JP3728930B2 - Exhaust gas recirculation control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in an exhaust gas recirculation control device for an internal combustion engine.
[0002]
[Prior art and problems to be solved]
An exhaust gas recirculation (EGR) device is known in which a part of the exhaust gas is recirculated into the intake air to reduce the combustion temperature for the purpose of reducing nitrogen oxide (NOx) exhausted from the internal combustion engine (as known literature) Is disclosed in, for example, JP-A-60-230555. This exhaust gas recirculation is effective in reducing nitrogen oxides, but unless the recirculated exhaust amount is controlled to an appropriate amount according to the operating state, the combustion deteriorates and adversely affects the operability such as a reduction in output. 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, and the EGR valve is set by a step motor or the like so as to reach this target opening. It is possible to achieve optimal control by driving the motor precisely.
[0003]
By the way, even if the control itself is accurate, an accurate exhaust gas recirculation amount cannot be obtained if combustion products or oil in the exhaust gas adhere to the EGR valve and the substantial opening degree changes. This problem is particularly noticeable in an in-cylinder fuel injection type internal combustion engine such as a diesel engine where combustion products are likely to be generated. In view of this, such a variation in the valve opening is considered as a change in the intake air amount, and the opening of the EGR valve is corrected in accordance with the intake air amount. Specifically, if the amount of exhaust gas that recirculates decreases, the amount of fresh air that is sucked increases accordingly, and at that time, the target exhaust gas recirculation amount can be obtained by correcting the opening degree of the EGR valve in the increasing direction. To do so. On the other hand, even if the engine speed and load state are the same, for example, the combustion state is different at the start / warm-up time and after the warm-up is completed, so the EGR valve opening is also corrected in consideration of the difference in these operating conditions. I need to do it.
[0004]
As described above, in order to ensure the exhaust gas recirculation control, it is necessary to perform a plurality of corrections such as a correction based on an air amount change and a correction based on a temperature condition on the opening degree of the EGR valve. However, in the conventional exhaust gas recirculation control, since these corrections are individually performed, calculation is required for each operation state detection amount and data used for the correction, and the calculation processing is complicated or data to be prepared accordingly. There was a problem that the amount would increase. The present invention has been made paying attention to such problems, and the calculation processing is simplified by determining the opening degree of the EGR valve after correcting the EGR rate value using the intake air amount as a parameter. It is intended.
[0005]
[Means for Solving the Problems]
(1) Operation In the first aspect of the invention, as shown in FIG. 1, the rotational speed N and the load state Tp as the first operating state of the internal combustion engine, the cooling water temperature Tw as the second operational state, detect a state detecting means 101, and the intake air amount detecting means 102 for detecting an intake air quantity QAC during exhaust gas recirculation, a target EGR rate calculating means 103 for calculating a target EGR rate MEGRM in response to the first operational state, the second a first correction amount calculating means 104 for calculating a first correction amount KEGR1 of EGR rate according to the operating condition, the target intake air amount calculating means for calculating a target intake air quantity BQAC in response to the first operational state 105 And a corrected target intake air amount calculating means 106 for correcting the target intake air amount BQAC based on the EGR rate MEGRM and its correction amount, and a deviation between the corrected target intake air amount BQACK and the detected intake air amount QAC. The second for calculating the second correction amount KEGR2 of the EGR rate A correction amount calculation means 107, provided an EGR rate correction means 108 for correcting the EGR rate MEGRM based on the first correction amount KEGR1 and second correction amount KEGR2.
[0006]
(2) In the invention of claim 2, the target EGR rate calculating means 103 of the invention of claim 1 calculates the EGR rate MEGRM from the target opening degree and the operating state of the EGR valve determined according to the operating state. It is assumed that
[0007]
(3) The invention of claim 3 is the opening command value calculating means 109 for calculating the opening command value SEGR of the EGR valve from the EGR rate corrected by the EGR rate correcting means and the operating state in the invention of claim 1 above. Shall be provided .
[0008]
(4) The invention of claim 4 has a configuration in which the EGR valve is driven to open and close by the step motor in the invention of claim 1, and the opening command value SEGR is calculated as the number of steps of the step motor . Shall.
[0009]
(5) In the invention of claim 5, the second correction amount calculation means 107 of the invention of claim 1 is increased in accordance with an increase in the ratio QAC / BQAC K 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 the characteristics to be set .
