JP4453187B2 - Control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for an internal combustion engine.
[0002]
[Prior art]
Conventionally, in an internal combustion engine that switches the combustion mode between stratified lean combustion by fuel injection in a compression stroke and homogeneous combustion by fuel injection in an intake stroke, such as an in-cylinder injection spark ignition internal combustion engine, nitrogen oxidation It is known that a part of the exhaust of the same engine is recirculated from the exhaust system to the intake system in order to reduce the amount of emission of NOx (NOx).
[0003]
In such an internal combustion engine, an EGR valve is provided in an exhaust gas recirculation passage (EGR passage) through which exhaust gas flows from the exhaust system to the intake system, and the EGR valve is set to a required opening set according to the engine operating state. By controlling, the recirculation exhaust amount (EGR amount) is adjusted. Since the required opening of the EGR valve needs to be increased during stratified lean combustion than during homogeneous combustion in order to reduce NOx emissions, it is more closed during homogeneous combustion than during stratified lean combustion. Set to the opening on the side.
[0004]
Therefore, when a request for switching to homogeneous combustion is made during the stratified lean combustion operation, the required opening of the EGR valve changes from the opening corresponding to stratified lean combustion to the opening corresponding to homogeneous combustion. The EGR valve is controlled to the closing side according to the change in the degree. However, even if the EGR valve is controlled to be closed as described above, the exhaust gas remaining in the EGR passage or the like continues to flow into the intake system for a while, so that the EGR amount is less than the required value during homogeneous combustion immediately after switching. Increasing misfire is likely.
[0005]
Therefore, for example, as described in JP-A-8-189405 and JP-A-9-195839, in response to a request for switching from stratified lean combustion to homogeneous combustion, first, the EGR valve is set to a required opening during homogeneous combustion. It is also conceivable to perform the homogeneous combustion by switching the fuel injection mode from the compression stroke injection to the intake stroke injection after a predetermined delay time elapses thereafter. By delaying the execution of the homogeneous combustion in this way, it is possible to suppress the possibility that misfire is likely to occur because the EGR amount is excessively larger than the required value when the combustion mode is actually switched to the homogeneous combustion. be able to.
[0006]
[Problems to be solved by the invention]
By the way, until the predetermined delay time elapses, the stratified lean combustion is performed, but the EGR valve is controlled to the required opening degree during the homogeneous combustion, and the EGR amount is required during the stratified lean combustion. Insufficiency against the value to be generated. In this way, if the EGR amount is insufficient during stratified lean combustion, NOx emission deteriorates. Therefore, it is preferable to set the predetermined delay time as short as possible.
[0007]
However, if the predetermined delay time is too short, when the combustion mode is switched to homogeneous combustion after the lapse of the predetermined time, the EGR amount does not decrease to the value required at the homogeneous combustion, and the EGR amount is excessive. Misfire may occur and drivability may deteriorate.
[0008]
As described above, even if the predetermined delay time is set so that drivability and NOx emission are optimal, reducing the predetermined delay time is disadvantageous in terms of drivability, and increasing the predetermined delay time results in NOx emission. Therefore, it has been difficult to achieve both reduction in drivability and NOx emissions.
[0009]
The present invention has been made in view of such circumstances, and its object is to suppress deterioration in drivability due to excessive recirculation exhaust amount (EGR amount) when switching from stratified lean combustion to homogeneous combustion. Another object of the present invention is to provide a control device for an internal combustion engine that can achieve both the suppression of deterioration of NOx emission caused by an insufficient EGR amount.
[0010]
[Means for Solving the Problems]
  In the following, means for achieving the above object and its effects are described.
  In order to achieve the above object, according to the first aspect of the invention, the amount of exhaust gas recirculated from the exhaust system to the intake system is adjusted by controlling the opening of the EGR valve, and stratified lean combustion by fuel injection in the compression stroke is performed. Applied to in-cylinder injection spark-ignition internal combustion engines, where the combustion mode is switched between homogeneous combustion by fuel injection in the intake stroke, and the fuel injection mode is compression stroke injection based on a request to switch from stratified lean combustion to homogeneous combustion In the control device for an internal combustion engine that performs homogeneous combustion by switching from intake stroke injection to intake stroke injection, when a request for switching from stratified lean combustion to homogeneous combustion is made, the opening degree of the EGR valve is changed from the requested opening degree during stratified lean combustion. Prior to switching from the compression stroke injection to the intake stroke injection based on the switching request, the intake stroke is switched to the required opening degree during homogeneous combustion. It includes both the stratified stoichiometric combustion by the morphism and the compression stroke injection and combustion control means for executing a predetermined timeThe fuel injection amount by the intake stroke injection and the compression stroke injection for the stratified stoichiometric combustion is adjusted so that the sum thereof becomes a value in which the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio.
