JP5152103B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an in-cylinder injection internal combustion engine in which a mixture of fuel and air directly injected into a cylinder is ignited and burned by a spark plug.

  In a spark ignition type internal combustion engine in which a mixture of fuel and air is ignited and burned by sparks of an ignition plug, the mixture may be ignited and burned at a timing before the original ignition by the spark plug. Various methods for preventing or suppressing such abnormal combustion have been proposed (see, for example, Patent Document 1).

  Patent Document 1 discloses a technique for suppressing the occurrence of abnormal combustion called so-called pre-ignition. Specifically, for example, an ion sensor is used to detect the occurrence of pre-ignition or immediately before the occurrence, and fuel injection is performed so that the fuel reaches the spark plug according to the situation.

JP 2003-206796 A

  By the way, in an internal combustion engine designed to have a high compression ratio, self-ignition combustion occurs in which the air-fuel mixture in the combustion chamber is ignited and combusted before the original ignition timing by the spark plug due to excessive pressure increase in the combustion chamber. It is thought that it becomes easy to do. In addition, once self-ignition combustion occurs, it can be considered that self-ignition combustion repeatedly occurs after each fuel injection. In such a case, an excessive load is applied to the internal combustion engine due to the combustion energy, which may cause a failure of the internal combustion engine. Therefore, when autoignition combustion occurs, it is necessary to suppress the autoignition combustion as early as possible.

  The present invention has been made to solve the above-described problems, and provides a control device for an internal combustion engine that can quickly suppress the occurrence of self-ignition combustion when self-ignition combustion occurs in the internal combustion engine. The main purpose.

  The present invention employs the following means in order to solve the above problems.

The present invention is applied to an in-cylinder injection type internal combustion engine in which an air-fuel mixture of fuel and air directly injected into a cylinder by a fuel injection valve is ignited by an ignition plug. The first configuration suppresses the occurrence of self-ignition combustion when it is determined by the self-ignition determination means that self-ignition combustion is present, by determining whether or not self-ignition combustion occurs due to cylinder compression. And an injection timing control means for changing the injection timing of the fuel injection valve.

  In short, it is conceivable that when self-ignition combustion occurs, the combustion energy becomes larger than when self-ignition combustion does not occur. Further, the present inventors have found that once self-ignition combustion occurs, combustion energy is gradually increased by repeatedly performing combustion thereafter. Therefore, when autoignition combustion occurs, it is considered necessary to suppress autoignition combustion as early as possible.

  Here, when the injection timing is changed to the retard side or the advance side with respect to the period during which the operating efficiency of the internal combustion engine is maximum, it is possible to reduce the combustion energy of the internal combustion engine (see, for example, FIG. 3). ). In view of this point, in the present invention, when self-ignition combustion occurs, the injection timing is changed, so that the combustion energy can be reduced. As a result, the pressure in the cylinder can be reduced, and as a result, the occurrence of autoignition combustion can be suppressed. In addition, if the injection timing is changed, the response of the internal combustion engine to the change in the control amount is relatively good. Therefore, the delay until the self-ignition combustion is actually suppressed after it is determined that there is self-ignition combustion. Time can be as short as possible. Therefore, according to the present invention, when self-ignition combustion occurs in the internal combustion engine, it is possible to quickly suppress the occurrence of self-ignition combustion.

When fuel injection is performed in the intake stroke, homogenization of the air-fuel mixture in the cylinder is promoted, and as a result, operation efficiency is increased. On the other hand, by changing the fuel injection timing to the retarded angle side with respect to the maximum operating efficiency point, the homogenization of the air-fuel mixture in the cylinder is suppressed, and as a result, the operating efficiency is lowered. In view of this point, in the second configuration , when the injection timing control means performs fuel injection in the intake stroke of the internal combustion engine, and the self-ignition determination means determines that self-ignition combustion is present. The injection timing is changed to the retard side with respect to the maximum operating efficiency point of the injection timing in the intake stroke. According to this structure, generation | occurrence | production of self-ignition combustion can be suppressed suitably.

  In consideration of the fact that when the self-ignition combustion occurs, the in-cylinder pressure becomes higher than when the self-ignition combustion occurs, it is conceivable to determine the presence or absence of self-ignition combustion based on the in-cylinder pressure. On the other hand, in a cylinder injection internal combustion engine designed to have a high compression ratio, for example, combustion may be slowed down to reduce combustion energy. In this case, a pressure increase may occur after compression top dead center due to the occurrence of self-ignition. For example, if the combustion of the internal combustion engine is slowed down by making the ignition timing by the spark plug more retarded than the compression stroke top dead center, the combustion energy associated with spark ignition is more retarded than the compression top dead center. Occur. Apart from this, in the vicinity of the compression top dead center, the cylinder pressure increases as the cylinder is compressed.

In view of this point, in the third configuration , the self-ignition determination means has the cylinder internal pressure when the cylinder internal pressure becomes a substantially constant value or starts to rise after the compression stroke top dead center of the internal combustion engine. Based on this, the presence or absence of the self-ignition combustion is determined. According to this configuration, it is possible to determine the presence or absence of self-ignition combustion during a period in which self-ignition combustion may occur, and it is possible to improve the determination accuracy of self-ignition combustion.

In a fourth configuration , the injection timing control means sets the basic injection timing calculated based on the operating state of the internal combustion engine based on the determination result of the occurrence of self-ignition by the self-ignition determination means as an advance side and a retard angle. The correction amount is corrected to any one of the sides, and the correction amount is learned. By learning the correction amount for the basic injection timing, when self-ignition combustion occurs in the injection timing control based on only the basic injection timing, it is possible to quickly shift to a state where self-ignition combustion does not occur.

