JP4388258B2 - Control device for direct-injection spark ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a direct-injection spark-ignition engine, and more particularly to control at the time of combustion mode switching in an engine that switches the combustion mode according to an operating state.
[0002]
[Prior art]
In recent years, direct-injection spark ignition engines that perform stratified combustion by injecting and supplying fuel directly into the combustion chamber of the engine have been adopted for the purpose of improving fuel efficiency and exhaust gas purification performance.
In the direct-injection spark-ignition engine, the fuel is divided into an intake stroke and a compression stroke and injected in order to promote the temperature increase activation of the exhaust purification catalyst. There is an engine in which an air-fuel mixture richer than the fuel ratio is formed and stratified combustion is performed. In stratified combustion (hereinafter referred to as split injection stratified combustion) in which the fuel injection is divided into a plurality of times, the average air-fuel ratio in the combustion chamber may be close to the stoichiometric range, but the most efficient is achieved particularly when λ = 1.1. The catalyst can be activated well (see JP-A-11-36919).
[0003]
[Problems to be solved by the invention]
By the way, when switching from the catalyst activation request to the split stratified combustion after startup, the air-fuel ratio is feedback controlled so that the average air-fuel ratio of the entire combustion chamber matches the target air-fuel ratio. Thus, the air-fuel ratio feedback control is started from a state where the air-fuel ratio is rich.
[0004]
However, since split injection stratified combustion has a narrow air-fuel ratio range in which stability can be ensured compared to homogeneous combustion, if the degree of rich at the start of air-fuel ratio feedback control is large, it is not possible to shift to stable split injection stratified combustion. .
After the air-fuel ratio feedback control, it may be judged that the stability can be secured when the detected value of the air-fuel ratio sensor reverses lean, but the stability can be secured by passing the stability limit on the rich side before the lean inversion. The judgment timing is delayed even though the air-fuel ratio region is entered, and the demand for warming up the catalyst by starting split injection stratified combustion as soon as possible after starting cannot be satisfied. In particular, when the average air-fuel ratio of the split injection stratified combustion is made lean, it takes more time to start the split injection stratified combustion when the air-fuel ratio reaches the target lean air-fuel ratio.
[0005]
When starting split injection stratified combustion, the control of closing the swirl control valve to improve the generation of the stratified mixture and the length of the divided injection period to extend the fuel injection valve open period-linearity of the injection amount In order to ensure, control to reduce the fuel pressure may be performed. Therefore, simultaneously with the start of the air-fuel ratio feedback control, these controls are started, and after completion of the control, further, the ignition timing retarding control for absorbing the torque step at the time of switching from homogeneous combustion to split injection stratified combustion is completed, and then split injection stratified combustion is performed If switching is performed, the air-fuel ratio may be in the stable region, but if the richness at the time of starting the air-fuel ratio feedback control is large, the stability may not be ensured even after the control is completed.
[0006]
The present invention has been made paying attention to such a conventional problem, and an object thereof is to enable switching from homogeneous combustion to split injection stratified combustion while ensuring stability.
[0007]
[Means for Solving the Problems]
Therefore, according to the present invention, at the time of switching from homogeneous combustion in which the air-fuel ratio is set rich to the target split injection stratified combustion in consideration of startability, first, air-fuel ratio feedback control in homogeneous combustion is started. And larger than the period of control required for the start of split injection stratified combustion, In addition, even if there is a rich shift at the start of feedback control, the subsequent feedback control ensures that the air-fuel ratio range is such that combustion is stably performed at the start of split injection stratified combustion. After the set delay period has elapsed, ignition timing retardation control for absorbing a torque step during combustion switching is started. Further, after completion of the ignition timing retardation control, the combustion is switched to split injection stratified combustion.
