JP3551744B2 - Exhaust gas recirculation control device for in-cylinder injection type internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas recirculation control device provided in a spark ignition type in-cylinder injection type internal combustion engine represented by a gasoline engine, and more particularly to an internal combustion engine which performs fuel injection to reduce fuel consumption in lean operation by stratified combustion. The present invention relates to an in-cylinder injection type exhaust gas recirculation control apparatus suitable for use in an in-cylinder injection type internal combustion engine.
[0002]
[Prior art]
A technique using exhaust gas recirculation (EGR) to reduce NOx during stratified combustion operation in an engine that performs stratified combustion and premixed combustion (uniform combustion) that has been developed in recent years has been proposed (for example, Japanese Patent Application Laid-Open No. HEI 9-208572). No. 7-269416).
[0003]
[Problems to be solved by the invention]
By the way, in the case of stratified combustion operation in which stratified combustion is performed to reduce fuel consumption, a large amount of EGR can be introduced to reduce NOx. However, if a large amount of EGR is introduced, the stable combustion operation region of the engine is restricted. Therefore, it is necessary to operate the engine in the stable combustion operation region under the restriction.
[0004]
Further, this stable combustion operation region has a characteristic that changes according to the intake air temperature. That is, as shown in FIG. 9, the stable combustion operation region defined by the fuel injection end timing and the ignition timing, which are the parameters of the operating characteristics of the engine, is such that, as long as the EGR introduction rate is constant, the intake air temperature increases. There is a narrowing characteristic. For this reason, if the stratified combustion operation is performed while the introduction of EGR is performed in the same manner when the intake air temperature rises, it becomes difficult to operate the engine in the stable combustion operation region, and combustion may be unstable.
[0005]
Japanese Patent Application Laid-Open No. 5-263717 discloses that a target intake pipe pressure, which is a feedback reference when performing feedback control of an exhaust gas recirculation amount, is corrected based on intake air temperature obtained by estimation or calculation, and the intake air temperature is corrected. Although a technique for preventing the exhaust gas recirculation amount from deviating from a target value due to a change has been disclosed, such a technique controls the exhaust gas recirculation amount in relation to the intake air temperature, but is not suitable for stratified combustion operation. No consideration is given to the stable combustion of the engine described above, and the above-mentioned problem cannot be solved.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been made in view of the advantages of the direct injection type engine by enabling the combustion stability to be secured while reducing the generation of NOx by exhaust gas recirculation during the stratified combustion operation. An object of the present invention is to provide an in-cylinder injection type exhaust gas recirculation control device for a direct injection internal combustion engine, which can promote reduction of fuel consumption by combustion operation.
[0007]
[Means for Solving the Problems]
Therefore, the exhaust gas recirculation control device for a direct injection type internal combustion engine according to the present invention according to the first aspect of the present invention provides a direct injection type internal combustion engine. In response to the detected intake air temperature, the exhaust gas recirculation amount adjusting means is controlled so that the exhaust gas recirculation amount is reduced or set to zero according to the rise of the intake air temperature. Therefore, the reduction in the stable combustion operation region that occurs in response to the rise in the intake air temperature during stratified combustion can be suppressed by reducing or reducing the exhaust gas recirculation amount to zero, and the stable combustion operation region can be secured.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
1 to 6 show an exhaust gas recirculation control device for a direct injection type internal combustion engine as a first embodiment of the present invention. Reference numeral 8 denotes an exhaust gas recirculation control device for a direct injection internal combustion engine as a second embodiment of the present invention.
[0009]
First, a first embodiment will be described.
First, a configuration of a spark ignition type direct injection internal combustion engine (hereinafter, also simply referred to as a direct injection engine) according to the present embodiment will be described with reference to FIG.
In FIG. 2, 1 is an engine body, 1A is a cylinder (cylinder), 1B is a piston, 2 is an intake passage, 3 is a throttle valve installation part, 4 is an air cleaner, 5 is a bypass passage (second bypass passage), and 6 is a bypass. This is a second air bypass valve that can adjust the amount of air flowing through the passage 5.
