the indicated mean effective pressure is calculated in order to capture the characteristics of the in-cylinder pressure in the intake stroke, but as described above, the in-cylinder pressure in the intake stroke is stable. Therefore, the characteristic can be grasped even with the in-cylinder pressure at a predetermined timing and can be used as an index of the exhaust gas recirculation amount. Further, when it is adopted in an engine equipped with a variable mechanism for varying the opening / closing timing of the intake valve and the lift amount, the basic control value EGRbase of the EGR control valve, the target indicated mean effective pressure PV10, the target stability SV0, etc. It is obvious that a value corresponding to the valve opening / closing characteristic should be separately provided or corrected.

[0052]

As described above, according to the present invention,
Based on the target value of the in-cylinder pressure state of the intake stroke set based on the operating state and the actual measured value of the actual in-cylinder pressure state that is accurately detected by the in-cylinder pressure detection means for each cycle, By the exhaust gas recirculation feedback control means, so that the actual in-cylinder pressure state approaches the target in-cylinder pressure state,
Since the control amount of the exhaust gas recirculation amount adjusting means is corrected, it is possible to control the actual exhaust gas recirculation amount to the target exhaust gas recirculation amount with high responsiveness and high accuracy, thereby minimizing NOx emission. Can be fastened.

[Brief description of drawings]

FIG. 1 is a block diagram according to the present invention.

FIG. 2 is an overall configuration diagram of an embodiment according to the present invention.

FIG. 3 is a flowchart illustrating a main routine in the above embodiment.

FIG. 4 is a flowchart illustrating a routine for setting a basic control amount of the EGR control valve 7 in the same embodiment.

FIG. 5 is a flowchart illustrating a routine for obtaining a correction coefficient for EGR control according to the embodiment.

FIG. 6 is a flowchart illustrating a routine for obtaining a correction coefficient dEGR1 in the same embodiment.

FIG. 7 is a flowchart illustrating a routine for obtaining a correction coefficient dEGR2 in the same embodiment.

FIG. 8 is a final correction coefficient EDR in the above embodiment.
Flowchart explaining the routine for finding _adj

FIG. 9 is a diagram for explaining the relationship between the number of correction coefficients dEGR1 and (| PV1 | − | PV10 |) in the embodiment.

FIG. 10 is a diagram showing a relationship between in-cylinder pressure and crank angle, and a diagram showing a relationship between in-cylinder pressure and in-cylinder volume.

[Explanation of symbols]

 1 engine 2 intake passage 3 air flow meter 5 exhaust passage 6 exhaust gas recirculation passage 7 EGR control valve 8 crank angle sensor 9 cylinder pressure sensor 50 control unit

Claims (1)

[Claims] 1. An exhaust gas recirculation passage for recirculating a part of exhaust gas to an engine intake system, an exhaust gas recirculation amount adjusting means for adjusting an exhaust gas recirculation amount, an in-cylinder pressure detecting means for detecting a pressure in a cylinder, and an engine. Operating state detecting means for detecting the operating state of the cylinder, target value setting means for setting a target value of the in-cylinder pressure state in the intake stroke based on the detected operating state, and the in-cylinder pressure detecting means. Measured value detection means for detecting the actual in-cylinder pressure state in the intake stroke based on the actual in-cylinder pressure, the set target value of the in-cylinder pressure state, and the actually measured in-cylinder pressure state And an exhaust gas recirculation amount feedback control means for feedback-controlling the exhaust gas recirculation amount adjusting means so as to bring the in-cylinder pressure state closer to a target value, and an exhaust gas recirculation control for an internal combustion engine, comprising: apparatus.