[0010]
(6) In the invention of claim 6, the opening command value calculation means of the invention of claim 1 is configured to calculate the opening of the intake throttle valve based on the EGR rate .
[0012]
[Action / Effect]
According to each of the above-described inventions, 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 degree. Is output to the actuator of the EGR valve. According to such a correction process, the EGR rate using the exhaust gas recirculation amount and the intake air amount as typified by the EGR valve opening is corrected, so that the EGR according to the engine state such as the cooling water temperature. Correction of the valve opening and correction according to the intake air amount can be performed collectively based on the common operation state detection result, and should be prepared for processing and correction of the detected operation state information The amount of data is minimized, so that the matching operation is facilitated, and the configuration of the control device including a microcomputer can be simplified.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 shows a schematic configuration of a diesel engine equipped 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 the engine 11 are connected via an EGR passage 14, and an EGR valve 15 is provided in the middle thereof. The position of the EGR valve 15 is almost continuously controlled by the actuator 16 from the fully closed position to the fully open position. A throttle valve 17 is interposed in the intake passage 12 upstream of the outlet portion of the EGR passage 14, and an actuator 18 that opens and closes the throttle valve 17 is provided. The actuators 16 and 18 are both controlled by a control device 19, and under operating conditions that require a relatively large amount of exhaust gas recirculation, the EGR is operated with the throttle valve 17 closed and adjusted to develop a negative pressure downstream thereof. The opening degree 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 17 is controlled to the fully open position.
[0014]
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 the functions of the respective arithmetic means of the present invention. The control circuit 19 receives the engine speed N as a basic operation state parameter for determining the fuel injection amount and the injection timing, and the target fuel injection amount Tp as a load representative value. These are the EGR rate. And the correction of the EGR valve opening. Further, the cooling water temperature Tp from the cooling water temperature sensor 20 and the intake air amount QAC from the air flow meter 21 are further inputted to correct the EGR valve opening. The air flow meter 21 is provided on the upstream side of the throttle valve 17 in the intake passage 12 and detects the flow rate of fresh air taken into the engine 11.
[0015]
3 and 4 show an example of an EGR valve opening control routine in an engine equipped with such an EGR device. This routine is periodically repeated by the microcomputer in the control circuit 19 every several milliseconds to several tens of milliseconds.
[0016]
As basic control, as shown in FIG. 3, first, the engine speed N, the fuel injection amount Tp, the intake air amount QAC, and the cooling water temperature Tw are detected, and the operating range in which exhaust gas recirculation should be performed based on these detection results. Is determined by collation with a preset table as shown in FIG. 5, for example (steps 301 and 302). Thus, for example, in the low load region, the low rotation region, the start time, the warm-up time, 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, when the exhaust gas recirculation is in an operating state, the opening calculation of the throttle valve 17 and the EGR valve 15 is performed next, and command values are output to the actuators 18 and 16 to reach a predetermined opening. Position control is performed as described above (steps 304 to 306).
[0017]
FIG. 4 shows the contents of the EGR valve opening control routine in step 305. First, the basic value MEGRM of the target EGR rate is calculated from N and Tp, and the first correction amount KEGR1 for the next EGR rate is calculated as follows. Calculation is performed (steps 401 and 402). In this case, the first correction amount KEGR1 is a correction amount based on the water temperature Tw. In general, NOx is not easily generated under low temperature conditions. Therefore, as illustrated in FIG. 6, the correction value of the characteristic that the exhaust gas recirculation amount decreases as the water temperature decreases. Is granted. In addition to this, the first correction amount KEGR1 may include a correction based on fuel injection timing, a correction based on atmospheric pressure, and the like.
[0018]
Next, in order to correct the fluctuation of the actual intake air amount, a correction amount Z for the throttle valve opening and the target intake air amount is calculated from the EGR rate target value MEGRM and the first correction amount KEGR1, and then N, A corrected target intake air amount BQACK is obtained by multiplying the target intake air amount BQAC calculated from Tp by the correction amount Z (steps 403 to 405). Here, the throttle valve opening is set with the characteristics shown in FIG. 7, while the intake air amount correction amount Z is calculated as follows according to the definition of the EGR rate.