[0008]
In this way, even when the rich degree at the start of air-fuel ratio feedback control in homogeneous combustion is the largest, at the start of split injection stratified combustion, it can be reliably converged in the air-fuel ratio region where stability can be ensured, Therefore, stable operation can be switched to ensure good operability.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
In FIG. 1 showing a system configuration of an embodiment of the present invention, an intake passage 2 of an engine 1 is provided with an air flow meter 3 for detecting an intake air flow rate Qa and a throttle valve 4 for controlling the intake air flow rate Qa. A fuel injection valve 5 is provided facing the combustion chamber.
[0010]
The fuel in the fuel tank 21 is sucked by the electric low-pressure fuel pump 22, and the low-pressure fuel discharged from the low-pressure fuel pump 22 is supplied to the high-pressure fuel pump 24 driven by the engine through the fuel filter 23. .
The fuel supply pressure to the high-pressure fuel pump 24 by the low-pressure fuel pump 22 is adjusted to a predetermined low pressure by a low-pressure pressure regulator 26 interposed in a return passage 25 returning from the upstream side of the high-pressure fuel pump 24 to the fuel tank 21. The
[0011]
The low pressure regulator 26 adjusts the fuel pressure to a predetermined low pressure by opening the return passage 25 and returning the fuel to the fuel tank 21 when the fuel pressure is higher than a target low pressure.
On the other hand, the fuel pressure discharged from the high-pressure fuel pump 24 and supplied to the fuel injection valve 5 is adjusted to a predetermined high pressure by the high-pressure pressure regulator 27.
[0012]
The high pressure regulator 27 continuously changes the opening area of the passage 28 for returning the fuel on the downstream side of the high pressure fuel pump 24 to the low pressure side in response to a control signal from the control unit 50 described later. The control unit 50 outputs the control signal to the high pressure regulator 27 so that the fuel pressure detected by the fuel pressure sensor 29 (fuel supply pressure to the fuel injection valve 5) becomes a target high pressure.
[0013]
The fuel injection valve 5 is driven to open by a drive pulse signal set in the control unit 50 so that the fuel controlled to a predetermined pressure by the high-pressure pressure regulator 27 can be directly injected into the combustion chamber. It has become.
A swirl control valve 30 is attached to the intake port. During stratified combustion, the swirl control valve 30 is closed to generate swirl in the combustion chamber, thereby generating a stratified mixture.
[0014]
An ignition plug (ignition plug) 6 that is mounted facing the combustion chamber and ignites the intake air mixture based on an ignition signal from the control unit 50 is provided in each cylinder.
On the other hand, in the exhaust passage 7, an air-fuel ratio sensor 8 (an oxygen sensor that performs rich / lean output) detects the air-fuel ratio of the exhaust gas mixture by detecting the concentration of a specific component (for example, oxygen) in the exhaust gas. Or a wide area air-fuel ratio sensor that linearly detects the air-fuel ratio over a wide area), and an exhaust purification catalyst 9 for purifying exhaust gas is provided downstream thereof. Has been. The exhaust purification catalyst 9 performs the oxidation of CO and HC in the exhaust gas and the reduction of NOx in the vicinity of stoichiometric, that is, the theoretical air-fuel ratio {λ = 1, A / F (air weight / fuel weight) · 14.7}. A three-way catalyst that can purify the exhaust gas, an oxidation catalyst that oxidizes CO and HC in the exhaust gas, or a three-way function in the vicinity of the theoretical air-fuel ratio, traps NOx in the exhaust gas at a lean air-fuel ratio. A NOx trap catalyst that reduces and releases NOx trapped when the stoichiometric or rich air-fuel ratio is reached can be used.
[0015]
Further, a downstream oxygen sensor 10 that detects the concentration of a specific component (for example, oxygen) in the exhaust and outputs a rich lean gas is provided on the exhaust downstream side of the exhaust purification catalyst 9.
Here, in order to suppress a control error associated with deterioration of the air-fuel ratio sensor 8 or the like by correcting the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 8 based on the detection value of the downstream oxygen sensor 10. Although the downstream oxygen sensor 10 is provided (in order to adopt a so-called double air-fuel ratio sensor system), when the air-fuel ratio feedback control based on the detected value of the air-fuel ratio sensor 8 only needs to be performed, The downstream oxygen sensor 10 can be omitted.