[0010]
The intake passage 2 is configured by connecting an intake pipe 7, a surge tank 8, and an intake manifold 9 in this order from the upstream side, and the bypass passage 5 is provided on the upstream side of the surge tank 8. Further, the opening of the bypass valve 6 provided in the bypass passage 5 is adjusted to a required opening by a stepper motor, or the opening is adjusted by duty control of the solenoid valve.
[0011]
Reference numeral 12 denotes an idle speed control function unit, which comprises a bypass passage (first bypass passage) 13 and a first air bypass valve 14 serving as a bypass valve. The first air bypass valve 14 is driven by, for example, a stepper motor (not shown). Is done. Reference numeral 15 denotes a throttle valve. The first bypass passage 13 and the second bypass passage 5 have their upstream end and downstream end connected to the intake passage 2 so as to bypass a portion of the intake passage 2 where the throttle valve 15 is mounted. ing.
[0012]
The opening / closing control of the second air bypass valve 6 and the first air bypass valve 14 is performed through an electronic control unit (ECU) 16.
Reference numeral 17 denotes an exhaust passage, and reference numeral 18 denotes a combustion chamber. An intake valve 19 and an exhaust valve 20 are provided at openings of the intake passage 2 and the exhaust passage 17 to the combustion chamber 18, that is, at the intake port 2A and the exhaust port 17A. Equipped.
[0013]
Reference numeral 21 denotes a fuel injection valve (injector). In the present engine, the injector 21 is arranged so as to directly inject fuel into the combustion chamber 18.
Further, 22 is a fuel tank, 23A to 23E are fuel supply paths, 24 is a low-pressure fuel pump (electric pump), 25 is a high-pressure fuel pump (engine drive pump), 26 is a low-pressure regulator, 27 is a high-pressure regulator, and 28 is a delivery. The fuel in the fuel tank 22 is driven by a low-pressure fuel pump 24, and is further pressurized by a high-pressure fuel pump 25 that operates directly in conjunction with the operation of the engine. 23B, supply to the injector 21 through the delivery pipe 28.
[0014]
At this time, the fuel pressure discharged from the low-pressure fuel pump 24 is regulated by the low-pressure regulator 26, and the fuel pressure that is pressurized by the high-pressure fuel pump 25 and guided to the delivery pipe 28 is regulated by the high-pressure regulator 27. Has become.
[0015]
An exhaust gas recirculation passage (EGR passage) 29 recirculates exhaust gas (exhaust gas) in the exhaust passage 17 of the engine 1 into the intake passage 2, and a recirculation amount of exhaust gas recirculated into the intake passage 2 through the EGR passage 29. , A stepper motor type valve (EGR valve) as exhaust gas recirculation amount adjusting means for adjusting pressure, 31 is a flow path for reducing blow-by gas, 32 is a passage for active ventilation of the crankcase, and 33 is active ventilation of the crankcase. Is a canister, and 35 is an exhaust gas purifying catalyst (here, a lean NOx catalyst).
[0016]
Incidentally, in the ECU 16, as shown in FIG. 2, in addition to the control of the first and second air bypass valves 14 and 6, the control of the ignition coil for the injector 21 and the spark plug 45, the control of the EGR valve, and the high-pressure regulator Since fuel pressure control is also performed by the 27, an air flow sensor 44, an intake air temperature sensor 36, a throttle position sensor (TPS) 37 for detecting a throttle opening, an idle switch 38, an air conditioner switch (not shown), a shift position sensor (not shown), A vehicle speed sensor (not shown), a power steering switch (not shown) for detecting an operation state of the power steering, a starter switch (not shown), a first cylinder detection sensor 40, a crank angle sensor 41, a water temperature sensor for detecting engine coolant temperature. 42, O for detecting oxygen concentration in exhaust gas ₂ A sensor 43 and the like are provided and connected to the ECU 16. The ECU 16 has a function of calculating the engine speed (engine speed) based on the crank angle sensor 41. The engine speed sensor is constituted by the crank angle sensor 41 and the engine speed calculation function. However, here, the crank angle sensor 41 is also called an engine speed sensor for convenience.
[0017]
In the present engine, as the operation modes of the engine, a late-stage lean combustion operation mode, a first-stage lean combustion operation mode, a stoichiometric feedback operation combustion operation mode, and an open-loop combustion operation mode are prepared. And the case where EGR is stopped, one of these modes is selected according to the operating state of the engine, the running state of the vehicle, and the like.