[0011]
In stratified stoichiometric combustion, fuel is collected around the spark plug by compression stroke injection, so it is possible to suppress the occurrence of misfire due to an excessive amount of exhaust gas around the spark plug, and to suppress the deterioration of drivability due to this misfire. Is done. In stratified stoichiometric combustion, NOx emissions do not increase as much as during stratified lean combustion, and therefore, NOx emissions are less likely to deteriorate due to insufficient exhaust gas recirculation. According to the above configuration, since the stratified stoichiometric combustion is performed in the switching process from the stratified lean combustion to the homogeneous combustion, it is possible to achieve both suppression of drivability deterioration and NOx emission deterioration in the switching process. it can.
[0012]
According to a second aspect of the present invention, in the first aspect of the invention, the combustion control means is configured such that the valve control means causes the opening degree of the EGR valve to change from a required opening degree during stratified lean combustion to a required opening degree during homogeneous combustion. The stratified stoichiometric combustion is performed after a predetermined time has elapsed since switching to the above.
[0013]
According to the above configuration, in the process in which the opening degree of the EGR valve is switched from the required opening degree in stratified lean combustion to the required opening degree in homogeneous combustion, and the exhaust gas recirculation amount changes to an amount suitable for homogeneous combustion. Stratified stoichiometric combustion is performed. Since stratified stoichiometric combustion is performed in this manner, misfire due to excessive exhaust around the spark plug can be reliably suppressed in the process in which the exhaust gas recirculation amount changes as described above.
[0014]
According to a third aspect of the present invention, in the first or second aspect of the present invention, a determination means for determining whether or not there is a possibility of knocking when the stratified stoichiometric combustion is performed, and the determination means And an ignition timing setting means for setting the ignition timing at the time of the stratified stoichiometric combustion to a retarded angle side when compared with the time when it is determined that there is no possibility of occurrence of knocking. .
[0015]
At the time of stratified stoichiometric combustion, an air-fuel mixture having a relatively high fuel concentration exists also in a part away from the spark plug, so abnormal combustion is likely to occur in that part, and knocking resistance becomes poor. However, according to the above configuration, when there is a possibility that knocking may occur during the execution of stratified stoichiometric combustion, the ignition timing at the time of stratified stoichiometric combustion is set to the retard side, thereby suppressing the temperature rise in the combustion chamber. Thus, abnormal combustion at a portion away from the spark plug and the occurrence of knocking associated therewith are suppressed.
[0016]
An example of a situation where knocking may occur during the execution of stratified stoichiometric combustion is a case where a fuel having a low octane number is used as a fuel for an internal combustion engine. In such a situation, the ignition timing at the time of stratified stoichiometric combustion set by the ignition timing setting means is set on the retarded side as compared with the case where fuel having a high octane number is used as the fuel for the internal combustion engine.
[0017]
According to a fourth aspect of the present invention, in the third aspect of the invention, the ignition timing setting means determines the ignition timing at the time of stratified stoichiometric combustion when there is a possibility that knocking may occur during execution of the stratified stoichiometric combustion. The ignition timing retard amount calculated based on the state is set to the retard side.
[0018]
According to the above configuration, the retard amount of the ignition timing at the time of stratified stoichiometric combustion can be optimally set according to the engine operating state, and it is possible to suppress the ignition timing from being excessively retarded. it can.
[0019]
The invention according to claim 5 is the invention according to claim 3 or 4, wherein the ignition timing of the internal combustion engine is suppressed by a correction value that increases or decreases depending on whether knocking occurs during stratified lean combustion or homogeneous combustion. The determination means is knocked during execution of the stratified stoichiometric combustion according to the magnitude of the ignition timing learning value that is a value stored with the correction value. It was decided to determine whether or not there is a possibility of occurrence.
[0020]
Since the magnitude of the ignition timing learning value varies depending on whether knocking occurs during stratified lean combustion or homogeneous combustion, the ignition timing learning value is a parameter corresponding to the magnitude of the possibility of knocking. According to the above configuration, since it is determined whether or not there is a possibility of knocking during the execution of stratified stoichiometric combustion according to the magnitude of the ignition timing learned value, the determination may be made accurate. it can.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an in-cylinder injection spark ignition engine mounted on an automobile will be described with reference to FIGS.