In the fifth configuration , when the injection timing control means determines that the self-ignition determination means does not have self-ignition, the injection timing is changed to the advance side by a predetermined amount, and it is determined that self-ignition is present by the change. The correction amount learning value is updated based on the correction amount at the time when the correction is made. According to this configuration, the learning value can be updated with a value immediately before the actual self-ignition combustion occurs, which is suitable for quickly shifting to a state where the self-ignition combustion does not occur.

The correction amount learning value is basically updated to change the injection timing to the retard side. However, from the viewpoint of improving the operating efficiency of the internal combustion engine, it is desirable to determine the injection timing as far as possible. On the other hand, if the injection timing is set to the advance side, there is a high possibility that auto-ignition combustion will occur. Therefore, it is desirable to perform the change to the advance side as carefully as possible. In view of this point, in the sixth configuration , when the correction amount is a value with the injection timing on the advance side of the correction amount learning value updated before the current time, the previous correction amount learning value If a predetermined time has elapsed since the update, the correction amount learning value is updated with the correction amount at that time. By doing so, it is possible to improve the operation efficiency of the internal combustion engine while suppressing the occurrence of self-ignition combustion as much as possible.

The block diagram which shows the whole engine control system outline. The time chart which shows the mode of a change of the pressure in a cylinder. The figure which shows the relationship between a fuel-injection start timing and a torque. The flowchart which shows the process sequence of a basic process. The flowchart which shows the process sequence of a CI gate setting process. The time chart which shows the production | generation process of CI gate. The block diagram which shows schematic structure of a self-ignition combustion determination process. The time chart which shows transition of the peak hold value in the CI gate open section. The flowchart which shows the process sequence of a self-ignition determination process. The flowchart which shows the process sequence of a self-ignition suppression process. The flowchart which shows the process sequence of learning value calculation processing. The time chart which shows transition of fuel injection start timing and self-ignition combustion.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. In the present embodiment, an engine control system is constructed for an in-vehicle multi-cylinder gasoline engine. In this control system, an electronic control unit (hereinafter referred to as ECU) is used as a center to control the fuel injection amount, control the ignition timing, and the like. FIG. 1 is a block diagram showing an overall outline of the engine control system.

  In the engine 10 shown in FIG. 1, an air cleaner (not shown) is provided at the most upstream portion of the intake pipe 11 (intake passage), and an air flow meter 12 for detecting the intake air amount Ga is provided downstream of the air cleaner. It has been. A throttle valve 14 whose opening degree is adjusted by a throttle actuator 13 such as a DC motor is provided on the downstream side of the air flow meter 12. The opening degree of the throttle valve 14 (throttle opening degree) is detected by a throttle opening degree sensor built in the throttle actuator 13. A surge tank 15 is provided on the downstream side of the throttle valve 14, and an intake manifold 16 that introduces air into each cylinder of the engine 10 is connected to the surge tank 15.

  An intake valve 17 and an exhaust valve 18 are provided at an intake port and an exhaust port of the engine 10, respectively. By the opening operation of the intake valve 17, a mixture of air and fuel is introduced into the combustion chamber 24, and the exhaust gas after combustion is discharged to the exhaust pipe 21 (exhaust passage) by the opening operation of the exhaust valve 18. Further, the intake valve 17 is provided with a variable valve device 19 that makes the opening / closing timing of the valve 17 variable. The variable valve device 19 controls the opening and closing of the intake valve 17 by controlling the operation of the hydraulic actuator 29.

  For example, an electromagnetically driven fuel injection valve 25 that directly supplies fuel into the combustion chamber 24 is attached to the upper part of each cylinder of the engine 10. A spark plug 22 is attached to the cylinder head of the engine 10 for each cylinder. A high voltage is applied to the spark plug 22 at a desired ignition timing through an ignition device 23 made of an ignition coil or the like. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 22, and the air-fuel mixture introduced into the combustion chamber 24 is ignited and used for combustion.

  In addition, the system includes a coolant temperature sensor 26 that detects the engine coolant temperature, and a crank angle signal that is rectangular at every predetermined crank angle of the engine 10 (for example, at a cycle of 30 ° CA). A crank angle sensor 27 for detecting the rotational position (crank angle), an in-cylinder pressure sensor 28 for detecting the pressure of the combustion chamber 24 (in-cylinder pressure), and the like are attached. Signals from these various sensors are input to an electronic control unit 40 (hereinafter referred to as ECU 40).

  As is well known, the ECU 40 is mainly composed of a microcomputer (hereinafter referred to as a microcomputer) 42 composed of a CPU, a ROM, a RAM, and the like, and executes various control programs stored in the ROM, so that the engine operation state can be changed each time. In response, various controls of the engine 10 are performed. Specifically, the microcomputer 42 of the ECU 40 receives detection signals from the various sensors described above, calculates the fuel injection amount, ignition timing, etc. based on the various detection signals, and calculates the fuel injection valve 25 and the ignition device. 23 is controlled, or opening / closing control of the intake valve 17 is performed.

  By the way, in the combustion control of the engine 10, it is desirable that the thermal efficiency is as high as possible from the viewpoint of fuel consumption and the like, and for that purpose, it is desirable to make the compression ratio as high as possible. In the present embodiment, in such a high compression engine, the actual compression ratio is changed by changing the closing timing of the intake valve 17 to the advance side or the retard side. For example, when the load is high, the intake valve 17 is closed. The actual compression ratio is increased by retarding the valve timing so that high output can be obtained. At this time, in a state where the actual compression ratio is relatively high, the air-fuel mixture in the combustion chamber 24 is ignited / combusted before ignition by the ignition plug 22 (regardless of ignition by the ignition plug 22) due to high pressure in the combustion chamber 24. Phenomenon (self-ignition combustion) is likely to occur. For example, it is considered that self-ignition combustion is likely to occur when the throttle valve is fully open (WOT) or when the engine speed is low.

