JP2006016973A - Control device of cylinder injection internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate a torque shock by accurately adjusting engine torque when switching its two combustion modes, in a cylinder injection internal combustion engine for operating by switching to a lean stratified combustion mode and a rich uniform combustion mode of the air-fuel ratio. <P>SOLUTION: For example, when switching to the uniform combustion mode from the stratified combustion mode, before switching a fuel injection mode, a throttle valve 20 is operated for closing by a predetermine quantity (the time t2 to t3). Thus, an intake air quantity reduces, and when the ce ratio becomes a predetermined value R (a stratified combustion limit), a (t4) fuel injection mode is switched to intake stroke injection from compression stroke injection. In this case, an ignition retard is performed for negating a sudden increase in engine torque caused by a jump of the air-fuel ratio, and a fuel injection quantity is increasingly corrected by the first one combustion cycle with respective cylinders 2 after its switching, by estimating an air quantity remaining in the respective cylinders 2 for switching the injection mode. Thus, the torque shock can be eliminated when switching the injection mode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for a direct injection internal combustion engine that is operated by switching between a lean stratified combustion state and a rich uniform combustion state of an air-fuel ratio, and in particular, a torque shock that is generated when switching between these operating states. It belongs to the technical field of correction control for suppression.

  In general, in a cylinder-injection gasoline engine (internal combustion engine) in which fuel is directly injected into a combustion chamber in a cylinder and burned, in a relatively light load operation state, injection is performed in a compression stroke of the cylinder. By igniting and igniting the mixed fuel mixture that is unevenly distributed around the spark plug (stratified combustion), the ratio of the amount of air to the fuel is very large (for example, the air-fuel ratio A / F is 30 or more) in a lean state. The engine can be operated, thereby significantly reducing pumping loss and heat loss and increasing engine efficiency.

  On the other hand, in an operation state where the load is relatively large, fuel is injected during the intake stroke of the cylinder, and is mixed with the intake air and then burned (uniform combustion). Specifically, first, the opening degree of the throttle valve is controlled in accordance with the operating state defined by the engine load and the rotational speed, thereby adjusting the intake air flow rate and detecting the intake air flow rate with a sensor. Based on the detected value, the fuel injection amount is controlled so as to achieve a target air-fuel ratio. At this time, the target air-fuel ratio is often set near the stoichiometric air-fuel ratio because of the high combustion efficiency and the high exhaust gas purification efficiency by the catalyst.

  The combustion state is switched in such a manner that the air-fuel ratio of the entire combustion chamber is still leaner than the stoichiometric air-fuel ratio if the fuel injection amount is increased as the load increases while the stratified combustion state is maintained. Even so, the air-fuel mixture that is unevenly distributed around the spark plug becomes richer than the stoichiometric air-fuel ratio, which may lead to deterioration of combustibility and misfire (this is stratified combustion) Called the limit).

  By the way, as a result of switching the combustion state during operation as described above, there is a possibility that an unpleasant torque shock may occur in the conventional in-cylinder injection type engine. That is, as described above, in the lean stratified combustion state of the air-fuel ratio, the throttle valve is greatly opened so that a large amount of air is sucked into the engine cylinder, while in the uniform combustion state, the air-fuel ratio is close to the stoichiometric air-fuel ratio. In order to make it richer than that, the opening of the throttle valve becomes relatively small.

  For this reason, for example, when switching the engine from the stratified combustion state to the uniform combustion state, the throttle valve is first closed to reduce the intake air amount, so that when the air-fuel ratio reaches the vicinity of the stratified combustion limit, the fuel injection mode is set to the compression stroke injection. The air-fuel ratio at this time is still leaner than the stoichiometric air-fuel ratio as described above, and the air-fuel ratio at this time is switched to the stoichiometric air-fuel ratio in spite of the large amount of air. For this reason (hereinafter also referred to as air-fuel ratio jump), the engine torque rapidly increases and a shock is generated.

With respect to this problem of torque shock, for example, in the ignition timing control device for a direct injection internal combustion engine disclosed in Patent Document 1, the ignition timing is greatly retarded substantially simultaneously with switching to the intake stroke injection as described above. Correction (ignition retard) to cancel out the increase in torque caused by the jump of the air-fuel ratio, so that the torque shock can be reduced to some extent.
Japanese Patent No. 3211679

  However, even if a large ignition retard is performed immediately after switching of the fuel injection mode as in the conventional example so as to offset the sudden increase in engine torque caused by the air-fuel ratio jump, that is not sufficient. It turns out that torque shock still remains.

  The reason is considered as follows. That is, when the combustion state is switched from stratified combustion to uniform combustion, the average air-fuel ratio in each cylinder changes to the rich side accordingly, but the first one combustion after switching for each cylinder In the cycle, burnt gas from stratified combustion remains, the air-fuel ratio is relatively lean, and the air volume is relatively large. Therefore, the air-fuel ratio of the newly formed air-fuel mixture in the cylinder is the target value (theoretical). The air / fuel ratio is slightly leaner than the air / fuel ratio.

  As described above, if the air-fuel ratio shifts to the lean side when a large ignition retard is being performed immediately after the fuel injection mode is switched, the engine torque also decreases due to this air-fuel ratio shift. Therefore, the torque reduction amount becomes too large, and the engine torque cannot be accurately adjusted before and after the switching.

  Based on the above knowledge, the present invention eliminates torque shock by accurately matching the engine torque when switching the engine combustion state between the lean stratified combustion state of the air-fuel ratio and the rich uniform combustion state. It is intended to do.

  In order to achieve the above object, the present invention estimates the amount of air remaining in the cylinder when the operating state of the engine (internal combustion engine) is switched from the stratified combustion state to the uniform combustion state. In only one combustion cycle, the engine torque is corrected to be increased based on the estimated value of the residual air amount.