[0022]
The engine 11 shown in FIG. 1 ignites the fuel injection valve 40 that directly injects fuel into the combustion chamber 16 to which the intake passage 32 and the exhaust passage 33 are connected, and the air-fuel mixture in the combustion chamber 16. And an ignition plug 41 for burning the air-fuel mixture. The piston 12 of the engine 11 reciprocates based on the combustion of the air-fuel mixture in the combustion chamber 16, and this reciprocation is converted into rotation of the crankshaft 14 by the connecting rod 13. Further, the air-fuel mixture after combustion in the combustion chamber 16 is sent to the exhaust passage 33 as exhaust.
[0023]
Connected to the intake passage 32 and the exhaust passage 33 of the engine 11 is an EGR passage 42 through which a part of the exhaust gas in the exhaust passage 33 flows to the intake passage 32. The amount of exhaust gas (EGR amount) recirculated from the exhaust passage 33 to the intake passage 32 through the EGR passage 42 is adjusted by controlling the opening degree of the EGR valve 43 provided in the EGR passage 42. Then, by performing the exhaust gas recirculation as described above, the combustion temperature is lowered, the generation of nitrogen oxide (NOx) is suppressed, and the NOx emission of the engine 11 is reduced.
[0024]
Further, in the intake passage 32 of the engine 11, a portion close to the downstream end is connected to the combustion chamber 16 in a state of being branched into two, and the flow state of the gas in the combustion chamber 16 is connected to one of the branched intake passages 32. An airflow control valve 48 for changing is provided. When the airflow control valve 48 is opened, the air flow area of the intake passage 32 is increased, and the intake resistance of the engine 11 is reduced. When the airflow control valve 48 is closed, the air flow area of the intake passage 32 is reduced and combustion is performed. The flow rate of the air sucked into the chamber 16 is increased.
[0025]
Various operation controls of the engine 11 configured as described above, that is, control such as fuel injection control, ignition timing control, EGR control, and airflow control valve opening / closing control are performed by an electronic control unit (hereinafter referred to as ECU 92) 92. The fuel injection valve 40 and the EGR valve 43 are connected to the ECU 92, and a knock sensor 11c that detects whether or not knocking has occurred in the engine 11 and a crank that outputs a pulse signal corresponding to the rotation of the crankshaft 14 Position sensor 14c, accelerator position sensor 26 for detecting the depression amount of the accelerator pedal 25 of the automobile (accelerator depression amount ACCP), pressure downstream of the throttle valve (not shown) in the intake passage 32 (intake pressure PM) Are connected to the vacuum sensor 36, an igniter 41a for controlling the ignition timing of the spark plug 41, an actuator 49 for opening and closing the airflow control valve 48, and the like.
[0026]
The ECU 92 switches the combustion mode of the air-fuel mixture between stratified lean combustion and homogeneous combustion according to the engine operating state. In the stratified lean combustion operation, combustion of the air-fuel mixture is performed in a state in which the combustible air-fuel mixture exists only around the spark plug 41 by fuel injection in the compression stroke, so that the air-fuel ratio of the air-fuel mixture is made leaner than the stoichiometric air-fuel ratio. It becomes possible to improve. In homogeneous combustion operation, the fuel / air mixture is combusted in a state where the fuel is evenly mixed with the air by fuel injection in the intake stroke, so that the fuel concentration of the whole air / fuel mixture is increased to obtain high output. Is possible.
[0027]
In such stratified lean combustion and homogeneous combustion, since the form of the air-fuel mixture in the combustion chamber 16 is different from each other, even under the same engine operating conditions, the fuel injection amount and fuel injection suitable for each combustion form The timing, the ignition timing, the opening degree of the EGR valve 43, and the like are different from each other. Therefore, the ECU 92 is provided with the fuel injection valve 40, the igniter 41a, the EGR valve 43, and the like so that the fuel injection amount, fuel injection timing, ignition timing, opening degree of the EGR valve 43, and the like suitable for the combustion mode to be executed can be obtained. To control.