  FIG. 2 is a time chart showing a state of the pressure in the cylinder when the self-ignition occurs. The self-ignition combustion will be described below with reference to this figure.

  In FIG. 2, it is assumed that the ignition timing by the spark plug 22 is changed to the retard side in order to suppress the combustion energy. In the present embodiment, the homogeneous combustion is basically performed, and the fuel injected into the combustion chamber 24 by the intake stroke injection is uniformly mixed with the air so that the air-fuel ratio is uniform. Basically, ignition is performed before compression top dead center. On the other hand, in the engine operation state in which the combustion energy is suppressed, the maximum operating efficiency of the injection timing in the intake stroke is retarded, and in FIG. 2, CA1 is retarded from the compression top dead center (compression TDC). Is the ignition timing. More specifically, for example, the ignition timing is set to be retarded from 10 ° CA after compression top dead center (ATDC 10 ° CA). As a result, as indicated by a solid line L1 in the figure, an increase in the cylinder pressure accompanying spark ignition appears after compression top dead center, and the increase amount becomes relatively small, and an increase in the combustion pressure is suppressed.

  However, even if the combustion energy is suppressed, the occurrence of self-ignition cannot be completely suppressed, and it is considered that self-ignition combustion is caused. In addition, once self-ignition combustion occurs, the present inventors generate self-ignition each time combustion is repeated, and the combustion pressure increases each time combustion is repeated (automatic combustion). I learned that ignition combustion will grow).

  The growth of self-ignition combustion will be further described with reference to FIG. In FIG. 2, the solid line L <b> 1 indicates the transition of the cylinder pressure when the self-ignition combustion does not occur, and the dotted lines L <b> 2 to L <b> 7 indicate the transition of the cylinder pressure when the self-ignition combustion occurs. The dotted line L2 indicates the time of the first self-ignition combustion, and the dotted lines L3 to L7 indicate the time of the second and subsequent self-ignition combustion.

  When the self-ignition combustion has not occurred, as shown by a solid line L1 in FIG. 2, the cylinder pressure gradually increases as the cylinder rises during the period up to the compression top dead center, and starts to fall at the compression top dead center. Thereafter, ignition by the ignition plug 22 is performed at the ignition timing CA1, so that the in-cylinder pressure becomes higher after the timing CA1 than when ignition is not performed (two-dot chain line L0 in the figure).

  In this situation, when self-ignition combustion occurs, that is, in the first self-ignition combustion, as shown by the dotted line L2, the pressure rises with the compression of the cylinder up to the compression top dead center as in the solid line L1, and then the compression top dead The pressure starts to drop at the point. However, at the time of occurrence of autoignition combustion (dotted line L2), the pressure in the cylinder after compression top dead center becomes higher than that in the case of no autoignition combustion (solid line L1), and the change of pressure change is Compared to the solid line L1, it is shifted to the advance side as a whole. In FIG. 2, when self-ignition occurs for the second time or later (dotted lines L3 to L7), a peak appears after compression top dead center, and the pressure increases as the peak advances from L3 to L7. Has appeared. That is, once self-ignition combustion occurs, the combustion pressure becomes high each time combustion is repeated, and the transition of the pressure change is shifted to the advance side as a whole.

  As described above, once self-ignition combustion occurs, the combustion energy gradually increases every time the combustion is repeated. As a result, in the worst case, engine failure may occur. There are various possible causes for this, but it is assumed that, for example, the in-cylinder temperature increases with the occurrence of self-ignition combustion, resulting in the formation of an environment in which self-ignition tends to occur. Therefore, once self-ignition combustion has occurred, it is necessary to deal with it quickly and promptly in order to suppress the repeated occurrence of self-ignition combustion.

  In view of the above problems, the present inventors have focused on the fact that combustion can be slowed down by changing the fuel injection timing and that the engine responsiveness to the change in the same period is good. FIG. 3 is a diagram illustrating a relationship between fuel injection start timing and torque. Regarding fuel injection control, in the present embodiment, the fuel injection amount is calculated from the engine rotational speed Ne, the intake air amount Ga, and the like, and the fuel injection valve 25 is opened for a time corresponding to the calculated injection amount. The amount is controlled.

  In FIG. 3, when the predetermined position CA2 of the intake stroke (for example, 280 ° CA or 290 ° CA before compression top dead center) is set as the injection start timing, the operation efficiency of the engine 10 becomes optimal (maximum torque), and the injection start timing Is gradually reduced from the optimum point CA2 to the retard side. This is considered to be because the homogenization of the air-fuel mixture is suppressed by changing the injection start timing to the retard side, and as a result, the torque is reduced. Further, it is considered that the combustion pressure decreases due to the torque reduction, thereby suppressing the self-ignition combustion.

  Therefore, in this embodiment, the presence or absence of self-ignition combustion is determined, and when it is determined that self-ignition combustion is present, the injection timing of the fuel injection valve 25 is delayed with respect to the maximum operating efficiency point of the injection timing in the intake stroke. Change to the corner. As a result, when auto-ignition combustion occurs, the auto-ignition combustion is suppressed as early and as quickly as possible so that the combustion pressure does not become excessive. In the present embodiment, the determination of self-ignition combustion is performed based on the cylinder pressure when the cylinder pressure becomes a substantially constant value or starts to rise after the compression top dead center.