Specifically, in the first aspect of the invention, in accordance with the operating state of the internal combustion engine, the fuel is injected at least in the compression stroke of the cylinder to be in the stratified lean combustion state, and the fuel is injected in the intake stroke. Switching control means for performing switching control of the intake stroke injection mode to achieve a uniform rich combustion state, and when the switching control means switches from the compression stroke injection mode to the intake stroke injection mode, the engine associated with this switching The present invention is directed to a fuel control device for a direct-injection internal combustion engine having retard control means for retarding ignition timing so as to cancel torque fluctuations, and is provided with an intake stroke injection from a compression stroke injection mode by the switching control means. A residual air amount estimating means for estimating an air amount remaining in the cylinder switched to the mode;
Torque-up correction means for increasing and correcting the engine torque based on at least the residual air amount estimated by the residual air amount estimation means, corresponding to the first one combustion cycle of the cylinder after switching to the intake stroke injection mode; Shall be provided.

  With the above configuration, first, the operating state of the direct injection internal combustion engine (hereinafter referred to as the engine) changes, and in response to this, the switching control means changes from the compression stroke injection mode (stratified combustion state) to the intake stroke injection mode (uniform). When the switching control to the combustion state) is performed, the ignition timing is greatly retarded by the retard control means so that the engine torque does not fluctuate even if the air-fuel ratio suddenly changes (jumps) to the rich side along with this switching. (Ignition retarded).

  In the cylinder that is switched from the compression stroke injection mode to the intake stroke injection mode in this way, burned gas (exhaust gas) due to stratified combustion remains, so the amount of residual air in the cylinder compared to normal uniform combustion Therefore, in the first one combustion cycle after switching, the air-fuel ratio of the air-fuel mixture newly formed in the cylinder slightly shifts to the lean side, which is incompatible with the significant ignition retard. As a result, the engine torque is slightly reduced.

  On the other hand, the residual air amount in the cylinder thus switched to the intake stroke injection mode is estimated by the residual air amount estimation means, and at least the estimated residual air in the first one combustion cycle of the cylinder after the switching. Based on the amount, the engine torque is increased and corrected by the torque-up correction means. As a result, a decrease in engine torque caused by the influence of the residual air can also be offset, and fluctuations in engine torque before and after fuel injection mode switching are eliminated, eliminating torque shock.

  As a specific configuration of the control device, a decrease in the engine torque caused by the influence of the residual air in the cylinder accompanying the switching control of the injection mode by the switching control means is used as an estimated value of the residual air quantity by the residual air quantity estimating means. Torque down amount estimation means for estimating the ignition timing based on the retard angle control amount by the retard angle control means is provided, and the torque up correction means increases and corrects the engine torque according to the estimated value by the torque down amount estimation means. What is necessary is just to be (the invention of Claim 2).

  That is, in general, the engine torque in the uniform combustion state decreases as the ignition timing is changed from the MBT to the retard side, but the torque reduction amount changes depending on the air-fuel ratio, and the torque decreases as the lean side near the stoichiometric air-fuel ratio. The amount tends to increase (see FIG. 8).

  Therefore, the air-fuel ratio in the cylinder is obtained from the estimated value of the residual air amount by the residual air amount estimating means, and the torque-down amount estimating means based on the air-fuel ratio and the retarded control amount of the ignition timing is influenced by the influence of the residual air. It is possible to accurately estimate the reduction in engine torque that occurs. By correcting the increase of the engine torque so as to cancel out the estimated torque reduction, fluctuations in the engine torque before and after the switching can be eliminated.

  More specifically, the torque-up correction unit is configured to increase the fuel injection amount for the first one combustion cycle of the cylinder after switching to the intake stroke injection mode based on the estimated value by the torque-down amount estimation unit. (The invention of claim 3) or the ignition timing retardation control amount may be corrected to decrease based on the estimated value by the torque reduction amount estimating means (invention of claim 4).

  If the engine is equipped with an electric motor capable of torque assist, the engine torque can be increased and corrected by assisting the electric motor for the first one combustion cycle after switching to the intake stroke injection mode. Is possible. In this case, a torque-up correction means is constituted by the electric motor and a controller that controls its operation.

  Further, as a specific configuration of the control device, an intake pressure detecting means for detecting an intake pressure of the engine (internal combustion engine) and a parameter value for detecting parameter values (for example, an intake flow rate and a fuel injection amount) relating to the exhaust pressure of the engine. Detection means, and the residual air amount estimation means may estimate the residual air amount in the cylinder based on the detected intake pressure and parameter values. (Invention of Claim 5) .

  In this way, after the exhaust stroke of the cylinder once flows into the intake / exhaust passage, the residual air amount in the cylinder, including the amount of air in the exhaust drawn into the cylinder again in the intake stroke, is very accurately determined. Can be estimated.

As described above, according to the control apparatus for a direct injection internal combustion engine according to the present invention, when the fuel injection mode of the engine is switched from the compression stroke injection mode (stratified combustion state) to the intake stroke injection mode (uniform combustion state). In addition, since the air amount remaining in the cylinder immediately after the switching becomes larger than the normal uniform combustion state, the air-fuel ratio shifts to the lean side, and the torque reduction occurs due to the interaction between this and the ignition retard. Paying attention to this, the amount of air remaining in the cylinder immediately after switching of the fuel injection mode is estimated, and the engine torque is increased and corrected based on at least the estimated value of the remaining air amount for only one combustion cycle immediately after switching. Since it did in this way, the fluctuation | variation of the engine torque before and after fuel injection mode switching can be eliminated, and a torque shock can be eliminated.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

(Schematic configuration of the engine)
FIG. 1 schematically shows a schematic configuration of a direct-injection gasoline engine 1 (internal combustion engine) equipped with a control device according to an embodiment of the present invention. Only a plurality of cylinders (cylinders) 2, 2,... Are arranged in series. As shown in the figure, the upper end of the cylinder 2 is opened at the upper end surface of the cylinder block 3 and is closed by the lower surface of the cylinder head 4 placed there. A piston 5 is fitted in the cylinder 2 so as to be able to reciprocate. A combustion chamber 6 is defined between the upper surface of the piston 5 and the lower surface of the cylinder head 4.