[0028]
The switching of the opening degree of the EGR valve 43 corresponding to the switching of the combustion mode is a value of the EGR mode MODE1 set through the ECU 92, for example, “0 (stratified lean combustion)”, “1 (homogenous combustion)”. This is performed according to the value set in. Further, the fuel injection amount, the fuel injection timing, and the ignition timing corresponding to the switching of the combustion mode are switched by the value of the injection / ignition mode MODE2 set through the ECU 92, for example, “0 (stratified lean combustion)” as described above. , According to a value set as “1 (homogeneous combustion)”.
[0029]
Here, an outline of a procedure for switching the combustion mode from stratified lean combustion to homogeneous combustion will be described with reference to the time charts of FIGS. 2A and 2B show switching modes of the EGR mode MODE1 and the injection / ignition mode MODE2, and FIG. 2C shows the switching mode of the opening degree of the EGR valve 43. It is.
[0030]
When there is a request for switching from stratified lean combustion to homogeneous combustion, the ECU 92 switches the EGR mode MODE1 from “0” to “1” as shown in FIG. 2A, and then a predetermined time t1 has elapsed. At this point, the injection / ignition mode MODE2 is switched from “0” to “1” as shown in FIG.
[0031]
When the EGR mode MODE1 is switched from “0” to “1”, the ECU 92 changes the opening of the EGR valve 43 from the required opening at the time of stratified lean combustion to the time of homogeneous combustion as shown in FIG. The required opening is controlled. The required opening of the EGR valve 43 is larger during stratified lean combustion than during homogeneous combustion, but this tends to increase the amount of NOx emission during stratified lean combustion than during homogeneous combustion. This is because of the appropriate reduction. Therefore, when switching from stratified lean combustion to homogeneous combustion, the opening degree of the EGR valve 43 changes to the closed side, and the EGR amount gradually decreases.
[0032]
On the other hand, when the injection / ignition mode MODE2 is “1”, the fuel injection amount, the fuel injection timing, and the ignition timing are in a state suitable for homogeneous combustion. As a result, a predetermined amount of fuel is injected during the intake stroke, ignition is performed on the air-fuel mixture in a state where the fuel is evenly mixed with air, and the air-fuel mixture is combusted. When such homogeneous combustion is executed immediately after the opening degree of the EGR valve 43 is switched to the required opening degree during the homogeneous combustion, there is a response delay in reducing the EGR amount with respect to the switching of the opening degree of the EGR valve 43. In the homogeneous combustion immediately after switching, there is a possibility that EGR becomes excessive and misfire occurs.
[0033]
Therefore, as a technique for suppressing such misfire, it is conceivable to delay the switching of the fuel injection amount, the fuel injection timing, and the ignition timing by a predetermined time with respect to the switching of the opening degree of the EGR valve 43. However, in this case, since the stratified lean combustion continues until the predetermined time elapses, the EGR amount gradually decreases toward a value suitable at the time of homogeneous combustion. Deterioration of NOx emissions is inevitable.
[0034]
From the viewpoint of NOx emission, it is preferable to set the predetermined time as short as possible. However, if the predetermined time is set too short, misfire as described above occurs and drivability deteriorates. Therefore, even if you try to set the above-mentioned predetermined time so that drivability and NOx emissions are optimal, both the drivability and NOx emissions will be disadvantageous as the predetermined time increases and decreases, and drivability deterioration will be suppressed. It was difficult to achieve a balance between NOx emissions and deterioration of NOx emissions.
[0035]
In view of such circumstances, in the present embodiment, when the injection / ignition mode MODE2 is switched from “0” to “1”, stratified stoichiometric combustion is performed by both the intake stroke injection and the compression stroke injection. After continuing for a predetermined time, homogeneous combustion is performed by intake stroke injection.
[0036]
In the stratified stoichiometric combustion as described above, fuel is collected around the spark plug 41 by the compression stroke injection. Therefore, even if the EGR amount is excessive, an excessive amount of exhaust gas exists around the spark plug 41, leading to misfire. It is suppressed. In stratified stoichiometric combustion, NOx emissions do not increase as much as during stratified lean combustion, so that NOx emissions are less likely to deteriorate due to insufficient EGR. Since such stratified stoichiometric combustion is performed in the switching process from stratified lean combustion to homogeneous combustion, it is possible to achieve both suppression of drivability deterioration and suppression of NOx emission deterioration in this switching process.
[0037]
Next, details of the procedure for switching the combustion mode from stratified lean combustion to homogeneous combustion will be described with reference to the flowcharts of FIGS. 3 and 4 showing the combustion mode switching routine. This combustion mode switching routine is executed, for example, by interruption at predetermined intervals through the ECU 92.