[0016]
By the way, the air-fuel ratio sensor 8 is provided on the exhaust upstream side of the exhaust purification catalyst 9 and has a small heat capacity. Therefore, the activation rate is extremely fast compared to the exhaust purification catalyst 9. Further, the air-fuel ratio sensor 8 can be forcibly heated (activated) by an electric heater or the like.
Therefore, in the present embodiment, the air-fuel ratio sensor 8 is activated immediately after the start and the stoichiometric control in the homogeneous combustion is performed for a predetermined delay time, and then the split injection in the stratified stoichiometric combustion described later is performed. Although switching to stratified lean combustion is performed, not only stoichiometric control in homogeneous combustion, but also feedback control can be performed based on the detection value of the air-fuel ratio sensor 8 so that the air-fuel ratio of the entire combustion chamber becomes stoichiometric during stratified stoichiometric combustion. it can.
[0017]
Further, a crank angle sensor 11 is provided, and the control unit 50 counts a crank unit angle signal output from the crank angle sensor 11 in synchronization with the engine rotation for a certain period of time or outputs a crank reference angle signal. The engine speed Ne can be detected by measuring the cycle.
A water temperature sensor 12 that is provided facing the cooling jacket of the engine 1 and detects the cooling water temperature Tw in the cooling jacket is provided.
[0018]
Further, a throttle sensor 13 (which can also function as an idle switch) for detecting the opening degree of the throttle valve 4 is provided, and the opening degree of the throttle valve 4 is controlled by an actuator such as a DC motor. A throttle valve control device 14 is provided.
The throttle valve control device 14 electronically controls the opening degree of the throttle valve 4 based on the drive signal from the control unit 50 so that the required torque calculated based on the driver's accelerator pedal operation amount and the like can be achieved. Can be configured.
[0019]
Detection signals from the various sensors are input to a control unit 50 including a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like. The opening of the throttle valve 4 is controlled via the throttle valve control device 14 in accordance with the operating state detected based on the signals from the sensors, and the fuel injection valve 5 is driven to drive the fuel injection amount (fuel The amount of supply) is controlled, the ignition timing is set, and the ignition plug 6 is ignited at the ignition timing.
[0020]
Note that, for example, stratified combustion may be performed by injecting fuel into the combustion chamber in a compression stroke in a predetermined operation state (low / medium load region, etc.) and forming a combustible air-fuel mixture layered around the spark plug 6 in the combustion chamber. On the other hand, in other operating conditions (high load region, etc.), fuel can be injected into the combustion chamber during the intake stroke, so that an air-fuel mixture with a substantially uniform mixing ratio can be formed in the entire cylinder to perform homogeneous combustion. The fuel injection timing (injection timing) can also be changed according to the operating state.
[0021]
The control unit 50 controls the key switch so that the exhaust purification catalyst 9 can be activated early while suppressing the discharge of HC into the atmosphere from the start to the activation of the exhaust purification catalyst 9. In response to input signals from various sensors such as 16, the following control is performed.
Specifically, for example, flowcharts as shown in FIGS. 2 and 3 are executed. FIG. 9 shows how each part changes during the control.
[0022]
In step (denoted as S in the figure, the same applies hereinafter) 1, whether or not the ignition signal of the key switch 16 is turned ON (whether the key position is set to the ignition ON position) is determined by a method similar to the prior art. To do. If YES, the process proceeds to Step 2, and if NO, this flow ends.
In step 2, it is determined whether or not the start signal of the key switch 16 is turned ON (whether or not the key position is set to the start position) by a method similar to the conventional technique. That is, it is determined whether or not there is a cranking request by a starter motor (not shown).
[0023]
If YES, it is determined that there is a start cranking request, and the process proceeds to step 3. If NO, it is determined that there is no cranking request yet, and the process returns to step 1.