  First, the basic process for carrying out the self-ignition combustion determination process and the suppression process will be described. FIG. 4 is a flowchart showing a processing procedure of basic processing. This process is executed by the microcomputer 42 of the ECU 40 at predetermined intervals.

  In FIG. 4, first, in step S1, the program is initialized, and in step S2, a CI gate setting process is executed. This CI gate setting process is performed by a self-ignition combustion detection gate (hereinafter referred to as CI) as a period in which self-ignition combustion is determined based on a cylinder pressure (cylinder pressure detection value CP) calculated based on a detection signal from the cylinder pressure sensor 28. This is a process of setting a section of “gate”.

  In subsequent step S3, a self-ignition determination process is performed, and in step S4, a self-ignition suppression process is performed. Here, the self-ignition determination process is a process of determining the presence or absence of self-ignition combustion based on the in-cylinder pressure detection value CP extracted at the set CI gate. The self-ignition suppression process is a process of suppressing self-ignition combustion when it is determined that self-ignition combustion is present. And after a self-ignition suppression process is complete | finished, the process of step S2-S4 is repeatedly implemented. Hereinafter, each process is explained in full detail.

  First, the CI gate setting process will be described. The CI gate is set to a period in which the transition of the in-cylinder pressure is significantly different between when auto-ignition combustion occurs and during normal operation. Specifically, the CI gate is a period after the compression top dead center and near the top dead center (for example, ATDC 30 ° CA to 90 ° CA). Here, the period in which the transition of the in-cylinder pressure is significantly different between when auto-ignition combustion occurs and when it is normal differs depending on the operating state of the engine 10 (specifically, the engine speed Ne and the intake air amount Ga). it is conceivable that. Therefore, in the present embodiment, the relationship between the engine operation state and the CI gate is stored in advance, and the CI gate corresponding to the current engine operation state is determined using the relationship.

  The CI gate setting process will be described with reference to the flowchart of FIG.

  In FIG. 5, first, in step S201, it is determined whether or not it is the CI gate setting timing. In the present embodiment, the gate setting is performed when the crank angle calculated based on the detection signal from the crank angle sensor 27 is a crank angle corresponding to the piston top dead center position and a predetermined engine operating condition is satisfied. Timing. Here, in the present embodiment, the predetermined engine operating condition includes that the ignition timing by the ignition plug 22 is retarded from the compression top dead center. Further, the closing timing of the intake valve 17 may include that the intake valve 17 is on the more advanced side than the predetermined crank angle.

  The process proceeds to step S202 on the condition that it is determined that it is the gate setting timing, and the engine speed Ne calculated based on the detection signal from the crank angle sensor 27 is read. In step S203, the intake air amount Ga calculated based on the detection signal from the air flow meter 12 is read. In step S204, the engine cooling water temperature THw calculated based on the detection signal from the cooling water temperature sensor 26 is read.

  In step S205, it is determined whether or not the read engine cooling water temperature THw is higher than a predetermined water temperature α. When the cooling water temperature THw is equal to or lower than the predetermined water temperature α, the warm-up state of the engine 10 is insufficient, so that the combustion is slow, and the possibility that self-ignition occurs is extremely low. Therefore, in this embodiment, when the cooling water temperature THw is in a low temperature region that is equal to or lower than the predetermined water temperature α, the determination of autoignition combustion is not performed. That is, when the cooling water temperature THw is equal to or lower than the predetermined water temperature α in step S205, the process proceeds to step S206, and the ON / OFF timing of the CI gate is initially set.

  On the other hand, if the coolant temperature THw is higher than the predetermined temperature α, the process proceeds to steps S207 and S208, and the ON / OFF timing of the CI gate is set. Specifically, a map indicating the relationship between the engine speed Ne, the intake air amount Ga, and the ON / OFF timing of the CI gate is stored in a predetermined area of the microcomputer 42 in advance, and the read Ne is read based on the map. And ON timing (A) and OFF timing (B) corresponding to Ga and Ga, respectively. An example of a map for calculating the ON timing and OFF timing of the CI gate is shown as maps M1 and M2 in FIG.

  The CI gate generation process will be described with reference to the time chart shown in FIG. In FIG. 6, at the timing t1 of the piston top dead center (TDC), for example, a time until the ON timing of the CI gate is set in the timer A built in the microcomputer 42, and the countdown is started. Then, the CI gate is turned on at the timing when the time count of the timer A becomes zero. Further, for example, the timer B built in the microcomputer 42 is set to the time until the CI gate is turned OFF, and the countdown is started. Then, the CI gate is turned OFF at the timing when the time count of the timer B becomes zero.

  Next, the self-ignition combustion determination process will be described. First, a schematic configuration of the self-ignition combustion determination process will be described with reference to the block diagram of FIG.

  7, the ECU 40 includes an A / D converter 41, a microcomputer 42, a gate circuit 43, and a peak hold circuit 44. Operation information (detection signal) of the engine 10 such as the engine rotation speed Ne, the intake air amount Ga, and the cooling water temperature THw is input to the microcomputer 42 from various sensors via the A / D converter 41 or directly.

  Further, the in-cylinder pressure detection value CP is input to the microcomputer 42 as the peak hold value CPPKH. Specifically, the in-cylinder pressure detection value CP is first input to the gate circuit 43. The gate circuit 43 is connected to the peak hold circuit 44 and outputs the in-cylinder pressure detection value CP to the peak hold circuit 44 only when the gate is instructed by the microcomputer 42. The peak hold circuit 44 extracts the maximum value of the in-cylinder pressure detection value CP input during the gate opening interval, and outputs the maximum value to the microcomputer 42 as the peak hold value CPPKH. That is, the ECU 40 detects the maximum value of the in-cylinder pressure detection value CP in the CI gate section.

