JP2004176610A - Fuel control device for cylinder injection type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel control device for a cylinder injection type internal combustion engine capable of maintaining combustion stability even to transitive increase of EGR quantity when valve overlap quantity is changed. <P>SOLUTION: This fuel control device for a cylinder injection type internal combustion engine is provided with a fuel injection valve to directly inject fuel into a combustion chamber parted by a piston, and an overlap quantity changing means to change valve overlap quantity by an intake valve to open/close the combustion chamber and an exhaust valve. In a case where the valve overlap quantity is increased to be over a prescribed threshold value (S208 and S209) during homogeneous operation by a fuel injection mode to inject fuel in an intake stroke mainly (S204), the fuel injection mode is changed (S211) by an injection mode changing means to execute a stratified combustion operation in a prescribed period. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel control device for a direct injection internal combustion engine, and more particularly, to a fuel control device for a direct injection internal combustion engine that ensures combustion stability against a transient increase in the amount of EGR.
[0002]
[Prior art]
Generally, exhaust gas recirculation (EGR) is used as a method for improving fuel efficiency and reducing NOx during partial load operation conditions of an internal combustion engine.
As a method of introducing the EGR, a method of providing a pipe and an EGR valve outside the cylinder and recirculating a part of the exhaust gas to a surge tank by opening and closing the valve (external EGR) has been generally performed. Recently, a part of the exhaust gas is recirculated by using a variable valve timing (VVT) mechanism that changes the opening / closing timing of the intake / exhaust valve and increasing the valve overlap amount in which the intake valve and the exhaust valve are both opened to some extent. (Internal EGR).
[0003]
One of the merits of the internal EGR due to the VVT is a good EGR responsiveness. The reason is that, in the external EGR, there is a response delay of the EGR in the process of introducing the EGR corresponding to the surge tank capacity or in the process of being sucked along the intake manifold and the intake port, whereas the direct exhaust is This is because there is almost no response delay in the internal EGR that is recirculated inside.
[0004]
As described above, the internal EGR has better EGR responsiveness than the external EGR, while the internal EGR has a response delay of fresh air. The reason for this is that the fresh air is dominated by the intake manifold pressure (manifold pressure), but it takes time for the manifold pressure to rise and stabilize after the valve overlap increases, and the fresh air is introduced. This is because the amount is insufficient until the manifold pressure is stabilized.
[0005]
That is, in the case of the internal EGR using the VVT, although there is a problem in the responsiveness of fresh air, the responsiveness of the EGR is good. Temporary excess. This situation causes a problem that combustion fluctuations increase and it becomes difficult to maintain combustion stability.
On the other hand, there has been proposed a technology of a direct injection internal combustion engine for maintaining combustion stability by VVT (for example, see Patent Document 1).
[0006]
In this technology, the fuel injection timing is corrected to the retard side as the valve overlap amount is increased, thereby shortening the period from fuel injection to ignition, suppressing the diffusion of fuel, and stabilizing the fuel. Performs stratified combustion operation.
[0007]
[Patent Document 1]
JP-A-11-218036 (paragraph numbers 0026 to 0027, FIG. 3 and the like)
[0008]
[Problems to be solved by the invention]
By the way, the prior art described in the above-mentioned Patent Document 1 discloses an in-cylinder injection for stabilizing combustion by delaying the fuel injection timing when the valve overlap amount increases during the stratified combustion operation in the fuel injection mode in the compression stroke. The present invention relates to an internal combustion engine.
However, the direct injection internal combustion engine performs not only the stratified combustion operation in the fuel injection mode in the compression stroke but also the homogeneous combustion operation in the fuel injection mode in the intake stroke. Here, simply delaying the fuel injection timing in the homogeneous combustion operation in the fuel injection mode in the intake stroke as in the above-described conventional technique does not not only contribute to the stability of the combustion but also worsens the combustion in some cases. is there.