In step 3, the starter motor is started and the engine 1 is cranked as in the prior art.
In step 4, as in the prior art, fuel injection for start-up (direct fuel injection in the intake stroke, see FIG. 4B) is performed to operate the engine 1 (direct injection homogeneous combustion). Here, the air-fuel ratio is set to be rich in consideration of startability.
[0024]
In the next step 5, it is determined whether or not the exhaust purification catalyst 9 is not activated. The determination can be made by detecting the temperature of the catalyst 9 by providing a sensor, or by estimating the temperature of the catalyst 9 from the operation history of the engine.
If the catalyst is not activated (if YES), go to step 6.
On the other hand, if the catalyst has already been activated, such as during a hot restart (if NO), it is determined that there is no need for control to promote catalyst activation, and the process proceeds to step 15 to improve the fuel consumption. Thus, combustion is performed in the same manner as in the prior art, ignition timing control corresponding to the combustion is performed, and this flow is finished.
[0025]
In step 6, it is determined whether the air-fuel ratio feedback control condition is satisfied. If the air-fuel ratio feedback control condition is not satisfied, the routine returns to step 4 where the homogeneous combustion with rich air-fuel ratio is continued.
If it is determined in step 6 that the air-fuel ratio feedback control condition is satisfied, the air-fuel ratio feedback control is started with the air-fuel ratio in stoichiometric combustion as the stoichiometric (theoretical air-fuel ratio), and the stability to the stratified stoichiometric combustion is continued. In order to perform the switching, the delay time of the air-fuel ratio feedback control is set in step 7.
[0026]
That is, as shown in FIG. 5, the air-fuel ratio range in which combustion is stabilized by stratified stoichiometric combustion is narrower than that of homogeneous combustion, and from the stoichiometric rich air-fuel ratio in homogeneous combustion when the air-fuel ratio feedback control condition is satisfied. Considering the case where the deviation is the largest, it is necessary to carry out the stoichiometric control in the homogeneous combustion continuously for a predetermined time or more and switch to the stratified stoichiometric combustion after the air-fuel ratio range in which the combustion is stabilized by the stratified stoichiometric combustion. . When switching to stratified stoichiometric combustion outside the air-fuel ratio range, even if the fuel injection amount is controlled to stoichiometric, the wall flow rate in rich homogeneous combustion before switching is large, so the actual air-fuel ratio becomes rich. And stable combustion cannot be obtained. Actually, since switching to stratified stoichiometric combustion is performed after completion of the closing of the swirl control valve 30, there is a valve closing delay time, and further, ignition timing delay control for subsequent torque absorption is performed. In addition, there may be an air-fuel ratio range where stable stratified stoichiometric combustion can be obtained, but when the deviation from the stoichiometric rich air-fuel ratio in homogeneous combustion when the air-fuel ratio feedback control condition is satisfied is the largest, Since it takes more time to complete the valve closing delay time and ignition timing retardation control to enter the air-fuel ratio range, an additional delay time is set so as to surely enter the air-fuel ratio range. When fuel is divided and injected during stratified stoichiometric combustion, the divided injection times may be shortened, and the linearity between the fuel injection valve opening time and the fuel injection amount may be reduced. For this reason, the fuel pressure may be decreased before the start of stratified stoichiometric combustion, and the divided injection times may be increased to ensure linearity (see the lowermost part of FIG. 9). Then, since the air-fuel ratio range in which stable stratified stoichiometric combustion is obtained may not be entered, an additional delay time is set so as to surely enter the air-fuel ratio range.
[0027]
In step 8, it is determined whether or not the stratified stoichiometric combustion permission condition is satisfied. Specifically, stratified stoichiometric combustion is permitted when the following conditions are both satisfied.
(1) The air-fuel ratio sensor 8 is activated (it may be replaced when a predetermined time has passed since the complete explosion).
[0028]
(2) The idle switch is ON.