[0038]
As the process of the combustion mode switching routine, it is first determined whether or not there is a request for switching from stratified lean combustion to homogeneous combustion (S101). Immediately after the request for switching is made, the EGR mode MODE 1 is switched from “0 (stratified lean combustion)” to “1 (homogenous combustion)”, and the air flow control valve 48 is fixed in the open state. Therefore, the actuator 49 is controlled (S102, S103). Here, the reason why the air flow control valve 48 is fixed in the open state is that the stratified lean combustion is performed without helping the gas flow in the combustion chamber 16 by closing the air flow control valve 48, This is because, when switching the combustion mode, it is preferable not to change the gas flow state in the combustion chamber 16 from the viewpoint of torque shock suppression.
[0039]
When the EGR mode MODE1 is switched to “1”, the opening degree of the EGR valve 43 is controlled to the closed side from the required opening degree in the stratified lean combustion to the required opening degree in the homogeneous combustion (S104, S105). Then, it is determined whether or not the time t1 has elapsed after the EGR mode MODE1 becomes “1” (S106). If the determination is affirmative, the injection / ignition mode MODE2 is “0 (stratified lean combustion). ) "To" 1 (homogeneous combustion) "(S107). While the injection / ignition mode MODE2 is “0”, the stratified lean combustion is performed by the compression stroke injection. Further, after the process of step S107 is executed, the stratified stoichiometric flag F used for determining whether or not to execute the stratified stoichiometric combustion is set to “1 (execute)” (S108).
[0040]
The stratified stoichiometric combustion is executed or stopped according to the stratified stoichiometric flag F based on a stratified stoichiometric combustion execution routine (FIG. 5) described later. That is, based on the fact that the injection / ignition mode MODE2 is switched from “0” to “1”, the stratified stoichiometric flag F is set to “1 (execute)” as shown in FIG. Stratified stoichiometric combustion by both the compression stroke injection and the intake stroke injection is started. Therefore, the stratified stoichiometric combustion is executed after the time t1 has elapsed since the opening degree of the EGR valve 43 is switched to the required opening degree during the homogeneous combustion based on the switching request from the stratified lean combustion to the homogeneous combustion. Become.
[0041]
When the injection / ignition mode MODE2 is switched to “1”, it is determined whether or not a predetermined time t2 has elapsed since the injection / ignition mode MODE2 became “1” (S109, S110). If the determination is affirmative, the airflow control valve 48 is released from being fixed (S111). When the airflow control valve 48 is unlocked, if the engine operating state is in an operation region where it is preferable to close the airflow control valve 48, the airflow control valve 48 is controlled by driving control of the actuator 49 through the ECU 92. The valve is closed as shown in 2 (e).
[0042]
Furthermore, when the injection / ignition mode MODE2 is “1”, it is determined whether or not a predetermined time t3 (t3> t2) has elapsed since the injection / ignition mode MODE2 became “1” ( S112). When it is determined that the time t3 has elapsed, the stratified stoichiometric flag F is set to “0 (stop)” (S113). When the stratified stoichiometric flag F is switched from “1” to “0” as shown in FIG. 2D, the stratified stoichiometric combustion is stopped based on the stratified stoichiometric combustion execution routine (FIG. 5) described later. Note that the time t3 is equal to or longer than the time necessary for convergence of fluctuations in the gas flow state in the combustion chamber 16 when the air flow control valve 48 opens and closes when the time t2 elapses. Set to
[0043]
When the stratified stoichiometric combustion is stopped in this way, the homogeneous combustion by the intake stroke injection is started based on the injection / ignition mode MODE2 being “1 (homogeneous combustion)”. Therefore, the stratified stoichiometric combustion is executed prior to switching from the compression stroke injection for performing the stratified lean combustion to the intake stroke injection for performing the homogeneous combustion.
[0044]
Next, the procedure for executing the stratified stoichiometric combustion will be described with reference to the flowchart of FIG. 5 showing the stratified stoichiometric combustion execution routine. This stratified stoichiometric combustion execution routine is executed through the ECU 92 by, for example, a time interruption every predetermined time.
[0045]
As processing of the stratified stoichiometric combustion execution routine, first, it is determined whether or not the stratified stoichiometric flag F is “1 (execution)” (S201). And if it is affirmation determination, the process after step S202 for performing stratified stoichiometric combustion will be performed, and if it is negative determination, a series of processes will be once complete | finished. Therefore, the stratified stoichiometric combustion is executed when the stratified stoichiometric flag F is “1”, and is stopped when the flag F is “0”.