[0009]
The present invention has been made in view of such a problem, and in-cylinder injection capable of maintaining combustion stability even with a transient increase in the EGR amount when the valve overlap amount is changed. It is an object of the present invention to provide a fuel control device for a type internal combustion engine.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a fuel control device for a direct injection internal combustion engine according to the present invention according to claim 1 includes a fuel injection valve that directly injects fuel into a combustion chamber defined by a piston; A fuel injection control device for an in-cylinder injection type internal combustion engine comprising: an intake valve for opening and closing the combustion chamber; and an overlap amount changing means for changing a valve overlap amount by an exhaust valve, wherein fuel is injected mainly in an intake stroke. Injection mode changing means for changing the fuel injection mode to perform the stratified combustion operation for a predetermined period when the valve overlap amount increases to a predetermined threshold or more during the homogeneous combustion operation in the fuel injection mode. It is characterized by:
[0011]
Therefore, in the fuel control device for a direct injection internal combustion engine according to the first aspect, even if the response of fresh air is delayed due to the expansion of the valve overlap amount during the homogeneous combustion operation and the EGR amount becomes excessive, the EGR amount is temporarily reduced. Since the stratified combustion operation is performed, the combustion period is not prolonged, combustion fluctuations are suppressed, and combustion stability is ensured. Further, deterioration of fuel efficiency and deterioration of exhaust performance due to an increase in unburned HC due to instability of the engine are prevented.
[0012]
In the invention according to claim 2, the injection mode changing means changes the fuel injection mode in the intake stroke to a split injection mode in which fuel is divided and injected when the operating load of the internal combustion engine is high, When the load is low, the fuel injection mode in the intake stroke is changed to the fuel injection mode in which fuel is injected mainly in the compression stroke.
[0013]
Thus, when a higher load is requested, the fuel injection mode in the intake stroke is changed to the split injection mode only during the transition period of EGR, while when a low load is requested, the compression stroke is changed only during the transition period of EGR. The fuel injection mode has been changed to all modes, and all of them perform stratified combustion operation. Therefore, even if the EGR amount is transiently increased, combustion fluctuations are suppressed and combustion stability is ensured, while accurately responding to the required load. I do.
[0014]
Furthermore, the invention according to claim 3 is characterized in that the predetermined threshold value is calculated from an operating load and a rotation speed of the internal combustion engine. As described above, the determination of the expansion of the valve overlap amount, that is, the determination of the change of the fuel injection mode is made to correspond to the operating condition of the engine, so that the fuel control according to the request of the engine becomes possible.
In the invention described in claim 4, the overlap amount changing means changes at least one of the opening / closing timing of the intake valve and the opening / closing timing of the exhaust valve. Thus, by making at least one of the intake valve and the exhaust valve variable, it is possible to cope with various types of internal combustion engines.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, there is shown a system configuration diagram applied to a fuel control apparatus for a direct injection internal combustion engine according to an embodiment of the present invention. The configuration of the fuel control device for the internal combustion engine will be described.
[0016]
The engine 1 is configured as a spark ignition type in-cylinder injection engine that directly injects fuel into a combustion chamber (not shown). That is, an injector (fuel injection valve) and a spark plug (both not shown) are disposed in the cylinder head of the engine 1 facing the combustion chamber defined by the reciprocating motion of the piston. And the exhaust passage 3 are connected. The ignition plug is connected to an ignition coil.
[0017]
In the intake passage 2, an air cleaner 4 and a throttle valve 5 are provided in order from the upstream side, and a surge tank 6 is further provided downstream.
As a result, air from the outside passes through the air cleaner 4 and flows into the combustion chamber via the throttle valve 5, the surge tank 6, and the intake passage 2. At this time, the intake air amount is detected by the air flow sensor 7. Further, a throttle position sensor (TPS) 8 is provided, and the TPS 8 detects the opening of the throttle valve 5.
[0018]
The throttle valve 5 is a so-called drive-by-wire type throttle valve (ETV) that is electrically connected to an accelerator pedal (not shown). The throttle valve 5 opens according to the engine operating state in addition to the accelerator pedal depression amount of the driver. The degree is changed.