(3) Above Step 7 The swirl control valve 30 is driven to close after the delay time set in step e has elapsed, and the valve closing completion time has elapsed. When the fuel pressure reduction control is also performed after the delay time has elapsed, the later of the closing of the swirl control valve 30 and the completion of the fuel pressure reduction control has elapsed.
[0029]
When it is determined that the stratified stoichiometric permission condition is satisfied, good ignitability, combustibility, and engine stability (engine driving performance) can be obtained even when stratified stoichiometric combustion is performed. , Step 9 Proceed to
On the other hand, in the case of NO, if the stratified stoichiometric combustion and the subsequent split injection stratified lean combustion are performed, the combustion stability and the engine stability (engine operability) may be lowered. Return to step 4 in order to prohibit the transition to stoichiometric combustion and continue the direct fuel injection (direct injection homogeneous combustion) in the intake stroke.
[0030]
When the stratified stoichiometric combustion permission condition is satisfied and the routine proceeds to step 9, fuel injection is performed in step 10 while performing ignition timing control to absorb the torque step corresponding to the switching from the homogeneous combustion to the stratified stoichiometric combustion. The stratified stoichiometric combustion is performed by dividing into an intake stroke and a compression stroke. In the stratified stoichiometric combustion, a stratified mixture that is richer than stoichiometric around the spark plug and leaner than stoichiometric is generated outside, and combustion is performed while the average air-fuel ratio in the combustion chamber is controlled to be substantially stoichiometric.
[0031]
In this way, after transiently switching to stratified stoichiometric combustion, the average air-fuel ratio of the entire combustion chamber is switched to split injection stratified lean combustion in which the average air-fuel ratio of the entire combustion chamber is made leaner than stratified stoichiometric combustion. Also in this case, the ignition timing control for absorbing the torque step due to the combustion switching is performed in step 11, while the combustion is switched by switching the air-fuel ratio (division ratio) in step 12, and after the switching, the divided injection stratification is performed in step 13. With lean combustion, the catalyst activation can be promoted most efficiently, and the angle is gradually retarded to near the retarded stability limit with good fuel efficiency.
[0032]
Then, while performing the maximally efficient split injection stratified lean combustion, it is determined again in step 14 whether or not the exhaust purification catalyst 9 is activated, and the divided injection stratification is performed until it is determined that the catalyst is activated. After it is determined that the lean combustion is continued and activated, in step 15, the ignition timing control for absorbing the torque step is performed, and in step 15, the combustion is switched to normal combustion by one fuel injection.
[0033]
FIG. 6 is a subroutine showing the control at the time of switching from the homogeneous stoichiometric combustion to the split injection stratified combustion.
When switching from homogeneous combustion to stratified stoichiometric combustion, which is a transient split injection stratified combustion, it is necessary to compensate for an increase in torque in order to eliminate the torque drop when switching to stratified stoichiometric combustion with low thermal efficiency. The ignition timing is controlled to MBT (maximum torque generation ignition timing) so that a predetermined fuel consumption (or engine stability) can be achieved. There is no.
[0034]
Therefore, first, in step 111, the ignition timing is gradually delayed to the target retarded ignition timing set near the retarded-side stability limit in homogeneous combustion until a lead angle allowing correction of torque increase at the time of combustion switching is secured. Corner correction is performed (FIG. 7 [A] → [B]).
When it is determined in step 112 that the target retarded ignition timing has been reached, the routine proceeds to step 113 where the combustion is switched from homogeneous combustion to stratified stoichiometric combustion. Specifically, the fuel injection from the fuel injection valve 5 is switched from intake stroke injection to intake stroke injection and compression stroke injection (split injection) to switch to stratified stoichiometric combustion. Further, simultaneously with the combustion switching, the total retardation correction amount from the start of the retardation correction is set to 0, and the ignition timing is returned to the MBT before the start of the retardation correction (FIG. 7 [B] → [C]). That is, by correcting the total retardation correction amount in the advance direction at once, occurrence of a torque step (a in FIG. 7) at the time of switching from homogeneous stoichiometric combustion to stratified stoichiometric combustion is eliminated. Thereby, stable drivability can be ensured.