  In the present embodiment, the presence or absence of self-ignition is determined based on the comparison result between the maximum value (peak hold value CPPKH) in the CI gate section and the self-ignition determination value TH1. FIG. 8 is a time chart showing the transition of the peak hold value CPPKH in the CI gate section. In FIG. 8, the CI gate is set after the compression top dead center. When ignition by the spark plug 22 is performed, the in-cylinder pressure detection value CP increases due to the combustion energy at that time, and thereby the peak hold value CPPKH increases. At this time, when self-ignition has occurred (in the solid line in the figure), the in-cylinder pressure detection value CP becomes higher than when self-ignition has not occurred (indicated by the one-dot chain line in the figure). Along with this, the peak hold value CPPKH increases. In view of this, in the present embodiment, when the peak hold value CPPKH in the CI gate section is higher than the self-ignition judgment value TH1, it is judged that self-ignition has occurred, and self-ignition judgment for indicating the presence or absence of self-ignition combustion. The value 1 is set in the flag XCI.

  In this embodiment, since the compression top dead center is not included in the CI gate, the in-cylinder pressure detection value CP (that is, the in-cylinder pressure detection value at the compression top dead center) accompanying cylinder compression is not extracted as the peak hold value. . Therefore, when the combustion energy is suppressed by ignition timing control or the like, it is avoided that the self-ignition is erroneously determined based on the in-cylinder pressure detection value at the compression top dead center even though the self-ignition has not occurred. .

  Next, the self-ignition determination process will be described using the flowchart of FIG.

  In FIG. 9, first, in step S301, it is determined whether or not it is the determination timing of self-ignition combustion. In the present embodiment, the OFF timing of the CI gate is set as the self-ignition determination timing. When it is determined that it is the self-ignition determination timing, the process proceeds to step S302, and the peak hold value CPPKH in the CI gate section is read. In a succeeding step S303, it is determined whether or not the peak hold value CPPKH is higher than the self-ignition determination value TH1. If the peak hold value CPPKH is equal to or less than the self-ignition determination value TH1, the process proceeds to step S304, and the self-ignition determination flag XCI is reset to 0 with no self-ignition combustion. On the other hand, if the peak hold value CPPKH is higher than the self-ignition determination value TH1, the process proceeds to step S305, and the self-ignition determination flag XCI is set to 1 with the presence of self-ignition combustion.

  When it is determined that there is self-ignition in the self-ignition determination process, the self-ignition combustion is suppressed by the self-ignition suppression process described below. FIG. 10 is a flowchart showing the processing procedure of the self-ignition suppression processing. This process is a process for setting an optimal fuel injection timing each time to achieve a high compression ratio of the engine 10 and suppression of self-ignition combustion. In FIG. 10, the fuel injection start timing is set as the fuel injection timing.

  In FIG. 10, first, in step S401, it is determined whether or not it is the execution timing of this process. In the present embodiment, the timing at which the crank angle calculated based on the detection signal from the crank angle sensor 27 becomes the crank angle corresponding to the piston top dead center position is set as the execution timing.

  If it is the execution timing, the process proceeds to step S402, in which the engine speed Ne and the intake air amount Ga are read, and the basic injection timing TINJBSE is calculated based on the read Ne and Ga. In the present embodiment, a map indicating the relationship between the engine speed Ne and the intake air amount Ga and the basic injection timing TINJBSE is stored in advance in a predetermined area of the microcomputer 42, and the read Ne and Ga are stored based on the map. The corresponding basic injection timing TINJBSE is read. An example of a map for calculating the basic injection timing TINJBSE is shown as a map M3 in FIG.

  In step S403, it is determined whether or not the self-ignition determination flag XCI has a value of 1. When the self-ignition determination flag XCI is 1, that is, when self-ignition combustion occurs, the process proceeds to step S404, and the change amount (retard side change amount) DCINJA is calculated to change the fuel injection start timing to the retard side. In this embodiment, the retard side change amount DCINJA is made variable according to the engine operating state. Specifically, a map indicating the relationship between the engine speed Ne and the intake air amount Ga and the retard side change amount DCINJA is stored in advance in a predetermined area of the microcomputer 42, and the read Ne and The retard side change amount DCINJA corresponding to Ga is read. An example of a map for calculating the retard side change amount DCINJA is shown as a map M4 in FIG.

In the subsequent step S405, the injection timing correction amount TDCRINJ is calculated. The injection timing correction amount TDCRINJ is expressed by the following equation (1) by using the previous value TDCRINJ (i−1).
TDCRINJ (i) = TDCRINJ (i-1) + DCINJA (i) (1)
On the other hand, if the self-ignition determination flag XCI is 0, that is, if self-ignition combustion has not occurred, the process proceeds to step S406, and the change amount (advance side change amount) to change the fuel injection start timing to the advance side. DCINJS is calculated. In step S407, an injection timing correction amount TDCRINJ is calculated. Note that the calculation method of the advance side change amount DCINJS and the correction amount TDCRINJ is basically the same as that for the change to the retard side.