The intake passage 2 includes an intake manifold and an intake port, and the intake port is formed in a substantially upright direction in a cylinder head for each cylinder. On the combustion chamber side of the intake port, there is provided an intake valve 12 for communicating and shutting off the intake port and the combustion chamber. The exhaust passage 3 includes an exhaust port and an exhaust manifold. The exhaust port is formed in a substantially horizontal direction in the cylinder head for each cylinder. On the combustion chamber side of the exhaust port, an exhaust valve 13 is provided for communicating and shutting off the exhaust port and the combustion chamber.
[0019]
The intake valve 12 and the exhaust valve 13 are connected to a variable valve timing mechanism (overlap amount changing means) whose opening / closing timing is made variable by hydraulic pressure adjustment. The variable valve timing mechanism has been put to practical use as a so-called VVT in which a coupling phase (VVT phase) between a camshaft and a cam sprocket rotating according to engine rotation is variable within a predetermined range, and the camshaft is advanced or retarded. By performing the angular operation, the opening / closing timing of only the intake valve, only the exhaust valve, or both the intake valve and the exhaust valve can be changed. In addition, it is also possible to change the opening / closing timing by selectively using a plurality of cams having different lift and timing characteristics according to operating conditions. The internal EGR amount increases with good response due to the expansion of the valve overlap amount by the variable valve timing mechanism.
[0020]
An ECU (electronic control unit) 10 including an input / output device, a memory (ROM, RAM, non-volatile RAM, and the like), a CPU, and the like is provided. The ECU 10 controls the overall operation of the engine 1 including fuel injection control. Control is performed.
On the input side of the ECU 10, in addition to the above-described air flow sensor 7 and TPS 8, a crank angle sensor 9 for detecting an engine rotation speed Ne based on a crank angle signal, a water temperature sensor 11 for detecting a coolant temperature of the engine 1, and a driver accelerator Various sensors such as an accelerator opening sensor (not shown) for detecting a required torque from the amount of depression are connected, and detection information from these sensors is input. Then, the operating state of the engine 1 is obtained from the outputs of these sensors, and the main operation amounts of the engine 1 such as the intake air amount, the fuel injection amount, the fuel injection timing, and the ignition timing are optimally calculated.
[0021]
On the other hand, various output devices such as a variable valve timing mechanism are connected to the output side of the ECU 10 in addition to the above-described injector and spark plug, and the fuel injection amount calculated in the ECU 10 is converted into a valve opening pulse signal. The ignition plug is then sent to the injector, and a spark plug drive signal is sent to the ignition coil based on the calculated ignition timing.
[0022]
The fuel injected from the injector is mixed with the conditioned air from the intake passage 2 to form an air-fuel mixture in the combustion chamber. The air-fuel mixture is generated by a spark generated from a spark plug at a predetermined ignition timing. And the combustion pressure drives the engine 1. Note that the exhaust gas after the explosion is sent to an exhaust purification catalytic converter (not shown) through the exhaust passage 3.
[0023]
The engine 1 performs at least a lean operation mode in which fuel injection is performed mainly in the compression stroke and a lean stratified combustion operation (stratified combustion operation) is performed in an air-fuel ratio region leaner than the stoichiometric air-fuel ratio, and a fuel injection is mainly performed in the intake stroke. A stoichiometric operation mode in which a stoichiometric feedback combustion operation (homogeneous combustion operation) is performed near the air-fuel ratio, and these operation modes are configured to be switchable. Then, in the engine 1, the ECU 10 performs operation mode switching control and various controls based on the input data from the various sensors described above.
[0024]
In particular, the ECU 10 according to the fuel control apparatus of the present embodiment has a function of changing the fuel injection mode in order to cope with a transient new air volume response delay when changing the valve overlap amount. Specifically, the ECU 10 includes an injection mode changing unit 10A. The injection mode changing unit 10A performs stratification for a predetermined period when the valve overlap amount increases to a predetermined threshold value or more during the homogeneous combustion operation. The fuel injection mode is changed to perform the combustion operation.