  On the other hand, a crankshaft 7 is disposed in a crankcase below the piston 5, and is connected to the piston 5 of each cylinder 2 by a connecting rod. Further, a crank angle sensor 8 for detecting the rotation angle is disposed in one end side of the crankshaft 7 in the crankcase.

  A spark plug 9 is disposed in the cylinder head 4 along the axis of each cylinder 2. The electrode at the tip of the spark plug 9 is disposed so as to face the combustion chamber 6, while the base end portion of the spark plug 9 is connected to the ignition circuit 10. The ignition circuit 10 includes an igniter and an ignition coil, and energizes the spark plug 9 at a predetermined timing for each cylinder 2 in response to a control signal from an ECU 30 described later.

  A fuel injection valve 12 is disposed at the peripheral edge of each cylinder 2, and a nozzle hole at the tip of the cylinder 2 faces the combustion chamber 6, while a base end portion of the fuel injection valve 12 is connected to a fuel supply system (not shown). ing. When the fuel injection valve 12 receives the control signal from the ECU 30 and performs the injection operation at a predetermined timing of the compression stroke of the cylinder 2, the fuel mixture sprayed from the injection port is a layer of the air-fuel mixture distributed in a layered manner around the spark plug 9 On the other hand, when the fuel injection valve 12 performs the injection operation in the intake stroke of the cylinder 2, the fuel spray diffuses into the combustion chamber 6 to form a uniform air-fuel mixture.

  Further, an intake port 13 and an exhaust port 14 are formed in the cylinder head 4 so as to open toward the combustion chamber 6 for each cylinder 2, and each port opening is opened and closed by a cam shaft (not shown). As shown, an intake valve 15 and an exhaust valve 16 are provided. One camshaft is provided on each of the intake side and the exhaust side, and the camshaft is rotated in synchronization with the crankshaft 7 by a common timing chain.

  An intake passage 17 is connected to the intake side (right side in the drawing) of the cylinder head 4 so as to communicate with the intake port 13. The intake passage 17 is for supplying intake air filtered by an air cleaner (not shown) to the combustion chamber 6 of each cylinder 2, and an electric actuator 19 is provided in a common passage upstream of the surge tank 18. A throttle valve 20 that is driven to throttle intake air is provided, and an intake manifold divided into independent passages for each cylinder 2 is provided downstream of the surge tank 18. The intake manifold is provided with an intake pressure sensor 21 for detecting an intake pressure state (manifold negative pressure).

  Further, an exhaust passage 22 for discharging burned gas from the combustion chamber 6 of each cylinder 2 is connected to the exhaust side (the left side in the figure) of the cylinder head 4 so as to communicate with the exhaust port 14. . The most upstream side of the exhaust passage 22 is constituted by an exhaust manifold comprising an independent passage for each cylinder 2, and although not shown in the exhaust passage 22 downstream of the exhaust manifold, HC, CO, NOx, etc. in the exhaust The catalyst for purifying is interposed.

  The exhaust manifold is provided with an oxygen concentration sensor 23 for detecting the oxygen concentration in the exhaust gas, and in order to circulate a part of the exhaust gas to the intake system so as to branch from the exhaust passage 22 on the upstream side. The upstream end of the EGR passage 24 is connected. The downstream end of the EGR passage 24 is connected to, for example, a surge tank 18 of the intake passage 17, and an EGR valve 25 for adjusting the exhaust gas flow rate is disposed in the vicinity thereof.

  Operation control of the engine 1 is performed by an engine control unit 30 (hereinafter referred to as ECU). That is, the ECU 30 includes at least signals from the crank angle sensor 8, the intake pressure sensor 21, and the oxygen concentration sensor 23, and a signal from the intake flow rate sensor 27 disposed in the intake passage 17 upstream of the throttle valve 20. A signal from a water temperature sensor 28 that detects the cooling water temperature of the engine 1 is input, a signal from an accelerator opening sensor 31 that detects a stepping amount (accelerator opening) of an accelerator pedal of the vehicle, and a vehicle running A signal from the vehicle speed sensor 32 that detects the speed is input, and the ignition circuit 10, the fuel injection valve 12, the throttle valve 20, the EGR valve 25, and the like are controlled in accordance with a predetermined control program in accordance with these input values.

(Outline of engine control)
Specifically, if the engine 1 according to this embodiment is warm, the fuel injection mode is largely switched to two according to the operation state, and is operated in two different combustion states. It has become. That is, first, as schematically shown in FIG. 2, the operation region defined by the load and the rotational speed of the engine 1 is a stratified combustion region on the relatively low load low rotation side and a uniform combustion region on the high load high rotation side. And two minutes.

  In the stratified combustion region, fuel is injected by the fuel injection valve 12 in the compression stroke of the cylinder 2 (compression stroke injection mode), and the air-fuel mixture distributed in a layered manner around the spark plug 9 is ignited and burned ( Hereinafter, this operation mode is referred to as a stratified combustion mode). At this time, the throttle valve 20 is opened wide so that a large amount of air is taken into the cylinder 2, so that the average air-fuel ratio of the combustion chamber 6 in the cylinder 2 is in a very lean state (for example, A / F> 30).

  On the other hand, in the uniform combustion region, fuel is injected in the intake stroke of the cylinder 2 by the fuel injection valve 12 (intake stroke injection mode), and this fuel is mixed with the intake air while diffusing, so that the combustion chamber 6 is almost uniformly mixed. After the gas is formed, it is ignited and burned (hereinafter, this operation mode is referred to as a uniform combustion mode). At this time, the fuel injection amount, the throttle opening, and the like are controlled so that the air-fuel ratio becomes substantially the stoichiometric air-fuel ratio (A / F = 14.7) except for a high load state close to the full load. In a high load state close to the full load, the air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio.

  Although not particularly shown in the figure, in the low load and medium load operation regions of the engine 1 including the stratified combustion region, the EGR valve 25 is opened and a part of the exhaust gas is recirculated to the intake passage 17 by the EGR passage 24. Thus, the heat capacity of the combustion chamber 6 can be increased, and the generation of NOx accompanying combustion can be suppressed.