  In step S408, an upper and lower limit guard for the injection timing correction amount TDCRINJ is set in order to suppress the setting of an excessive value and an excessive value in the injection timing correction amount TDCRINJ. In the present embodiment, the lower limit guard value is set to zero, and the upper limit guard value is set based on each engine operating state. Specifically, the upper limit guard value is stored in advance in a predetermined area of the microcomputer 42 indicating the relationship between the engine speed Ne, the intake air amount Ga, and the upper limit guard value GTDCRINJMAX, and is read based on the map. The upper limit guard value GTDCRINJMAX corresponding to Ne and Ga is read. An example of a map for calculating the upper guard value GTDCRINJMAX is shown as a map M5 in FIG.

  Thereafter, in step S409, a correction amount learning value TINJLA set in another routine (learning value calculation process) described later is read. The correction amount learning value TINJLA is a value for correcting the basic injection timing TINJBSE to an optimum value, and the injection timing correction amount TDCRINJ when self-ignition combustion actually occurs when the injection timing is changed to the advance side. It is a value that is updated each time based on.

In this embodiment, the correction amount learning value TINJLA is stored in a predetermined area of the microcomputer 42 in accordance with the engine speed Ne and the intake air amount Ga. Therefore, here, the correction amount learned value TINJLA corresponding to the current engine speed Ne and the intake air amount Ga is read. In step S410, the final injection timing TINJ is calculated by the following equation (2).
TINJ = TINJBSE-TDCRINJ-TINJLA (2)
Here, the learning value calculation process will be described. The injection timing correction amount TDCRINJ for suppressing the self-ignition combustion is different for each engine operating state. In the configuration in which the injection timing correction amount TDCRINJ is calculated for each operating state, the time until the self-ignition combustion is eliminated is long. It is possible to become. Therefore, in the present embodiment, the correction amount learning value TINJLA is calculated and added to the basic injection timing TINJBSE.

  FIG. 11 is a flowchart illustrating a processing procedure of learning value calculation processing. This process is executed by the microcomputer 42 of the ECU 40 every time the crank angle calculated based on the detection signal from the crank angle sensor 27 becomes the crank angle corresponding to the piston top dead center position (every TDC).

  In FIG. 11, first, in step S40401, it is determined whether or not the operating state of the engine 10 is a steady state. In this embodiment, it is determined whether or not the engine is in a steady state based on the fluctuation amount of the engine speed Ne and the fluctuation amount of the intake air amount Ga. Specifically, the fluctuation amount of the engine speed Ne and the fluctuation amount of the intake air amount Ga in a predetermined time (for example, 1500 msec) are calculated, and when both of the fluctuation values are equal to or less than the threshold value, it is determined that the steady state is reached.

  If the engine operating state is a steady state, the process proceeds to step S40402, and it is determined whether or not a value 0 is set in the self-ignition determination flag XCI. If the self-ignition determination flag XCI is set to 0, the process proceeds to step S40403, and the final injection timing TINJ that is currently set is stored as the advance-time injection timing TADVINJ.

In the above-described self-ignition suppression process, if self-ignition combustion occurs while the fuel injection start timing is gradually changed to the advance side, a negative determination is made in step S40402, and the flow proceeds to step S40404. In step S40404, it is determined whether or not the current advance injection timing TADVINJ is behind the current value of the start value TINJSTR represented by the sum of the basic injection timing TINJBSE and the correction amount learning value TINJLA. When the advance angle injection timing TADVINJ is behind the start value TINJSTR, the process proceeds to step S40405, and the correction amount learning value TINJLA is calculated by the following equation (3). That is, the correction amount learning value TINJLA is determined so that the start value TINJSTR is retarded by a change amount DCINJS that is, for example, twice the fuel injection start timing at the time of the first self-ignition combustion.
TINJLA (i) = TINJBSE (i) -TADVINJ (i) + 2DCINJS (i) (3)
In this process, basically, the correction amount learning value TINJLA is allowed to be updated only on the retard side. However, it is conceivable that the injection timing is set to be retarded from the optimum value due to machine differences, changes with time of each device, and the like. Therefore, in this embodiment, when a sufficient time has elapsed since the previous update, the correction amount learning value TINJLA is allowed to be updated to the advance side.

  That is, if a negative determination is made in step S40404, the process proceeds to step S40406, and the learning update timer RETIME is read. The learning update timer RETIME is a value indicating an elapsed time since the update processing of the correction amount learning value TINJLA by this processing is executed, and is measured by, for example, a count-up timer built in the microcomputer 42.

  In a succeeding step S40407, it is determined whether or not the learning update timer RETIME is equal to or greater than a predetermined value α (for example, a value corresponding to several months). Calculate TINJLA. That is, the correction amount learning value TINJLA update processing by this processing is performed every time a fixed time has elapsed since the previous execution.

  In subsequent step S40408, the correction amount learning value TINJLA corresponding to the current engine speed Ne and intake air amount Ga is updated with the value calculated in step S40405. A map M6 in FIG. 11 is an example of a map showing the relationship between the engine speed Ne, the intake air amount Ga, and the correction amount learning value TINJLA. In step S40409, the learning update timer RETIME is reset to a value of 0, and the advance timing injection timing TADVINJ is reset to an initial value.

  The transition of the injection start timing and the transition of the occurrence of self-ignition combustion in this embodiment will be described using the time chart of FIG. In addition, regarding the in-cylinder pressure detection value CP, two large and small peaks PEA and PEB appear repeatedly. Of these, the advanced-side peak PEA is due to cylinder compression, and the retarded-side peak PEB is the combustion of the air-fuel mixture. Is due to.