[0025]
The fuel injection mode is divided into a fuel injection mode in which fuel is injected mainly in the compression stroke and a fuel injection mode in which the fuel is split in the intake stroke and the compression stroke by the injection mode changing unit 10A of the present embodiment in accordance with the operation load request of the engine 1. The fuel injection mode is changed to the fuel injection mode (split injection mode) for performing the fuel injection. More specifically, the injection mode changing means changes the fuel injection mode in the intake stroke to the split injection mode when the operating load of the engine 1 is high, and changes the fuel injection mode in the intake stroke to the compression when the operating load of the engine 1 is low. Change to the fuel injection mode for the stroke.
[0026]
Accordingly, with respect to a transient increase in the internal EGR amount due to an increase in the valve overlap amount, the split injection mode or the split injection mode that corresponds to the required load while ensuring combustion stability by suppressing combustion fluctuations by the stratified combustion operation. The fuel injection in the fuel injection mode in the compression stroke for shortening the combustion period is performed so as to accurately correspond to the request of the engine 1.
Hereinafter, the operation of the fuel control device according to the present invention will be described based on a flowchart.
[0027]
FIG. 2 shows a flowchart of the fuel injection mode change determination control performed by the fuel control device.
In step S201 of FIG. 5, the engine rotation speed Ne is captured. In step S202, the operating load L is captured. In step S203, the target VVT phase of the intake valve and the exhaust valve is determined from the engine rotation speed Ne and the operating load L. The control proceeds to step S204.
[0028]
In step S204, it is determined whether or not the current fuel injection mode is the fuel injection mode in the intake stroke. If it is determined that the fuel injection mode is the homogeneous combustion operation as the fuel injection mode in the intake stroke, that is, if YES, step S205 is performed. To fetch the current VVT phase and go to step S206. On the other hand, when it is determined in step S204 that the operation is not the homogeneous combustion operation, the process exits this routine.
[0029]
In step S206, the actual valve overlap amount RVOL is calculated from the current VVT phase in step S205, and in step S207, it is determined whether the fuel injection mode needs to be changed based on the engine speed Ne and the operating load L. The valve overlap amount (predetermined threshold value) HVOL to be used is determined, and the process proceeds to step S208.
[0030]
In step S208, it is determined whether the previous actual valve overlap amount RVOL is smaller than a predetermined threshold value HVOL, and it is determined that the previous actual valve overlap amount RVOL is smaller than a predetermined threshold value HVOL. If this is the case, that is, if YES, the process proceeds to step S209. On the other hand, if it is determined that the previous actual valve overlap amount RVOL is equal to or greater than the predetermined threshold value HVOL, the routine exits.
[0031]
In step S209, it is determined whether or not the current actual valve overlap amount RVOL is equal to or greater than a predetermined threshold value HVOL, and it is determined that the current actual valve overlap amount RVOL is equal to or greater than the predetermined threshold value HVOL. If this is the case, that is, if YES, the process proceeds to step S210, and if it is determined that the current actual valve overlap amount RVOL is less than the predetermined threshold value HVOL, the routine exits. That is, the previous actual valve overlap amount and the present actual valve overlap amount are respectively compared with the predetermined threshold value HVOL, and when the current actual valve overlap amount exceeds the predetermined threshold value HVOL for the first time, Since there is a possibility that the amount of EGR transiently increases, the process proceeds to step S210.
[0032]
In step S210, the mode change execution timer ABTIMER is set from the fuel injection mode in the intake stroke for performing the homogeneous combustion operation to the split injection mode or the fuel injection mode for the compression stroke in which the stratified combustion operation is performed by increasing the valve overlap amount. To step S211 to exit this routine.
FIG. 3 is a flowchart of the fuel injection mode change control performed by the injection mode changing unit 10A of the fuel control device as in step S211 of FIG.
[0033]
In step S301 of the figure, the engine speed Ne and the operating load L are fetched, and the process proceeds to step S302.