[0046]
If it is determined that the stratified stoichiometric flag F is “1”, fuel injection is performed in both the intake stroke and the compression stroke (S202). The amount of fuel injection injected by the intake stroke injection and the compression stroke injection is adjusted so that the sum thereof becomes, for example, a value in which the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio. Further, the fuel injection timing of the compression stroke injection is set to a predetermined timing determined in advance by experiments, for example, and the fuel injection timing of the intake stroke injection is set to the same timing as the intake stroke injection at the time of homogeneous combustion, for example. Thereafter, the processing after step S203 for controlling the ignition timing at the time of stratified stoichiometric combustion is executed.
[0047]
For controlling the ignition timing during stratified stoichiometric combustion, an ignition timing command value SAt calculated from a map according to the engine operating state is used. This ignition timing command value SAt is calculated with reference to a map based on the engine speed NE obtained from the detection signal of the crank position sensor 14c and the load factor KL which is a value indicating the current load ratio with respect to the maximum engine load. The There are two types of maps, one corresponding to when the airflow control valve 48 is opened and one corresponding to when the airflow control valve 48 is closed. For example, ignition for homogeneous combustion corresponding to the open / closed state of the airflow control valve 48 during homogeneous combustion. Two types of maps for calculating the time command value are used as they are.
[0048]
Accordingly, at the time of stratified stoichiometric combustion, a map corresponding to the open / closed state of the airflow control valve 48 is selected from two types of maps used at the time of homogeneous combustion, and this map is referred to according to the engine speed NE and the load factor KL. The ignition timing command value SAt at the time of stratified stoichiometric combustion is set (S203). The load factor KL is a parameter corresponding to the intake air amount of the engine 11 such as the intake pressure PM obtained from the detection signal of the vacuum sensor 36 or the accelerator depression amount ACCP obtained from the detection signal of the accelerator position sensor 26, and the engine rotation. Calculated based on the number NE.
[0049]
By the way, at the time of stratified stoichiometric combustion, fuel from the intake stroke injection is distributed at a position away from the spark plug 41 in the combustion chamber 16 and an air-fuel mixture having a relatively high fuel concentration exists, so abnormal combustion occurs at that position. And the knocking resistance becomes poor. Therefore, when using a low octane fuel as the fuel for the engine 11, knocking is more likely to occur than when using a high octane fuel.
[0050]
In the processing of steps S204 to S206, it is determined whether or not there is a possibility of knocking during stratified stoichiometric combustion, such as whether or not the fuel used has a low octane number. If there is such a possibility, the ignition timing command value SAt is set. Reset to the retarded value to suppress knocking. Whether or not knocking may occur during stratified stoichiometric combustion is determined using a learning value RTD that is a value that stores a correction amount H of the ignition timing that increases or decreases to suppress knocking during stratified lean combustion or homogeneous combustion. .
[0051]
Here, ignition timing control for suppressing knocking during stratified lean combustion and homogeneous combustion will be described.
At the time of stratified lean combustion and homogeneous combustion, the ignition timing is controlled based on the ignition timing command value calculated according to the engine operating state. The ignition timing command value is increased or decreased depending on whether knocking occurs or not. It is corrected by. Then, when knocking occurs, the correction amount H is increased and the ignition timing command value is corrected to the retard side, and when knocking does not occur, the correction amount H is decreased and the ignition timing command value is advanced. It is corrected to. In this way, by correcting the ignition timing to the retard side as knocking occurs, the temperature rise in the combustion chamber 16 is suppressed and the occurrence of knocking due to abnormal combustion is suppressed.
[0052]
As described above, the correction amount H that increases or decreases during stratified lean combustion and the correction amount H that increases or decreases during homogeneous combustion are stored in the storage unit of the ECU 92 as learning values RTD under a predetermined condition. Since these learning values RTD become larger as knocking occurs more frequently during stratified lean combustion or homogeneous combustion, the greater the learning value RTD, the higher the possibility that knocking will occur during the execution of stratified stoichiometric combustion. Therefore, based on the magnitude of the learning value RTD, it can be determined whether or not there is a possibility that knocking may occur during the execution of stratified stoichiometric combustion.