  In FIG. 12, when the in-cylinder pressure detection value CP becomes larger than the self-ignition determination value TH1 at the timing t1, and it is determined that self-ignition exists, the value 1 is set to the self-ignition determination flag XCI. Further, the retard side change amount DCINJA is calculated for each TDC, and the injection start timing is gradually changed to the retard side by the retard side change amount DCINJA calculated each time. As a result, the in-cylinder pressure detection value CP decreases and eventually self-ignition combustion is not detected.

  When the in-cylinder pressure detection value CP becomes equal to or less than the self-ignition determination value TH1 at timing t2, it is determined that self-ignition is not present in the self-ignition determination, and the self-ignition determination flag XCI is reset to a value of zero. Further, the advance side change amount DCINJS is calculated for each TDC, and the injection start timing is gradually changed to the advance side by the advance side change amount DCINJS calculated each time.

  During the advance operation, the advance injection timing TADVINJ is changed to the advance side as the final injection timing TINJ is changed to the advance side. When the in-cylinder pressure detection value CP becomes larger than the self-ignition determination value TH1 at the timing t3 and it is determined by the self-ignition determination that there is self-ignition, a value 1 is set to the self-ignition determination flag XCI, The injection start timing is gradually changed to the retard side by the retard side change amount DCINJA. At this time, since the advance timing injection timing TADVINJ is on the retard side with respect to the start value TINJSTR, the correction amount learning value TINJLA is updated with the value expressed by the above equation (3).

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  When it is determined that there is self-ignition combustion, the fuel injection timing is changed to the retard side with respect to the maximum operating efficiency point of the injection timing in the intake stroke, so that the combustion pressure can be suppressed, As a result, generation | occurrence | production of self-ignition combustion can be suppressed. In addition, if the fuel injection timing is changed, the engine responsiveness to the change in the control amount is relatively good, so the delay time from when it is determined that self-ignition combustion is present until the self-ignition combustion is actually suppressed Can be made as short as possible. Therefore, when self-ignition combustion occurs, the occurrence of self-ignition combustion can be quickly suppressed.

  In particular, once self-ignition combustion occurs, it is not necessary to change the control value to the side that increases the actual compression ratio (specifically, the valve closing timing and ignition timing of the intake valve 17 are not changed to the advance side). However, since the combustion energy is increased by repeatedly performing the combustion thereafter, it is highly necessary to make it disappear as early as possible. Therefore, by suppressing self-ignition combustion by changing the fuel injection timing, an effect of reducing an excessive burden on the engine 10 can be suitably obtained.

  In the present embodiment, it may be erroneously determined that there is self-ignition combustion based on the peak of the in-cylinder detection value CP that accompanies cylinder compression. In this embodiment, the compression top dead center vicinity range that is retarded from the compression top dead center. Since the self-ignition combustion determination period (CI gate) is used, the determination accuracy of self-ignition combustion can be improved.

  When it is determined that self-ignition combustion is present, the fuel injection timing is changed to the retard side by the retard side change amount DCINJA until the self-ignition combustion is suppressed. Since the timing is changed to the advance side by the advance side change amount DCINJS until the auto ignition combustion occurs, the actual compression ratio can be increased while preventing the auto ignition combustion from occurring repeatedly.

  Since the injection start timing (basic injection timing TINJBSE) calculated based on the engine speed Ne and the intake air amount Ga is corrected by the correction amount learning value TINJLA, self-ignition combustion is not performed in the injection timing control based only on the basic injection timing. When it occurs, it is possible to quickly shift to a state where self-ignition combustion does not occur. Thereby, it is possible to avoid an increase in the period during which the self-ignition combustion continues, and as a result, the self-ignition combustion can be quickly suppressed.

  With respect to the correction amount learning value TINJLA, the injection timing when self-ignition combustion occurs by gradually changing the injection timing to the advance side is stored as the advance-time injection timing TADVINJ, and the advance-time injection is performed. Since the correction amount learning value TINJLA is updated with the value calculated by the above equation (3) when the timing TADVINJ is behind the start value TINJSTR, it is set to the value immediately before the self-ignition combustion actually occurs. Thus, the correction amount learned value TINJLA can be updated, which is suitable for promptly shifting to a state in which self-ignition combustion does not occur.

  When the injection timing is changed to the advance side by updating the correction amount learning value TINJLA, the correction amount learning value TINJLA based on the learning value is updated on the condition that a certain period has passed since the previous update. Therefore, the injection timing can be carefully changed to the advance side. Therefore, suppression of the occurrence of self-ignition combustion and improvement of the operating efficiency of the engine 10 can be performed in a well-balanced manner.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  The delay side change amount DCINJA is made variable according to the injection timing (for example, the last final injection timing TINJ or the current basic injection timing TINJBSE). Since the amount of decrease in operating efficiency with respect to the retard side change amount DCINJA of the injection timing differs depending on the injection timing (see FIG. 3), according to the above configuration, the self-ignition suppression is suppressed while the torque is decreased by a certain amount. It can be carried out.

  -Although the fuel injection timing is changed to the retarded angle side with respect to the maximum operating efficiency point CA2 of the injection timing in the intake stroke, it has been configured to suppress the occurrence of self-ignition combustion. It is set as the structure which suppresses generation | occurrence | production of self-ignition combustion by changing to the advance side with respect to the operating efficiency point CA2. This is because the torque of the engine 10 decreases and the combustion pressure is suppressed as the injection timing in the intake stroke becomes more advanced than the maximum operating efficiency point CA2, as shown in FIG.