In step S302, it is determined whether or not the mode change execution timer ABTIMER is larger than 0. If it is determined that the mode change execution timer ABTIMER is larger than 0, that is, if YES, the process proceeds to step S303 to execute the mode change execution. Subtract 1 from the timer ABTIMER and proceed to step S304.
[0034]
On the other hand, if it is determined in step S302 that the mode change execution timer ABTIMER is equal to or less than 0, the timer has not been set, and therefore, a step is taken in order to perform normal homogeneous combustion operation, which is the current fuel injection mode. Proceeding to S307, the fuel injection mode of the intake stroke is performed, and the routine exits.
In step S304, it is determined whether or not the operating load L is larger than a predetermined value. If it is determined that the operating load L is larger than the predetermined value, that is, if YES, the process proceeds to step S305 to perform the stratified combustion operation. The parameters for the split injection mode are determined in order to execute the split injection mode in step S308. This mode corresponds to a medium load.
[0035]
On the other hand, when it is determined in step S304 that the operating load L is equal to or smaller than the predetermined value, the process proceeds to step S306, in which a parameter for the fuel injection mode of the compression stroke is determined so as to perform the stratified combustion operation. Execute the fuel injection mode. This mode corresponds to a low load condition.
FIG. 4 shows a timing chart when the fuel injection mode change control (step S211) is performed in the injection mode changing unit 10A.
[0036]
As shown in the figure, during the homogeneous combustion operation Sto in the fuel injection mode in the intake stroke, the closing timing EC of the exhaust valve 13 is changed to the retard side, and the opening timing IO of the intake valve 12 is changed to the advance side. Then, the valve overlap amount RVOL increases. Then, the EGR rate increases with an increase in the EGR amount, and then the manifold pressure increases to the positive pressure side.
However, since there is a response delay of fresh air in the internal EGR, the rate of increase of the manifold pressure becomes slower than the rate of increase of the EGR rate, and as a result, the EGR rate overshoots.
[0037]
Therefore, when the injection mode changing means of the fuel control device 10A determines that the actual valve overlap amount RVOL has increased to a predetermined threshold or more during the homogeneous combustion operation Sto as described above, the EGR rate starts from the time when the EGR rate rises. In contrast to the prior art in which the homogeneous combustion operation indicated by the dotted line in the figure is continued until the rate overshoots toward the equilibrium state, that is, for a predetermined period t until the timer ABTIMER becomes 0, the solid line in the figure indicates In this embodiment, the fuel injection mode is changed to perform the stratified combustion operation lean. Then, after the elapse of the predetermined time t, the overshoot of the EGR rate subsides, and the operation is changed to the homogeneous combustion operation Sto again. Also, it can be seen that the torque fluctuation is smaller in the present embodiment shown by the solid line in the figure than in the conventional technique shown by the dotted line in the figure.
[0038]
As described above, in the present invention, the injection mode changing means temporarily performs the stratified combustion operation lean even when the response of fresh air is delayed due to the expansion of the actual valve overlap amount RVOL during the homogeneous combustion operation Sto. Also, the combustion period is not prolonged even when the EGR amount is transiently increased, and combustion fluctuation can be suppressed to ensure combustion stability.
In addition, in the fuel injection mode in the intake stroke, the fuel injection timing is not simply delayed, but the stratified combustion operation Lean is performed. Therefore, it is possible to prevent deterioration in fuel efficiency and deterioration in exhaust performance due to an increase in unburned HC. .
[0039]
Furthermore, since the split injection mode or the fuel injection mode of the compression stroke is performed according to the operating load L, it is possible to accurately correspond to the request of the engine 1.
The description of one embodiment of the present invention is finished above, but the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention.
[0040]
For example, in the above embodiment, the injection mode changing unit performs the fuel injection mode by dividing the intake stroke and the compression stroke twice as the split injection mode. However, the present invention is not limited to this embodiment. A continuous split injection mode in the stroke or a multiple split injection of two or more times may be used. In these cases, the effect that the load required by the engine 1 can be further satisfied is achieved.
