JPH11351068A - Exhaust gas reflux control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate calculation process by determining opening of a valve after correction of exhaust gas reflux factor value using intake air amount as a parameter. SOLUTION: First, base value MEGRM of a target exhaust gas reflux(EGR) factor based on engine rotation speed N and fuel injection amount TP, and next, a first corrective amount KEGR1 for this EGR factor are calculated. A corrective amount Z for a throttle valve opening and a target suction air amount are calculated from the target EGR factor value MEGRM and the first corrective amount KEGR1. Next, an after-correction target suction air amount BQACK is derived by multiplying a target suction air amount BQAC calculated from N and TP by the corrective amount Z. The corrective amount Z of the suction air is calculated according to definition of the EGR factor. A second corrective amount KEGR2 is calculated from deviation between the after-correction target suction air amount BQACK and net suction air amount QAC. A final target EGR factor MEGR is derived by multiplying the base value MEGRM of the target EGR factor by the corrective amounts KEGR1, KEGR2, and a command value for an actuator is provided by converting this to EGR valve opening based on N and TP.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in an exhaust gas recirculation control device for an internal combustion engine.

[0002]

2. Description of the Related Art Exhaust gas recirculation (EGR) in which a part of exhaust gas is recirculated into intake air to reduce combustion temperature in order to reduce nitrogen oxides (NOx) emitted from an internal combustion engine. An apparatus is known (for example, see JP-A-60-230555 as a known document). This exhaust gas recirculation is effective in reducing nitrogen oxides, but unless the recirculated exhaust gas amount is controlled to an appropriate amount in accordance with the operation state, combustion deteriorates and the operability such as output reduction is adversely affected. For this reason, in recent EGR devices, the target opening of the EGR valve for adjusting the exhaust gas recirculation amount is determined by detecting the engine speed and the load state,
EG is controlled by a stepping motor or the like to achieve this target opening.
Optimum control can be achieved by precisely driving the R valve.

[0003] Even if the control itself is accurate, if the combustion product or oil in the exhaust gas adheres to the EGR valve and the actual opening changes, an accurate exhaust gas recirculation amount cannot be obtained. This problem is particularly remarkable in an in-cylinder fuel injection type internal combustion engine, such as a diesel engine, in which combustion products are easily generated. Therefore, such a change in the valve opening may be considered as a change in the amount of intake air, and the opening of the EGR valve may be corrected in accordance with the amount of intake air. Specifically, the amount of fresh air to be taken in increases as the amount of recirculated exhaust gas decreases. At that time, the target exhaust gas recirculation amount can be obtained by correcting the opening of the EGR valve in the increasing direction. To do so. On the other hand, even when the engine speed and the load state are the same, for example, the combustion state is different at the time of start / warm-up and after the warm-up is completed. I need to do it.

As described above, in order to ensure the exhaust gas recirculation control, it is necessary to perform a plurality of corrections on the opening degree of the EGR valve, such as a correction based on a change in air amount and a correction based on temperature conditions. However, in the conventional exhaust gas recirculation control, these corrections are individually performed. Therefore, it is necessary to calculate for each operation state detection amount and data used for the correction. There is a problem that the amount increases. The present invention has been made in view of such a problem. The present invention corrects the EGR rate value using the intake air amount as a parameter, and then corrects the EG value.
The calculation processing is simplified by determining the opening of the R valve.

[0005]

(1) In the invention of claim 1, as shown in FIG. 1, an operating state detecting means 101 for detecting an operating state of an internal combustion engine, and an intake air amount at the time of exhaust gas recirculation.
Intake air amount detection means 102 for detecting QAC, target EGR rate calculation means 103 for calculating target EGR rate MEGRM according to the operation state, and first correction amount KEGR1 for calculating the EGR rate according to the operation state 1 correction amount calculating means 104, target intake air amount calculating means 105 for calculating a target intake air amount BQAC according to the operating state, EGR rate MEGRM and its correction amount K
A corrected target intake air amount calculating means 106 for correcting the target intake air amount BQAC based on EGR1; and a corrected target intake air amount
Second correction amount calculating means 1 for calculating a second correction amount KEGR2 of the EGR rate based on the difference between BQACK and the detected intake air amount QAC
07 and the EGR rate correction means 10 for correcting the EGR rate MEGRM based on the first correction amount KEGR1 and the second correction amount KEGR2.
8 and an opening command value calculating means 109 for calculating an opening command value SEGR of the EGR valve from the EGR rate and the operating state corrected by the EGR rate correcting means.