[0018]
Of these, in the latter lean combustion operation mode, in the present embodiment, the total air-fuel ratio is set to a region of about 24 or more, and the leanest combustion can be realized. However, in this mode, the fuel injection is performed as in the latter half of the compression stroke. It is performed at a stage very close to the ignition timing, and furthermore, the fuel is collected near the spark plug to make it partially rich and lean as a whole so that the fuel-saving operation is performed while ensuring the ignitability and combustion stability. . The region of the late lean combustion operation mode (stratified combustion lean combustion operation mode) may be set lower than the present embodiment and the total air-fuel ratio may be set to about 23, or may be set higher than the present embodiment. You may. This late lean combustion operation mode is also called a compression lean mode because fuel injection is performed in the compression stroke.
[0019]
In the first lean combustion operation mode, lean combustion can also be realized, but in this mode, fuel injection is performed before the second lean combustion operation mode, and the fuel is premixed to make the overall air-fuel ratio leaner than the stoichiometric air-fuel ratio. Meanwhile, while saving ignitability and combustion stability, a certain amount of output is obtained while saving operation is performed. Here, the region of the first-half lean combustion operation mode is set to a region where the total air-fuel ratio is about 24 or less and is equal to or more than the stoichiometric air-fuel ratio. In the first lean combustion operation mode, the fuel injection is mainly performed in the intake stroke, and is also referred to as an intake lean mode.
[0020]
The stoichiometric feedback combustion operation mode is O ₂ Based on the output of the sensor, a sufficient engine output can be efficiently obtained while maintaining the air-fuel ratio in a stoichiometric state. In the open-loop combustion operation mode, combustion is performed at a stoichiometric or rich air-fuel ratio by open-loop control so that a sufficient output can be obtained at the time of acceleration, starting, and the like. In these modes, premix combustion based on fuel injection in the intake stroke is performed.
[0021]
In the in-cylinder injection engine, one mode is selected from the various engine operation modes as described above. This selection is made based on the engine operation state, that is, the engine load state Pe and the engine speed Ne. Thus, for example, it is performed with characteristics as shown in the map of FIG. That is, in the low-load / low-speed region, the latter lean combustion operation mode is selected, and as the load or the rotation speed increases, the latter lean combustion operation mode, the stoichiometric combustion operation mode, or the open loop mode (the enrich combustion operation) is performed. Mode).
[0022]
In each mode, fuel injection control (that is, injection control of the injector 21), ignition timing control (that is, drive control of the ignition plug 45), intake air amount control (that is, control of the air bypass valves 6, 14), and Exhaust gas recirculation amount control (that is, control of the EGR valve 30) is also performed based on the operating state of the engine such as the engine load state Pe and the engine speed Ne.
[0023]
Each of these controls is performed through the ECU 16 based on the operating state detected (or calculated) by the operating state detecting means 101. For this reason, as shown in FIG. 3, the ECU 16 controls the driving of the injector 21 by setting the mode selection means 102 for selecting an operation mode, the fuel injection amount and the fuel injection timing (injection end timing and injection start timing), as shown in FIG. A fuel injection control means 103, an ignition timing control means 104 for setting a fuel ignition timing and controlling the driving of the ignition plug 45, an intake control means 105 for setting an intake air amount and controlling the air bypass valves 6, 14. An exhaust gas recirculation control means 106 for setting an exhaust gas recirculation amount (recirculation rate, hereinafter also referred to as an EGR introduction rate) and controlling the EGR valve 30 is provided.
[0024]
As shown in FIG. 1, the exhaust gas recirculation control device includes an EGR valve 30 as exhaust gas recirculation amount adjusting means, the above-described operating state detecting means 101, and an intake air temperature sensor (intake air temperature detecting means) for detecting intake air temperature. ) 36 and exhaust gas recirculation control means (control means) 106 for appropriately operating the EGR valve 30 in accordance with the set operation mode and the detected intake air temperature. The operating state detecting means 101 includes an engine speed sensor 41 and a throttle opening sensor 37.