  More specifically, FIG. 3 is a functional block diagram showing basic control logic of the fuel injection valve 12 and the throttle valve 20 in the ECU 30. In this embodiment, as shown in the drawing, first, based on the accelerator opening and the vehicle speed. A required torque Tr for the engine 1 is obtained. This may be read from a map in which the required torque Tr is set in advance in association with the accelerator opening and the vehicle speed, or may be obtained by a preset calculation formula. The required ISC torque is added to the required torque Tr thus determined to determine the net target load Pe.

  The required ISC torque is a control parameter for allowing fuel to be supplied even when the accelerator pedal is fully closed during the idling operation of the engine 1. The predetermined ISC torque has a predetermined value only during the idling operation. It is input, otherwise it is set to 0. Thus, if the accelerator opening and the vehicle speed are zero during idle operation, the net target load Pe corresponds to the required ISC torque, and based on this, fuel necessary for idle operation is supplied. .

  Next, the ECU 30 adds the estimated value Pf of the loss due to the mechanical loss or pumping loss of the engine 1 to the net target load Pe obtained as described above, and determines the target load Pi used for the following control. . Here, the magnitudes of the mechanical loss and the pumping loss are read from a preset table as shown in FIG. 4, and the magnitude of the mechanical loss is the operating state of the engine 1 in the example shown in the figure. Regardless of the engine water temperature, the pumping loss corresponding to the steady operating state of the engine 1 is calculated from, for example, the flow rate of the intake air and the engine speed. Is set in correspondence with the actual intake charging efficiency (actual ce) ((b) in the figure).

  Then, based on the control target load Pi and the engine speed, the ECU 30 determines the operation mode of the engine 1 from the map shown in FIG. 2, and also sets the target fuel injection amount F and the target air-fuel ratio A / F are determined respectively. That is, if the engine 1 is in the stratified combustion region on the map of FIG. 2, the ECU 30 sets the fuel injection form by the fuel injection valve 12 to the compression stroke injection mode, while setting the intake stroke injection mode in the uniform combustion region.

  Further, the target air-fuel ratio A / F is associated with the target load Pi and the engine speed in advance so that an optimum balance between the output characteristics and the exhaust properties of the engine 1 can be obtained in each of the stratified combustion mode and the uniform combustion mode. As described above, it is very lean in the stratified combustion mode, substantially the stoichiometric air-fuel ratio in most of the uniform combustion region, and further on the high load side of the uniform combustion region. It is set richer than the fuel ratio.

  Further, the target fuel injection amount F corresponds to the target load Pi and the engine speed in advance so that the engine torque corresponds to the required torque Tr in each of the stratified combustion mode and the uniform combustion mode. A small value Fa (hereinafter referred to as a required basic injection amount) is set as a map, and the target fuel injection amount F is set based on the required basic injection amount Fa read from this map.

  The map of the fuel injection amount is set in advance by taking into account the output characteristics of the engine 1 resulting from the difference in the combustion mode and the air-fuel ratio. In the compression stroke injection mode, the target fuel injection amount F is almost unchanged. The ECU 30 outputs a control signal (injection pulse) to the fuel injection valve 12 based on the target fuel injection amount Fs used for controlling the fuel injection valve 12. On the other hand, the target fuel injection amount Fh in the intake stroke injection mode is determined based on the target air-fuel ratio A / F and the actual ce with priority given to the control accuracy of the air-fuel ratio.

  Further, the ECU 30 sets the target intake charging efficiency (target ce) for each operation mode of the engine 1 based on the target fuel injection amount F (= required basic injection amount Fa) and the target air-fuel ratio A / F determined as described above. ) And the target ce is multiplied by the engine speed to determine the target intake air amount. A target throttle opening is determined based on the target intake air amount, and a control signal is output to the actuator 19 of the throttle valve 20 in accordance with the target throttle opening.

  As a result of controlling the throttle valve 20 in this manner, the actual ce and the target ce substantially coincide with each other in the steady operation state, so that the target fuel injection amount F is almost equal even in the intake stroke injection mode. Matches Fh. In addition, the ECU 30 calculates the ratio of the target ce to the actual ce (ce ratio) during the transition of the operation mode switching described below, and determines the fuel injection mode switching timing based on the ce ratio.

  As described above, the ECU 30 sets the target fuel injection amount F based on the required torque Tr to the engine 1 and the stratified combustion mode (compression stroke injection mode) according to the operating state of the engine 1. And a control unit 30b that performs switching control between the uniform combustion mode (intake stroke injection mode) and the target air-fuel ratio A / F according to the operating state of the engine 1, and the stoichiometric air-fuel ratio or smaller in the uniform combustion mode. The target air-fuel ratio setting unit 30c is set to a value on the rich side, while in the stratified combustion mode, is set to a value on the lean side that is larger than the stoichiometric air-fuel ratio, and the target fuel injection amount F and target air-fuel ratio A thus set A target throttle opening setting unit 30d that sets the target opening of the throttle valve 20 based on / F and the engine speed is provided.

  When the operating state of the engine 1 changes across two regions on the map as indicated by arrows in FIG. 2, the ECU 30 switches the fuel injection mode and changes the throttle opening, thereby changing the engine 1. The combustion mode is switched. At this time, the change in the intake air amount due to the change in the throttle opening has a relatively large response delay, while the change of the fuel injection mode responds quickly to the control signal. Considering this, the fuel injection mode is switched after the throttle valve 20 is first operated to change the intake air amount to some extent.

  In order to prevent hunting, the boundary from the stratified combustion region to the uniform combustion region (solid line) and the boundary from the uniform combustion region to the stratified combustion region (broken line) are different from each other as shown exaggeratedly in the figure. Has been. As will be described in detail later, when switching from stratified combustion to uniform combustion, the ignition timing is greatly retarded so as to cancel the sudden increase in engine torque caused by the air-fuel ratio jump. The ECU 30 includes an ignition timing control unit (retard angle control means) that controls the ignition timing.