(2) According to a second aspect of the present invention, the target EGR rate calculating means 103 according to the first aspect of the present invention is configured to calculate the EGR rate based on the target opening degree of the EGR valve determined according to the operating state and the operating state.
It is assumed that MEGRM is calculated.

(3) According to a third aspect of the present invention, the first correction amount calculating means 104 is configured to calculate the first correction amount KEGR1 based on at least the engine coolant temperature.

(4) The invention according to a fourth aspect is the same as the first aspect, except that the operating state detecting means 101 is replaced by a target EGR rate calculating means 103
Correction amount calculating means 104, target intake air amount calculating means 10
6. It is assumed that at least the rotational speed and the load state of the internal combustion engine are detected as the operation state given to the opening command value calculation means 109.

(5) According to a fifth aspect of the present invention, in the first aspect of the invention, the EGR valve is driven to be opened and closed by a step motor, and the opening command value SEGR is calculated as the number of steps of the step motor. It is assumed that this is configured.

(6) According to a sixth aspect of the present invention, the second correction amount calculating means 107 according to the first aspect of the present invention uses the second correction amount calculating means 107 according to an increase in the ratio QAC / BQACK between the actual intake air amount and the corrected target intake air amount. It is assumed that the second correction amount KEGR2 is set with a characteristic that increases.

(7) According to a seventh aspect of the present invention, the opening command value calculating means according to the first aspect of the present invention is configured to also calculate the opening of the intake throttle valve based on the EGR rate. .

[0012]

According to the present invention, the EGR rate determined according to the operating state is corrected according to the engine state such as the cooling water temperature, and the corrected EGR rate is converted into the EGR valve opening. Then, the command value STEPQ is output to the actuator of the EGR valve. According to such a correction process, EG
Since the EGR rate is corrected using the exhaust gas recirculation amount and the intake air amount represented by the R valve opening as parameters, the correction of the EGR valve opening according to the engine state such as the cooling water temperature,
Correction according to the intake air amount can be performed collectively based on the common operation state detection result, and the amount of data to be prepared for processing and correction of the detected operation state information is minimal. Thus, the matching operation is facilitated, and the configuration of the control device including the microcomputer can be simplified.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a schematic configuration of a diesel engine provided with an EGR device to which the present invention can be applied. In the figure, an intake passage 12 and an exhaust passage 13 of an engine 11 are connected via an EGR passage 14, and an EGR valve 15 is provided in the middle of the passage. EGR valve 15
Is controlled almost continuously from the fully closed position to the fully opened position by the actuator 16. EGR in the intake passage 12
A throttle valve 17 is provided upstream of the outlet of the passage 14, and an actuator 18 for opening and closing the throttle valve 17 is provided. Each actuator 16, 18
The operation is controlled by a control device 19, and in an operating condition requiring a relatively large amount of exhaust gas recirculation, the throttle valve 17 is closed and adjusted to develop an EGR with a negative pressure developed downstream thereof.
The opening of the valve 15 is controlled. When the exhaust gas recirculation amount is small or when exhaust gas recirculation is not performed, the throttle valve 1
7 is controlled to the fully open position.