[0053]
Then, when executing stratified stoichiometric combustion, it is determined whether or not there is a possibility of knocking based on whether or not the learning value RTD is equal to or greater than a predetermined value a (S204). When it is determined that the learning value RTD is equal to or greater than the predetermined value a and there is a possibility that knocking may occur during stratified stoichiometric combustion, an ignition timing retardation amount R is calculated based on the load factor KL and the engine speed NE ( In step S205, the ignition timing command value SAt set in step S203 is reset to the retard side by the ignition timing retard amount R (S206). On the other hand, when it is determined that the learning value RTD is less than the predetermined value a and there is no possibility of knocking during stratified stoichiometric combustion, the ignition timing command value SAt as described above is reset. Absent.
[0054]
During stratified stoichiometric combustion, the ignition timing is controlled by driving the igniter 41a based on the ignition timing command value SAt thus set (S207). The ignition timing at the time of stratified stoichiometric combustion changes according to the open / closed state of the airflow control valve 48 as shown in FIG. 2 (f), and when there is a possibility of occurrence of knocking (two-dot chain line), It is set on the retarded side compared to the case where there is no possibility of knocking (solid line). The retard amount of the ignition timing (the width between the two-dot chain line and the solid line in the figure) is optimized in accordance with the load factor KL and the engine speed NE.
[0055]
According to the embodiment described in detail above, the following effects can be obtained.
(1) Based on a request to switch from stratified lean combustion to homogeneous combustion, prior to switching the fuel injection mode from compression stroke injection for stratified lean combustion to intake stroke injection for homogeneous combustion, intake stroke injection and compression Stratified stoichiometric combustion with both stroke injection is performed for a predetermined time (during time t3). During stratified stoichiometric combustion, fuel is collected around the spark plug 41 by compression stroke injection, so misfire due to excessive EGR amount is suppressed, and NOx emissions do not increase as much as during stratified lean combustion, resulting in insufficient EGR amount. As a result, NOx emission deterioration and combustion noise increase are less likely to occur. Since this stratified stoichiometric combustion is performed in the switching process from stratified lean combustion to homogeneous combustion, both the suppression of drivability deterioration and the suppression of NOx emission deterioration and combustion noise increase due to EGR shortage are compatible. be able to.
[0056]
(2) Further, the stratified stoichiometric combustion is executed after a predetermined time (time t1) has elapsed since a request for switching from stratified lean combustion to homogeneous combustion is made. Therefore, the opening of the EGR valve 43 is switched to the closed side from the required opening at the time of stratified lean combustion to the required opening at the time of homogeneous combustion, and the stratified stoichiometry is reduced in the process of reducing the EGR amount to a value suitable for homogeneous combustion. Combustion is performed. Since stratified stoichiometric combustion is thus performed, misfire due to excessive exhaust around the spark plug 41 can be reliably suppressed in the process of reducing the EGR amount to a value suitable for homogeneous combustion.
[0057]
(3) At the time of stratified stoichiometric combustion, an air-fuel mixture having a relatively high fuel concentration exists also in a portion away from the spark plug 41 in the combustion chamber 16 due to intake stroke injection, so abnormal combustion is likely to occur in that portion, and knocking The resistance becomes inferior. However, when stratified stoichiometric combustion is performed, if there is a possibility that knocking may occur, the ignition timing is set to the retard side compared to the case where this possibility does not occur, and the temperature rise in the combustion chamber 16 is suppressed. Is planned. For this reason, even when stratified stoichiometric combustion is executed in a situation where knocking is likely to occur, such as when the fuel of the engine 11 is low, the abnormal combustion at a portion away from the spark plug 41, and The occurrence of knocking can be accurately suppressed.
[0058]
(4) The retardation amount of the ignition timing at the time of stratified stoichiometric combustion as described above is set according to the engine operating state such as the load factor KL and the engine speed NE. Therefore, the retard amount can be optimally set according to the engine operating state, and the ignition timing at the time of stratified stoichiometric combustion can be prevented from being excessively set to the retard side.
[0059]
(5) Whether or not knocking may occur when stratified stoichiometric combustion is performed is determined by an ignition timing correction amount H that increases or decreases depending on whether knocking occurs during stratified lean combustion or homogeneous combustion. Is determined based on the magnitude of the learning value RTD, which is a value stored as. Since the learning value RTD changes depending on whether knocking occurs during stratified lean combustion or homogeneous combustion, the learning value RTD is a parameter corresponding to the magnitude of the possibility of knocking. Therefore, the determination can be made accurate by determining whether or not there is a possibility of knocking when performing the stratified stoichiometric combustion based on the magnitude of the learned value RTD.