(Switching combustion mode)
In the following, the transitional control procedure at the time of switching the combustion mode is performed, for example, as indicated by a thick arrow in FIG. 2, the operating state of the engine 1 changes from the low load side to the high load side, The case of switching to the mode will be specifically described with reference to FIGS.

  First, in the control flow shown in FIG. 5 and FIG. 6, in step S1 after the start of FIG. 5, detection signals from various sensors and switches are read, and in step S2, the engine 1 is determined from the target load Pi, the engine speed, and the like. It is determined whether or not the stratified combustion mode is set. That is, if the engine 1 is constantly in the uniform combustion region on the map of FIG. 2 or is in the process of switching from the uniform combustion region to the stratified combustion region, it is determined NO and returns (from uniform combustion and uniform combustion). Detailed description of switching to stratified combustion is omitted). On the other hand, if the engine 1 is in the stratified combustion region or is in the middle of switching from the stratified combustion region to the uniform combustion region, it is determined YES and the process proceeds to step S3.

  In step S3, it is determined whether or not the combustion mode is being switched. For example, the determination flag is turned on when the engine 1 shifts from the stratified combustion region to the uniform combustion region on the map of FIG. 2, and this flag is turned off in step S17 described later. May be determined to be in the middle of switching based on the ON state of the flag. And if determination is YES, it will progress to below-mentioned steps S9-S16, and will perform switching control of combustion mode, while if determination is NO, it will progress to steps S4-S8 and will drive engine 1 in stratified combustion mode. .

  That is, as described above with reference to the block diagram of FIG. 3, first, the target load Pi for control is determined by adding the loss (estimated value Pf) of mechanical loss or pumping loss to the net target load Pe ( In step S4), the target fuel injection amount F (= Fa) and the target air-fuel ratio A / F are determined from the target load Pi (step S5). This target fuel injection amount F is used for controlling the fuel injection valve 12 (F = Fs). Further, the target air-fuel ratio A / F is set to a lean value that is larger than the stoichiometric air-fuel ratio.

  Subsequent to step S5, the target ce is determined from the target fuel injection amount F and the target air-fuel ratio A / F (step S6), thereby determining the target intake air amount (step S7). The target throttle opening is determined based on the target intake air amount, and thereby the opening of the throttle valve 20 is controlled to be relatively large, and the injection pulse width is set based on the target fuel injection amount Fs (= F). Then, the fuel injection valve 12 is controlled to inject fuel in the compression stroke of the cylinder 2 (step S8), and then the process returns.

  Thus, in the stratified combustion mode, the fuel spray sprayed from the fuel injection valve 12 to the combustion chamber 6 in the cylinder 2 is ignited in a state of being unevenly distributed around the spark plug 9, and the average air-fuel ratio of the combustion chamber 6 Will burn well in a very lean state.

  On the other hand, in step S9, which is determined as YES in step S3, it is first determined whether or not the EGR valve 25 is fully closed. This is because it is necessary to strictly control the air-fuel ratio in order to eliminate the torque shock at the time of switching the combustion mode. For this reason, as the engine 1 shifts to the uniform combustion region (for example, the flag as in step S3). This is because the EGR valve 25 is closed. Thus, when the combustion mode is switched, the EGR valve 25 is closed at time t = t1 to t2, as shown in the time chart of FIG.

  During the period from time t1 to time t2, the determination in step S9 is NO and the process proceeds to step S4. On the other hand, if the EGR valve 25 is closed at time t2, the determination is YES and the process proceeds to step S10. In step S10, the target load Pi is determined in the same manner as in step S4, and in step S11, the target fuel injection amount F and the target air-fuel ratio A / F are determined.

  Here, the target fuel injection amount F reads the required basic injection amount Fa from the same map as in step S5, and complements the torque decrease due to transient pumping loss increase and air-fuel ratio enrichment due to combustion mode switching. Therefore, the fuel is increased and corrected by adding the corrected fuel amounts Fb and Fc (F = Fa + Fb + Fc). On the other hand, the target air-fuel ratio A / F is immediately switched to the target value (theoretical air-fuel ratio) in the uniform combustion mode if the EGR valve 25 is closed at the time t2.

  Subsequently, in step S12, the target ce is determined from the target fuel injection amount F and the target air-fuel ratio A / F as in step S6. At this time, the magnitude of the required torque Tr for the engine 1 does not change, and the corresponding target fuel injection amount F does not change, so that the target air-fuel ratio A / F in step S11 is switched to the stoichiometric air-fuel ratio. The target ce suddenly drops by a predetermined amount.

  Subsequently, in step S13, the target intake air amount is calculated based on the target ce, and based on this, the fuel injection valve 12 and the throttle valve 20 are controlled in step S14 as in step S8. As a result, the target ce suddenly decreases as described above, and the target intake air amount also decreases correspondingly. Accordingly, the opening of the throttle valve 20 is accordingly set as shown at times t2 to t3 in FIG. Only a fixed amount will drop rapidly. As a result, the actual ce of intake air in each cylinder 2 also decreases rapidly, and the actual air-fuel ratio A / F rapidly changes to the rich side.

  Therefore, in step S15 following step S14, the target ce corresponding to the stoichiometric air-fuel ratio is divided by actual ce to calculate a ratio (ce ratio) of the target ce to actual ce, and in the subsequent step S16, the ce It is determined whether the ratio is equal to or greater than a predetermined value (a value smaller than 1 and set in advance in association with the stratified combustion limit). If this determination is NO (ce ratio ≧ predetermined value), the process returns. If the ce ratio exceeds a predetermined value, the routine proceeds to steps S17 to S22 shown in FIG. 6, and the fuel injection mode is switched to the intake stroke injection mode as will be described later.

  That is, when the throttle valve 20 is closed as described above, the intake air amount decreases, and when the actual air-fuel ratio A / F approaches the target air-fuel ratio A / F (theoretical air-fuel ratio), in the compression stroke injection mode, Even if the average air-fuel ratio of the entire combustion chamber 6 is still lean, the local air-fuel ratio around the spark plug 9 becomes richer than the stoichiometric air-fuel ratio, and it is difficult to achieve good ignition and combustion. It approaches the stratified combustion limit (for example, 18 to 19 in A / F).