The operation of the actuators 16 and 18 is controlled by a control circuit 19 based on detection results of various operating states. The control circuit 19 is composed of a microcomputer provided with an input / output circuit and a storage circuit, and has a function of each of the arithmetic means of the present invention. The control circuit 19 receives an engine speed N and a target fuel injection amount Tp as a load representative value as basic operating state parameters for determining the fuel injection amount and the injection timing. And the correction of the EGR valve opening. Further, in order to correct the EGR valve opening, the cooling water temperature Tp from the cooling water temperature sensor 20 and the air flow meter
The intake air amount QAC from is input. The air flow meter 21 is provided upstream of the throttle valve 17 in the intake passage 12 and detects the flow rate of fresh air sucked into the engine 11.

FIGS. 3 and 4 show an example of an EGR valve opening control routine in an engine having such an EGR device. This routine is executed by the control circuit 19
It is periodically repeated every few milliseconds to several tens of milliseconds by the microcomputer within.

As a basic control, first, as shown in FIG. 3, the engine speed N, the fuel injection amount Tp, the intake air amount QA
C, the cooling water temperature Tw is detected, and based on these detection results, it is determined whether or not the engine is in an operating range in which exhaust gas recirculation is to be performed, for example, by collating with a table set in advance as shown in FIG. (Steps 301 and 302). Thus, for example, in a low load range, a low rotation range, at the time of starting, during warm-up, etc., the throttle valve 17 is fully opened and the EGR valve 15 is fully closed to stop the exhaust gas recirculation (step 303). On the other hand, in the operation state in which the exhaust gas is recirculated, the opening degree of the throttle valve 17 and the EGR valve 15 is calculated next, and a command value is output to each of the actuators 18 and 16 to achieve the predetermined opening degree. (Steps 304 to 3)
06).

FIG. 4 shows the contents of the EGR valve opening control routine in step 305. First, a basic value MEGRM of the target EGR rate is calculated from N and Tp.
A first correction amount KEGR1 for the GR rate is calculated (steps 401 and 402). In this case, the first correction amount KEGR1 is a correction amount based on the water temperature Tw. Since NOx is generally not likely to be generated under low temperature conditions, as shown in FIG. Granted. As the first correction amount KEGR1, a correction based on the fuel injection timing, a correction based on the atmospheric pressure, and the like may be included.

Next, in order to correct the fluctuation of the actual intake air amount, the EGR rate target value MEGRM and the first correction amount KEGR1
From this, a correction amount Z for the throttle valve opening and the target intake air amount is calculated, and then the corrected target intake air amount BQACK is obtained by multiplying the target intake air amount BQAC calculated from N and Tp by the correction amount Z. (Steps 403 to 405). Here, the throttle valve opening is set with a characteristic as shown in FIG. 7, while the intake air amount correction amount Z is calculated as follows according to the definition of the EGR rate.

When EGR rate = exhaust gas recirculation gas amount / intake air amount Z = (1 + MEGRM) / (KEGR1 × MEGRM + 1) When EGR rate = exhaust gas recirculation gas amount / (exhaust gas recirculation gas amount + intake air amount) Z = (1−KEGR1 × MEGRM) / (1−MEGRM) Next, a second correction is performed based on the deviation between the corrected target intake air amount BQACK obtained as described above and the actual intake air amount QAC based on the output of the air flow meter 21. The quantity KEGR2 is calculated (step 406). As shown in FIG. 8, the second correction amount KEGR2 is a ratio QAC / BQAC between the actual value and the target value of the intake air amount.
The characteristic is set to increase in proportion to K. This is because, when the actual intake air amount is larger than the target value under the condition that the EGR valve opening is constant, the EGR rate decreases. This correction is effective to maintain the required EGR rate against a decrease in the effective opening due to the adhesion of combustion products to the EGR valve 15 and a change in the intake air amount due to a variation in the opening of the throttle valve 17.

Next, the two correction amounts KEGR1 and KEGR2 obtained as described above are multiplied by the basic value MEGRM of the target EGR rate to obtain a final target EGR rate MEGR.
The command value for the actuator 16 is obtained by converting the EGR valve opening into an EGR valve opening degree based on p (step 40).
7, 408). The command value is, for example, the number of steps when a step motor is used as the actuator 16.