[0060]
In addition, this embodiment can also be changed as follows, for example.
The retard amount when the ignition timing is set to the retard side to suppress knocking during stratified stoichiometric combustion does not necessarily need to be set according to the engine operating state such as the load factor KL and the engine speed NE. For example, it is conceivable to set the ignition timing at the time of stratified stoichiometric combustion to the retarded angle side by a certain retarded amount that can accurately suppress the occurrence of knocking.
[0061]
・ The stratified stoichiometric combustion is not started when a predetermined time (time t1) has elapsed since the request for switching from the stratified lean combustion to the homogeneous combustion has elapsed. May be.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an entire engine to which an engine control apparatus of an embodiment is applied.
FIG. 2 is a time chart showing switching modes of an EGR mode, an injection / ignition mode, an EGR valve opening, a stratified stoichiometric flag, an air flow control valve, and an ignition timing in accordance with switching from stratified lean combustion to homogeneous combustion. .
FIG. 3 is a flowchart showing a procedure for switching the combustion mode from stratified lean combustion to homogeneous combustion.
FIG. 4 is a flowchart showing a procedure for switching the combustion mode from stratified lean combustion to homogeneous combustion.
FIG. 5 is a flowchart showing a procedure for executing stratified stoichiometric combustion.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Engine, 11c ... Knock sensor, 14c ... Crank position sensor, 25 ... Accelerator pedal, 26 ... Accelerator position sensor, 32 ... Intake passage, 33 ... Exhaust passage, 36 ... Vacuum sensor, 40 ... Fuel injection valve, 41 ... Ignition Plug, 41a ... igniter, 42 ... EGR passage, 43 ... EGR valve, 92 ... Electronic control unit (ECU).

Claims (5)

The amount of exhaust gas recirculated from the exhaust system to the intake system is adjusted by controlling the opening degree of the EGR valve, and the combustion mode between stratified lean combustion by fuel injection in the compression stroke and homogeneous combustion by fuel injection in the intake stroke Is applied to an in-cylinder injection spark ignition type internal combustion engine, and based on a request to switch from stratified lean combustion to homogeneous combustion, the fuel injection mode is switched from compression stroke injection to intake stroke injection to perform homogeneous combustion. In the control device,
Valve control means for switching the opening degree of the EGR valve from the required opening degree during stratified lean combustion to the required opening degree during homogeneous combustion when a switching request from stratified lean combustion to homogeneous combustion is made;
Combustion control means for executing stratified stoichiometric combustion by both intake stroke injection and compression stroke injection for a predetermined time prior to switching from compression stroke injection to intake stroke injection based on the switching request;
With
The fuel injection amount by the intake stroke injection and the compression stroke injection for the stratified stoichiometric combustion is adjusted so that the sum thereof becomes a value in which the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio.
A control device for an internal combustion engine. The combustion control means executes the stratified stoichiometric combustion after a predetermined time has elapsed since the opening degree of the EGR valve is switched from the required opening degree during stratified lean combustion to the required opening degree during homogeneous combustion by the valve control means. The control apparatus for an internal combustion engine according to claim 1. The control apparatus for an internal combustion engine according to claim 1 or 2,
Determining means for determining whether or not there is a possibility of knocking when the stratified stoichiometric combustion is performed;
Ignition timing setting for setting the ignition timing at the time of stratified stoichiometric combustion to the retarded side when the determination means determines that there is a possibility of knocking compared to when it is determined that there is no possibility of knocking Means,
An internal combustion engine control device further comprising: When there is a possibility that knocking may occur during the execution of the stratified stoichiometric combustion, the ignition timing setting means retards the ignition timing at the stratified stoichiometric combustion by an ignition timing retarded amount calculated based on the engine operating state. 4. The control device for an internal combustion engine according to claim 3, wherein the control device is set on the side. The ignition timing of the internal combustion engine is corrected to the advance side or the retard side so that knocking is suppressed by a correction value that increases or decreases according to the presence or absence of knocking at the time of stratified lean combustion or homogeneous combustion,
The determination means determines whether or not there is a possibility of knocking during execution of the stratified stoichiometric combustion, according to the magnitude of an ignition timing learning value that is a value storing the correction value. The internal combustion engine control device described.

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