[0025]
In the present exhaust gas recirculation control device, EGR is introduced only when the engine is operating in the late lean combustion operation mode or the stoichiometric combustion operation mode, and in other cases, that is, in the first lean combustion operation mode or open loop mode. Then, EGR introduction is not performed. The reason for not introducing the EGR in this way is that if the EGR is introduced in the previous lean period, the combustion deteriorates. In particular, if the EGR flow rate is increased, a misfire may occur. Is very small. In addition, in the open loop mode, priority is given to securing the engine output.
[0026]
It should be noted that the amount of EGR introduced during the stoichiometric operation mode is set to be generally smaller than that in the latter-stage lean operation. This is because during the stoichiometric operation, EGR is introduced mainly for the purpose of improving fuel efficiency, but if a large amount of EGR is introduced, combustion deteriorates. The maximum EGR introduction rate during the stoichiometric operation is about 20 to 25%, and may be 0 in the minimum case.
[0027]
Then, during stratified combustion (during the late lean combustion operation mode), the exhaust gas recirculated into the intake passage is set to increase as the air-fuel ratio increases. The introduction rate of EGR at this time is about 30 to 60%.
Note that, depending on the engine, from the viewpoint of suppressing deterioration of combustion, the EGR introduction rate during stratified combustion may be set exceptionally lower during specific operation than during stoichiometric operation.
[0028]
Next, the setting of the EGR introduction rate (EGR rate) and the air-fuel ratio during the late lean combustion operation will be described with reference to FIG.
FIG. 5 shows an example of a general operation state as the latter-stage lean combustion operation, for example, under the condition that the engine rotation state is 1500 rpm and the net average effective pressure is 0.3 MPa.
[0029]
In FIG. 5, the horizontal axis represents the air-fuel ratio (A / F), and the vertical axis represents the NOx emission rate. This NOx emission rate is the ratio of the NOx emission amount during the late lean burn operation to the NOx emission amount during the stoichiometric operation. It is. In the figure, a curve L1 indicates a stable combustion limit, and stable combustion by the late lean combustion operation cannot be performed outside (ie, to the left or below) the curve. Curve L2 is a WOT (throttle fully opened) state in which the intake air (= fresh air + EGR) is 0.1 MPa (that is, about 1 atm), and the operation is performed outside (i.e., rightward and downward) of this curve. Can not do.
[0030]
Curves a1 to a3 show the fuel efficiency improvement rate, that is, the fuel efficiency improvement rate in the late lean burn operation with respect to the fuel efficiency in the stoichiometric operation. Curve a1 shows the fuel efficiency improvement rate of 10%, and curve a2 shows the fuel efficiency improvement rate of 20. %, A curve a3 indicates a fuel efficiency improvement rate of 30%. Curves b1 to b3 show the EGR introduction rate, that is, the ratio of the EGR introduction amount in the intake air amount. Curve b1 is the EGR introduction rate 0%, curve b2 is the EGR introduction rate 20%, and curve b3 is the EGR introduction rate. The rate is 40%.
[0031]
The latter lean combustion operation can be performed in a region above the curves L1 and L2 in FIG. 5, and within this region, the fuel consumption improvement rate is high and the NOx reduction rate is high (that is, the NOx emission rate is low). If the air-fuel ratio (A / F) and the EGR introduction rate are set so as to satisfy (2), both improvement in fuel efficiency and reduction in NOx can be achieved.
For example, in the region where the fuel efficiency improvement rate is 30% or more and the NOx reduction rate is 90% or more (that is, the NOx emission rate is 10% or more), as in a hatched region in FIG. Thus, it is conceivable to set the air-fuel ratio and the EGR introduction rate. In FIG. 5, L3 indicates a NOx reduction rate of 90%.
[0032]
In the example shown in FIG. 5, the air-fuel ratio is set to somewhere in the range of about 28 to 33, the EGR introduction rate is set to somewhere in the range of about 30 to 60%, and the fuel efficiency improvement rate is 30%. % Or more and the NOx reduction rate of 90% or more, while performing the latter-stage lean combustion operation by stable combustion.