[0019]
(1) EGR rate = exhaust recirculation gas amount / intake air amount Z = (1 + MEGRM) / (KEGR1 × MEGRM + 1)
(2) When EGR rate = exhaust recirculation gas amount / (exhaust recirculation gas amount + intake air amount), Z = (1-KEGR1 × MEGRM) / (1-MEGRM)
The second correction amount KEGR2 is then calculated based on the deviation between the corrected target intake air amount BQACK obtained in this way and the actual intake air amount QAC from the output of the air flow meter 21 (step 406). As illustrated in FIG. 8, the second correction amount KEGR2 is set to a characteristic that increases in proportion to the ratio QAC / BQACK between the actual value of the intake air amount and the target value. This is because the EGR rate decreases when the actual intake air amount increases above the target value under the condition that the EGR valve opening is constant. This correction is effective for maintaining the required EGR rate with respect to a decrease in the effective opening due to adhesion of combustion products to the EGR valve 15 and a change in intake air intake amount due to a change in the opening of the throttle valve 17.
[0020]
Next, the final target EGR rate MEGR is obtained by multiplying the two correction amounts KEGR1 and KEGR2 obtained as described above by the basic value MEGRM of the target EGR rate, and this is calculated based on N and Tp. The command value for the actuator 16 is obtained by converting to (steps 407 and 408). The command value is, for example, the number of steps when a step motor is used as the actuator 16.
[0021]
In this way, according to this EGR control, the EGR rate is corrected, so that the processing is simpler than when the correction amount is individually determined for the variation of the opening degree of the EGR valve and the intake air amount. This makes it possible to perform appropriate exhaust gas recirculation control. The present invention can also be applied 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 represented by N and Tp. The correction processing as described above may be performed after conversion from EGR to EGR rate.
[Brief description of the drawings]
FIG. 1 is a configuration conceptual diagram of the present invention.
FIG. 2 is a schematic configuration diagram of an embodiment of a diesel engine to which the present invention is applicable.
FIG. 3 is a flowchart showing an EGR control routine according to an embodiment of the present invention.
FIG. 4 is a flowchart showing a control routine related to the 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 engine speed N, fuel injection amount Tp, intake air amount QAC, and cooling water temperature Tw.
FIG. 6 is a characteristic diagram showing the relationship between the cooling water temperature Tw and the first correction amount KEGR1.
FIG. 7 is a characteristic diagram showing the relationship between the target EGR rate and the 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]
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 (6)

An operating state detecting means for detecting the rotational speed and the load state as the first operating state of the internal combustion engine and the coolant temperature as the second operating state ;
Intake air amount detection means for detecting the intake air amount QAC during exhaust gas recirculation,
Target EGR rate calculating means for calculating the target EGR rate MEGRM according to the first operating state;
A first correction amount calculating means for calculating a first correction amount KEGR1 of the EGR rate according to the second operating state;
Target intake air amount calculating means for calculating a target intake air amount BQAC according to the first operating state;
A corrected target intake air amount calculating means for correcting the target intake air amount BQAC based on the EGR rate and the correction amount KEGR1;
A second correction amount calculating means for calculating a second correction amount KEGR2 of the EGR rate based on a deviation between the corrected target intake air amount BQACK and the detected intake air amount QAC;
EGR rate correction means for correcting the EGR rate MEGRM based on the first correction amount KEGR1 and the second correction amount KEGR2 .
Exhaust gas recirculation control apparatus for an internal combustion engine having a.   2. The internal combustion engine according to claim 1, wherein the target EGR rate calculating means is configured to calculate an EGR rate MEGRM from a target opening degree of an EGR valve determined according to an operating state and the operating state. Engine exhaust gas recirculation device.   2. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, further comprising an opening command value calculation unit that calculates an opening command value SEGR of the EGR valve from the EGR rate corrected by the EGR rate correction unit and the first operating state. .   2. The internal combustion engine according to claim 1, wherein the EGR valve is configured to be opened and closed by a step motor, and the opening degree command value SEGR is calculated as the number of steps of the step motor. Exhaust gas recirculation control device.   The second correction amount calculating means is configured to set the second correction amount KEGR2 with a characteristic that increases with an increase in the ratio QAC / BQACK between the actual intake air amount and the corrected target intake air amount. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein the exhaust gas recirculation control device is an internal combustion engine.   2. The exhaust gas recirculation control apparatus for an internal combustion engine according to claim 1, wherein the opening command value calculation means is configured to also calculate the opening of the intake throttle valve based on the EGR rate.

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