[0035]
In step 114 and subsequent steps, switching from the transient stratified stoichiometric combustion to split injection stratified lean combustion in which the average air-fuel ratio in the combustion chamber, which is the final target, is leaner than the stoichiometric, is about λ = 1.1.
When comparing stratified stoichiometric combustion with stratified lean combustion, stratified lean combustion has a lower torque (so that it cannot be switched from homogeneous stoichiometric combustion to stratified lean combustion at a stretch). As with switching to stoichiometric combustion, the target retarded ignition timing is set near the retarded-side stability limit in stratified stoichiometric combustion until the advance angle that allows torque increase correction during combustion switching is secured. Correction is performed so that the angle is gradually retarded (FIG. 7 [C] → [D]).
[0036]
When it is determined at step 115 that the target retarded ignition timing has been reached, the routine proceeds to step 116 where the combustion is switched from stratified stoichiometric combustion to split injection stratified lean combustion. Specifically, the average air-fuel ratio is made lean (thus, the torque is smaller than that of stratified stoichiometric combustion), but the intake stroke injection amount is reduced and the injection ratio (split ratio) of the compression stroke injection amount is relatively increased. As a result, the exhaust gas oxygen concentration is increased while the HC emission amount is substantially constant, so that the catalytic activity effect can be maximized. Here, as shown in FIG. 8, the air-fuel ratio of the air-fuel mixture around the spark plug formed by the compression stroke injection is reduced even when the average air-fuel ratio is made lean as shown in FIG. This is to ensure a predetermined rich state and obtain good stratified lean combustion.
[0037]
Further, simultaneously with the combustion switching, the total retardation correction amount from the start of the retardation correction is set to 0, and the ignition timing is returned to the MBT before the start of the retardation correction (FIG. 7 [D] → [E]). That is, in this case as well, by correcting the total retardation correction amount in the advance direction at once, the occurrence of a torque step (b in FIG. 7) at the time of switching from stratified stoichiometric combustion to split injection stratified lean combustion is eliminated. And stable driving performance can be secured.
[0038]
After that, the routine proceeds to step 117, where control is performed to gradually retard the optimum target ignition timing that can most promote catalyst activation in split injection stratified lean combustion (FIG. 7 [E] → [F]). The target ignition timing in the split injection stratified lean combustion is in the vicinity of the retard side stability limit. This is because the exhaust temperature can be raised to the maximum by retarding while ensuring stability.
[0039]
In this way, it is possible to maximize the acceleration of catalyst activation while eliminating the torque step at the switching transition from homogeneous starting combustion to stratified stoichiometric combustion and stratified stoichiometric combustion to split injection stratified lean combustion. Can do.
In addition, as an arrangement according to the present invention, by providing an additional delay time, control necessary for starting stratified stoichiometric combustion after starting air-fuel ratio feedback control in homogeneous combustion (closing control of swirl control valve or reduction of fuel pressure) Since the ignition timing delay control for absorbing the torque difference at the time of combustion switching is started after the delay period set larger than the control) period has elapsed, and the ignition timing delay control is completed, the engine is switched to stratified stoichiometric combustion. The stratified stoichiometric combustion can be started in the air-fuel ratio region where the stability is ensured, and stable combustion switching can be performed.
[0040]
In this embodiment, the split ratio of split injection is kept constant in stratified stoichiometric combustion, and the intake stroke injection amount is reduced by a predetermined amount and the split ratio is switched at a stroke in stratified lean combustion. As shown in Fig. 4, the air-fuel ratio is made leaner while changing the split ratio by gradually decreasing the intake stroke injection amount in parallel with the control of the ignition timing in the retarded direction, so that the ignition timing is stabilized on the retarded side. When switching combustion at the limit, the air-fuel ratio (division ratio) is switched so as to cover the difference from the final target air-fuel ratio, and the ignition timing is advanced by the amount of absorption of the torque step corresponding to the air-fuel ratio difference. It may be. In this way, it is possible to approach the final target stratified lean combustion including the ignition timing more quickly, and the influence of the torque step due to control delay and variation can be reduced.