Of course, FIG. 5 shows one typical example in the latter-stage lean burn operation, and such a characteristic changes depending on the load state of the engine and the engine speed, and the fuel efficiency improvement rate is high according to each operation state. The air-fuel ratio and the EGR introduction rate may be set so as to increase the NOx reduction rate, and control may be performed based on these settings.
[0033]
In this case, it is not always possible to always achieve the target values such as the above-described fuel efficiency improvement rate of 30% or more and the NOx reduction rate of 90% or more. It is conceivable to set the EGR introduction rate or to set the air-fuel ratio and the EGR introduction rate with emphasis on the NOx reduction rate.
Note that the operation of the engine is not always steady operation, and the operation state often changes from time to time. As described above, the operation mode is appropriately switched according to the changed operation state. Even in the mode, the target air-fuel ratio and the target EGR introduction rate are changed according to the changing operation state. In this case, in addition to the method of simultaneously changing the target air-fuel ratio and the target EGR introduction rate, a method of giving importance to the target air-fuel ratio control, for example, changing the target air-fuel ratio and then changing the target EGR introduction rate is also considered. Can be
[0034]
The exhaust gas recirculation control means (control means) 106 of the present apparatus is configured to control the target EGR introduction rate (exhaust gas recirculation amount) according to the intake air temperature detected by the intake air temperature sensor (intake air temperature detection means) 36. Have been. In the present embodiment, in the stratified combustion mode, the intake air temperature Tain is set to the preset temperature T. ₀ If it becomes larger, the EGR is cut (that is, the exhaust gas recirculation is stopped).
[0035]
That is, as shown in FIG. 9, the stable combustion operation region has a characteristic that it becomes narrower as the intake air temperature increases, and it becomes more difficult to perform the stable combustion operation as the intake air temperature rises. Therefore, when the intake air temperature reaches a temperature at which the stable combustion operation range narrows below a predetermined value, the EGR is cut, that is, the EGR valve 30 is closed to secure the combustion stability of the engine. .
[0036]
Since the exhaust gas recirculation control device for a direct injection internal combustion engine as the first embodiment of the present invention is configured as described above, the exhaust gas recirculation control means (control means) 106 is used, for example, as shown in FIG. EGR control (exhaust gas recirculation control) is performed.
That is, first, the operating state detected (or calculated) by the operating state detecting means 101 (that is, the engine speed Ne detected by the engine speed sensor 41 and the throttle opening θth detected by the throttle opening sensor 37) ) Is read (step A10), and the intake air temperature detected by the intake air temperature sensor 36 is read (step A20). The mode selection means 102 selects an operation mode based on the operation state read in step S10, for example, using a map as shown in FIG.
[0037]
Then, the process proceeds to step A30, and the EGR introduction rate (EGR rate or EGR amount) is set according to the set operation mode and the operating state of the engine. The EGR introduction rate is often set to a value other than 0 in the case of the compression lean mode or the stoichiometric feedback combustion operation mode, but is 0 (EGR cut) in the case of the first half lean combustion operation mode or the open loop combustion operation mode. Is set.
[0038]
Further, the process proceeds to step A40, and it is determined whether the selected operation mode is the compression lean mode (late lean combustion operation mode). If it is not the compression lean mode (that is, stratified combustion), the process proceeds to step A70, where it is determined whether the selected operation mode is the stoichiometric mode (stoichiometric feedback combustion operation mode). The EGR control (exhaust gas recirculation control) is performed in accordance with the EGR introduction rate set in step A30. That is, the opening of the EGR valve 30 is controlled so that the set EGR introduction rate (EGR amount) is obtained.
[0039]
On the other hand, if the selected operation mode is not the stoichiometric mode, that is, if the first-stage lean combustion operation mode or the open-loop combustion operation mode is selected, the process proceeds to step A90, and the EGR cut (that is, the EGR valve 30 is turned off). (Closed) and no EGR is introduced.
On the other hand, if the mode is the compression lean mode (that is, stratified combustion), the process proceeds from step A40 to step A50, where the intake air temperature Tain detected by the intake air temperature sensor 36 is set to the preset temperature T. ₀ It is determined whether it is greater than or equal to. Here, the intake air temperature Tain is equal to the set temperature T. ₀ If not greater, the process proceeds to step A80, where EGR control (exhaust gas recirculation control) is performed. The opening of the EGR valve 30 is controlled so that the target EGR introduction rate set in step A30 is obtained.