  -It is set as the structure which changes a CI gate area according to transition of the timing when the peak PE of in-cylinder pressure detection value CP appears. Specifically, the occurrence timing of the peak PE (corresponding to PE2 to PE7 in FIG. 2) of the in-cylinder pressure detection value CP that appears on the retard side from the compression TDC is detected, and the period including the occurrence timing is Is stored (learned) as a CI gate section corresponding to the engine operating state (for example, the engine rotational speed Ne and the intake air amount Ga). Then, the subsequent CI gate interval is determined based on the learning value.

  A configuration in which the retard side change amount DCINJA is made variable in accordance with the relationship between the previous value CP (i−1) and the current value CP (i) of the in-cylinder pressure detection value CP when it is determined that there is self-ignition combustion; To do. Specifically, for example, the pressure increase amount ΔCP (CP (i) −CP (i−1)) of the current value CP (i) with respect to the previous value CP (i−1) is calculated, and the pressure increase amount ΔCP is large. The retard side change amount DCINJA is increased in order to suppress self-ignition combustion as quickly as possible.

  -Although it was set as the structure which implements determination of self-ignition combustion by comparison with in-cylinder pressure detection value CP and self-ignition determination value TH1, the determination method of self-ignition combustion is not specifically limited. For example, as another example of the detection method based on the in-cylinder pressure, attention is paid to the fact that ion current flows through both electrodes of the spark plug 22 with combustion in the combustion chamber 24, and an ion current detection circuit is provided. It is set as the structure which implements determination of self-ignition combustion by the magnitude of the detected ion current. At this time, the larger the flame due to combustion, the more ion current flows, so the higher the cylinder pressure, the more ion current flows.

  Alternatively, the previous value CP (i−1) of the in-cylinder pressure detection value CP is compared with the current value CP (i), and the pressure increase amount ΔCP of the current value CP (i) with respect to the previous value CP (i−1) is predetermined. When the value is greater than or equal to the value, it is determined that there is self-ignition. As described above, once self-ignition combustion occurs, self-ignition combustion is continued thereafter, but the in-cylinder pressure detection value CP increases each time combustion is repeated.

  Moreover, it is set as the structure which determines the presence or absence of self-ignition combustion based on the appearance timing of the peak PE of in-cylinder pressure detection value CP. Specifically, when a peak PE (corresponding to PE2 to PE7 in FIG. 2) on the retard side from the compression TDC is detected at a timing earlier than a predetermined value determined based on the ignition timing by spark ignition. It is determined that there is self-ignition combustion. Alternatively, when the appearance timing of the peak PE of the in-cylinder pressure detection value CP is earlier than the previous appearance timing, it is determined that there is self-ignition combustion.

  In FIG. 2, the case where the ignition timing is retarded from the compression top dead center has been described. However, in an engine operating state in which ignition (autoignition) occurs due to excessive pressure increase in the combustion chamber before spark ignition. If there is, the ignition timing is not particularly limited. Even in this case, the engine torque is suppressed by changing the fuel injection timing, and the self-ignition can be preferably suppressed.

  -The fuel injection start timing is calculated, and the fuel injection is performed at the calculated timing to suppress self-ignition combustion. However, this is changed, the fuel injection end timing is calculated, and the fuel injection is calculated at the calculated timing. It is good also as a structure which suppresses self-ignition combustion by doing.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 12 ... Air flow meter, 25 ... Fuel injection valve, 17 ... Intake valve, 19 ... Variable valve apparatus, 27 ... Crank angle sensor, 28 ... In-cylinder pressure sensor, 40 ... ECU, 42 ... Microcomputer (self-ignition judgment means , Injection timing control means), 43... Gate circuit, 44... Peak hold circuit.

Claims (5)

It is applied to an in-cylinder injection type internal combustion engine in which a fuel / air mixture directly injected into a cylinder by a fuel injection valve is ignited by an ignition plug,
Self-ignition determination means for determining the presence or absence of self-ignition combustion that occurs with cylinder compression;
The fuel injection is performed in the intake stroke of the internal combustion engine, and the maximum injection timing in the intake stroke is suppressed in order to suppress the occurrence of the self-ignition combustion when the self-ignition determination means determines that self-ignition combustion is present. Injection timing control means for changing the injection timing of the fuel injection valve on the retard side with respect to the operating efficiency point ,
The self-ignition determining means determines whether or not the self-ignition combustion is performed based on the cylinder pressure when the cylinder pressure that decreases after the top dead center of the compression stroke of the internal combustion engine becomes a substantially constant value or starts to increase. determination to the control device for an internal combustion engine characterized by Rukoto. The self-ignition determination means compares the internal pressure when the cylinder pressure, which decreases after top dead center of the compression stroke, becomes a substantially constant value or starts to increase, with a determination value, thereby comparing the self-ignition determination means. Determine the presence or absence of ignition and combustion,
The control device for an internal combustion engine according to claim 1, wherein the determination value is set to a value lower than a pressure peak value due to cylinder compression when the self-ignition combustion does not occur. The injection timing control means corrects the basic injection timing calculated based on the operating state of the internal combustion engine to either the advance side or the retard side based on the determination result of the occurrence of self-ignition by the self-ignition determination means. as well as, control apparatus for an internal combustion engine according to claim 1 or 2 learns the correction amount. The injection timing control means changes the injection timing to the advance side by a predetermined amount when the self-ignition determination means determines that there is no self-ignition, and the time at which the self-ignition is determined by the change is determined. The control device for an internal combustion engine according to claim 3 , wherein the correction amount learning value is updated based on the correction amount. If the correction amount is a value with the injection timing being advanced from the correction amount learning value updated before the present time, a predetermined time has elapsed since the last correction amount learning value was updated. in the control apparatus for an internal combustion engine according to claim 3 or 4 to update the correction amount learned value by the correction amount at that time.

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