[0041]
After the catalyst activity is completed by the split injection stratified lean combustion, when switching to the normal combustion in the single injection, for example, the homogeneous stoichiometric combustion, the process of switching from the homogenous stoichiometric combustion to the split injection stratified lean combustion should be substantially reversed. It may be controlled to.
That is, as shown in FIG. 9, after the combustion switching request is generated, the ignition timing is gradually advanced to absorb the torque step difference, and then the air-fuel ratio (division ratio) is switched to switch to stratified stoichiometric combustion, and the total advance amount In order to absorb the torque step by performing the retard control that makes the minute 0 at once, similarly, when switching from stratified stoichiometric combustion to homogeneous stoichiometric combustion, after gradually igniting the ignition timing to absorb the torque step, Switching to single fuel injection to switch to homogeneous stoichiometric combustion, and at the same time, retarding control is performed so that the total amount of advance is zero at a stroke to absorb the torque step. Thereafter, the ignition timing is gradually advanced to MBT. The swirl control valve opening control and the fuel pressure increase control are performed in parallel with the ignition timing advance control.
[0042]
Next, a second embodiment will be described.
In the first embodiment, at the time of switching from stratified stoichiometric combustion to split injection stratified lean combustion, the air-fuel ratio is left as it is or after the deviation is reduced to some extent, the deviation is switched stepwise, and the ignition timing is advanced stepwise at the same time. In this case, the second embodiment is configured to switch from stratified stoichiometric combustion to split injection stratified lean combustion while gradually reducing the air-fuel ratio.
[0043]
Although the control for gradually leaning the air-fuel ratio may be a control for simply reducing the fuel injection amount relative to the intake air amount, in this embodiment, the control is performed by gradually changing the control constant of the air-fuel ratio feedback control. To do.
Specifically, as shown in FIG. 10, when the air-fuel ratio sensor 8 reverses from rich to lean, a PL subtraction delay that delays a proportional amount PL given in the fuel injection amount increasing direction for a predetermined time is performed. The average air-fuel ratio can be gradually made lean by making the proportional amount PR given in the fuel injection amount decreasing direction larger than the proportional amount PL when reversing from lean to rich. Note that only one of the PL subtraction delay and the proportional component PR may be made larger than the proportional component PL.
[0044]
Since the change range of the air-fuel ratio from the stratified stoichiometric combustion (λ = 1.0) to the split injection stratified lean combustion (λ = 1.1) that is finally switched is small, the control constant of the air-fuel ratio feedback control as described above By gradually changing, high-precision switching control can be performed. At the same time as the air-fuel ratio is made lean, the compression stroke injection amount ratio (division ratio) is also gradually increased as shown in FIG.
[0045]
Further, as shown in FIG. 11, the ignition timing control is performed at once from the state (B in the figure) delayed to the vicinity of the stability limit of homogeneous stoichiometric combustion to the MBT (in the figure C) of stratified stoichiometric combustion as in the first embodiment. After advancing and absorbing the torque step, the angle is gradually retarded to the vicinity of the stability limit (F in the figure) of the split injection stratified lean combustion.
Changes in various states at the time of combustion switching in the present embodiment are shown in FIG.
[0046]
According to the present embodiment, it is possible to switch smoothly according to a desired combustion mode.
Further, as shown by a one-dot chain line in FIG. 12 (A / F, target A / F, ignition timing), the average air / fuel ratio (λ = 1.1 or so) that is the final target from the start of the air / fuel ratio feedback control in homogeneous combustion. In this case, the air-fuel ratio may be continuously made lean while gradually changing the control constant until split injection stratified combustion at (3), and the torque absorbed by the ignition timing when switching from homogeneous combustion to stratified stoichiometric combustion A level | step difference can be made small and switching of more smooth combustion can be performed.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram according to an embodiment of the present invention.