  Along with this, the ce ratio that is the ratio of the target ce (in this case, a value corresponding to the theoretical air-fuel ratio) to the actual ce increases as shown at times t2 to t4 in FIG. When a predetermined value (shown as R in the figure) corresponding to the combustion limit is reached (time t4), the fuel injection mode is switched to the intake stroke injection mode by the ECU 30.

  At that time, the average air-fuel ratio of the combustion chamber 6 is still leaner than the stoichiometric air-fuel ratio immediately before the fuel injection mode is switched, and the intake air amount is relatively large (ce ratio <1). After the switching of the injection mode, the target fuel injection amount Fh is determined based on the actual ce, and the fuel injection amount rapidly increases as shown in the figure (time t4), and the actual air-fuel ratio A / F is changed to the stoichiometric air-fuel ratio by a short jump. For this reason (air-fuel ratio jump), the engine torque suddenly increases and a shock occurs.

  With respect to this point, in this embodiment, the ignition timing is retarded (retarded angle correction) so as to correspond to the increase in the fuel injection amount from time t4 as shown in the figure, whereby the engine torque caused by the air-fuel ratio jump is reduced. I try to counter the surge.

(Fuel injection amount increase correction)
By the way, as described above, even if ignition retard is performed immediately after switching of the fuel injection mode to cancel the sudden increase in engine torque, it is not possible to eliminate the torque fluctuation before and after switching, and torque shock remains. . This is because when the engine 1 is switched from the stratified combustion state to the uniform combustion state, the amount of air remaining in the cylinder immediately after the switching is larger than in the normal uniform combustion state, so the air-fuel ratio A / F is the target. This is because the value slightly shifts to the lean side.

  That is, when the fuel injection mode is switched at time t4 in FIG. 7, the fuel injection control logic is switched for each cylinder 2 that reaches the fuel injection timing, and the air-fuel ratio A / F is changed to the stoichiometric air-fuel ratio. However, in the first combustion cycle for each cylinder 2 after this switching, burnt gas from stratified combustion remains, the air-fuel ratio is relatively lean, and the amount of air is large. Thus, the air-fuel ratio of the air-fuel mixture newly formed in the cylinder 2 is slightly shifted to the lean side (for example, A / F = 16) from the stoichiometric air-fuel ratio (A / F = 14.7).

  If the air-fuel ratio A / F deviates to the lean side when a large ignition retard is being performed as described above, the engine torque also decreases due to this air-fuel ratio deviation. As a result, the torque due to the ignition retard The down amount becomes too large, and if it is left as it is, the engine torque cannot be accurately adjusted before and after the switching.

  FIG. 8 shows the result of measuring the amount of decrease in engine torque due to ignition retard while gradually changing the air-fuel ratio in the vicinity of the theoretical air-fuel ratio in the uniform combustion state of the engine 1. The four graphs a to d shown are the four cases where the air-fuel ratios A / F are 14.76, 14.99, 15.42, and 16.02, respectively. In this embodiment, the fuel injection amount is fixed. Thus, the air-fuel ratio A / F is changed by changing the intake air amount.

  According to the test results shown in the figure, when the ignition timing is at a normal timing in the vicinity of MBT (in the example shown, about 25 ° CA before compression top dead center (TDC)) at any air-fuel ratio A / F, The torque is maximized, and the engine torque gradually decreases from there toward the retarded side. Further, when the ignition timing is on the more advanced side than BTDC 10 ° CA, the leaner air-fuel ratio A / F has a relatively larger engine torque, which is the leaner air-fuel ratio A / F. This is thought to be due to a decrease in pumping loss and cooling loss.

  On the other hand, when the ignition timing is retarded to the vicinity of TDC (in the example of the figure, the retarding side is approximately BTDC 10 ° CA), the engine torque is relatively larger when the air-fuel ratio A / F is rich. This is because the amount of torque reduction due to ignition retard increases due to the effect that the amount of torque reduction due to ignition retard varies with the air-fuel ratio A / F and the combustion period becomes longer as the air-fuel ratio becomes leaner. Conceivable.

  From the graph of FIG. 8, immediately after the engine 1 is switched from the stratified combustion state to the uniform combustion state near the stoichiometric air-fuel ratio, the air-fuel ratio shifts to the lean side from the target value due to the effect of air remaining in the cylinder. It can be seen that the engine torque slightly decreases due to the interaction with the ignition timing being retarded to near TDC at that time.

  In order to cancel such a decrease in engine torque, in this embodiment, as shown in the flowchart of FIG. 6 described below as a characteristic part of the present invention, the compression stroke injection mode is switched to the intake stroke injection mode. The amount of air remaining in the cylinder 2 immediately after is estimated, and the torque is increased by correcting the fuel injection amount based on the estimated value of the remaining air amount only for the first combustion cycle after the switching. This is to offset the down.

  That is, as described above, when YES is determined in step S16 of the flow of FIG. 5 and the flow proceeds to the flow of FIG. 6, first, in step S17, the fuel injection mode of the engine 1 is changed from the compression stroke injection mode to the intake stroke injection mode. In the subsequent step S18, it is determined whether or not it is the first combustion cycle after switching the injection mode. If this determination is NO and the first combustion cycle is not the first one, the routine proceeds to step S19, where the basic value of the target fuel injection amount Fh is obtained from the actual ce and the target air-fuel ratio A / F according to the normal uniform combustion state control logic, This is multiplied by various correction factors to set the target fuel injection amount Fh. In step S20, the injection pulse width is determined based on the target fuel injection amount Fh, thereby controlling the fuel injection valve 12 to inject fuel in the intake stroke of the cylinder 2, and then returning. .