[0040]
The intake air temperature Tain is equal to the set temperature T ₀ If it is larger, the process proceeds to step A60, in which the EGR is cut (that is, the EGR valve 30 is closed), and the exhaust gas is not recirculated.
In this way, the intake air temperature Tain becomes equal to the set temperature T. ₀ If EGR is introduced in the latter lean combustion operation mode (compression lean mode), the stable combustion operation becomes more difficult to perform as the intake air temperature increases, and unstable combustion may be caused. (See FIG. 9), the compression lean mode is continued to obtain a high fuel consumption reduction effect, avoid such a risk of unstable combustion, and secure stable combustion. There are advantages.
[0041]
Next, a second embodiment will be described.
In the second embodiment, the configuration of the in-cylinder injection type internal combustion engine according to the exhaust gas recirculation control device and the main configuration of the exhaust gas recirculation control device are the same as those of the first embodiment, and the exhaust gas recirculation control means (control means) 106 Of the EGR control (exhaust gas recirculation control) with respect to the intake air temperature, which is performed through the ECU.
[0042]
That is, the exhaust gas recirculation control means 106 of the present embodiment performs the EGR introduction rate (in accordance with the rise of the intake air temperature Tain) during the stratified combustion, that is, at the time of introducing a large amount of EGR in the late lean combustion operation mode (compression lean mode). EGR control is performed so as to decrease the EGR amount.
Here, for the EGR introduction rate set together with the air-fuel ratio (A / F) so that the fuel efficiency improvement rate and the NOx reduction rate are high, the correction gain Kegr is set based on, for example, a map as shown in FIG. The EGR introduction rate (EGR amount) is corrected by setting the correction gain Kegr. Here, as shown in FIG. 7, the intake air temperature ₁ In the following cases, the correction gain Kegr is set to 1.0, no substantial correction is made, and the intake air temperature ₁ In the above case, the correction gain Kegr is set to decrease from 1.0 in accordance with the rise of the intake air temperature Tain.
[0043]
Since the exhaust gas recirculation control device for a direct injection internal combustion engine as the second embodiment of the present invention is configured as described above, the exhaust gas recirculation control means (control means) 106 is used as shown in FIG. EGR control (exhaust gas recirculation control) is performed.
That is, first, the operating state (engine speed Ne and throttle opening θth) detected (or calculated) by the operating state detecting means 101 is read (step B10), and the intake air temperature detected by the intake air temperature sensor 36 is calculated. Read (step B20). The mode selection means 102 selects an operation mode based on the operation state read in step B10, for example, using a map as shown in FIG.
[0044]
Then, the process proceeds to step B30, and the EGR introduction rate (EGR rate or EGR amount) is set according to the set operation mode and the operating state of the engine. The EGR introduction rate is often set to a value other than 0 in the case of the compression lean mode or the stoichiometric feedback combustion operation mode, but is 0 (EGR cut) in the case of the first half lean combustion operation mode or the open loop combustion operation mode. Is set.
[0045]
Further, the process proceeds to step B40, where it is determined whether the selected operation mode is the compression lean mode (late lean combustion operation mode). If it is not the compression lean mode (stratified combustion), the process proceeds to step B80, where it is determined whether the selected operation mode is the stoichiometric mode (stoichiometric feedback combustion operation mode). If it is the stoichiometric mode, the process proceeds to step B70. Then, EGR control (exhaust gas recirculation control) is performed according to the EGR introduction rate set in step B30. That is, the opening of the EGR valve 30 is controlled so that the set EGR introduction rate (EGR amount) is obtained.
[0046]
On the other hand, if the selected operation mode is not the stoichiometric mode, that is, if the first-stage lean combustion operation mode or the open-loop combustion operation mode is selected, the process proceeds to step B90, and the EGR cut (that is, the EGR valve 30 is turned off). (Closed) and no EGR is introduced.