As described above, according to the EGR control, the correction is performed on the EGR rate, so that the correction amount is individually determined with respect to the fluctuation of the opening degree of the EGR valve and the intake air amount. Appropriate exhaust gas recirculation control is possible with simple processing. Note that the present invention is also applicable to a control system that calculates not the EGR rate but the EGR valve opening according to the operating state. In this case, the initially determined target EGR valve opening is determined by N and Tp. And then to the EGR rate, and then perform the above-described correction processing.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the configuration of the present invention.

FIG. 2 is a schematic configuration diagram of an embodiment of a diesel engine to which the present invention can be applied.

FIG. 3 is a flowchart showing an EGR control routine according to one embodiment of the present invention.

FIG. 4 is a flowchart showing a control routine relating to an EGR valve opening degree.

FIG. 5 is a control characteristic diagram corresponding to a table for determining the presence or absence of exhaust gas recirculation according to an engine speed N, a fuel injection amount Tp, an intake air amount QAC, and a cooling water temperature Tw.

FIG. 6 is a characteristic diagram showing a relationship between a cooling water temperature Tw and a first correction amount KEGR1.

FIG. 7 is a characteristic diagram showing a relationship between a target EGR rate and a throttle valve opening.

FIG. 8 is a characteristic diagram showing an example of a table for giving a second correction amount KEGR2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Diesel engine 12 Intake passage 13 Exhaust passage 14 EGR passage 15 EGR valve 16 Actuator 17 Throttle valve 18 Actuator 19 Control circuit 20 Water temperature sensor 21 Air flow meter

Claims (7)

[Claims] 1. An operating state detecting means for detecting an operating state of an internal combustion engine, an intake air amount detecting means for detecting an intake air amount QAC at the time of exhaust gas recirculation, and a target E for calculating a target EGR rate MEGRM according to the operating state.
GR rate calculation means, first correction amount calculation means for calculating a first correction amount KEGR1 of the EGR rate according to the operation state, target intake air amount calculation means for calculating the target intake air amount BQAC according to the operation state, EGR A corrected target intake air amount calculating means for correcting the target intake air amount BQAC based on the ratio MEGRM and the correction amount KEGR1, a EGR rate based on a deviation between the corrected target intake air amount BQACK and the detected intake air amount QAC. A second correction amount calculating means for calculating the second correction amount KEGR2, E based on the first correction amount KEGR1 and the second correction amount KEGR2.
An exhaust gas of an internal combustion engine comprising: an EGR rate correction means for correcting the GR rate MEGRM; and an opening command value calculating means for calculating an opening command value SEGR of the EGR valve from the EGR rate and the operating state corrected by the EGR rate correcting means. Reflux control device. 2. An EGR rate calculating means for calculating an EGR value based on a target opening degree of an EGR valve determined according to an operation state and the operation state.
The exhaust gas recirculation device for an internal combustion engine according to claim 1, wherein the system is configured to calculate an R rate MEGRM. 3. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein the first correction amount calculation means is configured to calculate the first correction amount KEGR1 based on at least the engine cooling water temperature. . The operating state detecting means includes at least a rotational speed of the internal combustion engine as operating states to be given to the target EGR rate calculating means, the first correction amount calculating means, the target intake air amount calculating means, and the opening command value calculating means. 2. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein the exhaust gas recirculation control device is configured to detect a load state. 5. The EGR valve according to claim 1, wherein the EGR valve is configured to be driven to open and close by a step motor, and the opening command value SEGR is calculated as the number of steps of the step motor. An exhaust gas recirculation control device for an internal combustion engine according to the above. 6. The second correction amount calculating means is configured to set the second correction amount KEGR2 with a characteristic that increases as the ratio QAC / BQACK between the actual intake air amount and the corrected target intake air amount increases. 2. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein: 7. The exhaust gas recirculation of an internal combustion engine according to claim 1, wherein the opening command value calculating means is configured to also calculate the opening of the intake throttle valve based on the EGR rate. Control device.