  On the other hand, if the determination in step S18 is YES and the first combustion cycle after switching to the intake stroke injection mode, the process proceeds to step S21, and the residual air amount in the cylinder 2 is estimated. That is, for example, based on the combustion chamber volume of the cylinder 2 (the volume when the piston 5 is at top dead center) and the exhaust density (previously set as a map according to the operating state of the engine 1), the cylinder 2 The amount of burned gas remaining in the exhaust gas is obtained, and then the amount of exhaust gas re-intaken into the cylinder 2 from the intake / exhaust passage during the overlap period of the intake / exhaust valves 14 and 15 is determined based on the intake pressure and the exhaust pressure. Obtained and added together, the residual gas amount in the cylinder 2 is obtained. Then, the amount of air in the residual gas is obtained based on the air-fuel ratio A / F and the combustion efficiency in the stratified combustion state immediately before switching the injection mode.

  The intake pressure is detected by the intake pressure sensor 21 of the intake manifold, while the exhaust pressure is the actual fuel injection amount obtained from the intake flow rate (parameter value related to the exhaust pressure) detected by the intake flow rate sensor 27 and the injection pulse width. (Same parameter value). This estimation may be performed by reading values corresponding to the intake flow rate and the fuel injection amount F from a preset map.

  By the above-described calculation, the air remaining in the cylinder 2 including the amount of air in the exhaust gas that once flows into the intake passage 17 and the exhaust passage 22 and is again taken into the cylinder 2 during the valve overlap period. The quantity can be estimated very accurately.

  In step S22 subsequent to step S21, the basic value of the target fuel injection amount Fh is obtained from the actual ce and the target air-fuel ratio A / F as in step S19, and is multiplied by various correction coefficients to obtain the target fuel injection amount. Fh is set, but the effect of the residual air amount estimated in step S21 is reflected in this correction coefficient. That is, for example, the correlation between the air-fuel ratio A / F and ignition timing of the engine 1 and the engine torque as shown in the graph of FIG. 8 is experimentally examined in advance, and based on this, the operating state of the engine 1 and the cylinder 2 A map for determining a correction coefficient for increasing the amount of fuel from the residual air amount in the inside may be set.

  Then, after setting the target fuel injection amount Fh by using the correction coefficient read from the map and taking into account the deviation of the air-fuel ratio A / F to the lean side due to the residual air in the cylinder 2, the step S20 Then, a control signal (injection pulse) is output to the fuel injection valve 12 to control the fuel injection valve 12 to inject fuel in the intake stroke of the cylinder 2 and then return.

  That is, when the combustion state of the engine 1 is switched from stratified combustion to uniform combustion, only one combustion cycle for each cylinder 2 immediately after switching from the compression stroke injection mode to the intake stroke injection mode remains in each cylinder 2. The degree of deviation of the air-fuel ratio A / F to the lean side caused by the influence of the air that is being used is estimated, and the fuel injection amount is corrected to increase so as to offset the decrease in engine torque caused by this. .

  Step S17 in the flow of FIG. 6 corresponds to the switching control from the compression stroke injection mode to the intake stroke injection mode by the switching control unit 30b of the ECU 30, and the switching control unit 30b performs the intake control by the subsequent steps S18 and S21. Residual air amount estimation means 30e for estimating the amount of air remaining in the cylinder 2 switched to the stroke injection mode is configured.

  Specifically, the procedure of detecting the intake pressure of the engine 1 based on the signal from the intake pressure sensor 21 in the step S21 constitutes the intake pressure detecting means 30f, and similarly, the intake flow rate based on the signal from the intake flow rate sensor 27. And the procedure for obtaining the actual fuel injection amount from the fuel injection pulse width constitutes the parameter value detection means 30g for detecting the parameter value related to the exhaust pressure of the engine 1, and the residual air amount estimation means 30e includes: The residual air amount in the cylinder 2 is estimated based on the detected intake pressure and exhaust pressure.

  Further, in step S22 of the flow, based on the estimated value of the residual air amount and the retarded control amount of the ignition timing, the engine torque generated by the influence of the residual air in the cylinder 2 upon switching to the intake stroke injection mode The target fuel injection amount Fh is increased only in the first one combustion cycle for each cylinder 2 after switching the injection mode, based on the estimated torque reduction amount 30h for estimating the decrease in the amount of decrease. Torque-up correction means 30i for correction is configured.

  Therefore, according to the control apparatus for a direct injection internal combustion engine according to this embodiment, the operating state of the engine 1 changes from the low load side to the high load side as shown by a thick arrow in FIG. When the mode is switched from the stratified combustion mode to the uniform combustion mode, first, prior to the switching of the fuel injection mode (compression stroke injection mode → intake stroke injection mode), the ECU 30 shows the time t2 to t3 in FIG. In this way, the throttle valve 20 is controlled to be closed.

  When the throttle valve 20 is closed, the intake air flow rate decreases, and the actual air-fuel ratio A / F in the cylinder 2 approaches the target air-fuel ratio A / F (theoretical air-fuel ratio). Becomes the excessive stratified combustion limit (time t4), the fuel injection mode is switched to the intake stroke injection mode by the ECU 30, and the actual air-fuel ratio A / F suddenly changes (jumps) to the rich side in accordance with this switching. However, the ignition timing is significantly changed to the retarded side (ignition retard) so that the engine torque does not increase rapidly.

  In the cylinder 2 that is switched from the compression stroke injection mode to the intake stroke injection mode in this way, burnt gas due to stratified combustion remains, so the amount of residual air in the cylinder 2 is smaller than that during normal uniform combustion. It is increasing. Therefore, in the first combustion cycle after switching, the air-fuel ratio A / F of the air-fuel mixture newly formed in the cylinder 2 slightly shifts to the lean side, and the ignition timing is significantly retarded as described above. In combination with this, the engine torque will decrease slightly.

  On the other hand, in the first combustion cycle after the switching of the injection mode, the fuel injection amount is corrected to increase in accordance with the estimated value of the residual air amount in the cylinder 2 and the ignition retard amount (from time t4). Therefore, the decrease in engine torque caused by the residual air is also canceled out. Thus, the sudden increase of the engine torque due to the air-fuel ratio jump is canceled and the engine torque does not decrease due to the influence of the air remaining in the cylinder 2, so that the engine torque matches before and after the injection mode switching, and the torque The shock is resolved.