FIG. 2 is a flowchart showing the first half of a main routine of combustion switching control in the present invention.
FIG. 3 is a flowchart showing the second half of the main routine;
FIG. 4A is a schematic diagram for explaining direct injection compression stroke injection. (B) is a schematic diagram for explaining direct injection intake stroke injection.
FIG. 5 is a diagram for explaining the necessity of delay in homogeneous stoichiometric combustion due to the difference in combustion stability depending on the combustion form;
FIG. 6 is a flowchart showing a subroutine for switching control from homogeneous stoichiometric combustion to stratified stoichiometric combustion to split injection stratified lean combustion in the first embodiment.
FIG. 7 is a diagram showing ignition timing control when switching from homogeneous stoichiometric combustion to stratified stoichiometric combustion to split injection stratified lean combustion in the same embodiment.
FIG. 8 is a view showing a fuel injection ratio (split ratio) between an intake stroke and a compression stroke according to an air-fuel ratio between stratified stoichiometric combustion and split injection stratified lean combustion.
FIG. 9 is a time chart showing how various states change during combustion switching control in the embodiment.
FIG. 10 is a time chart showing a state of air-fuel ratio feedback control at the time of switching from stratified stoichiometric combustion to split injection stratified lean combustion in the second embodiment.
FIG. 11 is a diagram showing ignition timing control in the second embodiment.
FIG. 12 is a time chart showing how various states change during combustion switching control in the second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine 4 ... Throttle valve 5 ... Fuel injection valve 6 ... Spark plug 7 ... Exhaust passage 8 ... Air-fuel ratio sensor 9 ... Exhaust gas purification catalyst 50 ... Control knit

Claims (7)

As a combustion mode according to the engine operating state, a homogeneous fuel mixture is formed in the entire combustion chamber by one fuel injection and burned, and an air-fuel ratio around the spark plug is outside by fuel injection divided into multiple times. In a control device for a direct-injection spark-ignition engine including split injection stratified combustion that forms and burns an air-fuel mixture richer than the air-fuel ratio of
Switching from homogeneous combustion with rich air-fuel ratio to split injection stratified combustion in consideration of startability, the control necessary for starting split injection stratified combustion after starting air-fuel ratio feedback control in homogeneous combustion A delay period that is set to ensure that the air-fuel ratio is within the range that allows stable combustion at the start of split injection stratified combustion even if there is a rich shift at the start of feedback control, even if there is a rich shift at the start of feedback control. After the elapse of time, an ignition timing retarding control for absorbing a torque step at the time of combustion switching is started, and after completion of the ignition timing retarding control, the combustion is switched to split injection stratified combustion. Control device. The control apparatus for a direct injection spark ignition engine according to claim 1, wherein the control necessary for starting the split injection stratified combustion includes a control for driving a swirl control valve for generating a swirl in the combustion chamber. The direct injection spark ignition engine according to claim 1 or 2, wherein the control necessary for starting the split injection stratified combustion includes a control for reducing a fuel pressure supplied to a fuel injection valve for supplying fuel to the engine. Control device. The direct injection spark ignition engine control device according to any one of claims 1 to 3, wherein the split injection stratified combustion is performed when an activation of an exhaust purification catalyst mounted on an exhaust system is requested. . The direct injection spark ignition engine control device according to any one of claims 1 to 4, wherein fuel injection in the split injection stratified combustion is performed by being divided into an intake stroke and a compression stroke. . The control device for a direct injection spark ignition engine according to any one of claims 1 to 5, wherein an average air-fuel ratio in the combustion chamber in the split injection stratified combustion is in the vicinity of stoichiometry. 6. The control device for a direct injection spark ignition engine according to claim 1, wherein an average air-fuel ratio in the combustion chamber in the split injection stratified combustion is slightly leaner than stoichiometric.

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