On the other hand, if the mode is the compression lean mode (that is, stratified combustion), the process proceeds from step B40 to step B50, where the EGR rate correction gain Kegr is set based on the intake air temperature Tain detected by the intake air temperature sensor 36. Further, the process proceeds to step B60, and the EGR introduction rate set in step B30 is corrected by the EGR rate correction gain Kegr. Then, the process proceeds to step B70 to perform EGR control (exhaust gas recirculation control) after correcting with the correction gain Kegr.
[0047]
That is, the target EGR introduction rate (EGR amount or EGR amount) according to the operating state is appropriately reduced and corrected by the correction gain Kegr, and the opening of the EGR valve 30 is controlled so as to obtain the corrected target EGR introduction rate. .
In this manner, the EGR introduction rate (EGR amount) is reduced in accordance with the intake air temperature Tain. Therefore, when EGR is introduced in the late lean combustion operation mode (compression lean mode), the more stable the combustion, the higher the intake air temperature. While the operation becomes difficult and the risk of causing unstable combustion increases (see FIG. 9), the compression lean mode is continued to avoid the risk of such unstable combustion while obtaining a high fuel consumption reduction effect. In addition, there is an advantage that stable combustion can be ensured while reducing NOx as much as possible.
[0048]
Note that the exhaust gas recirculation control device for a direct injection internal combustion engine of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
[0049]
【The invention's effect】
As described above in detail, according to the exhaust gas recirculation control device for a direct injection type internal combustion engine of the present invention, the intake air temperature is reduced while the NOx in the exhaust gas generated by the stratified combustion is constantly reduced by the exhaust gas recirculation. When the intake gas temperature rises, the amount of exhaust gas recirculation is reduced or reduced to zero, thereby suppressing the reduction of the stable combustion operation region that occurs in response to the rise in intake air temperature during stratified combustion, securing a stable combustion operation region, and In addition, there is an advantage that it is possible to continue the fuel efficiency reduction operation by the stable stratified combustion.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a main configuration of an in-cylinder injection type internal combustion engine exhaust gas recirculation control device as a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of a direct injection internal combustion engine according to the first embodiment of the present invention.
FIG. 3 is a block diagram showing a control system configuration of the direct injection internal combustion engine according to the first embodiment of the present invention.
FIG. 4 is a diagram showing a control map used for setting an operation mode of the direct injection internal combustion engine according to the first embodiment of the present invention.
FIG. 5 is a diagram for explaining setting of an EGR introduction rate (EGR rate) in the exhaust gas recirculation control device for a direct injection internal combustion engine as the first embodiment of the present invention.
FIG. 6 is a flowchart showing the operation of the exhaust gas recirculation control device for a direct injection internal combustion engine as the first embodiment of the present invention.
FIG. 7 is a diagram showing a map for correcting a recirculation amount of an in-cylinder injection type internal combustion engine exhaust gas recirculation control device as a second embodiment of the present invention.
FIG. 8 is a flowchart showing an operation of an exhaust gas recirculation control device for a direct injection internal combustion engine as a second embodiment of the present invention.
FIG. 9 is a diagram for explaining the problem of the present invention, and is a characteristic diagram showing a stable combustion operation region of the engine.
[Explanation of symbols]
1 Engine body
2 Intake passage
2A intake port
16 Electronic control unit (ECU) as control means
17 Exhaust passage
17A exhaust port
18 Combustion chamber
21 Fuel injection valve (injector)
29 Exhaust gas recirculation passage (EGR passage)
30 Exhaust gas recirculation amount adjusting means (EGR valve)
36 Intake temperature detection means (intake temperature sensor)
45 spark plug
101 Operating state detecting means
102 Mode selection means
106 Exhaust gas recirculation control means (control means)

Claims (1)

A fuel injection valve that injects fuel directly into the combustion chamber to perform stratified combustion;
A spark plug provided to face the combustion chamber;
Intake air temperature detecting means for detecting the intake air temperature;
Exhaust gas recirculation amount adjusting means for adjusting the exhaust gas recirculation amount according to the intake air temperature detected by the intake air temperature detecting means,
Control means for controlling the exhaust gas recirculation amount adjusting means such that the exhaust gas recirculation amount decreases or becomes zero in accordance with the rise of the intake air temperature during the stratified combustion. Exhaust gas recirculation control device for injection type internal combustion engine.

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