(Other embodiments)
The configuration of the present invention is not limited to the above-described embodiment, and includes other various configurations. That is, for example, in the embodiment, when the fuel injection mode of the engine 1 is switched from the compression stroke injection mode to the intake stroke injection mode, the first one combustion cycle of each cylinder 2 after the switching is the cylinder 2 Although the fuel injection amount is increased and corrected based on the residual air amount, the present invention is not limited to this. For example, the retard control amount of the ignition timing may be corrected to decrease.

  Specifically, as shown in the flow of FIG. 9 in which a part of the flow of FIG. 6 is changed, in step S22 ′, the fuel injection amount is set in the same manner as in step S19 according to the normal control logic of uniform combustion, In the subsequent step S23, a correction value for reducing and correcting the ignition retard amount is set so as to offset the decrease in engine torque due to the influence of the residual air amount. The ignition retard reduction correction value is calculated based on the correlation between the air-fuel ratio A / F, the ignition timing, and the engine torque, such as the graph shown in FIG. A map for determining the correction value from the air amount may be set. The procedure of other steps in the flow of FIG. 9 is the same as that of FIG.

  In this case, the influence of the residual air in the cylinder 2 in accordance with the switching to the intake stroke injection mode based on the estimated value of the residual air amount and the retarded control amount of the ignition timing in step S23 of the flow of FIG. Torque reduction amount estimation means 30h for estimating a decrease in engine torque caused by the above-mentioned, and based on the estimated value of the torque reduction amount, the ignition timing is applied only for the first one combustion cycle for each cylinder 2 after switching the injection mode. Torque-up correction means 30i for reducing and correcting the retard control amount.

  Alternatively, instead of correcting either the fuel injection amount or the ignition timing according to the residual air amount in the cylinder 2 as described above, both of them may be corrected. In this case, the fuel injection amount is increased and corrected so that the stoichiometric air-fuel ratio is accurately set based on the residual air amount in the cylinder 2, and the torque fluctuation can be absorbed by correcting the ignition timing.

  Further, when the engine 1 is equipped with an electric motor capable of torque assist, the electric motor can be assisted for only the first combustion cycle after switching the injection mode to increase the engine torque. In addition, it is possible to correct the engine torque by changing the driving load of an auxiliary machine such as an alternator. In this case, a torque-up correction means is constituted by the electric motor or auxiliary machine and a controller that controls the operation thereof.

The schematic structure figure of the engine provided with the control device concerning the embodiment of the present invention. The schematic diagram which shows an example of the control map for switching the operation mode of an engine. The functional block diagram which shows the basic control logic of fuel and intake control. The schematic diagram which shows an example of the table used for basic control. The flowchart figure which shows the control procedure of the first half of fuel and intake control. The flowchart figure which shows the control procedure of the latter half of fuel and intake control. The time chart which shows changes, such as EGR, throttle opening, ce ratio, fuel injection amount, ignition timing, when switching from a stratified combustion mode to a uniform combustion mode. The graph which shows the result of having measured the fall amount of the engine torque by ignition retard, changing an air fuel ratio in the vicinity of a theoretical air fuel ratio little by little in a uniform combustion state. FIG. 6 is a diagram corresponding to FIG. 6 according to another embodiment in which the ignition retard amount is corrected to decrease according to the residual air amount in the cylinder when the fuel injection mode is switched.

Explanation of symbols

1 engine (cylinder injection internal combustion engine)
2 cylinder 21 intake pressure sensor (intake pressure detection means)
27 Intake flow sensor (parameter value detection means)
30 Engine control unit (ECU)
30b Switching control unit 30e Residual air amount estimating means 30f Intake pressure detecting means 30g Parameter value detecting means 30h Torque down amount estimating means 30i Torque up correcting means

Claims (5)

A compression stroke injection mode in which fuel is injected at least in the compression stroke of the cylinder in accordance with the operating state of the internal combustion engine to make a stratified lean combustion state, and an intake stroke injection mode in which fuel is injected in the intake stroke to make a uniform rich combustion state Switching control means for performing switching control of, and
A retard control means for retarding the ignition timing so as to cancel the fluctuation of the engine torque accompanying the switching when the switching control means is switched from the compression stroke injection mode to the intake stroke injection mode. A control device for a direct injection internal combustion engine,
A residual air amount estimating means for estimating an air amount remaining in the cylinder switched from the compression stroke injection mode to the intake stroke injection mode by the switching control means;
Torque-up correction means for increasing and correcting the engine torque based on at least the residual air amount estimated by the residual air amount estimation means, corresponding to the first one combustion cycle of the cylinder after switching to the intake stroke injection mode; A control device for a direct injection internal combustion engine, comprising: The control device according to claim 1,
Along with the switching control from the compression stroke injection mode to the intake stroke injection mode by the switching control means, the decrease in engine torque caused by the influence of the residual air in the cylinder is compared with the estimated value of the residual air quantity by the residual air quantity estimation means and the delay. A torque-down amount estimating means for estimating the ignition timing based on the ignition timing retarding control amount by the angle control means,
The control apparatus for a cylinder injection internal combustion engine, wherein the torque-up correction means is for increasing and correcting the engine torque according to the estimated value by the torque-down amount estimation means. The control device according to claim 2,
The torque-up correction means corrects the fuel injection amount to be increased based on the estimated value by the torque-down amount estimation means only for the first one combustion cycle of the cylinder after switching to the intake stroke injection mode. Control device for internal injection internal combustion engine. The control device according to claim 2,
The torque up correction means corrects the ignition timing retarded control amount to be decreased and corrected only for the first one combustion cycle of the cylinder after switching to the intake stroke injection mode based on the estimated value by the torque down amount estimation means. A control apparatus for a cylinder injection internal combustion engine. In the control device according to any one of claims 1 to 4,
Intake pressure detecting means for detecting the intake pressure of the internal combustion engine;
Parameter value detecting means for detecting a parameter value related to the exhaust pressure of the internal combustion engine,
The residual air amount estimation means estimates the residual air amount in the cylinder based on the detected intake pressure and parameter value, and controls the in-cylinder injection internal combustion engine.

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