[0041]
Further, in the above embodiment, the overlap amount changing means changes both the opening and closing timings of the intake valve 12 and the exhaust valve 13. However, in addition to this embodiment, the overlap amount changing unit may adjust the opening and closing timing of the intake valve or the opening and closing timing of the exhaust valve. Either one may be variable, and in this case, it is possible to cope with various types of engines.
Furthermore, although the engine 1 of the above embodiment uses the internal EGR, the engine 1 may use an internal EGR and an external EGR together.
[0042]
【The invention's effect】
As can be understood from the above description, according to the fuel control apparatus for a direct injection internal combustion engine of the present invention described in claim 1, the response of fresh air is delayed due to the expansion of the valve overlap amount during the homogeneous combustion operation. Also temporarily performs the stratified combustion operation, so that the combustion period does not become longer due to the transient increase in the EGR amount, the combustion fluctuation can be suppressed, the combustion stability can be ensured, and the engine becomes unstable. Therefore, it is possible to prevent deterioration of fuel efficiency and deterioration of exhaust performance due to an increase in unburned HC resulting from the above.
[0043]
According to the second aspect of the present invention, when a higher load is required, the fuel injection mode in the intake stroke is changed to the split injection mode only during the transition period of EGR, while when a low load is required. The fuel injection mode is changed to the compression stroke only during the transition period of EGR, and the stratified combustion operation is performed in each case. Therefore, even when the EGR amount is transiently increased, the combustion fluctuation is suppressed and the combustion stability is ensured. In addition, it is possible to appropriately cope with a required load.
[0044]
According to the third aspect of the present invention, the determination of the expansion of the valve overlap amount, that is, the determination of the change of the fuel injection mode is made to correspond to the operating condition of the engine, so that the fuel control according to the request of the engine can be performed. .
According to the fourth aspect of the present invention, by making at least one of the intake valve and the exhaust valve variable, it is possible to cope with various types of internal combustion engines.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram applied to a fuel control device for a direct injection internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a control routine for fuel injection mode change determination executed by the fuel control device of FIG. 1;
FIG. 3 is a flowchart illustrating a control routine for changing a fuel injection mode performed by the fuel control device of FIG. 1;
FIG. 4 is a time chart when the fuel injection mode change control is performed in the fuel control device of FIG. 1;
[Explanation of symbols]
1 In-cylinder injection type internal combustion engine 7 Air flow sensor 8 TPS
9 Crank angle sensor 10 ECU (electronic control unit)
10A Injection mode changing unit (injection mode changing means)
11 Water temperature sensor 12 Intake valve 13 Exhaust valve

Claims (4)

A fuel injection valve for directly injecting fuel into a combustion chamber defined by a piston; and an overlap amount changing means for changing a valve overlap amount by an intake valve and an exhaust valve for opening and closing the combustion chamber. In a fuel control device of a direct injection internal combustion engine,
During the homogeneous combustion operation mainly in the fuel injection mode in which fuel is injected in the intake stroke, when the valve overlap amount increases to a predetermined threshold value or more, the fuel injection mode is set to perform the stratified combustion operation for a predetermined period. A fuel control apparatus for a direct injection internal combustion engine, comprising: an injection mode changing means for changing. The injection mode changing means changes the fuel injection mode in the intake stroke to a split injection mode in which fuel is divided and injected when the operating load of the internal combustion engine is high, and the fuel injection mode in the intake stroke when the operating load is low. 2. The fuel control system for a direct injection type internal combustion engine according to claim 1, wherein the mode is changed to a fuel injection mode for injecting fuel mainly in a compression stroke. 3. The fuel control device for a direct injection internal combustion engine according to claim 1, wherein the predetermined threshold value is calculated from an operation load and a rotation speed of the internal combustion engine. The in-cylinder injection type according to any one of claims 1 to 3, wherein the overlap amount changing means changes at least one of opening / closing timing of the intake valve and opening / closing timing of the exhaust valve. Fuel control device for internal combustion engine.

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